Divergent phenological response to hydroclimate variability in forested mountain watersheds

Treesearch

Taehee Hwang; Lawrence E. Band; Chelcy F. Miniat; Conghe Song; Paul V . Bolstad; James M. Vose; Jason P. Love

2014-01-01

Mountain watersheds are primary sources of freshwater, carbon sequestration, and other ecosystem services. There is significant interest in the effects of climate change and variability on these processes over short to long time scales. Much of the impact of hydroclimate variability in forest ecosystems is manifested in vegetation dynamics in space and time. In steep...

Hydroclimate variability in the Nile River Basin during the past 28,000 years

NASA Astrophysics Data System (ADS)

Castañeda, Isla S.; Schouten, Stefan; Pätzold, Jürgen; Lucassen, Friedrich; Kasemann, Simone; Kuhlmann, Holger; Schefuß, Enno

2016-03-01

It has long been known that extreme changes in North African hydroclimate occurred during the late Pleistocene yet many discrepancies exist between sites regarding the timing, duration and abruptness of events such as Heinrich Stadial (HS) 1 and the African Humid Period (AHP). The hydroclimate history of the Nile River is of particular interest due to its lengthy human occupation history yet there are presently few continuous archives from the Nile River corridor, and pre-Holocene studies are rare. Here we present new organic and inorganic geochemical records of Nile Basin hydroclimate from an eastern Mediterranean (EM) Sea sediment core spanning the past 28 ka BP. Our multi-proxy records reflect the fluctuating inputs of Blue Nile versus White Nile material to the EM Sea in response to gradual changes in local insolation and also capture abrupt hydroclimate events driven by remote climate forcings, such as HS1. We find strong evidence for extreme aridity within the Nile Basin evolving in two distinct phases during HS1, from 17.5 to 16 ka BP and from 16 to 14.5 ka BP, whereas peak wet conditions during the AHP are observed from 9 to 7 ka BP. We find that zonal movements of the Congo Air Boundary (CAB), and associated shifts in the dominant moisture source (Atlantic versus Indian Ocean moisture) to the Nile Basin, likely contributed to abrupt hydroclimate variability in northern East Africa during HS1 and the AHP as well as to non-linear behavior of hydroclimate proxies. We note that different proxies show variable gradual and abrupt responses to individual hydroclimate events, and thus might have different inherent sensitivities, which may be a factor contributing to the controversy surrounding the abruptness of past events such as the AHP. During the Late Pleistocene the Nile Basin experienced extreme hydroclimate fluctuations, which presumably impacted Paleolithic cultures residing along the Nile corridor.

400 years of summer hydroclimate from stable isotopes in Iberian trees

NASA Astrophysics Data System (ADS)

Andreu-Hayles, Laia; Ummenhofer, Caroline C.; Barriendos, Mariano; Schleser, Gerhard H.; Helle, Gerhard; Leuenberger, Markus; Gutierrez, Emilia; Cook, Edward R.

2017-04-01

Tree rings are natural archives that annually record distinct types of past climate variability depending on the parameters measured. Here, we use ring-width and stable isotopes in cellulose of trees from the northwestern Iberian Peninsula (IP) to understand regional summer hydroclimate over the last 400 years and the associated atmospheric patterns. Correlations between tree rings and climate data demonstrate that isotope signatures in the targeted Iberian pine forests are very sensitive to water availability during the summer period, and are mainly controlled by stomatal conductance. Non-linear methods based on extreme events analysis allow for capturing distinct seasonal climatic variability recorded by tree-ring parameters and asymmetric signals of the associated atmospheric features. Moreover, years with extreme high (low) values in the tree-ring records were characterised by coherent large-scale atmospheric circulation patterns with reduced (enhanced) moisture transport onto the northwestern IP. These analyses of extremes revealed that high/low proxy values do not necessarily correspond to mirror images in the atmospheric anomaly patterns, suggesting different drivers of these patterns and the corresponding signature recorded in the proxies. Regional hydroclimate features across the broader IP and western Europe during extreme wet/dry summers detected by the northwestern IP trees compare favourably to an independent multicentury sea level pressure and drought reconstruction for Europe. Historical records also validate our findings that attribute non-linear moisture signals recorded by extreme tree-ring values to distinct large-scale atmospheric patterns and allow for 400-yr reconstructions of the frequency of occurrence of extreme conditions in summer hydroclimate. We will discuss how the results for Lillo compare with other records.

Remembrance of ecohydrologic extremes past

NASA Astrophysics Data System (ADS)

Band, L. E.; Hwang, T.

2013-12-01

Ecohydrological systems operate at time scales that span several orders of magnitude. Significant processes and feedbacks range from subdaily physiologic response to meteorological drivers, to soil forming and geomorphic processes ranging up through 10^3-10^4 years. While much attention in ecohydrology has focused on ecosystem optimization paradigms, these systems can show significant transience in structure and function, with apparent memory of hydroclimate extremes and regime shifts. While optimization feedbacks can be reconciled with system transience, a better understanding of the time scales and mechanisms of adjustment to increased hydroclimate variability and to specific events is required to understand and predict dynamics and vulnerability of ecosystems. Under certain circumstances of slowly varying hydroclimate, we hypothesize that ecosystems can remain adjusted to changing climate regimes, without displaying apparent system memory. Alternatively, rapid changes in hydroclimate and increased hydroclimate variability, amplified with well expressed non-linearity in the processes controlling feedbacks between water, carbon and nutrients, can move ecosystems far from adjusted states. The Coweeta Hydrological Laboratory is typical of humid, broadleaf forests in eastern North America, with a range of forest biomes from northern hardwoods at higher elevations, to oak-pine assemblages at lower elevations. The site provides almost 80 years of rainfall-runoff records for a set of watersheds under different management, along with multi-decadal forest plot structural information, soil moisture conditions and stream chemistry. An initial period of multi-decadal cooling, was followed by three decades of warming and increased hydroclimate variability. While mean temperature has risen over this time period, precipitation shows no long term trends in the mean, but has had a significant rise in variability with repeated extreme drought and wet periods. Over this latter period, intra and interannual shifts of canopy structure and phenology are discernable, along with long term canopy adjustment. We use a combination of field observations, long term remote sensing records and distributed ecohydrological modeling to investigate transient behavior, apparent memory and mechanisms of ecosystem adjustment to hydroclimate variability and change over the range of biomes in the watershed.

A Northern Hemisphere perspective on Holocene hydroclimate trends in the tropical Andes

NASA Astrophysics Data System (ADS)

Larsen, D. J.; Polissar, P. J.; Abbott, M. B.

2016-12-01

Reconstructions of tropical precipitation are important for determining the sensitivity of rainfall patterns in the tropics to climate variability and improving the accuracy of projected hydrologic changes in a warming world. In tropical South America, precipitation is dominantly controlled by the South American Monsoon system (SAM), which operates in conjunction with the position of the Intertropical Convergence Zone (ITCZ) and the El Niño Southern Oscillation (ENSO) to deliver water resources to hundreds of millions of people. The classic model of South American hydroclimate evolution during the Holocene (past 11 ka) invokes an anti-phased pattern of precipitation between hemispheres, whereby orbital forcing drove a gradual displacement of the ITCZ, causing a southerly shift in seasonal convection and precipitation, and strengthening the SAM as Southern Hemisphere summer insolation increased. Indeed, paleoclimate records derived from multiple geologic archives support this pattern. However, the vast majority of existing records come from the southern tropics and emerging terrestrial datasets from the northern tropics appear contrary to the paradigm. Here, we present lake sediment evidence for coupled hydroclimate and environmental changes from the Venezuelan Andes, a key region for investigating interhemispheric linkages and drivers of tropical hydroclimate variability. Compound specific hydrogen isotope ratios from terrestrial plant waxes and algal lipids, together with supporting sedimentary indicators of runoff and aridity, provide a comprehensive reconstruction of Northern Hemisphere tropical precipitation at local and regional scales. Our results are consistent in sign and magnitude to precipitation reconstructions from both hemispheres, indicating interhemispheric similarities in tropical hydroclimate variability and calling into question the synchronicity and phasing of hydroclimate trends in South America.

Increased tree-ring network density reveals more precise estimations of sub-regional hydroclimate variability and climate dynamics in the Midwest, USA

NASA Astrophysics Data System (ADS)

Maxwell, Justin T.; Harley, Grant L.

2017-08-01

Understanding the historic variability in the hydroclimate provides important information on possible extreme dry or wet periods that in turn inform water management plans. Tree rings have long provided historical context of hydroclimate variability of the U.S. However, the tree-ring network used to create these countrywide gridded reconstructions is sparse in certain locations, such as the Midwest. Here, we increase ( n = 20) the spatial resolution of the tree-ring network in southern Indiana and compare a summer (June-August) Palmer Drought Severity Index (PDSI) reconstruction to existing gridded reconstructions of PDSI for this region. We find both droughts and pluvials that were previously unknown that rival the most intense PDSI values during the instrumental period. Additionally, historical drought occurred in Indiana that eclipsed instrumental conditions with regard to severity and duration. During the period 1962-2004 CE, we find that teleconnections of drought conditions through the Atlantic Meridional Overturning Circulation have a strong influence ( r = -0.60, p < 0.01) on secondary tree growth in this region for the late spring-early summer season. These findings highlight the importance of continuing to increase the spatial resolution of the tree-ring network used to infer past climate dynamics to capture the sub-regional spatial variability. Increasing the spatial resolution of the tree-ring network for a given region can better identify sub-regional variability, improve the accuracy of regional tree-ring PDSI reconstructions, and provide better information for climatic teleconnections.

Megadroughts in Southwestern North America in ECHO-G Millennial Simulations and Their Comparison to Proxy Drought Reconstructions

NASA Technical Reports Server (NTRS)

Coats, Sloan; Smerdon, Jason E.; Seager, Richard; Cook, Benjamin I.; Gozalez-Rouco, J. F.

2013-01-01

Simulated hydroclimate variability in millennium-length forced transient and control simulations from the ECHAM and the global Hamburg Ocean Primitive Equation (ECHO-G) coupled atmosphere-ocean general circulation model (AOGCM) is analyzed and compared to 1000 years of reconstructed Palmer drought severity index (PDSI) variability from the North American Drought Atlas (NADA). The ability of the model to simulate megadroughts in the North American southwest is evaluated. (NASW: 25deg42.5degN, 125deg-105degW). Megadroughts in the ECHO-G AOGCM are found to be similar in duration and magnitude to those estimated from the NADA. The droughts in the forced simulation are not, however, temporally synchronous with those in the paleoclimate record, nor are there significant differences between the drought features simulated in the forced and control runs. These results indicate that model-simulated megadroughts can result from internal variability of the modeled climate system rather than as a response to changes in exogenous forcings. Although the ECHO-G AOGCM is capable of simulating megadroughts through persistent La Nina-like conditions in the tropical Pacific, other mechanisms can produce similarly extreme NASW moisture anomalies in the model. In particular, the lack of low-frequency coherence between NASW soil moisture and simulated modes of climate variability like the El Nino-Southern Oscillation, Pacific decadal oscillation, and Atlantic multidecadal oscillation during identified drought periods suggests that stochastic atmospheric variability can contribute significantly to the occurrence of simulated megadroughts in the NASW. These findings indicate that either an expanded paradigm is needed to understand multidecadal hydroclimate variability in the NASW or AOGCMs may incorrectly simulate the strength and/or dynamics of the connection between NASW hydroclimate variability and the tropical Pacific.

Late Pleistocene and Holocene Hydroclimate Variability in the Tropical Andes from Alpine Lake Sediments, Cordillera de Mérida, Venezuela

NASA Astrophysics Data System (ADS)

Larsen, D. J.; Abbott, M. B.; Polissar, P. J.

2014-12-01

The tropics play a major role in the global hydrologic cycle and changes to tropical rainfall patterns have critical implications for water resources and ecosystem dynamics over large geographic scales. In tropical South America, late Pleistocene and Holocene precipitation variability has been documented in geologic records and associated with numerous external and internal variables, including changes in summer insolation, South American summer monsoon strength, Pacific Ocean sea surface temperatures, continental moisture recycling, and other climate processes. However, there are few records from the northern hemisphere tropical Americas, a key region for understanding interhemispheric linkages and the drivers of tropical hydroclimate variability. Here, we present a ~13 ka record of coupled hydroclimate and environmental changes from Laguna Brava, a small (~0.07 km2), hydrologically closed lake basin situated at 2400 m asl in the Cordillera de Mérida, Venezuela. Sediment cores collected from varying water depths and proximity to shore are placed in a chronologic framework using radiocarbon ages from terrestrial macrofossils, and analyzed for a suite of physical, bulk geochemical, and stable isotopic parameters. Compound specific hydrogen isotope (D/H) measurements of terrestrial plant waxes (long-chain n-alkanes) show a sharp increase in the late Pleistocene, followed by a long-term trend toward more negative values that suggest a ~20‰ decrease in the D/H ratios of South American tropical precipitation during the Holocene. This pattern is consistent in sign and magnitude to other South American precipitation reconstructions from both hemispheres, indicating interhemispheric similarities in tropical hydroclimate variability. Superimposed on this continent-scale trend are changes in moisture balance and environmental conditions in the Venezuelan Andes. We reconstruct these parameters at Laguna Brava at multidecadal and centennial resolution and evaluate this record within the context of late Pleistocene and Holocene South American tropical hydroclimate variability and global climate changes.

Climate change patterns in Amazonia and biodiversity.

PubMed

Cheng, Hai; Sinha, Ashish; Cruz, Francisco W; Wang, Xianfeng; Edwards, R Lawrence; d'Horta, Fernando M; Ribas, Camila C; Vuille, Mathias; Stott, Lowell D; Auler, Augusto S

2013-01-01

Precise characterization of hydroclimate variability in Amazonia on various timescales is critical to understanding the link between climate change and biodiversity. Here we present absolute-dated speleothem oxygen isotope records that characterize hydroclimate variation in western and eastern Amazonia over the past 250 and 20 ka, respectively. Although our records demonstrate the coherent millennial-scale precipitation variability across tropical-subtropical South America, the orbital-scale precipitation variability between western and eastern Amazonia exhibits a quasi-dipole pattern. During the last glacial period, our records imply a modest increase in precipitation amount in western Amazonia but a significant drying in eastern Amazonia, suggesting that higher biodiversity in western Amazonia, contrary to 'Refugia Hypothesis', is maintained under relatively stable climatic conditions. In contrast, the glacial-interglacial climatic perturbations might have been instances of loss rather than gain in biodiversity in eastern Amazonia, where forests may have been more susceptible to fragmentation in response to larger swings in hydroclimate.

400 Years of summer hydroclimate from stable isotopes in Iberian trees

NASA Astrophysics Data System (ADS)

Andreu-Hayles, Laia; Ummenhofer, Caroline C.; Barriendos, Mariano; Schleser, Gerhard H.; Helle, Gerhard; Leuenberger, Markus; Gutiérrez, Emilia; Cook, Edward R.

2017-07-01

Tree rings are natural archives that annually record distinct types of past climate variability depending on the parameters measured. Here, we use ring-width and stable isotopes in cellulose of trees from the northwestern Iberian Peninsula (IP) to understand regional summer hydroclimate over the last 400 years and the associated atmospheric patterns. Correlations between tree rings and climate data demonstrate that isotope signatures in the targeted Iberian pine forests are very sensitive to water availability during the summer period, and are mainly controlled by stomatal conductance. Non-linear methods based on extreme events analysis allow for capturing distinct seasonal climatic variability recorded by tree-ring parameters and asymmetric signals of the associated atmospheric features. Moreover, years with extreme high (low) values in the tree-ring records were characterised by coherent large-scale atmospheric circulation patterns with reduced (enhanced) moisture transport onto the northwestern IP. These analyses of extremes revealed that high/low proxy values do not necessarily correspond to mirror images in the atmospheric anomaly patterns, suggesting different drivers of these patterns and the corresponding signature recorded in the proxies. Regional hydroclimate features across the broader IP and western Europe during extreme wet/dry summers detected by the northwestern IP trees compare favourably to independent multicentury sea level pressure and drought reconstructions for Europe. Historical records also validate our findings that attribute non-linear moisture signals recorded by extreme tree-ring values to distinct large-scale atmospheric patterns and allow for 400-year reconstructions of the frequency of occurrence of extreme conditions in late spring and summer hydroclimate.

Impact of external forcing on simulated hydroclimate from interannual to multicentennial timescales

NASA Astrophysics Data System (ADS)

Roldán, Pedro; Fidel González-Rouco, Jesús; Melo-Aguilar, Camilo

2017-04-01

During the last millennium, external forcing experienced important changes in different timescales. It has been demostrated that these changes had an impact on climate. In particular, changes in solar activity, volcanic eruptions and emissions of greenhouse gases are related to short-term and long-term changes in global temperatures, with situations of higher total external forcing generally related with higher global and hemispherical temperatures, and conversely with situations of lower forcing. This connection is clearly observed in climate simulations from different models and in proxy-based reconstructions. The changes in external forcing can also explain certain changes in atmospheric dynamics and hydroclimate, although in this case it is in general more difficult to trace causality arguments. Analyses based on simulations from two different models (ECHO-G and CESM-LME) have been performed, to assess the impact of external forcing on climate in timescales ranging from interannual to multicentennial. Various climatic variables have been analysed, including temperature, sea level pressure, surface wind, precipitation and soil moisture. For interannual timescales, composites have been defined with the years before and after the main volcanic eruptions of the last millennium as well as the minima of solar activity during this period. For longer timescales, a Principal Component analysis has been performed, to try to separate the signal of external forcing from that of internal variability. This has been done for the whole millennium and for the pre-industrial period, to assess the difference between natural and anthropogenic forcing. For multicentennial timescales, composites for the Medieval Climate Anomaly (MCA; ca. 950-1250), the Little Ice Age (LIA; ca. 1450-1850) and the 20th Century have been compared. These three periods were respectively characterised by higher, lower and higher forcing. This allows to assess the contribution of external forcing to the evolution of climate over longer time intervals. These analyses have shown that external forcing is an important factor in the evolution of the simulated hydroclimate of the last millennium. In the short-term, it has been observed that volcanic eruptions and other situations of extreme forcing significantly alter the global precipitation in the subsequent years. In the long-term, variations of external forcing can be related to changes in atmospheric dynamics and in hydroclimate. However, this impact is not homogeneously distributed. There are areas where hydroclimate is mainly influenced by the external forcing and other areas more influenced by internal variability, with spatial decorrelation being higher in precipitation or drought related variables than in temperature. The regional sensitivity to external forcing of hydroclimate is model and, to a lesser degree, simulation dependent.

High-resolution paleoclimate records of Holocene hydroclimatic variability in the Eastern Colombian Andes from Lago de Tota

NASA Astrophysics Data System (ADS)

Ahmed, M. N.; Bird, B. W.; Escobar, J.; Polissar, P. J.

2017-12-01

The Northern Hemisphere (NH) South American Monsoon (SAM) is a significant source of precipitation for the North Andes (north of 0˚) and has major control over regional hydroclimate variability. Holocene-length histories of NH SAM variability are few compared to the Southern Hemisphere (SH), limiting understanding of how these systems are connected on orbital and shorter timescales. Here, we present multi-proxy lake-sediment-based paleoclimate and paleohydrologic reconstructions from Lago de Tota, Colombia, using sedimentological, geochemical and leaf-wax hydrogen isotopic indicators from radiometically dated cores. The results indicate periods of wet and dry climate phases during the past 9000 BP with an average Holocene sedimentation rate 33cm/kyr. An increase in total organic matter (TOM) content and finer grain-size distributions was observed from 8000 to 3200 BP, suggesting a period of high lake level. This was followed by lower TOM and coarser grain sizes, suggesting lower lake levels from 3200 BP to the present. Although Tota's lake level pattern is antiphased with other lake level reconstructions from the NH and SH Andes, it is consistent with hypothesized changes in atmospheric convection over the Andes during the Holocene and the way in which they would be modified by the so-called dry island effect in the Colombian Andes. This suggests that a common forcing mechanism can be invoked to explain differing millennial-scale Andean hydroclimate changes, namely atmospheric convection. Orbital and Pacific atmosphere-forcing are therefore likely to have played a significant role in driving pan-Andean hydroclimate variability based on their inter-hemispheric influence on Andean convection.

Extremes in East African hydroclimate and links to Indo-Pacific variability on interannual to decadal timescales

NASA Astrophysics Data System (ADS)

Ummenhofer, Caroline C.; Kulüke, Marco; Tierney, Jessica E.

2018-04-01

East African hydroclimate exhibits considerable variability across a range of timescales, with implications for its population that depends on the region's two rainy seasons. Recent work demonstrated that current state-of-the-art climate models consistently underestimate the long rains in boreal spring over the Horn of Africa while overestimating the short rains in autumn. This inability to represent the seasonal cycle makes it problematic for climate models to project changes in East African precipitation. Here we consider whether this bias also has implications for understanding interannual and decadal variability in the East African long and short rains. Using a consistent framework with an unforced multi-century global coupled climate model simulation, the role of Indo-Pacific variability for East African rainfall is compared across timescales and related to observations. The dominant driver of East African rainfall anomalies critically depends on the timescale under consideration: Interannual variations in East African hydroclimate coincide with significant sea surface temperature (SST) anomalies across the Indo-Pacific, including those associated with the El Niño-Southern Oscillation (ENSO) in the eastern Pacific, and are linked to changes in the Walker circulation, regional winds and vertical velocities over East Africa. Prolonged drought/pluvial periods in contrast exhibit anomalous SST predominantly in the Indian Ocean and Indo-Pacific warm pool (IPWP) region, while eastern Pacific anomalies are insignificant. We assessed dominant frequencies in Indo-Pacific SST and found the eastern equatorial Pacific dominated by higher-frequency variability in the ENSO band, while the tropical Indian Ocean and IPWP exhibit lower-frequency variability beyond 10 years. This is consistent with the different contribution to regional precipitation anomalies for the eastern Pacific versus Indian Ocean and IPWP on interannual and decadal timescales, respectively. In the model, the dominant low-frequency signal seen in the observations in the Indo-Pacific is not well-represented as it instead exhibits overly strong variability on subdecadal timescales. The overly strong ENSO-teleconnection likely contributes to the overestimated role of the short rains in the seasonal cycle in the model compared to observations.

D/H Ratios From Sierra Nevada Varved Lake Sediments Record Decadal Hydroclimate Variability During The Medieval Period

NASA Astrophysics Data System (ADS)

Roach, L. D.; Cayan, D. R.; Sessions, A. L.; Charles, C. D.; Anderson, R. S.

2009-12-01

Assessment of the risks of persistent drought requires multiple realizations of decadal and centennial scale hydroclimate variability that extend beyond the relatively short period of instrumental record. Much remains to be learned about the so called “mega droughts” in the Sierra Nevada Mountains, where various lines of evidence point toward the occurrence of severe, decades-long droughts during Medieval times, approximately 900-1400 AD. Here we present a continuous, decadal scale record of hydroclimate variability in the Sierra Nevada Mountains that extends through the heart of the purported Medieval mega droughts. Previous work on the stable hydrogen isotope (D/H) ratios of refractory plant lipid compounds stored in lake sediments demonstrated that these compounds reflect the D/H values of lake water and/or shallow ground water--reservoirs both fed by local precipitation. Lake sediment D/H can therefore reflect the processes that determine D/H of precipitation, including temperature, humidity and moisture source. We have measured D/H of aquatic and terrestrial plant fatty acids extracted from a suite of sediment cores collected at Swamp Lake (elevation: 1554m), in Yosemite National Park, along the Sierra Nevada crest. Measurements with biennial resolution were made for two time periods: the 20th century and the 13th-15th centuries. D/H fluctuations in 20th century sediment contain relatively strong decadal structure. Comparison with instrumentally recorded climate variability reveals that lower D/H concentrations are associated with years of higher than normal annual precipitation, cooler than normal wintertime temperatures, and positive April 1 Snow Water Equivalent (SWE) anomalies throughout the Sierra Nevada, (and conversely for elevated D/H concentrations). The range of variability is approximately 50‰. These associations may be driven by the variable mass-balance impact of evaporation on the isotopic composition of lake water and shallow groundwater in the Swamp Lake watershed, depending on the extent to which these reservoirs are replenished seasonally by wintertime precipitation. Throughout the Medieval period, we observe significant (>30‰), reproducible D/H variability that also fluctuates on multi-year to decadal time scales, with mean values falling within the same range as those recorded over the 20th century. Strong covariance among the aquatic and terrestrial plant fatty acids analyzed, along with the mean values, lends confidence that primary isotopic signatures have been retained. These results can therefore be compared directly to other measures of hydroclimate variability throughout the last millennium, offering a unique new perspective on the mega-drought intervals.

A North American Hydroclimate Synthesis (NAHS) of the Common Era

NASA Astrophysics Data System (ADS)

Rodysill, Jessica R.; Anderson, Lesleigh; Cronin, Thomas M.; Jones, Miriam C.; Thompson, Robert S.; Wahl, David B.; Willard, Debra A.; Addison, Jason A.; Alder, Jay R.; Anderson, Katherine H.; Anderson, Lysanna; Barron, John A.; Bernhardt, Christopher E.; Hostetler, Steven W.; Kehrwald, Natalie M.; Khan, Nicole S.; Richey, Julie N.; Starratt, Scott W.; Strickland, Laura E.; Toomey, Michael R.; Treat, Claire C.; Wingard, G. Lynn

2018-03-01

This study presents a synthesis of century-scale hydroclimate variations in North America for the Common Era (last 2000 years) using new age models of previously published multiple proxy-based paleoclimate data. This North American Hydroclimate Synthesis (NAHS) examines regional hydroclimate patterns and related environmental indicators, including vegetation, lake water elevation, stream flow and runoff, cave drip rates, biological productivity, assemblages of living organisms, and salinity. Centennial-scale hydroclimate anomalies are obtained by iteratively sampling the proxy data on each of thousands of age model realizations and determining the fractions of possible time series indicating that the century-smoothed data was anomalously wet or dry relative to the 100 BCE to 1900 CE mean. Results suggest regionally asynchronous wet and dry periods over multidecadal to centennial timescales and frequent periods of extended regional drought. Most sites indicate drying during previously documented multicentennial periods of warmer Northern Hemisphere temperatures, particularly in the western U.S., central U.S., and Canada. Two widespread droughts were documented by the NAHS: from 50 BCE to 450 CE and from 800 to 1100 CE. Major hydroclimate reorganizations occurred out of sync with Northern Hemisphere temperature variations and widespread wet and dry anomalies occurred during both warm and cool periods. We present a broad assessment of paleoclimate relationships that highlights the potential influences of internal variability and external forcing and supports a prominent role for Pacific and Atlantic Ocean dynamics on century-scale continental hydroclimate.

Indices and Dynamics of Global Hydroclimate Over the Past Millennium from Data Assimilation

NASA Astrophysics Data System (ADS)

Steiger, N. J.; Smerdon, J. E.

2017-12-01

Reconstructions based on data assimilation (DA) are at the forefront of model-data syntheses in that such reconstructions optimally fuse proxy data with climate models. DA-based paleoclimate reconstructions have the benefit of being physically-consistent across the reconstructed climate variables and are capable of providing dynamical information about past climate phenomena. Here we use a new implementation of DA, that includes updated proxy system models and climate model bias correction procedures, to reconstruct global hydroclimate on seasonal and annual timescales over the last millennium. This new global hydroclimate product includes reconstructions of the Palmer Drought Severity Index, the Standardized Precipitation Evapotranspiration Index, and global surface temperature along with dynamical variables including the Nino 3.4 index, the latitudinal location of the intertropical convergence zone, and an index of the Atlantic Multidecadal Oscillation. Here we present a validation of the reconstruction product and also elucidate the causes of severe drought in North America and in equatorial Africa. Specifically, we explore the connection between droughts in North America and modes of ocean variability in the Pacific and Atlantic oceans. We also link drought over equatorial Africa to shifts of the intertropical convergence zone and modes of ocean variability.

What We Talk About When We Talk About Drought: Tree-ring Perspectives on Model-Data Comparisons in Hydroclimate Research

NASA Astrophysics Data System (ADS)

Cook, B.; Anchukaitis, K. J.

2017-12-01

Comparative analyses of paleoclimate reconstructions and climate model simulations can provide valuable insights into past and future climate events. Conducting meaningful and quantitative comparisons, however, can be difficult for a variety of reasons. Here, we use tree-ring based hydroclimate reconstructions to discuss some best practices for paleoclimate-model comparisons, highlighting recent studies that have successfully used this approach. These analyses have improved our understanding of the Medieval-era megadroughts, ocean forcing of large scale drought patterns, and even climate change contributions to future drought risk. Additional work is needed, however, to better reconcile and formalize uncertainties across observed, modeled, and reconstructed variables. In this regard, process based forward models of proxy-systems will likely be a critical tool moving forward.

Impact of large-scale circulation changes in the North Atlantic sector on the current and future Mediterranean winter hydroclimate

NASA Astrophysics Data System (ADS)

Barcikowska, Monika J.; Kapnick, Sarah B.; Feser, Frauke

2018-03-01

The Mediterranean region, located in the transition zone between the dry subtropical and wet European mid-latitude climate, is very sensitive to changes in the global mean climate state. Projecting future changes of the Mediterranean hydroclimate under global warming therefore requires dynamic climate models to reproduce the main mechanisms controlling regional hydroclimate with sufficiently high resolution to realistically simulate climate extremes. To assess future winter precipitation changes in the Mediterranean region we use the Geophysical Fluid Dynamics Laboratory high-resolution general circulation model for control simulations with pre-industrial greenhouse gas and aerosol concentrations which are compared to future scenario simulations. Here we show that the coupled model is able to reliably simulate the large-scale winter circulation, including the North Atlantic Oscillation and Eastern Atlantic patterns of variability, and its associated impacts on the mean Mediterranean hydroclimate. The model also realistically reproduces the regional features of daily heavy rainfall, which are absent in lower-resolution simulations. A five-member future projection ensemble, which assumes comparatively high greenhouse gas emissions (RCP8.5) until 2100, indicates a strong winter decline in Mediterranean precipitation for the coming decades. Consistent with dynamical and thermodynamical consequences of a warming atmosphere, derived changes feature a distinct bipolar behavior, i.e. wetting in the north—and drying in the south. Changes are most pronounced over the northwest African coast, where the projected winter precipitation decline reaches 40% of present values. Despite a decrease in mean precipitation, heavy rainfall indices show drastic increases across most of the Mediterranean, except the North African coast, which is under the strong influence of the cold Canary Current.

Tree-ring based reconstruction of spring hydroclimate variability in the Caucasus

NASA Astrophysics Data System (ADS)

Martin-Benito, Dario; Köse, Nesibe; Güner, Tuncay; Pederson, Neil

2015-04-01

The Caucasus region has been identified as one of the most prominent biodiversity hotspots in the world. The region experiences recurrent droughts that not only affect natural vegetation but also the agriculturally-based economies in the Caucasus. Across northeastern Turkey and the Caucasus region, instrumental records providing information on climate variability are generally scarce. Thus the magnitude and frequency of past droughts in this biologically important region are less known. Additionally, despite the increase of climate reconstructions in the past decades for many parts of Europe and Asia, relatively little work has been done to understand hydroclimate variability in the Caucasus region. Nearly all efforts in the region have focused on the Mediterranean part of Turkey and the Middle East region. We developed new tree-ring width chronologies from different elevation sites in northeastern Turkey with the goal to reconstruct annually-resolved estimates of temperature and hydroclimate across the region. We developed the first reconstruction of spring hydroclimate variability for the Caucasus and the southeastern Black Sea Region since 1750 CE using a nested procedure. Despite the high mean annual precipitation in the region, our reconstruction accounted for over 45% of May-June precipitation variability from 1925 to 2006. We observed no evidence of a decrease in spring precipitation during the recent decades. However, we do see a decrease in precipitation variability over the last 75 years with respect to previous periods that, at this time, does not appear to be related to sample replication. Although our reconstructed precipitation shows important similarities with previous work from Mediterranean and northern Turkey, we find distinct drought periods are also evident suggesting a wider range of climate dynamics in the broader Black Sea region than what has been previously identified. Distinct episodes of drought at the larger scales could have important implications for the dynamics of ecosystems prior to and after the 20th century.

Early Holocene hydroclimate of Baffin Bay: Understanding the interplay between abrupt climate change events and ice sheet fluctuations

NASA Astrophysics Data System (ADS)

Corcoran, M. C.; Thomas, E. K.; Castañeda, I. S.; Briner, J. P.

2017-12-01

Understanding the causes of ice sheet fluctuations resulting in sea level rise is essential in today's warming climate. In high-latitude ice-sheet-proximal environments such as Baffin Bay, studying both the cause and the rate of ice sheet variability during past abrupt climate change events aids in predictions. Past climate reconstructions are used to understand ice sheet responses to changes in temperature and precipitation. The 9,300 and 8,200 yr BP events are examples of abrupt climate change events in the Baffin Bay region during which there were multiple re-advances of the Greenland and Laurentide ice sheets. High-resolution (decadal-scale) hydroclimate variability near the ice sheet margins during these abrupt climate change events is still unknown. We will generate a decadal-scale record of early Holocene temperature and precipitation using leaf wax hydrogen isotopes, δ2Hwax, from a lake sediment archive on Baffin Island, western Baffin Bay, to better understand abrupt climate change in this region. Shifts in temperature and moisture source result in changes in environmental water δ2H, which in turn is reflected in δ2Hwax, allowing for past hydroclimate to be determined from these compound-specific isotopes. The combination of terrestrial and aquatic δ2Hwax is used to determine soil evaporation and is ultimately used to reconstruct moisture variability. We will compare our results with a previous analysis of δ2Hwax and branched glycerol dialkyl glycerol tetraethers, a temperature and pH proxy, in lake sediment from western Greenland, eastern Baffin Bay, which indicates that cool and dry climate occurred in response to freshwater forcing events in the Labrador Sea. Reconstructing and comparing records on both the western and eastern sides of Baffin Bay during the early Holocene will allow for a spatial understanding of temperature and moisture balance changes during abrupt climate events, aiding in ice sheet modeling and predictions of future sea level rise.

Detrital events and hydroclimate variability in the Romanian Carpathians during the mid-to-late Holocene

NASA Astrophysics Data System (ADS)

Longman, Jack; Ersek, Vasile; Veres, Daniel; Salzmann, Ulrich

2017-07-01

The Romanian Carpathians are located at the confluence of three major atmospheric pressure fields: the North Atlantic, the Mediterranean and the Siberian. Despite its importance for understanding past human impact and climate change, high-resolution palaeoenvironmental reconstructions of Holocene hydroclimate variability, and in particular records of extreme precipitation events in the area, are rare. Here we present a 7500-year-long high-resolution record of past climatic change and human impact recorded in a peatbog from the Southern Carpathians, integrating palynological, geochemical and sedimentological proxies. Natural climate fluctuations appear to be dominant until 4500 years before present (yr BP), followed by increasing importance of human impact. Sedimentological and geochemical analyses document regular minerogenic deposition within the bog, linked to periods of high precipitation. Such minerogenic depositional events began 4000 yr BP, with increased depositional rates during the Medieval Warm Period (MWP), the Little Ice Age (LIA) and during periods of societal upheaval (e.g. the Roman conquest of Dacia). The timing of minerogenic events appears to indicate a teleconnection between major shifts in North Atlantic Oscillation (NAO) and hydroclimate variability in southeastern Europe, with increased minerogenic deposition correlating to low NAO index values. By linking the minerogenic deposition to precipitation variability, we state that this link persists throughout the mid-to-late Holocene.

Divergent phenological response to hydroclimate variability in forested mountain watersheds.

PubMed

Hwang, Taehee; Band, Lawrence E; Miniat, Chelcy F; Song, Conghe; Bolstad, Paul V; Vose, James M; Love, Jason P

2014-08-01

Mountain watersheds are primary sources of freshwater, carbon sequestration, and other ecosystem services. There is significant interest in the effects of climate change and variability on these processes over short to long time scales. Much of the impact of hydroclimate variability in forest ecosystems is manifested in vegetation dynamics in space and time. In steep terrain, leaf phenology responds to topoclimate in complex ways, and can produce specific and measurable shifts in landscape forest patterns. The onset of spring is usually delayed at a specific rate with increasing elevation (often called Hopkins' Law; Hopkins, 1918), reflecting the dominant controls of temperature on greenup timing. Contrary with greenup, leaf senescence shows inconsistent trends along elevation gradients. Here, we present mechanisms and an explanation for this variability and its significance for ecosystem patterns and services in response to climate. We use moderate-resolution imaging spectro-radiometer (MODIS) Normalized Difference Vegetation Index (NDVI) data to derive landscape-induced phenological patterns over topoclimate gradients in a humid temperate broadleaf forest in southern Appalachians. These phenological patterns are validated with different sets of field observations. Our data demonstrate that divergent behavior of leaf senescence with elevation is closely related to late growing season hydroclimate variability in temperature and water balance patterns. Specifically, a drier late growing season is associated with earlier leaf senescence at low elevation than at middle elevation. The effect of drought stress on vegetation senescence timing also leads to tighter coupling between growing season length and ecosystem water use estimated from observed precipitation and runoff generation. This study indicates increased late growing season drought may be leading to divergent ecosystem response between high and low elevation forests. Landscape-induced phenological patterns are easily observed over wide areas and may be used as a unique diagnostic for sources of ecosystem vulnerability and sensitivity to hydroclimate change. © 2014 John Wiley & Sons Ltd.

A discrete wavelet spectrum approach for identifying non-monotonic trends in hydroclimate data

NASA Astrophysics Data System (ADS)

Sang, Yan-Fang; Sun, Fubao; Singh, Vijay P.; Xie, Ping; Sun, Jian

2018-01-01

The hydroclimatic process is changing non-monotonically and identifying its trends is a great challenge. Building on the discrete wavelet transform theory, we developed a discrete wavelet spectrum (DWS) approach for identifying non-monotonic trends in hydroclimate time series and evaluating their statistical significance. After validating the DWS approach using two typical synthetic time series, we examined annual temperature and potential evaporation over China from 1961-2013 and found that the DWS approach detected both the warming and the warming hiatus in temperature, and the reversed changes in potential evaporation. Further, the identified non-monotonic trends showed stable significance when the time series was longer than 30 years or so (i.e. the widely defined climate timescale). The significance of trends in potential evaporation measured at 150 stations in China, with an obvious non-monotonic trend, was underestimated and was not detected by the Mann-Kendall test. Comparatively, the DWS approach overcame the problem and detected those significant non-monotonic trends at 380 stations, which helped understand and interpret the spatiotemporal variability in the hydroclimatic process. Our results suggest that non-monotonic trends of hydroclimate time series and their significance should be carefully identified, and the DWS approach proposed has the potential for wide use in the hydrological and climate sciences.

Drought multiproxy reconstruction in the Czech Lands from AD 1500

NASA Astrophysics Data System (ADS)

Dobrovolný, Petr; Brázdil, Rudolf; Možný, Martin; Trnka, Miroslav; Rybníček, Michal; Kolář, Tomáš

2017-04-01

Whereas the air temperature variability in the past and recent climate is well understood, our knowledge on hydroclimate (drought/precipitation) from various proxy archives and instrumental measurements are sketchy and sometimes even contradictory. This is related to huge spatial and temporal hydroclimate variability that underlines the importance of detailed local/regional studies on long-term hydroclimate variability. We present main results of summer drought reconstruction for the territory of the Czech Republic (CR) spanning the last 500 years. Drought is represented by the Standardized Precipitation Evapotranspiration Index (SPEI). Summer (JJA) SPEI values calculated from various instrumental measurements from the CR and covering most of the 19th and 20th centuries represent the target data. Three different proxy archives were used for SPEI reconstruction: a) Central European monthly temperature and Czech seasonal precipitation index series derived from documentary evidence (1500-1854); b) grape harvest dates for the Czech Lands (1499-2012); c) oak (Quercus spp.) ring width chronologies from Bohemia (western part of the CR, 1500-2012). Linear regression with subsequent variance scaling were used for calibration in different time intervals covering mostly second part of the 19th and the first part of the 20th centuries. Response functions were further verified on independent proxy and target data. The strongest hydroclimate signal was found for grape harvest dates (more that 70% of explained variance) while oak ring width series show relatively weak reconstruction skill (30% of common variance between proxy and target data). The three SPEI reconstructions show several common features in their long-term variability. Distinctly dry periods cover the first half of the 16th century, which included an extremely dry 1540, and the years since the late 1970s. Higher humidity was characteristic for the second part of the 16th century and also for the turn of the 19th and 20th centuries.

Release of dissolved phosphorus from riparian wetlands: Evidence for complex interactions among hydroclimate variability, topography and soil properties.

PubMed

Gu, Sen; Gruau, Gérard; Dupas, Rémi; Rumpel, Cornélia; Crème, Alexandra; Fovet, Ophélie; Gascuel-Odoux, Chantal; Jeanneau, Laurent; Humbert, Guillaume; Petitjean, Patrice

2017-11-15

In agricultural landscapes, establishment of vegetated buffer zones in riparian wetlands (RWs) is promoted to decrease phosphorus (P) emissions because RWs can trap particulate P from upslope fields. However, long-term accumulation of P risks the release of dissolved P, since the unstable hydrological conditions in these zones may mobilize accumulated particulate P by transforming it into a mobile dissolved P species. This study evaluates how hydroclimate variability, topography and soil properties interact and influence this mobilization, using a three-year dataset of molybdate-reactive dissolved P (MRDP) and total dissolved P (TDP) concentrations in soil water from two RWs located in an agricultural catchment in western France (Kervidy-Naizin), along with stream P concentrations. Two main drivers of seasonal dissolved P release were identified: i) soil rewetting during water-table rise after dry periods and ii) reductive dissolution of soil Fe (hydr)oxides during prolonged water saturation periods. These mechanisms were shown to vary greatly in space (according to topography) and time (according to intra- and interannual hydroclimate variability). The concentration and speciation of the released dissolved P also varied spatially depending on soil chemistry and local topography. Comparison of sites revealed a similar correlation between soil P speciation (percentage of organic P ranging from 35-70%) and the concentration and speciation of the released P (MRDP from <0.10 to 0.40mgl -1 ; percentage of MRDP in TDP from 25-70%). These differences propagated to stream water, suggesting that the two RWs investigated were the main sources of dissolved P to streams. RWs can be critical areas due to their ability to biogeochemically transform the accumulated P in these zones into highly mobile and highly bioavailable dissolved P forms. Hydroclimate variability, local topography and soil chemistry must be considered to decrease the risk of remobilizing legacy soil P when establishing riparian buffer zones in agricultural landscapes. Copyright © 2017 Elsevier B.V. All rights reserved.

30,000 years of hydroclimatic variability in the coastal southwest United States: regional synthesis and forcings analysis.

NASA Astrophysics Data System (ADS)

Kirby, M. E.

2015-12-01

The coastal southwest United States is characterized by a winter dominated hydroclimate. Far from dependable, this region's supply of winter precipitation is highly variable and often characterized by hydrologic opposites - droughts and floods. Predicting future precipitation and hydrologic dynamics requires a paleoperspective. Here, we present an up-to-date synthesis of hydroclimatic variability over the past 30,000 years. A variety of terrestrial-based studies are examined and compared to understand patterns of regional hydroclimatic change. This comparison is extended into the San Joaquin Basin of California where future climate change will impact the region's agricultural stability and economy. Particularly interesting is the apparent role that Pacific sea surface temperatures (SSTs) play in modulating the region's hydroclimate over a variety of timescales. Are past periods of above average Pacific SSTs analogs for future global warming? If yes, the region might expect an increase in winter precipitation as SSTs rise in response to global warming. However, how this potential precipitation increase is manifest is unknown. For example, will the intensity of precipitation events increase and thus present increased flood hazards and diminished freshwater capture? Finally, we present evidence for changes in the source of winter precipitation over time as well as ecological responses to past hydrologic change.

Investigation of n-Alkane Distributions in Modern Plant Litter from Hawaii wetlands: a potential proxy for past vegetation and hydroclimate changes?

NASA Astrophysics Data System (ADS)

Massa, C.; Beilman, D. W.; Nichols, J. E.; Elison Timm, O.

2016-12-01

Holocene peat deposits from the Hawaiian Islands provide a unique opportunity to resolve millennial to centennial-scale climate variability over the central Pacific region, where data remain scarce. Because both extratropical and tropical modes of climate variability have a strong influence on modern rainfall over the archipelago, hydroclimate proxies from peat would provide valuable information about past Pacific climate changes. The few terrestrial records studied, based on pollen or leaf wax biomarkers, showed evidence for substantial vegetation changes that have been linked to a drying trend over the Holocene. Leaf wax n-alkanes, as well as their stable isotopic compositions (δ13C and δD), are indeed increasingly used to reconstruct past hydroclimate conditions. The interpretation of n-alkanes as biomarkers requires however a thorough knowledge of their distribution in modern plants that contribute to sediments, but in Hawaii the modern vegetation is understudied compared to proxy applications. Here we report results from a preliminary investigation of n-alkanes distributions in dominant modern plant litter collected at a bog site at the summit of the Waianae mountains on the Island of Oahu. We compared n-alkane distributions among species and plant groups in order to test whether taxa or plant functional types (mosses, ferns, woody plants, and sedges) can be discriminated from their n-alkane profiles. Results showed that general plant groups were difficult to distinguish based on individual n-alkanes abundances, chain lengths, or ratios. At the species level, the sedge Machaerina augustifolia, was largely dominated by n-C29 ( 60%), suggesting some chain lengths could be useful as proxies for identifying the contribution of sedges to sedimentary records. Woody plant average chain length was highly variable but overall was not shorter (even slightly higher) than in other terrestrial plants, as it is often assumed. A sedimentary profile from this site shows variation and an overall decrease in n-alkane chain length over the Holocene, but patterns across common modern plants suggest that caution should be exercised when ascribing n-alkane distribution parameters to a specific group of tropical vegetation.

Pronounced centennial-scale Atlantic Ocean climate variability correlated with Western Hemisphere hydroclimate.

PubMed

Thirumalai, Kaustubh; Quinn, Terrence M; Okumura, Yuko; Richey, Julie N; Partin, Judson W; Poore, Richard Z; Moreno-Chamarro, Eduardo

2018-01-26

Surface-ocean circulation in the northern Atlantic Ocean influences Northern Hemisphere climate. Century-scale circulation variability in the Atlantic Ocean, however, is poorly constrained due to insufficiently-resolved paleoceanographic records. Here we present a replicated reconstruction of sea-surface temperature and salinity from a site sensitive to North Atlantic circulation in the Gulf of Mexico which reveals pronounced centennial-scale variability over the late Holocene. We find significant correlations on these timescales between salinity changes in the Atlantic, a diagnostic parameter of circulation, and widespread precipitation anomalies using three approaches: multiproxy synthesis, observational datasets, and a transient simulation. Our results demonstrate links between centennial changes in northern Atlantic surface-circulation and hydroclimate changes in the adjacent continents over the late Holocene. Notably, our findings reveal that weakened surface-circulation in the Atlantic Ocean was concomitant with well-documented rainfall anomalies in the Western Hemisphere during the Little Ice Age.

Pronounced centennial-scale Atlantic Ocean climate variability correlated with Western Hemisphere hydroclimate

USGS Publications Warehouse

Thirumalai, Kaustubh; Quinn, Terrence M.; Okumura, Yuko; Richey, Julie; Partin, Judson W.; Poore, Richard Z.; Moreno-Chamarro, Eduardo

2018-01-01

Surface-ocean circulation in the northern Atlantic Ocean influences Northern Hemisphere climate. Century-scale circulation variability in the Atlantic Ocean, however, is poorly constrained due to insufficiently-resolved paleoceanographic records. Here we present a replicated reconstruction of sea-surface temperature and salinity from a site sensitive to North Atlantic circulation in the Gulf of Mexico which reveals pronounced centennial-scale variability over the late Holocene. We find significant correlations on these timescales between salinity changes in the Atlantic, a diagnostic parameter of circulation, and widespread precipitation anomalies using three approaches: multiproxy synthesis, observational datasets, and a transient simulation. Our results demonstrate links between centennial changes in northern Atlantic surface-circulation and hydroclimate changes in the adjacent continents over the late Holocene. Notably, our findings reveal that weakened surface-circulation in the Atlantic Ocean was concomitant with well-documented rainfall anomalies in the Western Hemisphere during the Little Ice Age.

Continuous 1.3-million-year record of East African hydroclimate, and implications for patterns of evolution and biodiversity

NASA Astrophysics Data System (ADS)

Lyons, Robert P.; Scholz, Christopher A.; Cohen, Andrew S.; King, John W.; Brown, Erik T.; Ivory, Sarah J.; Johnson, Thomas C.; Deino, Alan L.; Reinthal, Peter N.; McGlue, Michael M.; Blome, Margaret W.

2015-12-01

The transport of moisture in the tropics is a critical process for the global energy budget and on geologic timescales, has markedly influenced continental landscapes, migratory pathways, and biological evolution. Here we present a continuous, first-of-its-kind 1.3-My record of continental hydroclimate and lake-level variability derived from drill core data from Lake Malawi, East Africa (9-15° S). Over the Quaternary, we observe dramatic shifts in effective moisture, resulting in large-scale changes in one of the world's largest lakes and most diverse freshwater ecosystems. Results show evidence for 24 lake level drops of more than 200 m during the Late Quaternary, including 15 lowstands when water levels were more than 400 m lower than modern. A dramatic shift is observed at the Mid-Pleistocene Transition (MPT), consistent with far-field climate forcing, which separates vastly different hydroclimate regimes before and after ∼800,000 years ago. Before 800 ka, lake levels were lower, indicating a climate drier than today, and water levels changed frequently. Following the MPT high-amplitude lake level variations dominate the record. From 800 to 100 ka, a deep, often overfilled lake occupied the basin, indicating a wetter climate, but these highstands were interrupted by prolonged intervals of extreme drought. Periods of high lake level are observed during times of high eccentricity. The extreme hydroclimate variability exerted a profound influence on the Lake Malawi endemic cichlid fish species flock; the geographically extensive habitat reconfiguration provided novel ecological opportunities, enabling new populations to differentiate rapidly to distinct species.

Continuous 1.3-million-year record of East African hydroclimate, and implications for patterns of evolution and biodiversity

PubMed Central

Lyons, Robert P.; Scholz, Christopher A.; Cohen, Andrew S.; King, John W.; Brown, Erik T.; Ivory, Sarah J.; Johnson, Thomas C.; Deino, Alan L.; Reinthal, Peter N.; McGlue, Michael M.; Blome, Margaret W.

2015-01-01

The transport of moisture in the tropics is a critical process for the global energy budget and on geologic timescales, has markedly influenced continental landscapes, migratory pathways, and biological evolution. Here we present a continuous, first-of-its-kind 1.3-My record of continental hydroclimate and lake-level variability derived from drill core data from Lake Malawi, East Africa (9–15° S). Over the Quaternary, we observe dramatic shifts in effective moisture, resulting in large-scale changes in one of the world’s largest lakes and most diverse freshwater ecosystems. Results show evidence for 24 lake level drops of more than 200 m during the Late Quaternary, including 15 lowstands when water levels were more than 400 m lower than modern. A dramatic shift is observed at the Mid-Pleistocene Transition (MPT), consistent with far-field climate forcing, which separates vastly different hydroclimate regimes before and after ∼800,000 years ago. Before 800 ka, lake levels were lower, indicating a climate drier than today, and water levels changed frequently. Following the MPT high-amplitude lake level variations dominate the record. From 800 to 100 ka, a deep, often overfilled lake occupied the basin, indicating a wetter climate, but these highstands were interrupted by prolonged intervals of extreme drought. Periods of high lake level are observed during times of high eccentricity. The extreme hydroclimate variability exerted a profound influence on the Lake Malawi endemic cichlid fish species flock; the geographically extensive habitat reconfiguration provided novel ecological opportunities, enabling new populations to differentiate rapidly to distinct species. PMID:26644580

Continuous 1.3-million-year record of East African hydroclimate, and implications for patterns of evolution and biodiversity.

PubMed

Lyons, Robert P; Scholz, Christopher A; Cohen, Andrew S; King, John W; Brown, Erik T; Ivory, Sarah J; Johnson, Thomas C; Deino, Alan L; Reinthal, Peter N; McGlue, Michael M; Blome, Margaret W

2015-12-22

The transport of moisture in the tropics is a critical process for the global energy budget and on geologic timescales, has markedly influenced continental landscapes, migratory pathways, and biological evolution. Here we present a continuous, first-of-its-kind 1.3-My record of continental hydroclimate and lake-level variability derived from drill core data from Lake Malawi, East Africa (9-15° S). Over the Quaternary, we observe dramatic shifts in effective moisture, resulting in large-scale changes in one of the world's largest lakes and most diverse freshwater ecosystems. Results show evidence for 24 lake level drops of more than 200 m during the Late Quaternary, including 15 lowstands when water levels were more than 400 m lower than modern. A dramatic shift is observed at the Mid-Pleistocene Transition (MPT), consistent with far-field climate forcing, which separates vastly different hydroclimate regimes before and after ∼800,000 years ago. Before 800 ka, lake levels were lower, indicating a climate drier than today, and water levels changed frequently. Following the MPT high-amplitude lake level variations dominate the record. From 800 to 100 ka, a deep, often overfilled lake occupied the basin, indicating a wetter climate, but these highstands were interrupted by prolonged intervals of extreme drought. Periods of high lake level are observed during times of high eccentricity. The extreme hydroclimate variability exerted a profound influence on the Lake Malawi endemic cichlid fish species flock; the geographically extensive habitat reconfiguration provided novel ecological opportunities, enabling new populations to differentiate rapidly to distinct species.

Sensitivity of Hydrologic Extremes to Spatial Resolution of Meteorological Forcings: A Case Study of the Conterminous United States

NASA Astrophysics Data System (ADS)

Kao, S. C.; Naz, B. S.; Gangrade, S.; Ashfaq, M.; Rastogi, D.

2016-12-01

The magnitude and frequency of hydroclimate extremes are projected to increase in the conterminous United States (CONUS) with significant implications for future water resource planning and flood risk management. Nevertheless, apart from the change of natural environment, the choice of model spatial resolution could also artificially influence the features of simulated extremes. To better understand how the spatial resolution of meteorological forcings may affect hydroclimate projections, we test the runoff sensitivity using the Variable Infiltration Capacity (VIC) model that was calibrated for each CONUS 8-digit hydrologic unit (HUC8) at 1/24° ( 4km) grid resolution. The 1980-2012 gridded Daymet and PRISM meteorological observations are used to conduct the 1/24° resolution control simulation. Comparative simulations are achieved by smoothing the 1/24° forcing into 1/12° and 1/8° resolutions which are then used to drive the VIC model for the CONUS. In addition, we also test how the simulated high and low runoff conditions would react to change in precipitation (±10%) and temperature (+1°C). The results are further analyzed for various types of hydroclimate extremes across different watersheds in the CONUS. This work helps us understand the sensitivity of simulated runoff to different spatial resolutions of climate forcings and also its sensitivity to different watershed sizes and characteristics of extreme events in the future climate conditions.

HydroClimATe: hydrologic and climatic analysis toolkit

USGS Publications Warehouse

Dickinson, Jesse; Hanson, Randall T.; Predmore, Steven K.

2014-01-01

The potential consequences of climate variability and climate change have been identified as major issues for the sustainability and availability of the worldwide water resources. Unlike global climate change, climate variability represents deviations from the long-term state of the climate over periods of a few years to several decades. Currently, rich hydrologic time-series data are available, but the combination of data preparation and statistical methods developed by the U.S. Geological Survey as part of the Groundwater Resources Program is relatively unavailable to hydrologists and engineers who could benefit from estimates of climate variability and its effects on periodic recharge and water-resource availability. This report documents HydroClimATe, a computer program for assessing the relations between variable climatic and hydrologic time-series data. HydroClimATe was developed for a Windows operating system. The software includes statistical tools for (1) time-series preprocessing, (2) spectral analysis, (3) spatial and temporal analysis, (4) correlation analysis, and (5) projections. The time-series preprocessing tools include spline fitting, standardization using a normal or gamma distribution, and transformation by a cumulative departure. The spectral analysis tools include discrete Fourier transform, maximum entropy method, and singular spectrum analysis. The spatial and temporal analysis tool is empirical orthogonal function analysis. The correlation analysis tools are linear regression and lag correlation. The projection tools include autoregressive time-series modeling and generation of many realizations. These tools are demonstrated in four examples that use stream-flow discharge data, groundwater-level records, gridded time series of precipitation data, and the Multivariate ENSO Index.

Glacial forcing of central Indonesian hydroclimate since 60,000 y B.P.

PubMed Central

Russell, James M.; Vogel, Hendrik; Konecky, Bronwen L.; Bijaksana, Satria; Huang, Yongsong; Melles, Martin; Wattrus, Nigel; Costa, Kassandra; King, John W.

2014-01-01

The Indo-Pacific warm pool houses the largest zone of deep atmospheric convection on Earth and plays a critical role in global climate variations. Despite the region’s importance, changes in Indo-Pacific hydroclimate on orbital timescales remain poorly constrained. Here we present high-resolution geochemical records of surface runoff and vegetation from sediment cores from Lake Towuti, on the island of Sulawesi in central Indonesia, that continuously span the past 60,000 y. We show that wet conditions and rainforest ecosystems on Sulawesi present during marine isotope stage 3 (MIS3) and the Holocene were interrupted by severe drying between ∼33,000 and 16,000 y B.P. when Northern Hemisphere ice sheets expanded and global temperatures cooled. Our record reveals little direct influence of precessional orbital forcing on regional climate, and the similarity between MIS3 and Holocene climates observed in Lake Towuti suggests that exposure of the Sunda Shelf has a weaker influence on regional hydroclimate and terrestrial ecosystems than suggested previously. We infer that hydrological variability in this part of Indonesia varies strongly in response to high-latitude climate forcing, likely through reorganizations of the monsoons and the position of the intertropical convergence zone. These findings suggest an important role for the tropical western Pacific in amplifying glacial–interglacial climate variability. PMID:24706841

Sub-annual North Pacific hydroclimate variability since 1450AD from updated St. Elias ice core isotope and accumulation rate records

NASA Astrophysics Data System (ADS)

Kreutz, K. J.; Campbell, S. W.; Winski, D.; Osterberg, E. C.; Kochtitzky, W. H.; Copland, L.; Dixon, D.; Introne, D.; Medrzycka, D.; Main, B.; Bernsen, S.; Wake, C. P.

2017-12-01

A growing array of high-resolution paleoclimate records from the terrestrial region bordering the Gulf of Alaska (GoA) continues to reveal details about ocean-atmosphere variability in the region during the Common Era. Ice core records from high-elevation ranges in proximity to the GoA provide key information on extratropical hydroclimate, and potential teleconnections to low latitude regions. In particular, stable water isotope and snow accumulation reconstructions from ice cores collected in high precipitation locations are uniquely tied to regional water cycle changes. Here we present new data collected in 2016 and 2017 from the St. Elias Mountains (Eclipse Icefield, Yukon Territories, Canada), including a range of ice core and geophysical measurements. Low- and high-frequency ice penetrating radar data enable detailed mapping of icefield bedrock topography and internal reflector stratigraphy. The 1911 Katmai eruption layer can be clearly traced across the icefield, and tied definitively to the coeval ash layer found in the 345 meter ice core drilled at Eclipse Icefield in 2002. High-resolution radar data are used to map spatial variability in 2015/16 and 2016/17 snow accumulation. Ice velocity data from repeat GPS stake measurements and remote sensing feature tracking reveal a clear divide flow regime on the icefield. Shallow firn/ice cores (20 meters in 2017 and 65 meters in 2016) are used to update the 345 meter ice core drilled at Eclipse Icefield in 2002. We use new algorithm-based layer counting software to improve and provide error estimates on the new ice core chronology, which extends from 2017 to 1450AD. 3D finite element modeling, incorporating all available geophysical data, is used to refine the reconstructed accumulation rate record and account for vertical and horizontal ice flow. Together with high-resolution stable water isotope data, the updated Eclipse record provides detailed, sub-annual resolution data on several aspects of the regional water cycle (e.g., accumulation/precipitation, moisture source and trajectory, coupled ocean/atmosphere variability). We compare the updated Eclipse record with other data in the North Pacific region, including the new Denali 1200-year ice core datasets, to assess regional hydroclimate variability during the Common Era.

Ocean-atmosphere forcing of centennial hydroclimatic variability in the Pacific Northwest

USGS Publications Warehouse

Steinman, Byron A.; Abbott, Mark B.; Mann, Michael E.; Ortiz, Joseph D.; Feng, Song; Pompeani, David P.; Stansell, Nathan D.; Anderson, Lesleigh; Finney, Bruce P.; Bird, Broxton W.

2014-01-01

Reconstructing centennial timescale hydroclimate variability during the late Holocene is critically important for understanding large-scale patterns of drought and their relationship with climate dynamics. We present sediment oxygen isotope records spanning the last two millennia from 10 lakes, as well as climate model simulations, indicating that the Little Ice Age was dry relative to the Medieval Climate Anomaly in much of the Pacific Northwest of North America. This pattern is consistent with observed associations between the El Niño Southern Oscillation (ENSO), the Northern Annular Mode and drought as well as with proxy-based reconstructions of Pacific ocean-atmosphere variations over the past 1000 years. The large amplitude of centennial variability indicated by the lake data suggests that regional hydroclimate is characterized by longer-term shifts in ENSO-like dynamics, and that an improved understanding of the centennial timescale relationship between external forcing and drought conditions is necessary for projecting future hydroclimatic conditions in western North America.

Examining Basin-Scale Water and Climate Relations across the Pampa del Tamarugal, Atacama Desert through Spatial Analysis of Hydrogen, Carbon and Oxygen Isotopes in Tree Rings

NASA Astrophysics Data System (ADS)

Olson, E. J.; Dodd, J. P.; Rivera, M. A.

2016-12-01

Arid regions are extremely sensitive to variations hydroclimate. However, our understanding of past hydroclimate variations in these regions is often limited by a paucity of spatially resolved proxy data. The Atacama Desert of northern Chile is one of the driest regions on Earth, and hydroclimatic processes in the Atacama Desert may be a useful proxy for understanding the implications of expanding global aridity. In order to assess the ability of tree-ring isotope studies to record changes in hydrology and terrestrial climate in the Atacama Desert, oxygen (δ18O), carbon (δ13C) and hydrogen (δ2H) isotope values in tree rings of Prosopis tamarugo are analyzed for the modern period (1954-2014) when anthropogenic change to regional groundwater levels have been most notable. Samples of wood cellulose were collected throughout the Pampa del Tamarugal basin from 14 individuals and used to create an interpolated surface of isotope variations. The isotope data were then compared to groundwater depth from well monitoring data provided by the Dirección de General de Agua of Chile. There is a significant correlation between groundwater level and isotope values with best agreement occurring during the past two decades for δ18O (r = 0.58), δ13C (r = 0.55), and δ2H (r = 0.66) values. This spatial correlation analysis reveals that tree ring a-cellulose isotope values are a suitable proxy for reconstructing groundwater depth in the Pampa del Tamarugal Basin. A stepwise multiregression analysis between δ18O values of cellulose and several other environmental variables including groundwater level, relative humidity, and temperature suggest that groundwater depth is the dominate control of variation in the modern δ18O tree ring record. The response of tree cellulose to the hydroclimate in this region suggests that tree ring isotope variations may be used to reconstruct past hydroclimate conditions in arid regions throughout the globe.

Insight into the Pacific Sea Surface Temperature- North American Hydroclimate Connection from an Eastern Tropical North Pacific Coral Record

NASA Astrophysics Data System (ADS)

Sanchez, S. C.; Charles, C. D.; Carriquiry, J. D.

2015-12-01

The last few years of record-breaking climate anomalies across North America--a resilient atmospheric ridge and extreme drought over the West Coast, and severe winters across the Midwest and East Coast regions--have been linked to anomalous Pacific sea surface temperatures (Seager et al. 2014, Wang et al. 2014, Hartmann 2015). The synoptic associations prompt important questions on the relation between these unusual phenomena and extreme expressions of known Pacific decadal modes, such as the North Pacific Gyre Oscillation (NPGO). These questions motivate our pursuit to document multiple realizations of decadal variability in the Pacific-North American region through periods of varied radiative forcing. Here we introduce a 178 year, seasonally resolved Porites coral record from Clarion Island (18N, 115W), the westernmost island of the Revillagigedo Archipelago, a region both highly influenced by NPGO SST and SSS variability and critical for NPGO tropical-extratropical communication via the Seasonal Footprinting Mechanism (Vimont et al. 2003). When coupled with tree ring records from the western United States (Griffin and Anchukaitis 2014, MacDonald and Case 2005) and coral records from the central tropical Pacific (Cobb et al. 2001), the δ18O signal from the Clarion coral offers an extended framework of coherent continental hydroclimate and oceanic variability across the Pacific basin beyond the instrumental record. Over the last 200 years, we find clear commonality in the timing, magnitude and spatial expression of variability (illustrated through the NADA Atlas, Cook et al. 2004) amongst the proxy records. The strong relationship between Northeastern Pacific Clarion and the Central Pacific Palmyra record with the North American hydroclimate records can be viewed within the mechanistic framework of the NPGO; this framework is then explored over the last millennium across intervals of varied radiative forcing.

Insight into the Pacific Sea Surface Temperature- North American Hydroclimate Connection from an Eastern Tropical North Pacific Coral Record

NASA Astrophysics Data System (ADS)

Svendsen, J. I.; Briner, J. P.; Mangerud, J.; Hughes, A. L. C.; Young, N. E.; Vasskog, K.

2014-12-01

The last few years of record-breaking climate anomalies across North America--a resilient atmospheric ridge and extreme drought over the West Coast, and severe winters across the Midwest and East Coast regions--have been linked to anomalous Pacific sea surface temperatures (Seager et al. 2014, Wang et al. 2014, Hartmann 2015). The synoptic associations prompt important questions on the relation between these unusual phenomena and extreme expressions of known Pacific decadal modes, such as the North Pacific Gyre Oscillation (NPGO). These questions motivate our pursuit to document multiple realizations of decadal variability in the Pacific-North American region through periods of varied radiative forcing. Here we introduce a 178 year, seasonally resolved Porites coral record from Clarion Island (18N, 115W), the westernmost island of the Revillagigedo Archipelago, a region both highly influenced by NPGO SST and SSS variability and critical for NPGO tropical-extratropical communication via the Seasonal Footprinting Mechanism (Vimont et al. 2003). When coupled with tree ring records from the western United States (Griffin and Anchukaitis 2014, MacDonald and Case 2005) and coral records from the central tropical Pacific (Cobb et al. 2001), the δ18O signal from the Clarion coral offers an extended framework of coherent continental hydroclimate and oceanic variability across the Pacific basin beyond the instrumental record. Over the last 200 years, we find clear commonality in the timing, magnitude and spatial expression of variability (illustrated through the NADA Atlas, Cook et al. 2004) amongst the proxy records. The strong relationship between Northeastern Pacific Clarion and the Central Pacific Palmyra record with the North American hydroclimate records can be viewed within the mechanistic framework of the NPGO; this framework is then explored over the last millennium across intervals of varied radiative forcing.

Insights into hydroclimatic variability of Southern California since 125 ka, from multi-proxy analyses of alpine lakes

NASA Astrophysics Data System (ADS)

Glover, K. C.; MacDonald, G. M.; Kirby, M.

2016-12-01

Hydroclimatic variability is especially important in California, a water-stressed and increasingly populous region. We assess the range of past hydroclimatic sensitivity and variability in the San Bernardino Mountains of Southern California based on 125 ka of lacustrine sediment records. Geochemistry, charcoal and pollen highlight periods of sustained moisture, aridity and sudden variability driven by orbital and oceanic variations. Marine Isotope Stage 3 (MIS 3) is one such period of greater moisture availability that lasted c. 30 kyr, with smaller-scale perturbations likely reflect North Atlantic Dansgaard-Oeschgar events. Past glacial periods, MIS 4 and MIS 2, display high-amplitude changes. These include periods of reduced forest cover that span millennia, indicating long-lasting aridity. Rapid forest expansion also occurs, marking sudden shifts towards wet conditions. Fire regimes have also changed in tandem with hydroclimate and vegetation. Higher-resolution analysis of the past 10 ka shows that Southern California hydroclimate was broadly similar to other regions of the Southwest and Great Basin, including an orbital and oceanic-driven wet Early Holocene, dry Mid-Holocene, and highly variable Late Holocene. Shorter-term pluvial conditions occur throughout the Holocene, with episodic moisture likely derived from a Pacific source.

Relative impacts of mitigation, temperature, and precipitation on 21st-Century megadrought risk in the American Southwest.

NASA Astrophysics Data System (ADS)

Ault, T.; Mankin, J. S.; Cook, B.; Smerdon, J. E.

2016-12-01

Megadroughts are comparable in severity to the worst droughts of the 20th Century, but of much longer duration. A megadrought in the American Southwest would impose unprecedented stress on the limited water resources of the area, making it critical to evaluate future risks under different climate change mitigation scenarios, as well as for different aspects of regional hydroclimate. We find changes in the mean hydroclimate state, rather than its variability, determine megadrought risk in the American Southwest. Estimates of megadrought probability based on precipitation alone tend to underestimate risk. Furthermore, business-as-usual emissions of greenhouse gases will drive regional warming and drying, despite the high uncertainty regarding precipitation. We find regional temperature increases alone push megadrought risk above 70%, 90%, or 99% by the end of the century, even if precipitation increases moderately, does not change, or decreases, respectively. While each outcome is supported by some climate models, the latter is the most common projection for the American Southwest. An aggressive reduction in global greenhouse gas emissions cuts these risks nearly in half.

Late Holocene Hydroclimate Variability of West-Central Guatemala Driven by NAO and ENSO

NASA Astrophysics Data System (ADS)

Stansell, N.; Feller, J. R.; Steinman, B. A.; Lachniet, M. S.; Shea, C.; Avendaño, C.

2016-12-01

Finely-laminated sediments from Lake San Francisco in the Huehuetenango province of west-central Guatemala provide a sub-decadal resolution record of hydroclimate variability spanning the last 5200 years. Age control is based on 7 radiocarbon samples of charcoal and lead-210 dating of surface sediments. Modern water isotope samples indicate the lake is currently an open system, and variations of δ18O values of precipitation in the region are driven largely by the amount effect. In contrast, a strong covariance of δ18O and δ13C values combined with pollen evidence in the lower part of the record suggests the lake was a seasonally closed-basin from 5200 to 3200 BP, and was sensitive to evaporation under more arid conditions. There was an overall trend of increasingly wetter conditions during the late Holocene, and a lack of covariance between δ18O and δ13C indicates that the lake transitioned to an open-basin after 3200 BP. The Medieval Climate Anomaly was the wettest period of the late Holocene, and there was a shift to lower precipitation amounts during the Little Ice Age. Present conditions are more arid than most of the last millennium, but δ18O values in the modern sediments are intermediate compared to the full late Holocene. The Lake San Francisco record provides additional evidence that the hydroclimate of Central America is sensitive to both changes in North Atlantic Oscillation (NAO) and the El Niño Southern Oscillation (ENSO). Drier conditions at San Francisco over the length of the record were associated with more negative phases of NAO and vice versa. During the last 1500 years, drier conditions at San Francisco were also associated with warmer sea-surface temperatures (SSTs) in the Niño3 region, and it was wetter when SSTs were colder.

Climate change effects on water allocations with season dependent water rights.

PubMed

Null, Sarah E; Prudencio, Liana

2016-11-15

Appropriative water rights allocate surface water to competing users based on seniority. Often water rights vary seasonally with spring runoff, irrigation schedules, or other non-uniform supply and demand. Downscaled monthly Coupled Model Intercomparison Project multi-model, multi-emissions scenario hydroclimate data evaluate water allocation reliability and variability with anticipated hydroclimate change. California's Tuolumne watershed is a study basin, chosen because water rights are well-defined, simple, and include competing environmental, agricultural, and urban water uses representative of most basins. We assume that dedicated environmental flows receive first priority when mandated by federal law like the Endangered Species Act or hydropower relicensing, followed by senior agricultural water rights, and finally junior urban water rights. Environmental flows vary by water year and include April pulse flows, and senior agricultural water rights are 68% larger during historical spring runoff from April through June. Results show that senior water right holders receive the largest climate-driven reductions in allocated water when peak streamflow shifts from snowmelt-dominated spring runoff to mixed snowmelt- and rainfall-dominated winter runoff. Junior water right holders have higher uncertainty from inter-annual variability. These findings challenge conventional wisdom that water shortages are absorbed by junior water users and suggest that aquatic ecosystems may be disproportionally impaired by hydroclimate change, even when environmental flows receive priority. Copyright © 2016 Elsevier B.V. All rights reserved.

Assessing the climate-scale variability of atmospheric rivers affecting western North America

NASA Astrophysics Data System (ADS)

Gershunov, Alexander; Shulgina, Tamara; Ralph, F. Martin; Lavers, David A.; Rutz, Jonathan J.

2017-08-01

A new method for automatic detection of atmospheric rivers (ARs) is developed and applied to an atmospheric reanalysis, yielding an extensive catalog of ARs land-falling along the west coast of North America during 1948-2017. This catalog provides a large array of variables that can be used to examine AR cases and their climate-scale variability in exceptional detail. The new record of AR activity, as presented, validated and examined here, provides a perspective on the seasonal cycle and the interannual-interdecadal variability of AR activity affecting the hydroclimate of western North America. Importantly, AR intensity does not exactly follow the climatological pattern of AR frequency. Strong links to hydroclimate are demonstrated using a high-resolution precipitation data set. We describe the seasonal progression of AR activity and diagnose linkages with climate variability expressed in Pacific sea surface temperatures, revealing links to Pacific decadal variability, recent regional anomalies, as well as a generally rising trend in land-falling AR activity. The latter trend is consistent with a long-term increase in vapor transport from the warming North Pacific onto the North American continent. The new catalog provides unprecedented opportunities to study the climate-scale behavior and predictability of ARs affecting western North America.

A new space-time characterization of Northern Hemisphere drought in model simulations of the past and future as compared to the paleoclimate record

NASA Astrophysics Data System (ADS)

Coats, S.; Smerdon, J. E.; Stevenson, S.; Fasullo, J.; Otto-Bliesner, B. L.

2017-12-01

The observational record, which provides only limited sampling of past climate variability, has made it difficult to quantitatively analyze the complex spatio-temporal character of drought. To provide a more complete characterization of drought, machine learning based methods that identify drought in three-dimensional space-time are applied to climate model simulations of the last millennium and future, as well as tree-ring based reconstructions of hydroclimate over the Northern Hemisphere extratropics. A focus is given to the most persistent and severe droughts of the past 1000 years. Analyzing reconstructions and simulations in this context allows for a validation of the spatio-temporal character of persistent and severe drought in climate model simulations. Furthermore, the long records provided by the reconstructions and simulations, allows for sufficient sampling to constrain projected changes to the spatio-temporal character of these features using the reconstructions. Along these lines, climate models suggest that there will be large increases in the persistence and severity of droughts over the coming century, but little change in their spatial extent. These models, however, exhibit biases in the spatio-temporal character of persistent and severe drought over parts of the Northern Hemisphere, which may undermine their usefulness for future projections. Despite these limitations, and in contrast to previous claims, there are no systematic changes in the character of persistent and severe droughts in simulations of the historical interval. This suggests that climate models are not systematically overestimating the hydroclimate response to anthropogenic forcing over this period, with critical implications for confidence in hydroclimate projections.

Synchronous precipitation reduction in the American Tropics associated with Heinrich 2.

PubMed

Medina-Elizalde, Martín; Burns, Stephen J; Polanco-Martinez, Josué; Lases-Hernández, Fernanda; Bradley, Raymond; Wang, Hao-Cheng; Shen, Chuan-Chou

2017-09-11

During the last ice age temperature in the North Atlantic oscillated in cycles known as Dansgaard-Oeschger (D-O) events. The magnitude of Caribbean hydroclimate change associated with D-O variability and particularly with stadial intervals, remains poorly constrained by paleoclimate records. We present a 3.3 thousand-year long stalagmite δ 18 O record from the Yucatan Peninsula (YP) that spans the interval between 26.5 and 23.2 thousand years before present. We estimate quantitative precipitation variability and the high resolution and dating accuracy of this record allow us to investigate how rainfall in the region responds to D-O events. Quantitative precipitation estimates are based on observed regional amount effect variability, last glacial paleotemperature records, and estimates of the last glacial oxygen isotopic composition of precipitation based on global circulation models (GCMs). The new precipitation record suggests significant low latitude hydrological responses to internal modes of climate variability and supports a role of Caribbean hydroclimate in helping Atlantic Meridional Overturning Circulation recovery during D-O events. Significant in-phase precipitation reduction across the equator in the tropical Americas associated with Heinrich event 2 is suggested by available speleothem oxygen isotope records.

Global Synthesis of Common Era Hydroclimate using Water Isotope Proxies from Multiple Archives: First Results from the PAGES Iso2k Project

NASA Astrophysics Data System (ADS)

Konecky, B. L.; Partin, J. W.; Conroy, J. L.; Fischer, M.; Jones, M.; Jonkers, L.; McKay, N.; Stevenson, S.; Thompson, D. M.; Tyler, J. J.; Churakova (Sidorova), O.; Comas-Bru, L.; Dassie, E. P.; Dee, S.; DeLong, K. L.; Falster, G.; Martrat, B.

2017-12-01

Global, multi-proxy paleoclimate data syntheses for the Common Era (CE) have revealed a long-term cooling over the past millennium followed by a recent warming, with possible multi-decadal to centennial temperature variability in some regions. However, changes in atmospheric-oceanic circulation or hydroclimate have yet to be assessed on a global scale. Excellently suited to this purpose are proxies for the δ18O and δD of environmental waters found in glacier and ground ice, speleothems, corals, tree rings, and lake and marine sediments, which track common signals related to circulation and hydroclimate. Here, we utilize the new PAGES Iso2k database, a global compilation of CE δ18O and δD records, to investigate spatiotemporal variability and secular trends in global hydroclimate during the past 2 kyr. Overall, subtle but robust circulation shifts are apparent during the CE. We find preliminary evidence for secular trends in δ18O of lake water, precipitation/soil water, and seawater, with the direction and magnitude of trends varying by the type of environmental water (e.g., precipitation vs. seawater) and by region. We also find evidence for centennial-scale variations in regional δ18O and δD, for example a basin-wide Atlantic δ18Oseawater anomaly emerging during the 18th century and possible freshening of the western Pacific during the 20th century. On land, latitudinal trends in mean CE δ18Olake are consistent with present day gradients of δ18Oprecipitation, with evaporation exerting additional strong influence at mid-latitudes. In the ocean, coral δ18O in the western equatorial Pacific is found to reflect salinity rather than (or in addition to) temperature, providing potential quantitative constraints on past moisture balance from corals. We evaluate the dynamics of these spatiotemporal patterns through comparison with isotope-enabled model simulations, discuss relevant climatic inferences, and reexamine proxy interpretations.

A leaf wax biomarker record of early Pleistocene hydroclimate from West Turkana, Kenya

NASA Astrophysics Data System (ADS)

Lupien, R. L.; Russell, J. M.; Feibel, C.; Beck, C.; Castañeda, I.; Deino, A.; Cohen, A. S.

2018-04-01

Climate is thought to play a critical role in human evolution; however, this hypothesis is difficult to test due to a lack of long, high-quality paleoclimate records from key hominin fossil locales. To address this issue, we analyzed organic geochemical indicators of climate in a drill core from West Turkana, Kenya that spans ∼1.9-1.4 Ma, an interval that includes several important hominin evolutionary transitions. We analyzed the hydrogen isotopic composition of terrestrial plant waxes (δDwax) to reconstruct orbital-timescale changes in regional hydrology and their relationship with global climate forcings and the hominin fossil record. Our data indicate little change in the long-term mean hydroclimate during this interval, in contrast to inferred changes in the level of Lake Turkana, suggesting that lake level may be responding dominantly to deltaic progradation or tectonically-driven changes in basin configuration as opposed to hydroclimate. Time-series spectral analyses of the isotopic data reveal strong precession-band (21 kyr) periodicity, indicating that regional hydroclimate was strongly affected by changes in insolation. We observe an interval of particularly high-amplitude hydrologic variation at ∼1.7 Ma, which occurs during a time of high orbital eccentricity hence large changes in processionally-driven insolation amplitude. This interval overlaps with multiple hominin species turnovers, the appearance of new stone tool technology, and hominin dispersal out of Africa, supporting the notion that climate variability played an important role in hominin evolution.

HydroClim: a Continental-Scale Database of Contemporary and Future Streamflow and Stream Temperature Estimates for Aquatic Ecosystem Studies

NASA Astrophysics Data System (ADS)

Knouft, J.; Ficklin, D. L.; Bart, H. L.; Rios, N. E.

2017-12-01

Streamflow and water temperature are primary factors influencing the traits, distribution, and diversity of freshwater species. Ongoing changes in climate are causing directional alteration of these environmental conditions, which can impact local ecological processes. Accurate estimation of these variables is critical for predicting the responses of species to ongoing changes in freshwater habitat, yet ecologically relevant high-resolution data describing variation in streamflow and water temperature across North America are not available. Considering the vast amount of web-accessible freshwater biodiversity data, development and application of appropriate hydrologic data are critical to the advancement of our understanding of freshwater systems. To address this issue, we are developing the "HydroClim" database, which will provide web-accessible (www.hydroclim.org) historical and projected monthly streamflow and water temperature data for stream sections in all major watersheds across the United States and Canada from 1950-2099. These data will also be integrated with FishNet 2 (www.fishnet2.net), an online biodiversity database that provides open access to over 2 million localities of freshwater fish species in the United States and Canada, thus allowing for the characterization of the habitat requirements of freshwater species across this region. HydroClim should provide a vast array of opportunities for a greater understanding of water resources as well as information for the conservation of freshwater biodiversity in the United States and Canada in the coming century.

Potential for western US seasonal snowpack prediction

USGS Publications Warehouse

Kapnick, Sarah B.; Yang, Xiaosong; Vecchi, Gabriel A.; Delworth, Thomas L.; Gudgel, Rich; Malyshev, Sergey; Milly, Paul C. D.; Shevliakova, Elena; Underwood, Seth; Margulis, Steven A.

2018-01-01

Western US snowpack—snow that accumulates on the ground in the mountains—plays a critical role in regional hydroclimate and water supply, with 80% of snowmelt runoff being used for agriculture. While climate projections provide estimates of snowpack loss by the end of th ecentury and weather forecasts provide predictions of weather conditions out to 2 weeks, less progress has been made for snow predictions at seasonal timescales (months to 2 years), crucial for regional agricultural decisions (e.g., plant choice and quantity). Seasonal predictions with climate models first took the form of El Niño predictions 3 decades ago, with hydroclimate predictions emerging more recently. While the field has been focused on single-season predictions (3 months or less), we are now poised to advance our predictions beyond this timeframe. Utilizing observations, climate indices, and a suite of global climate models, we demonstrate the feasibility of seasonal snowpack predictions and quantify the limits of predictive skill 8 month sin advance. This physically based dynamic system outperforms observation-based statistical predictions made on July 1 for March snowpack everywhere except the southern Sierra Nevada, a region where prediction skill is nonexistent for every predictor presently tested. Additionally, in the absence of externally forced negative trends in snowpack, narrow maritime mountain ranges with high hydroclimate variability pose a challenge for seasonal prediction in our present system; natural snowpack variability may inherently be unpredictable at this timescale. This work highlights present prediction system successes and gives cause for optimism for developing seasonal predictions for societal needs.

Relative impacts of mitigation, temperature, and precipitation on 21st-century megadrought risk in the American Southwest

PubMed Central

Ault, Toby R.; Mankin, Justin S.; Cook, Benjamin I.; Smerdon, Jason E.

2016-01-01

Megadroughts are comparable in severity to the worst droughts of the 20th century but are of much longer duration. A megadrought in the American Southwest would impose unprecedented stress on the limited water resources of the area, making it critical to evaluate future risks not only under different climate change mitigation scenarios but also for different aspects of regional hydroclimate. We find that changes in the mean hydroclimate state, rather than its variability, determine megadrought risk in the American Southwest. Estimates of megadrought probabilities based on precipitation alone tend to underestimate risk. Furthermore, business-as-usual emissions of greenhouse gases will drive regional warming and drying, regardless of large precipitation uncertainties. We find that regional temperature increases alone push megadrought risk above 70, 90, or 99% by the end of the century, even if precipitation increases moderately, does not change, or decreases, respectively. Although each possibility is supported by some climate model simulations, the latter is the most common outcome for the American Southwest in Coupled Model Intercomparison 5 generation models. An aggressive reduction in global greenhouse gas emissions cuts megadrought risks nearly in half. PMID:27713927

Relative Impacts of Mitigation, Temperature, and Precipitation on 21st-Century Megadrought Risk in the American Southwest

NASA Technical Reports Server (NTRS)

Ault, Toby R.; Mankin, Justin S.; Cook, Benjamin I.; Smerdon, Jason E.

2015-01-01

Megadroughts are comparable in severity to the worst droughts of the 20th century but are of much longer duration. A megadrought in the American Southwest would impose unprecedented stress on the limited water resources of the area, making it critical to evaluate future risks not only under different climate change mitigation scenarios but also for different aspects of regional hydroclimate. We find that changes in the mean hydroclimate state, rather than its variability, determine megadrought risk in the American Southwest. Estimates of megadrought probabilities based on precipitation alone tend to underestimate risk. Furthermore, business-as-usual emissions of greenhouse gases will drive regional warming and drying, regardless of large precipitation uncertainties. We find that regional temperature increases alone push megadrought risk above 70, 90, or 99% by the end of the century, even if precipitation increases moderately, does not change, or decreases, respectively. Although each possibility is supported by some climate model simulations, the latter is the most common outcome for the American Southwest in Coupled Model Intercomparison 5 generation models. An aggressive reduction in global greenhouse gas emissions cuts megadrought risks nearly in half.

Centennial-scale links between Atlantic Ocean dynamics and hydroclimate over the last 4400 years: Insights from the northern Gulf of Mexico

NASA Astrophysics Data System (ADS)

Thirumalai, K.; Quinn, T. M.; Okumura, Y.; Richey, J. N.; Partin, J. W.; Poore, R. Z.

2015-12-01

Surface circulation in the Atlantic Ocean is an important mediator of global climate and yet its variability is poorly constrained on centennial timescales. Changes in the Atlantic meridional overturning circulation (AMOC) have been implicated in late Holocene climate variability in the Western Hemisphere, although the relationship between AMOC variability and hydroclimate is uncertain due to the lack of sufficiently highly resolved proxy records. Here we present a replicated reconstruction of sea-surface temperature (SST) and salinity (SSS) from the Garrison Basin in the northern Gulf of Mexico (NGOM) spanning the last 4,400 years to better constrain past sea-surface conditions. We generated time series of paired Mg/Ca (SST proxy) and δ18O (SST and SSS proxy) variations in planktic foraminifer Globigerinoides ruber (white variety) from three multi-cores collected in 2010. Using a Monte Carlo-based technique we produce a stacked record from the three multi-cores and constrain analytical, calibration, chronological, and sampling uncertainties. We apply this technique to existing paired Mg/Ca- δ18O studies in the Gulf of Mexico and Atlantic Ocean to facilitate comparison between time-uncertain proxy reconstructions. The Garrison Basin stack exhibits large centennial-scale variability (σSST~0.6°C; δ18Osw~0.17‰) and indicates a substantially cool (0.9±0.5°C) and fresh (0.26±0.1‰) Little Ice Age (LIA; 1450-1850 A.D.), corroborating extant records from the Gulf of Mexico. Focusing on the last millennium, we analyze a suite of oceanic and terrestrial proxy records to demonstrate a centennial-scale link between salt advection in the Atlantic Ocean, a diagnostic parameter of ocean circulation, and hydroclimate in the adjacent continents. The ensuing multiproxy relationships seem to be consistent with spatial field correlations of limited salinity and rainfall instrumental/reanalysis data, which suggest that NGOM salinity varies with large-scale Atlantic Ocean circulation and continental precipitation. Our results imply significant centennial-scale variability over the late Holocene and are consistent with limited observational analysis indicating a slowdown of AMOC during the LIA.

River chemistry as a monitor of Yosemite Park mountain hydroclimates

USGS Publications Warehouse

Peterson, David; Smith, Richard; Hager, Stephen; Hicke, Jeffrey A.; Dettinger, Michael; Huber, King

2005-01-01

Climate is the major source of variability in U.S. and global water resources. For example, large-scale variations in the global atmosphere and the Pacific Ocean are responsible for much of the variability in river discharge in Hawaii, Alaska, the U.S. Pacific Northwest, and the U.S. Southwest [Cayan and Peterson, 1989], and thus are closely linked to water and energy resources of the western United States [Cayan et al., 2003].

Linking hydroclimate to fish phenology and habitat use with ichthyographs

Treesearch

Rebecca L. Flitcroft; Sarah L. Lewis; Ivan Arismendi; Rachel LovellFord; Mary V. Santelmann; Mohammad Safeeq; Gordon Grant; Kyle A. Young

2016-01-01

Streamflow and water temperature (hydroclimate) influence the life histories of aquatic biota. The relationship between streamflow and temperature varies with climate, hydrogeomorphic setting, and season. Life histories of native fishes reflect, in part, their adaptation to regional hydroclimate (flow and water temperature), local habitats, and natural disturbance...

Examining the utility of coral Ba/Ca as a proxy for river discharge and hydroclimate variability at Coiba Island, Gulf of Chirquí, Panamá.

PubMed

Brenner, Logan D; Linsley, Braddock K; Dunbar, Robert B

2017-05-15

Panamá's extreme hydroclimate seasonality is driven by Intertropical Convergence Zone rainfall and resulting runoff. River discharge (Q) carries terrestrially-derived barium to coastal waters that can be recorded in coral. We present a Ba/Ca record (1996-1917) generated from a Porites coral colony in the Gulf of Chiriquí near Coiba Island (Panamá) to understand regional hydroclimate. Here coral Ba/Ca is correlated to instrumental Q (R=0.67, p<0.001), producing a seasonally-resolved Reduced Major Axis regression of Ba/Ca (μmol/mol)=Q (m 3 /s)×0.006±0.001 (μmol/mol)(m 3 /s) -1 +4.579±0.151. Our results support work in the neighboring Gulf of Panamá that determined seawater Ba/Ca, controlled by Q, is correlated to coral Ba/Ca (LaVigne et al., 2016). Additionally, the Coiba coral Ba/Ca records at least 5 El Niño events and identified 22 of the 37 wet seasons with below average precipitation. These data corroborate the Q proxy and provide insight into the use of coral Ba/Ca as an El Niño and drought indicator. Copyright © 2017 Elsevier Ltd. All rights reserved.

Patterns of precipitation and soil moisture extremes in Texas, US: A complex network analysis

NASA Astrophysics Data System (ADS)

Sun, Alexander Y.; Xia, Youlong; Caldwell, Todd G.; Hao, Zengchao

2018-02-01

Understanding of the spatial and temporal dynamics of extreme precipitation not only improves prediction skills, but also helps to prioritize hazard mitigation efforts. This study seeks to enhance the understanding of spatiotemporal covariation patterns embedded in precipitation (P) and soil moisture (SM) by using an event-based, complex-network-theoretic approach. Events concurrences are quantified using a nonparametric event synchronization measure, and spatial patterns of hydroclimate variables are analyzed by using several network measures and a community detection algorithm. SM-P coupling is examined using a directional event coincidence analysis measure that takes the order of event occurrences into account. The complex network approach is demonstrated for Texas, US, a region possessing a rich set of hydroclimate features and is frequented by catastrophic flooding. Gridded daily observed P data and simulated SM data are used to create complex networks of P and SM extremes. The uncovered high degree centrality regions and community structures are qualitatively in agreement with the overall existing knowledge of hydroclimate extremes in the study region. Our analyses provide new visual insights on the propagation, connectivity, and synchronicity of P extremes, as well as the SM-P coupling, in this flood-prone region, and can be readily used as a basis for event-driven predictive analytics for other regions.

Centennial and millennial-scale hydroclimate changes in northwestern Patagonia since 16,000 yr BP

NASA Astrophysics Data System (ADS)

Moreno, Patricio I.; Videla, Javiera

2016-10-01

We examine hydroclimate changes at centennial/millennial timescales since 16,000 yr BP in northwestern Patagonia based on the pollen and charcoal record from Lago El Salto, a small closed-basin lake located in the Chilean Lake District (41°38‧48.02″S, 73° 5‧48.42″W). We observe cold/wet conditions between 14,500-16,000 yr BP, followed by further cooling with increased precipitation until 13,000 yr BP, enhanced precipitation seasonality and/or variability between 11,600-13,000 yr BP, and an extended warm-and-dry interval between 7600 and 11,300 yr BP with peak paleofire activity. Colder-and-wetter than present conditions and muted paleofire activity prevail between 5300 and 7600 yr BP, followed by alternating cold/wet and centennial-scale warm/dry phases starting at 5300 yr BP with three conspicuous megadroughts since 2500 yr BP. The most recent megadrought occurred during the Medieval Climate Anomaly. We identify a cold reversal that spans the Antarctic Cold Reversal (ACR) and the Younger Dryas (YD) chrons with stronger-than-present westerly influence during the former and enhanced variability during the latter. These results extend the northern limit of strong cooling and increase in precipitation during the ACR and the southern limit of influence of strong hydrologic variations during the YD in terrestrial environments, suggesting an overlap in the spheres of influence of processes originating from southern and northern polar latitudes. An extended warm southern westerly wind (SWW)-minimum interval is evident between 7600 and 11,300 yr BP, followed by a rapid shift to cool-moist conditions between 5300 and 7600 yr BP brought by a mid-Holocene SWW maximum. Since then we observe centennial-scale hydroclimate variability, which has driven biodiversity and fire-regime shifts of evergreen temperate rainforests.

Regional dry-season climate changes due to three decades of Amazonian deforestation

NASA Astrophysics Data System (ADS)

Khanna, Jaya; Medvigy, David; Fueglistaler, Stephan; Walko, Robert

2017-02-01

More than 20% of the Amazon rainforest has been cleared in the past three decades, triggering important hydroclimatic changes. Small-scale (a few kilometres) deforestation in the 1980s has caused thermally triggered atmospheric circulations that increase regional cloudiness and precipitation frequency. However, these circulations are predicted to diminish as deforestation increases. Here we use multi-decadal satellite records and numerical model simulations to show a regime shift in the regional hydroclimate accompanying increasing deforestation in Rondônia, Brazil. Compared with the 1980s, present-day deforested areas in downwind western Rondônia are found to be wetter than upwind eastern deforested areas during the local dry season. The resultant precipitation change in the two regions is approximately +/-25% of the deforested area mean. Meso-resolution simulations robustly reproduce this transition when forced with increasing deforestation alone, showing that large-scale climate variability plays a negligible role. Furthermore, deforestation-induced surface roughness reduction is found to play an essential role in the present-day dry-season hydroclimate. Our study illustrates the strong scale sensitivity of the climatic response to Amazonian deforestation and suggests that deforestation is sufficiently advanced to have caused a shift from a thermally to a dynamically driven hydroclimatic regime.

Regional influence of decadal to multidecadal Atlantic Oscillations during the last two millennia in Morocco, inferred from two high resolution δ18O speleothem records

NASA Astrophysics Data System (ADS)

Ait Brahim, Yassine; Sifeddine, Abdelfettah; Khodri, Myriam; Bouchaou, Lhoussaine; Cruz, Francisco W.; Pérez-Zanón, Núria; Wassenburg, Jasper A.; Cheng, Hai

2017-04-01

Climate projections predict substantial increase of extreme heats and drought occurrences during the coming decades in Morocco. It is however not clear what can be attributed to natural climate variability and to anthropogenic forcing, as hydroclimate variations observed in areas such as Morocco are highly influenced by the Atlantic climate modes. Since observational data sets are too short to resolve properly natural modes of variability acting on decadal to multidecadal timescales, high resolution paleoclimate reconstructions are the only alternative to reconstruct climate variability in the remote past. Herein, we present two high resolution and well dated speleothems oxygen isotope (δ18O) records sampled from Chaara and Ifoulki caves (located in Northeastern and Southwestern Morocco respectively) to investigate hydroclimate variations during the last 2000 years. Our results are supported by a monitoring network of δ18O in precipitation from 17 stations in Morocco. The new paleoclimate records are discussed in the light of existing continental and marine paleoclimate proxies in Morocco to identify significant correlations at various lead times with the main reconstructed oceanic and atmospheric variability modes and possible climate teleconnections that have potentially influenced the climate during the last two millennia in Morocco. The results reveal substantial decadal to multidecadal swings between dry and humid periods, consistent with regional paleorecords. Evidence of dry conditions exist during the Medieval Climate Anomaly (MCA) period and the Climate Warm Period (CWP) and humid conditions during the Little Ice Age (LIA) period. Statistical analyses suggest that the climate of southwestern Morocco remained under the combined influence of both the Atlantic Multidecadal Oscillation (AMO) and the North Atlantic Oscillation (NAO) over the last two millennia. Interestingly, the generally warmer MCA and colder LIA at longer multidecadal timescales probably influenced the regional climate in North Africa through the influence on Sahara Low which weakened and strengthened the mean moisture inflow from the Atlantic Ocean during the MCA and LIA respectively. Keywords: Speleothems, δ18O, Morocco, Hydroclimate, AMO, NAO.

Spatiotemporal drought variability of the eastern Tibetan Plateau during the last millennium

NASA Astrophysics Data System (ADS)

Deng, Yang; Gou, Xiaohua; Gao, Linlin; Yang, Meixue; Zhang, Fen

2017-09-01

Tibetan Plateau is the headwater region of many major Asian rivers and very susceptive to climate change. Therefore, knowledge about climate and its spatiotemporal variability in this area is very important for ecological conservation, water resource management and social development. The aim of this study was to reconstruct and analyze the hydroclimate variation on eastern Tibetan Plateau (ETP) over many centuries and explore possible forcing factors on regional hydroclimate variability. We used 118 tree-ring chronologies from ETP to reconstruct the gridded May-July Standardized Precipitation Evapotranspiration Index for the ETP over the last millennium. The reconstruction was developed using an ensemble point-by-point reconstruction method, and a searching region method was used to locate the candidate tree-ring chronologies. The reconstructions have nicely captured the spatial and temporal features of the regional drought variation. The drought variations in south and north of 32.5°N are notably different, which may be related to the divergence influence of North Atlantic Oscillation on the climate systems in the south and north, as well as differences in local climate. Spectral analysis and series comparison suggest that the drought variation in the northeastern Tibetan Plateau has been possibly influenced by solar activity on centurial and longer time scale.

Beyond the NAO: Dynamics and Precipitation Implications of the Azores High Since AD 800

NASA Astrophysics Data System (ADS)

Thatcher, D.; Wanamaker, A. D.; Denniston, R. F.; Asmerom, Y.; Ummenhofer, C.; Polyak, V. J.; Haws, J.; Gillikin, D. P.

2016-12-01

Atmospheric circulation in the North Atlantic region during the last millennium, particularly the state of the North Atlantic Oscillation (NAO), a system closely tied to regional precipitation dynamics, remains the subject of considerable debate in both proxy- and model-based studies. It has been suggested that the winter NAO was in a persistently positive state during the Medieval Climate Anomaly (MCA; AD 850-1250), resulting in increased precipitation across much of northern Europe and decreased rainfall across Iberia. However, besides changes in atmospheric circulation and precipitation dynamics that could be associated with an altered mean state of the NAO, relatively little attention has been given to atmospheric dynamics, namely the intensity and location, of the subtropical high system (Azores High, the southern node of the NAO) in driving hydroclimate in Iberia. Presented here is a continuous, precisely dated, and sub-decadally-resolved stalagmite isotopic and elemental time series from Buraca Gloriosa (BG) cave, western Portugal, situated within the center of the Azores High at the southern node of the NAO, which preserves evidence of regional hydroclimate from approximately AD 800 to the present. Stalagmite oxygen and carbon isotopic values and magnesium/calcium ratios primarily reflect effective moisture and reveal generally dry conditions during the MCA with a rapid shift to wetter conditions during the Little Ice Age (LIA; AD 1250-1850) at this location. Our proxy data reveal that substantial short-term hydroclimate variability characterized the last 1200 years. They support the hypothesis that while an intensified, semi-persistent subtropical high (and likely positive NAO state) characterized much of the MCA, the NAO remained variable over this time period. Climate model results also suggest that the Azores High pressure system both migrated southward and weakened from the MCA into the LIA.

Rocky Mountain hydroclimate: Holocene variability and the role of insolation, ENSO, and the North American Monsoon

USGS Publications Warehouse

Anderson, Lesleigh

2012-01-01

Over the period of instrumental records, precipitation maximum in the headwaters of the Colorado Rocky Mountains has been dominated by winter snow, with a substantial degree of interannual variability linked to Pacific ocean–atmosphere dynamics. High-elevation snowpack is an important water storage that is carefully observed in order to meet increasing water demands in the greater semi-arid region. The purpose here is to consider Rocky Mountain water trends during the Holocene when known changes in earth's energy balance were caused by precession-driven insolation variability. Changes in solar insolation are thought to have influenced the variability and intensity of the El Niño Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and North American Monsoon and the seasonal precipitation balance between rain and snow at upper elevations. Holocene records are presented from two high elevation lakes located in northwest Colorado that document decade-to-century scale precipitation seasonality for the past ~ 7000 years. Comparisons with sub-tropical records of ENSO indicate that the snowfall-dominated precipitation maxima developed ~ 3000 and 4000 years ago, coincident with evidence for enhanced ENSO/PDO dynamics. During the early-to-mid Holocene the records suggest a more monsoon affected precipitation regime with reduced snowpack, more rainfall, and net moisture deficits that were more severe than recent droughts. The Holocene perspective of precipitation indicates a far broader range of variability than that of the past century and highlights the non-linear character of hydroclimate in the U.S. west.

Forest tree growth response to hydroclimate variability in the southern Appalachians

Treesearch

Katherine J. Elliott; Chelcy Ford Miniat; Neil Pederson; Stephanie H. Laseter

2015-01-01

Climate change will affect tree species growth and distribution; however, under the same climatic conditions species may differ in their response according to site conditions. We evaluated the climate-driven patterns of growth for six dominant deciduous tree species in the southern Appalachians. We categorized species into two functional groups based on their stomatal...

Hydrological responses of the Chihuahua Desert of Mexico to possible Heinrich Stadials: A study inferred from geochemistry and stable isotopes of lacustrine sediments

NASA Astrophysics Data System (ADS)

Quiroz-Jiménez, J. D.; Roy, P. D.; Lozano-SantaCruz, R.; López Balbiaux, N.; Girón-García, P.

2016-12-01

The Heinrich Stadials (H6-H1) were cooler intervals of different duration characterized by massive discharge of icebergs from the Laurentide Ice Sheet mainly through the Hudson Straight into the Atlantic Ocean. In this paper, we present a proxy record to infer hydrological responses of the Chihuahua Desert of Mexico to all the Heinrich Stadials (HS) from element ratios, CO3 abundance, and oxygen and carbon isotope compositions of lacustrine calcite of the sediments deposited between depths of 560-78 cm ( 66-8 ka) of a new core collected from the Santiaguillo Basin. Sediments deposited during different HS were identified by radiocarbon dating up to 27.3 ka, extrapolation of an average sediment rate and tuning the CO3 abundance record with insolation in rest of the sequence, and oxygen isotope composition of authigenic CO3. Proxies suggest that hydroclimate of the Chihuahua Desert of Mexico responded differently to different HS. The overall runoff and hence precipitation remained below average during H6, H4, H2 and H1. Both of them were above average during H5 and H3. Similarly, runoff during H4 showed the least variability and it was the most variable during H5. Except for H2, negative excursions in δ18O values suggest cooler conditions during all other HS. In general, dissolved HCO3- was mainly sourced from the atmospheric CO2 during arid intervals. Both the lake productivity and atmospheric CO2 influenced the carbon isotope composition of dissolved HCO3- during humid intervals. During the H2, δ13C values indicate dominant influence of lacustrine productivity. Similar to Chihuahua Desert of Mexico, speleothem records from Fort Stanton and Cave of the Bells (Asmerom et al., 2010; Wagner et al., 2010) showed that hydroclimate of southwest USA also experienced millennial-scale variability and some intervals were more homogeneous compared to others. We did not observe concurrency in proxy records of the Chihuahua Desert of Mexico and southwest USA. Instead, we observed a possible hemispheric link between hydroclimate of the Chihuahua Desert of Mexico and the East Asian Monsoon. Characterized by millennial-scale fluctuations, tendencies of runoff into the Santiaguillo Basin and intensity of the East Asian Monsoon inferred from speleothems from the Hulu Cave of China (Wang et al., 2001) across the six HS were similar.

Interannual-to-multidecadal hydroclimate variability and its sectoral impacts in northeastern Argentina

NASA Astrophysics Data System (ADS)

Lovino, Miguel A.; Müller, Omar V.; Müller, Gabriela V.; Sgroi, Leandro C.; Baethgen, Walter E.

2018-06-01

This study examines the joint variability of precipitation, river streamflow and temperature over northeastern Argentina; advances the understanding of their links with global SST forcing; and discusses their impacts on water resources, agriculture and human settlements. The leading patterns of variability, and their nonlinear trends and cycles are identified by means of a principal component analysis (PCA) complemented with a singular spectrum analysis (SSA). Interannual hydroclimatic variability centers on two broad frequency bands: one of 2.5-6.5 years corresponding to El Niño Southern Oscillation (ENSO) periodicities and the second of about 9 years. The higher frequencies of the precipitation variability (2.5-4 years) favored extreme events after 2000, even during moderate extreme phases of the ENSO. Minimum temperature is correlated with ENSO with a main frequency close to 3 years. Maximum temperature time series correlate well with SST variability over the South Atlantic, Indian and Pacific oceans with a 9-year frequency. Interdecadal variability is characterized by low-frequency trends and multidecadal oscillations that have induced a transition from dryer and cooler climate to wetter and warmer decades starting in the mid-twentieth century. The Paraná River streamflow is influenced by North and South Atlantic SSTs with bidecadal periodicities. The hydroclimate variability at all timescales had significant sectoral impacts. Frequent wet events between 1970 and 2005 favored floods that affected agricultural and livestock productivity and forced population displacements. On the other hand, agricultural droughts resulted in soil moisture deficits that affected crops at critical growth stages. Hydrological droughts affected surface water resources, causing water and food scarcity and stressing the capacity for hydropower generation. Lastly, increases in minimum temperature reduced wheat and barley yields.

Hydroclimate of the northeastern United States is highly sensitive to solar forcing

NASA Astrophysics Data System (ADS)

Nichols, Jonathan E.; Huang, Yongsong

2012-02-01

Dramatic hydrological fluctuations strongly impact human society, but the driving mechanisms for these changes are unclear. One suggested driver is solar variability, but supporting paleoclimate evidence is lacking. Therefore, long, continuous, high-resolution records from strategic locations are crucial for resolving the scientific debate regarding sensitivity of climate to solar forcing. We present a 6800-year, decadally-resolved biomarker and multidecadally-resolved hydrogen isotope record of hydroclimate from a coastal Maine peatland, The Great Heath (TGH). Regional moisture balance responds strongly and consistently to solar forcing at centennial to millennial timescales, with solar minima concurrent with wet conditions. We propose that the Arctic/North Atlantic Oscillation (AO/NAO) can amplify small solar fluctuations, producing the reconstructed hydrological variations. The Sun may be entering a weak phase, analogous to the Maunder minimum, which could lead to more frequent flooding in the northeastern US at this multidecadal timescale.

Western Pacific hydroclimate linked to global climate variability over the past two millennia

NASA Astrophysics Data System (ADS)

Griffiths, Michael L.; Kimbrough, Alena K.; Gagan, Michael K.; Drysdale, Russell N.; Cole, Julia E.; Johnson, Kathleen R.; Zhao, Jian-Xin; Cook, Benjamin I.; Hellstrom, John C.; Hantoro, Wahyoe S.

2016-06-01

Interdecadal modes of tropical Pacific ocean-atmosphere circulation have a strong influence on global temperature, yet the extent to which these phenomena influence global climate on multicentury timescales is still poorly known. Here we present a 2,000-year, multiproxy reconstruction of western Pacific hydroclimate from two speleothem records for southeastern Indonesia. The composite record shows pronounced shifts in monsoon rainfall that are antiphased with precipitation records for East Asia and the central-eastern equatorial Pacific. These meridional and zonal patterns are best explained by a poleward expansion of the Australasian Intertropical Convergence Zone and weakening of the Pacific Walker circulation (PWC) between ~1000 and 1500 CE Conversely, an equatorward contraction of the Intertropical Convergence Zone and strengthened PWC occurred between ~1500 and 1900 CE. Our findings, together with climate model simulations, highlight the likelihood that century-scale variations in tropical Pacific climate modes can significantly modulate radiatively forced shifts in global temperature.

Capturing species-level drought responses in a temperate deciduous forest using ratios of photochemical reflectance indices between sunlit and shaded canopies

Treesearch

Taehee Hwang; Hamed Gholizadeh; Daniel A. Sims; Kimberly A. Novick; Edward R. Brzostek; Richard P. Phillips; Daniel T. Roman; Scott M. Robeson; Abdullah F. Rahman

2017-01-01

To classify trees along a spectrum of isohydric to anisohydric behavior is a promising new framework for identifying tree species' sensitivities to drought stress, directly related to the vulnerability of carbon uptake of terrestrial ecosystems with increased hydroclimate variability. Trees with isohydric strategies regulate stomatal conductance to maintain...

Added value from 576 years of tree-ring records in the prediction of the Great Salt Lake level

Treesearch

Robert R. Gillies; Oi-Yu Chung; S.-Y. Simon Wang; R. Justin DeRose; Yan Sun

2015-01-01

Predicting lake level fluctuations of the Great Salt Lake (GSL) in Utah - the largest terminal salt-water lake in the Western Hemisphere - is critical from many perspectives. The GSL integrates both climate and hydrological variations within the region and is particularly sensitive to low-frequency climate cycles. Since most hydroclimate variable records cover...

Extrapolar climate reversal during the last deglaciation.

PubMed

Asmerom, Yemane; Polyak, Victor J; Lachniet, Matthew S

2017-08-02

Large ocean-atmosphere and hydroclimate changes occurred during the last deglaciation, although the interplay between these changes remains ambiguous. Here, we present a speleothem-based high resolution record of Northern Hemisphere atmospheric temperature driven polar jet variability, which matches the Greenland ice core records for the most of the last glacial period, except during the last deglaciation. Our data, combined with data from across the globe, show a dramatic climate reversal during the last deglaciation, which we refer to as the Extrapolar Climate Reversal (ECR). This is the most prominent feature in most tropical and subtropical hydroclimate proxies. The initiation of the ECR coincides with the rapid rise in CO 2 , in part attributed to upwelling in the Southern Ocean and the near collapse of the Atlantic Meridional Overturning Circulation. We attribute the ECR to upwelling of cold deep waters from the Southern Ocean. This is supported by a variety of proxies showing the incursion of deep Southern Ocean waters into the tropics and subtropics. Regional climate variability across the extropolar regions during the interval previously referred to as the "Mystery Interval" can now be explained in the context of the ECR event.

The paleoclimate context and future trajectory of extreme summer hydroclimate in eastern Australia.

PubMed

Cook, Benjamin I; Palmer, Jonathan G; Cook, Edward R; Turney, Chris S M; Allen, Kathryn; Fenwick, Pavla; O'Donnell, Alison; Lough, Janice M; Grierson, Pauline F; Ho, Michelle; Baker, Patrick J

2016-11-16

Eastern Australia recently experienced an intense drought (Millennium Drought, 2003-2009) and record-breaking rainfall and flooding (austral summer 2010-2011). There is some limited evidence for a climate change contribution to these events, but such analyses are hampered by the paucity of information on long-term natural variability. Analyzing a new reconstruction of summer (December-January-February) Palmer Drought Severity Index (the Australia-New Zealand Drought Atlas; ANZDA, 1500-2012 CE), we find moisture deficits during the Millennium Drought fall within the range of the last 500 years of natural hydroclimate variability. This variability includes periods of multi-decadal drought in the 1500s more persistent than any event in the historical record. However, the severity of the Millennium Drought, which was caused by autumn (March-April-May) precipitation declines, may be underestimated in the ANZDA because the reconstruction is biased towards summer and antecedent spring (September-October-November) precipitation. The pluvial in 2011, however, which was characterized by extreme summer rainfall faithfully captured by the ANZDA, is likely the wettest year in the reconstruction for Coastal Queensland. Climate projections (RCP 8.5 scenario) suggest that eastern Australia will experience long-term drying during the 21 st century. While the contribution of anthropogenic forcing to recent extremes remains an open question, these projections indicate an amplified risk of multi-year drought anomalies matching or exceeding the intensity of the Millennium Drought.

Relationship between annual precipitation variability and ENSO in Southern California for the Common Era (last 2,000 years)

NASA Astrophysics Data System (ADS)

DU, X.; Hendy, I. L.; Hinnov, L.; Brown, E. T.; Schimmelmann, A.; Pak, D. K.

2017-12-01

The El Niño-Southern Oscillation (ENSO) has a major influence on Southern California's hydroclimate as demonstrated by both historical observations and model simulations. Santa Barbara Basin (SBB) off Southern California preserves a unique varved (i.e. annually laminated) marine sedimentary archive of modern and Holocene hydroclimate variability, notably including the transition from the regionally dry Medieval Climate Anomaly (MCA) to the wetter Little Ice Age (LIA). Here we present sub-annually resolved scanning XRF elemental counts for the last 2,000 years in SBB from core SPR0901-03KC. Titanium (associated with silicate minerals) is delivered more efficiently to SBB sediments during times of enhanced river flow and in the Mediterranean climate of Southern California, river flow only occurs after precipitation. The Ti record suggests that the precipitation frequency was reduced during the MCA except for a pluvial episode at CE 1075-1121, but increased during the LIA. Time series analysis of Ti counts indicates ENSO variability robustly increased during the intervals CE 450-520, 650-720, 980-1150, 1380-1550 and 1720-1750, and experienced relatively quiescent intervals between CE 50-150, 250-400, 550-650, 750-950, 1150-1280 and 1580-1620. Generally the LIA in Southern California is characterized by more active ENSO variability with long periodicities (4-7 yr) and multi-decadal variability (54 yr). MCA drought episodes were associated with less active ENSO. Active ENSO variability in Southern California during the last 2,000 years coincided with reconstructed southward migration of the Intertropical Convergence Zone (ITCZ) suggesting the ITCZ may play a role in the waxing and waning of ENSO teleconnections between the central Pacific and the west coast of North America.

Hydroclimate variability in the low-elevation Atacama Desert over the last 2500 years

NASA Astrophysics Data System (ADS)

Gayo, E. M.; Latorre, C.; Santoro, C. M.; Maldonado, A.; de Pol-Holz, R.

2011-10-01

Paleoclimate reconstructions reveal that Earth system has experienced sub-millennial scale climate changes over the past two millennia in response to internal/external forcing. Although sub-millennial hydroclimate fluctuations have been detected in the central Andes during this interval, the timing, magnitude, extent and direction of change of these events remain poorly defined. Here, we present a reconstruction of hydroclimate variations on the Pacific slope of the central Andes based on exceptionally well-preserved plant macrofossils and associated archaeological remains from a hyperarid drainage (Quebrada Maní, ~21° S, 1000 m a.s.l.) in the Atacama Desert. During the late Holocene, riparian ecosystems and farming social groups flourished in the hyperarid Atacama core as surface water availability increased throughout this presently sterile landscape. Twenty-six radiocarbon dates indicate that these events occurred between 1050-680, 1615-1350 and 2500-2040 cal yr BP. Regional comparisons with rodent middens and other records suggest that these events were synchronous with pluvial stages detected at higher-elevations in the central Andes over the last 2500 years. These hydroclimate changes also coincide with periods of pronounced SST gradients in the Tropical Pacific (La Niña-like mode), conditions that are conducive to significantly increased rainfall in the central Andean highlands and flood events in the low-elevation watersheds at inter-annual timescales. Our findings indicate that the positive anomalies in the hyperarid Atacama over the past 2500 years represent a regional response of the central Andean climate system to changes in the global hydrological cycle at centennial timescales. Furthermore, our results provide support for the role of tropical Pacific sea surface temperature gradient changes as the primary mechanism responsible for climate fluctuations in the central Andes. Finally, our results constitute independent evidence for comprehending the major trends in cultural evolution of prehistoric peoples that inhabited the region.

Hydroclimate variability in the low-elevation Atacama Desert over the last 2500 yr

NASA Astrophysics Data System (ADS)

Gayo, E. M.; Latorre, C.; Santoro, C. M.; Maldonado, A.; de Pol-Holz, R.

2012-02-01

Paleoclimate reconstructions reveal that Earth system has experienced sub-millennial scale climate changes over the past two millennia in response to internal/external forcing. Although sub-millennial hydroclimate fluctuations have been detected in the central Andes during this interval, the timing, magnitude, extent and direction of change of these events remain poorly defined. Here, we present a reconstruction of hydroclimate variations on the Pacific slope of the central Andes based on exceptionally well-preserved plant macrofossils and associated archaeological remains from a hyperarid drainage (Quebrada Maní, ∼21° S, 1000 m a.s.l.) in the Atacama Desert. During the late Holocene, riparian ecosystems and farming social groups flourished in the hyperarid Atacama core as surface water availability increased throughout this presently sterile landscape. Twenty-six radiocarbon dates indicate that these events occurred between 1050-680, 1615-1350 and 2500-2040 cal yr BP. Regional comparisons with rodent middens and other records suggest that these events were synchronous with pluvial stages detected at higher-elevations in the central Andes over the last 2500 yr. These hydroclimate changes also coincide with periods of pronounced SST gradients in the Tropical Pacific (La Niña-like mode), conditions that are conducive to significantly increased rainfall in the central Andean highlands and flood events in the low-elevation watersheds at inter-annual timescales. Our findings indicate that the positive anomalies in the hyperarid Atacama over the past 2500 yr represent a regional response of the central Andean climate system to changes in the global hydrological cycle at centennial timescales. Furthermore, our results provide support for the role of tropical Pacific sea surface temperature gradient changes as the primary mechanism responsible for climate fluctuations in the central Andes. Finally, our results constitute independent evidence for comprehending the major trends in cultural evolution of prehistoric peoples that inhabited the region.

Holocene palaeohydrological history of the Tǎul Muced peat bog (Northern Carpathians, Romania) based on testate amoebae (Protozoa) and plant macrofossils

NASA Astrophysics Data System (ADS)

Cosmin Diaconu, Andrei; Feurdean, Angelica; Lamentowicz, Mariusz; Gałka, Mariusz; Tanţǎu, Ioan

2016-04-01

Knowledge of past local vs. regional hydro-climate variability is a priority in climate research. This is because ecosystems and human depend on local climatic conditions and the magnitude of these climate changes is more variable at local and regional rather than at global scales. Ombrotrophic bogs are highly suitable for hydro-climate reconstructions as they are entirely dependent on the water from precipitation. We used stratigraphy, radiocarbon dating, testate amoebae (TA) and plant macrofossils on a peat profile from an ombrotrophic bog (Tǎul Muced) located in the Biosphere Reserve of the Rodna National Park Romania. We performed quantitative reconstruction of the depth to water table (DWT) and pH over the last 8000 years in a continental area of CE Europe. We identified six main stages in the development of the bog based on changes in TA assemblages in time. Wet conditions and pH between 2 and 4.5 were recorded between 4600-2750 and 1300-400 cal. yr BP, by the occurrence of Archerella flavum, Amphitrema wrightianum and Hyalosphenia papilio. This was associated to a local vegetation primarily composed of Sphagnum magellanicum and S. angustifolium. Dry stages and pH of 2.5 to 5 were inferred between 7550-4600, 2750-1300 and -50 cal. yr BP, by the dominance of Nebela militaris, Difflugia pulex and Phryganella acropodia. These overall dry conditions were also connected with increased abundance of Eriophorum vaginatum. The period between 400 and -50 cal. yr BP was characterized by a rapid shift from dry to wet conditions on the surface of the bog. Vegetation shifted from Sphagnum magellanicum to Sphagnum russowii dominated community. Our reconstruction remains in relatively good agreement with other palaeohydrological records from Central Eastern Europe. However, it shows contrasting conditions to others particularly with records from NW Europe. The valuable information regarding bog hydrology offered by our record puts an accent on the need of more regional TA based reconstruction studies, to get a compressive picture of larger spatial scales of hydro-climate variability in Europe.

Western Pacific Hydroclimate Linked to Global Climate Variability Over the Past Two Millennia

NASA Technical Reports Server (NTRS)

Griffiths, Michael L.; Kimbrough, Alena K.; Gagan, Michael K.; Drysdale, Russell N.; Cole, Julia E.; Johnson, Kathleen R.; Zhao, Jian-Xin; Cook, Benjamin I.; Hellstrom, John C.; Hantoro, Wahyoe S.

2016-01-01

Interdecadal modes of tropical Pacific ocean-atmosphere circulation have a strong influence on global temperature, yet the extent to which these phenomena influence global climate on multicentury timescales is still poorly known. Here we present a 2,000-year, multiproxy reconstruction of western Pacific hydroclimate from two speleothem records for southeastern Indonesia. The composite record shows pronounced shifts in monsoon rainfall that are antiphased with precipitation records for East Asia and the central-eastern equatorial Pacific. These meridional and zonal patterns are best explained by a poleward expansion of the Australasian Intertropical Convergence Zone and weakening of the Pacific Walker circulation (PWC) between B1000 and 1500 CE Conversely, an equatorward contraction of the Intertropical Convergence Zone and strengthened PWC occurred between B1500 and 1900 CE. Our findings, together with climate model simulations, highlight the likelihood that century-scale variations in tropical Pacific climate modes can significantly modulate radiatively forced shifts in global temperature.

Decadal covariability of Atlantic SSTs and western Amazon dry-season hydroclimate in observations and CMIP5 simulations

NASA Astrophysics Data System (ADS)

Fernandes, Katia; Giannini, Alessandra; Verchot, Louis; Baethgen, Walter; Pinedo-Vasquez, Miguel

2015-08-01

The unusual severity and return time of the 2005 and 2010 dry-season droughts in western Amazon is attributed partly to decadal climate fluctuations and a modest drying trend. Decadal variability of western Amazon hydroclimate is highly correlated to the Atlantic sea surface temperature (SST) north-south gradient (NSG). Shifts of dry and wet events frequencies are also related to the NSG phase, with a 66% chance of 3+ years of dry events per decade when NSG > 0 and 19% when NSG < 0. The western Amazon and NSG decadal covariability is well reproduced in general circulation models (GCMs) historical (HIST) and preindustrial control (PIC) experiments of the Coupled Model Intercomparison Project Phase 5 (CMIP5). The HIST and PIC also reproduce the shifts in dry and wet events probabilities, indicating potential for decadal predictability based on GCMs. Persistence of the current NSG positive phase favors above normal frequency of western Amazon dry events in coming decades.

Indo-Pacific hydroclimate over the past millennium and links with global climate variabilty

NASA Astrophysics Data System (ADS)

Griffiths, M. L.; Drysdale, R.; Kimbrough, A. K.; Hua, Q.; Johnson, K. R.; Gagan, M. K.; Cole, J. E.; Cook, B. I.; Zhao, J. X.; Hellstrom, J. C.; Hantoro, W. S.

2016-12-01

The El Niño-Southern Oscillation (ENSO) and Interdecadal Pacific Oscillation (IPO) are the dominant modes of hydroclimate variability in the tropical Pacific and have far-reaching impacts on Earth's climate. Experiments combining instrumental records with climate-model simulations have highlighted the dominant role of the Pacific Walker circulation in shaping recent trends in global temperatures (Kosaka and Xie, 2013, 2016). However, the paucity of high-resolution terrestrial paleoclimate records of deep atmospheric convection over the Indo-Pacific Warm Pool (IPWP) precludes a comprehensive assessment as to role of the tropical Pacific in modulating radiative-forced shifts in global temperature on multidecadal to centennial timescales. Here we present a suite of new high-resolution oxygen-isotope records from Indo-Pacific speleothems, which, based on modern rainfall and cave drip-water monitoring studies, along with trace element (Mg/Ca, Sr/Ca) analyses, are interpreted to reflect changes in Australasian monsoon variability during the Common Era (C.E.). Our results reveal a protracted decline in southern Indonesian monsoon rainfall between 1000-1400 C.E. but stronger between 1500-1900 C.E. These centennial-scale patterns over southern Indonesia are consistent with other proxy records from the region but anti-phased with records from India and China, supporting the paradigm that Northern Hemisphere cooling increased the interhemispheric thermal gradient, displacing the Australasian ITCZ southward. However, our findings are also compatible with a recent synthesis of paleohydrologic records for the Australasian monsoon region, which, collectively, suggest that rather than moving southward during the LIA, the latitudinal range of monsoon-ITCZ migration probably contracted equatorward (Yan et al., 2015). This proposed LIA ITCZ contraction likely occurred in parallel with a strengthening of the Walker circulation (as indicated through comparison with our hydroclimate records from the central-eastern equatorial Pacific Ocean and western Indian Ocean, and eastern Australia), and thus, the tropical Pacific may have played a critical role in amplifying the radiative-forced global cooling already underway.

Hydroclimate variability in NE Brazil over the last 2K

NASA Astrophysics Data System (ADS)

Giselle, Utida; Ioanna, Bouloubassi; Francisco, Cruz; Enno, Schefuβ; Abdel, Sifeddine; Vincent, Klein; Johan, Etourneau; Renata, Zocatelli; André, Zular; Hai, Cheng; Laurence, Edwards R.

2016-04-01

Precipitation associated with the South American Summer Monsoon (SASM) and the Intertropical Convergence Zone (ITCZ) supplies more than 70% of tropical South America's annual precipitation and is fundamental in sustaining the water regime for regional socioeconomic activities. Motivated by the fact that the greatest uncertainty in model projections of future precipitation trends lies in the tropics, and particularly in South America, a number of recent proxy and modeling studies have aimed at understanding SASM spatiotemporal variability regarding its dynamics, driving mechanisms and teleconnections. Exact reconstructions of past meridional ITCZ displacements (timing, sign, amplitude), however, are currently lacking, mainly because of the paucity of suited high-resolution archives. This restricts our ability to assess regional rainfall variability at decadal to centennial timescales, especially in the hydroclimatic-sensitive semi-arid Nordeste, needed to understand the interactions between SASM and ITCZ and to evaluate the impact of Pacific-Atlantic climate interactions on the regional rainfall variability at decadal/multi-decadal scale. Here we present two new and complementary high-resolution records of past precipitation over the last 2K from the north area of Nordeste, an area ideally located to track fluctuations in the southernmost edge of ITCZ movement. We present a new δO18 record from a local speleothem and combine it, for the first time, with δD analyses of wax lipids in well-dated sediments from a nearby lake. The two independent records show a remarkable similarity and are characterized by strong decadal to multidecadal variability as well as century-scale changes. The period 250-450 yrs CE appears as the wettest phase over the last 2K, while the Medieval Climate Anomaly (MCA) is characterized by extremely dry conditions. Following the MCA, the Little Ice Age (LIA) is a relatively wetter phase. The data document fluctuations of southern meridional ITCZ movements during the last millennium that compare well with available records of fluctuations in northern ITCZ extension (Cariaco Basin). Comparisons to proxy records from tropical South America regions affected by the SASM and the South America Convergence Zone (SACZ) allow evaluating the SAMS/SACZ-ITCZ linkages. Furthermore, the data are discussed in terms of the role of the Atlantic and Pacific modes of variability in modulating regional hydroclimate.

Variability of North African hydroclimate during the last two climatic cycles: New insights from dust flux and provenance

NASA Astrophysics Data System (ADS)

Skonieczny, C.; McGee, D.; Bory, A. J. M.; Winckler, G.; Bradtmiller, L.; Bout-Roumazeilles, V.; Perala-Dewey, J.; Delattre, M.; Kinsley, C. W.; Polissar, P. J.; Malaizé, B.

2016-12-01

Every year, several hundred teragrams of dust are emitted from the Sahara and Sahel regions. These mineral particles sensitively track variations in atmospheric circulation and continental aridity. Sediments of the Northeastern Tropical Atlantic Ocean (NETAO) are fed by this intense dust supply and comprise unique long-term archives of past Saharan/Sahelian dust emissions. Past modifications of dust characteristics in these sedimentary archives can provide unique insights into changes in environmental conditions in source areas (aridity, weathering), as well as changes in atmospheric transport (wind direction and strength). Here we document changes in sediment supply to the NETAO using marine sediment core MD03-2705 (18°05N; 21°09W; 3085m water depth). This record is strategically located under the influence of seasonal dust plumes, and marine sediments of this area have revealed that past dust inputs were sensitive to global climate changes over the late Quaternary. We will focus our study on the last two climatic cycles (0-240ka), a period orbitally characterized by changes in the amplitude of both precession (MIS6-5 vs. MIS1-2) and ice volume (MIS 7 vs. MIS5). We will present, for the first time in this area, a continuous high-resolution record of dust, opal, carbonate and organic matter fluxes using 230Th-normalization. The constant flux proxy 230Thxs provides flux data that are not substantially affected by lateral advection or age model errors. These fluxes data will be complemented by grain-size, clay mineralogical and geochemical (major elements) analysis. By pairing dust flux measurements with complementary proxy data reflecting changes in aridity, wind strength and dust source, this study will provide a robust, continuous record of the magnitude and pacing of the North African hydroclimate variability through the last two climatic cycles. In particular, this long-term study will offer the opportunity to compare the well-documented North African climate variability over the last glacial cycle with the less studied variability recorded during previous glacial-interglacial cycles in order to improve our understanding of the balance of high and low-latitude controls on the climate of North Africa.

How are streamflow responses to the El Nino Southern Oscillation affected by watershed characteristics?

NASA Astrophysics Data System (ADS)

Rice, Joshua S.; Emanuel, Ryan E.

2017-05-01

Understanding the factors that influence how global climate phenomena, such as the El-Nino Southern Oscillation (ENSO), affect streamflow behavior is an important area of research in the hydrologic sciences. While large-scale patterns in ENSO-streamflow relationships have been thoroughly studied, and are relatively well-understood, information is scarce concerning factors that affect variation in ENSO responses from one watershed to another. To this end, we examined relationships between variability in ENSO activity and streamflow for 2731 watersheds across the conterminous U.S. from 1970 to 2014 using a novel approach to account for the intermediary role of precipitation. We applied an ensemble of regression techniques to describe relationships between variability in ENSO activity and streamflow as a function of watershed characteristics including: hydroclimate, topography, geomorphology, geographic location, land cover, soil characteristics, bedrock geology, and anthropogenic influences. We found that variability in watershed scale ENSO-streamflow relationships was strongly related to factors including: precipitation timing and phase, forest cover, and interactions between watershed topography and geomorphology. These, and other influential factors, share in common the ability to affect the partitioning and movement of water within watersheds. Our results demonstrate that the conceptualization of watersheds as signal filters for hydroclimate inputs, commonly applied to short-term rainfall-runoff responses, also applies to long-term hydrologic responses to sources of recurrent climate variability. These results also show that watershed processes, which are typically studied at relatively fine spatial scales, are also critical for understanding continental scale hydrologic responses to global climate.

Hydroclimate temporal variability in a coastal Mediterranean watershed: the Tafna basin, North-West Algeria

NASA Astrophysics Data System (ADS)

Boulariah, Ouafik; Longobardi, Antonia; Meddi, Mohamed

2017-04-01

One of the major challenges scientists, practitioners and stakeholders are nowadays involved in, is to provide the worldwide population with reliable water supplies, protecting, at the same time, the freshwater ecosystems quality and quantity. Climate and land use changes undermine the balance between water demand and water availability, causing alteration of rivers flow regime. Knowledge of hydro-climate variables temporal and spatial variability is clearly helpful to plan drought and flood hazard mitigation strategies but also to adapt them to future environmental scenarios. The present study relates to the coastal semi-arid Tafna catchment, located in the North-West of Algeria, within the Mediterranean basin. The aim is the investigation of streamflow and rainfall indices temporal variability in six sub-basins of the large catchment Tafna, attempting to relate streamflow and rainfall changes. Rainfall and streamflow time series have been preliminary tested for data quality and homogeneity, through the coupled application of two-tailed t test, Pettitt test and Cumsum tests (significance level of 0.1, 0.05 and 0.01). Subsequently maximum annual daily rainfall and streamflow and average daily annual rainfall and streamflow time series have been derived and tested for temporal variability, through the application of the Mann Kendall and Sen's test. Overall maximum annual daily streamflow time series exhibit a negative trend which is however significant for only 30% of the station. Maximum annual daily rainfall also e exhibit a negative trend which is intend significant for the 80% of the stations. In the case of average daily annual streamflow and rainfall, the tendency for decrease in time is unclear and, in both cases, appear significant for 60% of stations.

The paleoclimate context and future trajectory of extreme summer hydroclimate in eastern Australia

PubMed Central

Cook, Benjamin I; Palmer, Jonathan G; Cook, Edward R; Turney, Chris S M; Allen, Kathryn; Fenwick, Pavla; O’Donnell, Alison; Lough, Janice M; Grierson, Pauline F; Ho, Michelle; Baker, Patrick J

2018-01-01

Eastern Australia recently experienced an intense drought (Millennium Drought, 2003–2009) and record-breaking rainfall and flooding (austral summer 2010–2011). There is some limited evidence for a climate change contribution to these events, but such analyses are hampered by the paucity of information on long-term natural variability. Analyzing a new reconstruction of summer (December–January–February) Palmer Drought Severity Index (the Australia–New Zealand Drought Atlas; ANZDA, 1500–2012 CE), we find moisture deficits during the Millennium Drought fall within the range of the last 500 years of natural hydroclimate variability. This variability includes periods of multi-decadal drought in the 1500s more persistent than any event in the historical record. However, the severity of the Millennium Drought, which was caused by autumn (March–April–May) precipitation declines, may be underestimated in the ANZDA because the reconstruction is biased towards summer and antecedent spring (September-October-November) precipitation. The pluvial in 2011, however, which was characterized by extreme summer rainfall faithfully captured by the ANZDA, is likely the wettest year in the reconstruction for Coastal Queensland. Climate projections (RCP 8.5 scenario) suggest that eastern Australia will experience long-term drying during the 21st century. While the contribution of anthropogenic forcing to recent extremes remains an open question, these projections indicate an amplified risk of multi-year drought anomalies matching or exceeding the intensity of the Millennium Drought. PMID:29780675

Gradual onset and recovery of the Younger Dryas abrupt climate event in the tropics.

PubMed

Partin, J W; Quinn, T M; Shen, C-C; Okumura, Y; Cardenas, M B; Siringan, F P; Banner, J L; Lin, K; Hu, H-M; Taylor, F W

2015-09-02

Proxy records of temperature from the Atlantic clearly show that the Younger Dryas was an abrupt climate change event during the last deglaciation, but records of hydroclimate are underutilized in defining the event. Here we combine a new hydroclimate record from Palawan, Philippines, in the tropical Pacific, with previously published records to highlight a difference between hydroclimate and temperature responses to the Younger Dryas. Although the onset and termination are synchronous across the records, tropical hydroclimate changes are more gradual (>100 years) than the abrupt (10-100 years) temperature changes in the northern Atlantic Ocean. The abrupt recovery of Greenland temperatures likely reflects changes in regional sea ice extent. Proxy data and transient climate model simulations support the hypothesis that freshwater forced a reduction in the Atlantic meridional overturning circulation, thereby causing the Younger Dryas. However, changes in ocean overturning may not produce the same effects globally as in Greenland.

Observations and simulations of the western United States' hydroclimate

NASA Astrophysics Data System (ADS)

Guirguis, Kristen

While very important from an economical and societal point of view, estimating precipitation in the western United States remains an unsolved and challenging problem. This is due to difficulties in observing and modeling precipitation in complex terrain. This research examines this issue by (i) providing a systematic evaluation of precipitation observations to quantify data uncertainty; and (ii) investigating the ability of the Ocean-Land-Atmosphere Model (OLAM) to simulate the winter hydroclimate in this region. This state-of-the-art, non-hydrostatic model has the capability of simulating simultaneously all scales of motions at various resolutions. This research intercompares nine precipitation datasets commonly used in hydrometeorological research in two ways. First, using principal component analysis, a precipitation climatology is conducted for the western U.S. from which five unique precipitation climates are identified. From this analysis, data uncertainty is shown to be primarily due to differences in (i) precipitation over the Rocky Mountains, (ii) the eastward wet-to-dry precipitation gradient during the cold season, (iii) the North American Monsoon signal, and (iv) precipitation in the desert southwest during spring and summer. The second intercomparison uses these five precipitation regions to provide location-specific assessments of uncertainty, which is shown to be dependent on season, location. Long-range weather forecasts on the order of a season are important for water-scarce regions such as the western U.S. The modeling component of this research looks at the ability of the OLAM to simulate the hydroclimate in the western U.S. during the winter of 1999. Six global simulations are run, each with a different spatial resolution over the western U.S. (360 km down to 11 km). For this study, OLAM is configured as for a long-range seasonal hindcast but with observed sea surface temperatures. OLAM precipitation compares well against observations, and is generally within the range of data uncertainty. Observed and simulated synoptic meteorological conditions are examined during the wettest and driest events. OLAM is shown to reproduce the appropriate anomaly fields, which is encouraging since it demonstrates the capability of a global climate model, driven only by SSTs and initial conditions, to represent meteorological features associated with daily precipitation variability.

Mapping tropical hydroclimate changes with speleothem δ18O records

NASA Astrophysics Data System (ADS)

Wang, X.; Liu, G.; Yuan, S.; Chiang, H. W.

2017-12-01

Speleothem δ18O records have been extensively used to study tropical hydroclimate change. However, less attention has been paid to the spatial distribution of speleothem δ18O values. Despite some caveats, we advocate an approach to reconstruct spatial and temporal transects ("maps") of speleothem δ18O, thus time series of precipitation δ18O distribution in a region. We present here two examples in using speleothem δ18O records to establish a spatial and temporal pattern of tropical hydroclimate changes. In the first case, we compare the speleothem δ18O records from caves located separately in the eastern and western Amazon lowlands. The decrease in speleothem δ18O values from the east to the west indicates an overall continental rainout effect of water isotopes when surface moisture is transported across the lowlands. A much large δ18O gradient however exists during the last glacial maximum than in the Holocene, suggesting that the Amazon was probably widely dry during the glacial, with much less recycling of water and reduced plant transpiration. And in the second case, we compare speleothem δ18O records obtained from caves along a SW-NE transect from coastal Myanmar to southwestern China. These records similarly show a larger gradient in speleothem δ18O along the transport path of Indian monsoon moisture during the glacial period than in the Holocene. Caution therefore is needed when interpreting the speleothem δ18O records from the monsoon downwind region.

Client-Friendly Forecasting: Seasonal Runoff Predictions Using Out-of-the-Box Indices

NASA Astrophysics Data System (ADS)

Weil, P.

2013-12-01

For more than a century, statistical relationships have been recognized between atmospheric conditions at locations separated by thousands of miles, referred to as teleconnections. Some of the recognized teleconnections provide useful information about expected hydrologic conditions, so certain records of atmospheric conditions are quantified and published as hydroclimate indices. Certain hydroclimate indices can serve as strong leading indicators of climate patterns over North America and can be used to make skillful forecasts of seasonal runoff. The methodology described here creates a simple-to-use model that utilizes easily accessed data to make forecasts of April through September runoff months before the runoff season begins. For this project, forecasting models were developed for two snowmelt-driven river systems in Colorado and Wyoming. In addition to the global hydroclimate indices, the methodology uses several local hydrologic variables including the previous year's drought severity, headwater snow water equivalent and the reservoir contents for the major reservoirs in each basin. To improve the skill of the forecasts, logistic regression is used to develop a model that provides the likelihood that a year will fall into the upper, middle or lower tercile of historical flows. Categorical forecasting has two major advantages over modeling of specific flow amounts: (1) with less prediction outcomes models tend to have better predictive skill and (2) categorical models are very useful to clients and agencies with specific flow thresholds that dictate major changes in water resources management. The resulting methodology and functional forecasting model product is highly portable, applicable to many major river systems and easily explained to a non-technical audience.

The International Summer School on Land Cover Change and Hydroclimate of the La Plata Basin

NASA Technical Reports Server (NTRS)

Berbery, Ernesto Hugo; Herdies, Dirceu L.; Alcaraz-Segura, Domingo; de Goncalves, Luis G. G.; Lettenmaier, Dennis P.; Toll, David

2011-01-01

The La Plata Basin (LPB) in southern South America has been subject to land cover and land use changes (LCLUCs) since colonial times and with an accelerated rate in the last decades and over extensive areas. The work of Ameghino even suggested that there were relations between those land use changes and the frequency of droughts and floods in the region. Despite this early knowledge, not much is known of the potential impacts of LCLUC on the hydroclimate of the La Plata basin. Besides, over the last century much of the La Plata Basin has had a reported increase in precipitation and heavy rains, and these changes along with an increase in population growth - have resulted in more adverse effects from flooding. To draw attention to these issues, during two weeks in November 2009 the International Summer School on Land Cover Change and Hydroclimate of the La Plata Basin was organized at the grounds of the Itaip Hydropower Plant in Brazil. The school was the result of the combination of interests between the La Plata Basin Regional Hydroclimate Project, the Inter-American Institute for Global Change Research (IAI), and the International Hydroinformatics Center (IHC) in Itaip . LPB is an umbrella project endorsed by the Global Energy and Water Cycle Experiment (GEWEX) and the Climate Prediction and Variability (CLIVAR), both of the World Climate Research Programme (WCRP). LPB has made a priority to train young scientists and promote interdisciplinary collaborations in areas related to Climate, Hydrology, Ecology and Agriculture. The IAI, with a similar agenda, was a natural partner to develop this Summer School, which in turn benefited from Itaipu s interest in relating with the scientific community of neighboring countries. The choice of location (Itaip Technological Park) was made so that participants could relate research usually done at academic institutions to applications and operations at one of the largest hydropower plants in the world. The school was attended by 45 advanced graduate students and young scientists with different backgrounds from seven countries, including less technically advanced ones in the region..

Efficacy of Radiative Transfer Model Across Space, Time and Hydro-climates

NASA Astrophysics Data System (ADS)

Mohanty, B.; Neelam, M.

2017-12-01

The efficiency of radiative transfer model for better soil moisture retrievals is not yet clearly understood over natural systems with great variability and heterogeneity with respect to soil, land cover, topography, precipitation etc. However, this knowledge is important to direct and strategize future research direction and field campaigns. In this work, we present global sensitivity analysis (GSA) technique to study the influence of heterogeneity and uncertainties on radiative transfer model (RTM) and to quantify climate-soil-vegetation interactions. A framework is proposed to understand soil moisture mechanisms underlying these interactions, and influence of these interactions on soil moisture retrieval accuracy. Soil moisture dynamics is observed to play a key role in variability of these interactions, i.e., it enhances both mean and variance of soil-vegetation coupling. The analysis is conducted for different support scales (Point Scale, 800 m, 1.6 km, 3.2 km, 6.4 km, 12.8 km, and 36 km), seasonality (time), hydro-climates, aggregation (scaling) methods and across Level I and Level II ecoregions of contiguous USA (CONUS). For undisturbed natural environments such as SGP'97 (Oklahoma, USA) and SMEX04 (Arizona, USA), the sensitivity of TB to land surface variables remain nearly uniform and are not influenced by extent, support scales or averaging method. On the contrary, for anthropogenically-manipulated environments such as SMEX02 (Iowa, USA) and SMAPVEX12 (Winnipeg, Canada), the sensitivity to variables are highly influenced by the distribution of land surface heterogeneity and upscaling methods. The climate-soil-vegetation interactions analyzed across all ecoregions are presented through a probability distribution function (PDF). The intensity of these interactions are categorized accordingly to yield "hotspots", where the RTM model fails to retrieve soil moisture. A ecoregion specific scaling function is proposed for these hotspots to rectify RTM for retrieving soil moisture.

Scientist-Practitioner Engagement to Inform Regional Hydroclimate Model Evaluation

NASA Astrophysics Data System (ADS)

Jones, A. D.; Jagannathan, K. A.; Ullrich, P. A.

2017-12-01

Water mangers face significant challenges in planning for the coming decades as previously stationary aspects of the regional hydroclimate shift in response to global climate change. Providing scientific insights that enable appropriate use of regional hydroclimate projections for planning is a non-trivial problem. The system of data, models, and methods used to produce regional hydroclimate projections is subject to multiple interacting uncertainties and biases, including uncertainties that arise from general circulation models, re-analysis data products, regional climate models, hydrologic models, and statistical downscaling methods. Moreover, many components of this system were not designed with the information needs of water managers in mind. To address this problem and provide actionable insights into the sources of uncertainty present in regional hydroclimate data products, Project Hyperion has undertaken a stakeholder engagement process in four case study water basins across the US. Teams of water managers and scientists are interacting in a structured manner to identify decision-relevant metrics of model performance. These metrics are in turn being used to drive scientific investigations to uncover the sources of uncertainty in these quantities. Thus far, we have found that identification of climate phenomena of interest to stakeholders is relatively easy, but translating these into specific quantifiable metrics and prioritizing metrics is more challenging. Iterative feedback among scientists and stakeholders has proven critical in resolving these challenges, as has the roles played by boundary spanners who understand and can speak to the perspectives of multiple professional communities. Here we describe the structured format of our engagement process and the lessons learned so far, as we aim to improve the decision-relevance of hydroclimate projections through a collaborative process.

Continental U.S. streamflow trends from 1940 to 2009 and their relationships with watershed spatial characteristics

NASA Astrophysics Data System (ADS)

Rice, Joshua S.; Emanuel, Ryan E.; Vose, James M.; Nelson, Stacy A. C.

2015-08-01

Changes in streamflow are an important area of ongoing research in the hydrologic sciences. To better understand spatial patterns in past changes in streamflow, we examined relationships between watershed-scale spatial characteristics and trends in streamflow. Trends in streamflow were identified by analyzing mean daily flow observations between 1940 and 2009 from 967 U.S. Geological Survey stream gages. Results indicated that streamflow across the continental U.S., as a whole, increased while becoming less extreme between 1940 and 2009. However, substantial departures from the continental U.S. (CONUS) scale pattern occurred at the regional scale, including increased annual maxima, decreased annual minima, overall drying trends, and changes in streamflow variability. A subset of watersheds belonging to a reference data set exhibited significantly smaller trend magnitudes than those observed in nonreference watersheds. Boosted regression tree models were applied to examine the influence of watershed characteristics on streamflow trend magnitudes at both the CONUS and regional scale. Geographic location was found to be of particular importance at the CONUS scale while local variability in hydroclimate and topography tended to have a strong influence on regional-scale patterns in streamflow trends. This methodology facilitates detailed, data-driven analyses of how the characteristics of individual watersheds interact with large-scale hydroclimate forces to influence how changes in streamflow manifest.

Atmospheric River Importance to Extratropical Climate and Hydrology

NASA Astrophysics Data System (ADS)

Nash, D.; Waliser, D. E.; Guan, B.; Ye, H.; Ralph, F. M.

2017-12-01

Atmospheric Rivers (ARs) are narrow, long, water vapor rich corridors of the atmosphere that are responsible for over 90% of the poleward moisture transport across mid-latitudes and into high latitudes. This suggests a crucial role for ARs in helping establish the extra-tropical atmospheric water budget and hydroclimate variability. However, the contribution of ARs to the extra-tropical atmospheric water budget has yet to be quantified, including impacts on water vapor transport and storage, and precipitation. This study characterizes the roles of AR related atmospheric transport on combined and individual atmospheric water budget variables over extratropical regions of both hemispheres based on MERRA2 reanalysis products during 1997-2014. Results show that poleward water vapor transport related to ARs is strongly related to changes in water vapor storage and especially precipitation in higher latitudes in both hemispheres, with the relationship dependent on averaging period. For example, for the annual cycle climatology, both AR transport and local evaporation support the variation in precipitation. However, on monthly time scales, the water budget at higher latitudes tends to be dominated by the balance between AR transport and precipitation. On pentad and daily time scales, AR transport is related to both precipitation and water vapor storage changes. These results indicate the important role of the episodic, extreme moisture transports associated with ARs in helping establish the high latitude water and energy cycles, and associated hydroclimate.

Proxy system modeling of tree-ring isotope chronologies over the Common Era

NASA Astrophysics Data System (ADS)

Anchukaitis, K. J.; LeGrande, A. N.

2017-12-01

The Asian monsoon can be characterized in terms of both precipitation variability and atmospheric circulation across a range of spatial and temporal scales. While multicentury time series of tree-ring widths at hundreds of sites across Asia provide estimates of past rainfall, the oxygen isotope ratios of annual rings may reveal broader regional hydroclimate and atmosphere-ocean dynamics. Tree-ring oxygen isotope chronologies from Monsoon Asia have been interpreted to reflect a local 'amount effect', relative humidity, source water and seasonality, and winter snowfall. Here, we use an isotope-enabled general circulation model simulation from the NASA Goddard Institute for Space Science (GISS) Model E and a proxy system model of the oxygen isotope composition of tree-ring cellulose to interpret the large-scale and local climate controls on δ 18O chronologies. Broad-scale dominant signals are associated with a suite of covarying hydroclimate variables including growing season rainfall amounts, relative humidity, and vapor pressure deficit. Temperature and source water influences are region-dependent, as are the simulated tree-ring isotope signals associated with the El Nino Southern Oscillation (ENSO) and large-scale indices of the Asian monsoon circulation. At some locations, including southern coastal Viet Nam, local precipitation isotope ratios and the resulting simulated δ 18O tree-ring chronologies reflect upstream rainfall amounts and atmospheric circulation associated with monsoon strength and wind anomalies.

Southern Arizona hydroclimate over the last 3000 years: a comparison of speleothem elemental data and climate model simulations

NASA Astrophysics Data System (ADS)

King, J.; Harrington, M. D.; Cole, J. E.; Drysdale, R.; Woodhead, J. D.; Fasullo, J.; Stevenson, S.; Otto-Bliesner, B. L.; Overpeck, J. T.; Edwards, R. L.; Henderson, G. M.

2017-12-01

Understanding long-term hydroclimate is particularly important in semiarid regions where prolonged droughts may be exacerbated by a warming climate. In many regions, speleothem trace elements correlate with regional wet and dry climate signals. In the drought-prone Southwestern US (SW), wet and dry episodes are strongly influenced by seasonal changes in atmospheric circulation and teleconnections to remote forcing. Here, we address the need for seasonal moisture reconstructions using paleoclimate and climate model approaches. First, we present a high-resolution (sub-annual) record of speleothem trace elements spanning the last 3000 years from Fort Huachuca Cave, AZ, to investigate the variability of regional seasonal precipitation and sustained regional droughts. In a principal component (PC) analysis of the speleothem, trace elements associated with wet (Sr, Ba) and dry (P, Y, Zn) episodes load strongly and inversely, and the associated PC signals correlate with local gridded precipitation data over the last 50 years (R > 0.6, p < 0.1). These results suggest that the elemental signals provide a seasonal moisture record for Southern Arizona. We use the record to examine the frequency and timing of extreme droughts in the region and compare the speleothem record's frequency domain characteristics with other regional moisture records and with climate model output. The speleothem record demonstrates strong low-frequency variability with pronounced multi-decadal dry periods, a feature notably lacking in drought metrics from simulations of the last millennium. We also examine the seasonal SW precipitation response to modes of climate variability and external forcings, including volcanic eruptions, in both the speleothem record and the Community Earth System Model's Last Millennium Ensemble (CESM-LME). Notably, ENSO and volcanic forcing have a discernable effect on SW seasonal precipitation in model simulations, particularly when the two processes combine to shift the position of the ITCZ. This integrated analysis of paleodata with climate model results will help us identify and explain discrepancies between these information sources and improve stakeholders' ability to anticipate and prepare for future drought.

Hydroclimate variability of High Arctic Svalbard during the Holocene inferred from hydrogen isotopes of leaf waxes

NASA Astrophysics Data System (ADS)

Balascio, Nicholas L.; D'Andrea, William J.; Gjerde, Marthe; Bakke, Jostein

2018-03-01

The response of the Arctic hydrologic cycle to global warming includes changes in precipitation patterns and moisture availability associated with variable sea ice extent and modes of atmospheric circulation. Reconstructions of past hydroclimate changes help constrain the natural range of these systems, identify the manners in which they respond to different forcing mechanisms, and reveal their connections to other components of the climate system, all of which lead to a better understanding of present and future changes. Here we examine hydroclimate changes during the Holocene in the High Arctic archipelago of Svalbard by reconstructing the isotopic composition of precipitation. We measured the hydrogen isotopic composition (δD values) of leaf wax compounds (n-alkanes; C25-C31) in a sediment core from Lake Hakluytvatnet on the island of Amsterdamøya, northwest Spitsbergen. We interpret δD values of mid-chain (C25) and long-chain (C29, C31) length n-alkanes to represent changes in the isotopic composition of lake water and precipitation over the last 12.9 ka. After deglaciation of the catchment, water supply became restricted and the lake experienced significant evaporative isotopic enrichment indicating warmer conditions from 12.8 to 7.5 ka. The isotope values suggest an increase in the delivery of moisture from warmer sub-polar air masses between 12.8 and 9.5 ka, followed by generally warm, but unstable conditions between 9.5 and 7.5 ka, possibly indicating a response to meltwater forcing. Sedimentary evidence indicates a hiatus in deposition c. 7.5-5.0 ka, likely as a result of desiccation of the lake. At c. 5.0 ka lacustrine sedimentation resumed and over the last 5 ka there was a progressive increase in the influence of polar air masses and colder conditions, which culminated in an abrupt shift to colder conditions at c. 1.8 ka. This late Holocene cooling ended c. 0.18 ka, when isotopic data indicate warmer conditions and greater influence of moisture derived from lower latitudes.

Lake oxygen isotopes as recorders of North American Rocky Mountain hydroclimate: Holocene patterns and variability at multi-decadal to millennial time scales

USGS Publications Warehouse

Anderson, Lesleigh; Max Berkelhammer,; Barron, John A.; Steinman, Byron A.; Finney, Bruce P.; Abbott, Mark B.

2016-01-01

Lake sediment oxygen isotope records (calcium carbonate-δ18O) in the western North American Cordillera developed during the past decade provide substantial evidence of Pacific ocean–atmosphere forcing of hydroclimatic variability during the Holocene. Here we present an overview of 18 lake sediment δ18O records along with a new compilation of lake water δ18O and δ2H that are used to characterize lake sediment sensitivity to precipitation-δ18O in contrast to fractionation by evaporation. Of the 18 records, 14 have substantial sensitivity to evaporation. Two records reflect precipitation-δ18O since the middle Holocene, Jellybean and Bison Lakes, and are geographically positioned in the northern and southern regions of the study area. Their comparative analysis indicates a sequence of time-varying north–south precipitation-δ18O patterns that is evidence for a highly non-stationary influence by Pacific ocean–atmosphere processes on the hydroclimate of western North America. These observations are discussed within the context of previous research on North Pacific precipitation-δ18O based on empirical and modeling methods. The Jellybean and Bison Lake records indicate that a prominent precipitation-δ18O dipole (enriched-north and depleted-south) was sustained between ~ 3.5 and 1.5 ka, which contrasts with earlier Holocene patterns, and appears to indicate the onset of a dominant tropical control on North Pacific ocean–atmosphere dynamics. This remains the state of the system today. Higher frequency reversals of the north–south precipitation-δ18O dipole between ~ 2.5 and 1.5 ka, and during the Medieval Climate Anomaly and the Little Ice Age, also suggest more varieties of Pacific ocean–atmosphere modes than a single Pacific Decadal Oscillation (PDO) type analogue. Results indicate that further investigation of precipitation-δ18O patterns on short (observational) and long (Holocene) time scales is needed to improve our understanding of the processes that drive regional precipitation-δ18O responses to Pacific ocean–atmosphere variability, which in turn, will lead to a better understanding of internal Pacific ocean–atmosphere variability and its response to external climate forcing mechanisms.

Ocean-atmosphere interactions as drivers of mid-to-late Holocene rapid climate changes: Evidence from high-resolution stalagmite records at DeSoto Caverns, Southeast USA

NASA Astrophysics Data System (ADS)

Aharon, Paul; Dhungana, Rajesh

2017-08-01

Oxygen and carbon isotope time-series derived from an actively growing aragonitic stalagmite in DeSoto Caverns exhibit with unusual clarity rapid hydroclimate changes in the mid-to-late Holocene. Data consist of 1884 δ18O and δ13C determinations whose chronology is anchored on 35 230Th/234U absolute dates in the interval 6.0-1.1 cal ka BP. Exceptional 18O and 13C-enrichments centered at 4.8 ± 0.14 cal ka BP likely represent the imprints of a severe drought. Isotope cycles from 4.7 to 1.3 cal ka BP, exhibit a dominant periodicity of 68 ± 4 yrs. A gradual cooling trend of ∼0.6 °C/103 yrs is attributed to a declining seasonal contrast in insolation. The synchronicity of the mega-drought in the Southeast US with the (1) termination of the African Humid Period; (ii) abrupt reduction of the North Atlantic Deep Water production, and (iii) rapid sea-ice expansion in the polar regions of both Hemispheres testifies to the global extent and rapidity of the "5 ka" event and points to the North Atlantic Deep Water variability as the likely controlling factor. The multidecadal cycles are consistent with alternating dry and wet summers occurring during a long-term switch in the seasonal rainfall amount dominance from winter to summer. The periodic summer droughts in the Southeast US support climate models that predict profound hydroclimate changes in the late Holocene governed by the Atlantic Multidecadal Oscillation. The relatively short and rapid hydroclimate phase transitions documented in this study introduce a complication in the correlation of late Holocene drought events that had significant societal impacts.

Extreme Monsoon Rainfall Signatures Preserved in the Invasive Terrestrial Gastropod Lissachatina fulica

NASA Astrophysics Data System (ADS)

Ghosh, Prosenjit; Rangarajan, Ravi; Thirumalai, Kaustubh; Naggs, Fred

2017-11-01

Indian summer monsoon (ISM) rainfall lasts for a period of 4 months with large variations recorded in terms of rainfall intensity during its period between June and September. Proxy reconstructions of past ISM rainfall variability are required due to the paucity of long instrumental records. However, reconstructing subseasonal rainfall is extremely difficult using conventional hydroclimate proxies due to inadequate sample resolution. Here, we demonstrate the utility of the stable oxygen isotope composition of gastropod shells in reconstructing past rainfall on subseasonal timescales. We present a comparative isotopic study on present day rainwater and stable isotope ratios of precipitate found in the incremental growth bands of giant African land snail Lissachatina fulica (Bowdich) from modern day (2009) and in the historical past (1918). Isotopic signatures present in the growth bands allowed for the identification of ISM rainfall variability in terms of its active and dry spells in the modern as well as past gastropod record. Our results demonstrate the utility of gastropod growth band stable isotope ratios in semiquantitative reconstructions of seasonal rainfall patterns. High resolution climate records extracted from gastropod growth band stable isotopes (museum and archived specimens) can expand the scope for understanding past subseasonal-to-seasonal climate variability.

Application of Multi-Model CMIP5 Analysis in Future Drought Adaptation Strategies

NASA Astrophysics Data System (ADS)

Casey, M.; Luo, L.; Lang, Y.

2014-12-01

Drought influences the efficacy of numerous natural and artificial systems including species diversity, agriculture, and infrastructure. Global climate change raises concerns that extend well beyond atmospheric and hydrological disciplines - as climate changes with time, the need for system adaptation becomes apparent. Drought, as a natural phenomenon, is typically defined relative to the climate in which it occurs. Typically a 30-year reference time frame (RTF) is used to determine the severity of a drought event. This study investigates the projected future droughts over North America with different RTFs. Confidence in future hydroclimate projection is characterized by the agreement of long term (2005-2100) multi-model precipitation (P) and temperature (T) projections within the Coupled model Intercomparison Project Phase 5 (CMIP5). Drought severity and the propensity of extreme conditions are measured by the multi-scalar, probabilistic, RTF-based Standard Precipitation Index (SPI) and Standard Precipitation Evapotranspiration Index (SPEI). SPI considers only P while SPEI incorporates Evapotranspiration (E) via T; comparing the two reveals the role of temperature change in future hydroclimate change. Future hydroclimate conditions, hydroclimate extremity, and CMIP5 model agreement are assessed for each Representative Concentration Pathway (RCP 2.6, 4.5, 6.0, 8.5) in regions throughout North America for the entire year and for the boreal seasons. In addition, multiple time scales of SPI and SPEI are calculated to characterize drought at time scales ranging from short to long term. The study explores a simple, standardized method for considering adaptation in future drought assessment, which provides a novel perspective to incorporate adaptation with climate change. The result of the analysis is a multi-dimension, probabilistic summary of the hydrological (P, E) environment a natural or artificial system must adapt to over time. Studies similar to this with specified criteria (SPI/SPEI value, time scale, RCP, etc.) can provide professionals in a variety of disciplines with necessary climatic insight to develop adaptation strategies.

Unraveling North-African riverine and eolian contributions to central Mediterranean sediments during Holocene sapropel S1 formation

NASA Astrophysics Data System (ADS)

Wu, Jiawang; Böning, Philipp; Pahnke, Katharina; Tachikawa, Kazuyo; de Lange, Gert J.

2016-11-01

Hydroclimate variability has exerted a fundamental control on the alternating deposition of organic-lean marl and organic-rich sapropel sediments in the eastern Mediterranean Sea (EMS). However, the exact mechanisms regarding the freshwater sources and related changes are still debated. Here, Sr and Nd isotopes and high-resolution elemental data are used to constrain different riverine and eolian supplies to the central Mediterranean over the past 9.8 ka. The detrital sediments in core CP10BC, taken at the margin of the Libyan shelf in the southwestern Ionian Sea, can be described by a three-endmember mixing system based on Sr and Nd isotopic compositions. The same systematics can also be deduced from Ti and K compositional variability. The endmembers comprise: Saharan Dust, Aegean/Nile, and Libyan Soil, representing the eolian supply from North Africa, the riverine inputs from the Aegean/Nile areas, as well as the riverine and shelf-derived fluxes from the Libyan-Tunisian margin, respectively. For the sapropel S1 period in particular, we find important detrital supplies from fossil river/wadi systems along the Libyan-Tunisian margin, activated by intensified African monsoon precipitation. Combining the temporal profiles with the consistent variability observed in the 87Sr/86Sr-1000/Sr diagram, such Libyan contribution has been most prominent during the uppermost period of sapropel S1 in core CP10BC. This observation is in agreement with hydroclimate reconstructions of northwestern Libya. Comparison of the Sr-Nd isotope data between core CP10BC and four cores taken along a west-east transect throughout the EMS shows that this detrital supply originated mainly from western Libya/Tunisia, and was transported as far eastward as ∼25°E while being diluted by an increasing Nile contribution.

An investigation of the role of winter and spring precipitation as drivers of streamflow in the Missouri River Headwaters using tree-ring reconstructions

NASA Astrophysics Data System (ADS)

Frederick, S. E.; Woodhouse, C. A.; Martin, J. T.; Pederson, G. T.

2017-12-01

The Missouri River supplies water to over 3 million basin residents and is a driving force for the nation's agricultural and energy sectors. However, with changing climate and declining snowpack in western North America, seasonal water yields are becoming less predictable, revealing a gap in our understanding of regional hydroclimate and drivers of streamflow within the basin. By analyzing the relationship between seasonal precipitation and streamflow in the Missouri River Headwaters sub-basin, this study seeks to expand our knowledge based on the instrumental record alone. Here we present the first annually-resolved tree-ring reconstruction of spring precipitation for the Missouri River Headwaters. This reconstruction along with existing tree-ring reconstructions of April 1 snow-water equivalence (SWE) (Pederson et al. 2011) and natural streamflow (Martin, J.T. & Pederson, G.T., personal communication, June 2017) are used to test the feasibility of detecting a variable influence of winter and spring precipitation on streamflow over past centuries, and relative to the modern period. Initial analyses indicate that April 1 SWE is a significant control on streamflow, however, the April 1 SWE record does not fully account for anomalies observed in the streamflow record. This study therefore seeks to determine whether spring precipitation can account for some of this asynchronous variability observed between the April 1 SWE and streamflow records. Aside from improved understanding of the relationship between hydroclimate and streamflow in the headwaters of the Missouri River, our findings offer insights relating to changing contributions from snowmelt and spring precipitation, and long-term hydrologic variability and trends relevant to water resource management and planning efforts.

Using Seismic Reflection Analysis of Lacustrine Sediment Stratigraphy to Reconstruct 40,000 Years of Northern Hemisphere Andean Hydroclimate

NASA Astrophysics Data System (ADS)

Gibson, D. K.; Bird, B. W.; Wattrus, N. J.; Escobar, J.; Fonseca, H.; Velasco, F.; Polissar, P. J.

2017-12-01

Geophysical analysis of lacustrine seismic stratigraphy at Laguna de Tota (hereafter "Tota"), Boyaca, Colombia, provides a record of lake level fluctuations that ranges from the Late Quaternary to the present. Changes in Tota's volume indicated by off-lap and on-lap sequences show that regional hydroclimate varied considerably during at least the last 40 Ka. Modern lake level variability at Tota has been directly linked to the El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO), suggesting that past lake level changes identified in CHIRP seismic data may provide insight into past Pacific atmosphere-ocean dynamics. Here, we use high-resolution CHIRP data spanning the top 15 meters of sediment column and a preliminary age model based on Holocene sedimentation rates to investigate lake level variability over the past 40 Ka. Our data demonstrates that lake levels at Tota were generally lower between 40 and 30 Ka, experienced rapid and extreme fluctuations between 30 and 20 Ka (including the lowest recorded lake level at Tota during the LGM at 22 Ka), and gradually rose to the present day high stand between 20 and 0 Ka. Although the CHIRP data indicate significant late Quaternary lake level fluctuations, the timing and duration of these events needs to be more firmly constrained with additional investigations combining sediment core collection and analysis, geochronology, and other lake level proxies. Future work combining these methods holds tremendous potential in terms of reconstructing Late Quaternary atmosphere-ocean cycles.

A 27cal ka biomarker-based record of ecosystem changes from lacustrine sediments of the Chihuahua Desert of Mexico

NASA Astrophysics Data System (ADS)

Chávez-Lara, C. M.; Holtvoeth, J.; Roy, P. D.; Pancost, R. D.

2018-07-01

Hydroclimate variation of the northwest Mexico during the late Pleistocene and Holocene is an active area of debate, with uncertainty in the nature and sources of precipitation. Previous research has inferred the influences of winter storms, summer monsoonal rain and autumn tropical cyclones. The impacts on regional and local ecosystems, however, are not well constrained. Here, we investigate the response of lacustrine and terrestrial habitats of the Santiaguillo Basin in the Chihuahua Desert (Mexico) to hydrological changes occurring since the late last glacial. Biomarkers from the sediments reflect variable input of organic matter (OM) from algal and bacterial biomass, aquatic microfauna and surrounding vegetation, revealing distinct stages of ecosystem adaption over the last 27 cal ka. Based on previously published and new data, we show that a perennial productive lake was present during the late glacial and it persisted until 17.5 cal ka BP. Coinciding with Heinrich event 1, OM supply from deteriorating wetland soils may have been caused by early dry conditions. Further phases of increasing aridity and a shrinking water body drove changing OM quality and biomarker composition during the early and mid-Holocene. A pronounced shift in biomarker distributions at 4 cal ka BP suggests that the supply of plant litter from resinous trees and grasses increased, likely reflecting the establishment of modern vegetation. Our results illustrate the potential of biomarker applications in the area, adding to the evidence of hydroclimate variability and enabling reconstructions of local ecosystem dynamics.

A 300-year Vietnam hydroclimate and ENSO variability record reconstructed from tree ring δ18O

NASA Astrophysics Data System (ADS)

Sano, Masaki; Xu, Chenxi; Nakatsuka, Takeshi

2012-06-01

A tree ring δ18O chronology is developed for the past 300 years (1705-2004) using 6 cypress trees from northern Vietnam to reconstruct long-term hydroclimatic variations in the summer monsoon season. To the best of our knowledge, this is the first well-replicated tree ringδ18O chronology from Southeast Asia, as well as the longest yet produced. Response analyses reveal that tree ring δ18O is significantly correlated with temperature, precipitation, and the Palmer Drought Severity Index (PDSI) during the period May-October, with highest correlation to the PDSI. Our δ18O chronology accounts for 44% of the PDSI variance, and is in good agreement with a 52-year tree ringδ18O chronology from northern Laos (r = 0.77), indicating that regional hydroclimatic signals are well recorded in the δ18O data. Spatial correlation analyses with global sea surface temperatures suggest that the tropical Pacific plays an important role in modulating hydroclimate over the study region. Further, the δ18O chronology correlates significantly with El Niño-Southern Oscillation (ENSO)-related indices, and is therefore used to reconstruct the annual Multivariate ENSO Index. Because previously published ENSO reconstructions are based mainly on proxy records originating from North America and/or the tropical Pacific, the future development of a tree ringδ18O network from mainland Southeast Asia could lead to an independent and more robust reconstruction of ENSO variability.

Medieval Aridity in the Central Tropical Pacific

NASA Astrophysics Data System (ADS)

Higley, M. C.; Conroy, J. L.; Schmitt, S.

2016-12-01

Reconstructing last millennium hydroclimate history in the tropical Pacific requires continuous, high temporal resolution archives of past moisture balance. Such records remain rare, particularly in the central tropical Pacific (CTP), where to date only one 1300-year terrestrial record of hydroclimate is available. Here we present a new brackish lake sediment record from Kiritimati Island (1.9° N, 157.4° W). 2000 years of geochemical and sedimentological data indicate centennial periods of fresher and more saline lake water. An episode of increased microbial mat development and gypsum precipitation marks the period 900 to 1250 CE, coincident with the Medieval Climate Anomaly (MCA), indicating a period of enhanced salinity and extended aridity. A shift from gypsum and microbial mats to carbonate sediment at the transition between the MCA and the Little Ice Age (LIA) supports the hypothesis of a southward shift in the Intertropical Convergence Zone (ITCZ) at this time and increased precipitation over Kiritimati. The LIA does not appear anomalously wet in Kiritimati relative to the 20th century, and higher frequency variability in the Kiritimati sediment laminae indicates microbial mats continued to grow at multidecadal intervals until 1700 AD. The periodicity of sub-mm scale laminations within the buried microbial mats is highly variable, and indicates mat-carbonate laminae are too frequent to be related to seasonal or ENSO periodicity. Such laminae are likely related to the organization of microbial communities and organomineralization along environmental microgradients in microbial mats.

Improving medium-range and seasonal hydroclimate forecasts in the southeast USA

NASA Astrophysics Data System (ADS)

Tian, Di

Accurate hydro-climate forecasts are important for decision making by water managers, agricultural producers, and other stake holders. Numerical weather prediction models and general circulation models may have potential for improving hydro-climate forecasts at different scales. In this study, forecast analogs of the Global Forecast System (GFS) and Global Ensemble Forecast System (GEFS) based on different approaches were evaluated for medium-range reference evapotranspiration (ETo), irrigation scheduling, and urban water demand forecasts in the southeast United States; the Climate Forecast System version 2 (CFSv2) and the North American national multi-model ensemble (NMME) were statistically downscaled for seasonal forecasts of ETo, precipitation (P) and 2-m temperature (T2M) at the regional level. The GFS mean temperature (Tmean), relative humidity, and wind speed (Wind) reforecasts combined with the climatology of Reanalysis 2 solar radiation (Rs) produced higher skill than using the direct GFS output only. Constructed analogs showed slightly higher skill than natural analogs for deterministic forecasts. Both irrigation scheduling driven by the GEFS-based ETo forecasts and GEFS-based ETo forecast skill were generally positive up to one week throughout the year. The GEFS improved ETo forecast skill compared to the GFS. The GEFS-based analog forecasts for the input variables of an operational urban water demand model were skillful when applied in the Tampa Bay area. The modified operational models driven by GEFS analog forecasts showed higher forecast skill than the operational model based on persistence. The results for CFSv2 seasonal forecasts showed maximum temperature (Tmax) and Rs had the greatest influence on ETo. The downscaled Tmax showed the highest predictability, followed by Tmean, Tmin, Rs, and Wind. The CFSv2 model could better predict ETo in cold seasons during El Nino Southern Oscillation (ENSO) events only when the forecast initial condition was in ENSO. Downscaled P and T2M forecasts were produced by directly downscaling the NMME P and T2M output or indirectly using the NMME forecasts of Nino3.4 sea surface temperatures to predict local-scale P and T2M. The indirect method generally showed the highest forecast skill which occurs in cold seasons. The bias-corrected NMME ensemble forecast skill did not outperform the best single model.

Calibration of hydroclimate proxies in freshwater bivalve shells from Central and West Africa

NASA Astrophysics Data System (ADS)

Kelemen, Zita; Gillikin, David P.; Graniero, Lauren E.; Havel, Holly; Darchambeau, François; Borges, Alberto V.; Yambélé, Athanase; Bassirou, Alhou; Bouillon, Steven

2017-07-01

Freshwater bivalve shell oxygen and carbon stable isotope ratios (δ18O, δ13C) may act as recorders of hydroclimate (e.g., precipitation-evaporation balance, discharge) and aquatic biogeochemistry. We investigate the potential of these hydroclimate proxies measured along the growth axis of shells collected from the Oubangui River (Bangui, Central African Republic) and the Niger River (Niamey, Niger). Biweekly water samples and in situ measurements collected over several years, along with daily discharge data from both sites allowed a direct comparison with proxies recorded in the shells. Data from a total of 14 unionid shells, including three species (Chambardia wissmanni, Aspatharia dahomeyensis, and Aspatharia chaiziana), confirmed that shells precipitate carbonate in oxygen isotope equilibrium with ambient water. Because water temperature variations were small, shell δ18O values (δ18Oshell) also accurately record the seasonality and the range observed in water δ18O (δ18Ow) values when calculated using an average temperature. Calculated δ18Ow values were in good agreement over the entire record of measured δ18Ow values, thus δ18Oshell records can be reliably used to reconstruct past δ18Ow values. Discharge and δ18Ow values from both rivers fit a logarithmic relationship, which was used to attempt reconstruction of past hydrological conditions, after calculating δ18Ow values from δ18Oshell values. A comparison with measured discharge data suggests that for the two rivers considered, δ18Oshell data are good proxies for recording discharge conditions during low(er) discharge levels, but that high discharge values cannot be accurately reconstructed due to the large scatter in the discharge-δ18Ow relationship. Moreover, periods of bivalve shell growth cessation due to high turbidity or air exposure should be taken into account. While δ13C values of dissolved inorganic carbon in both rivers showed clear seasonality and correlated well with discharge, most of the shells analyzed did not record these variations adequately, likely due to the complication of vital effects including the variable contribution of metabolic CO2. Thus, tropical African unionid δ18Oshell values can be used to reconstruct δ18Ow values with high confidence to provide insight on past hydroclimate such as precipitation-evaporation balance and periods of low discharge.

Hydro-climate variability and teleconnection patterns during the last millennium in NW Africa, inferred from speleothem records

NASA Astrophysics Data System (ADS)

Ait Brahim, Y.; Cheng, H.; Sifeddine, A.; Wassenburg, J. A.; Khodri, M.; Cruz, F. W., Sr.

2017-12-01

In this study, we present new paleoclimate records from two well dated Moroccan speleothems. Our stalagmites were sampled from Ifoulki cave in the Western High Atlas Mountains in SW Morocco and Chaara cave in the Eastern Middle Atlas Mountains in NE Morocco. The new paleo-records cover the last 1000 years with a high resolution and reveal substantial swings of dry and humid periods with decadal to multidecadal frequencies. The Medieval Climate Anomaly (MCA) is characterized by generally dry conditions, while wetter conditions are recorded during the Little Ice Age (LIA) and a trend towards dry conditions during the 20th century. These observations are consistent with regional climate signals, providing new insights on common climate controls and teleconnection patterns in NW Africa. We emphasize that the hydro-climate conditions in Morocco remained under the influence of the Atlantic Multidecadal Oscillation (AMO) and the North Atlantic Oscillation (NAO). At longer timescales, we hypothesize that the generally warmer MCA and colder LIA influenced the regional climate in NW Africa through interactions with local mechanisms, such as the Sahara Low, which weakened and strengthened the mean moisture inflow from the Atlantic Ocean during the MCA and LIA respectively.

The Lake Towuti Drilling Project: A New, 1-Million Year Record of Indo-Pacific Hydroclimate

NASA Astrophysics Data System (ADS)

Russell, J. M.; Bijaksana, S.; Vogel, H.; Melles, M.; Crowe, S.; Fajar, S. J.; Hasberg, A. K.; Ivory, S.; Kallmeyer, J.; Kelly, C. S.; Kirana, K. H.; Morlock, M.; Tamuntuan, G. H.; Wicaksono, S. A.

2015-12-01

­The Indo-Pacific region plays an integral role in the Earth's climate system. Changes in local insolation, greenhouse gas concentrations, ice volume, and local sea level are each hypothesized to exert a dominant control on Indo-Pacific hydroclimate variations through the Pleistocene, yet existing records from the region are generally short and exhibit fundamental differences in orbital-scale patterns that limit our understanding of the regional climate responses to these global forcings. New paleoclimate records spanning multiple glacial-interglacial cycles are therefore required to document the region's hydroclimatic response to the full range of global climate boundary conditions observed during the late Quaternary. Lake Towuti is located in central Indonesia and is the only known terrestrial sedimentary archive in the region that spans multiple glacial-interglacial cycles. From May - July, 2015, the Towuti Drilling Project, consisting of nearly 40 scientists from eight countries, recovered over 1,000 meters of new sediment core from Lake Towuti. This includes cores though the entire sediment column to bedrock, which likely provide a >1-million-year records of regional hydroclimate. On-site borehole and sediment core logging data document major shifts in sediment composition, including transitions from lake clays to peats, calcareous sediments, and gravels. These data show excellent agreement with major lithological transitions recorded in seismic reflection data, and indicate large changes in lake levels and hydroclimate through the late Quaternary. Prior work on Lake Towuti indicated a dominant control by global ice volume on regional hydroclimate, a hypothesis we aim to test through the analysis of these new cores. This presentation will review existing records from the region and show the first long geochemical and sedimentological records from Lake Towuti to understand orbital-scale hydrologic change during the last ~1 million years.

Regional hydroclimate response to freshwater fluxes from the Fennoscandian Ice Sheet during the Last Termination

NASA Astrophysics Data System (ADS)

Macdonald, F. A.; Schmitz, M. D.; Condon, D. J.; Zhu, M.; Rooney, A. D.; Brandon, A. D.

2014-12-01

Resolving the effects of freshwater forcing during the last glacial-interglacial transition, the Last Termination, is critical to our comprehension of rapid climate change. In particular, the role of Fennoscandian Ice Sheet (FIS) and freshwater from the eastern seaboard of the North Atlantic has been entirely disregarded in the context of the abrupt regional hydroclimate shifts that characterized this period. Here we infer freshwater input variations from the FIS to the Nordic Seas based on two accurately dated hydroclimate reconstructions from lake sediment records from Southern Sweden and one SST reconstruction from the Nordic Seas. The records indicate a number of abrupt freshwater discharges into the Nordic Seas at the start of the Bølling interstadial and during the Allerød interstadial. We observe that these intervals of enhanced FIS freshwater outflow correspond to different modalities of hydroclimate regime shifts in Greenland. Using a set of climate model simulations, we show that the dominant Greenland hydroclimate state can be influenced by the degree of FIS freshwater recirculation in the Nordic Seas, which redirects the excess of sea ice partitioned into the Barents Sea towards the eastern Greenland Current. The tradeoff between buildup and recirculation of sea ice in the Nordic Seas generate large-scale sea-level pressure anomalies that may explain the sign and magnitude of the isotopic and temperature changes inferred from Greenland and North European reconstructions. We conclude that air-sea interactions in the North Atlantic are more sensitive to Fennoscandian freshwater forcing than previously thought. These results could help to solve the problematic relationship between origin, timing and magnitude of freshwater perturbations and abrupt deglacial changes in North Atlantic Ocean circulation in numerical simulations.

Streamflow variability in the Chilean Temperate-Mediterranean climate transition (35°S-42°S) during the last 400 years inferred from tree-ring records

NASA Astrophysics Data System (ADS)

Muñoz, Ariel A.; González-Reyes, Alvaro; Lara, Antonio; Sauchyn, David; Christie, Duncan; Puchi, Paulina; Urrutia-Jalabert, Rocío; Toledo-Guerrero, Isadora; Aguilera-Betti, Isabella; Mundo, Ignacio; Sheppard, Paul R.; Stahle, Daniel; Villalba, Ricardo; Szejner, Paul; LeQuesne, Carlos; Vanstone, Jessica

2016-12-01

As rainfall in South-Central Chile has decreased in recent decades, local communities and industries have developed an understandable concern about their threatened water supply. Reconstructing streamflows from tree-ring data has been recognized as a useful paleoclimatic tool in providing long-term perspectives on the temporal characteristics of hydroclimate systems. Multi-century long streamflow reconstructions can be compared to relatively short instrumental observations in order to analyze the frequency of low and high water availability through time. In this work, we have developed a Biobío River streamflow reconstruction to explore the long-term hydroclimate variability at the confluence of the Mediterranean-subtropical and the Temperate-humid climate zones, two regions represented by previous reconstructions of the Maule and Puelo Rivers, respectively. In a suite of analyses, the Biobío River reconstruction proves to be more similar to the Puelo River than the Maule River, despite its closer geographic proximity to the latter. This finding corroborates other studies with instrumental data that identify 37.5°S as a latitudinal confluence of two climate zones. The analyzed rivers are affected by climate forcings on interannual and interdecadal time-scales, Tropical (El Niño Southern Oscillation) and Antarctic (Southern Annular Mode; SAM). Longer cycles found, around 80-years, are well correlated only with SAM variation, which explains most of the variance in the Biobío and Puelo rivers. This cycle also has been attributed to orbital forcing by other authors. All three rivers showed an increase in the frequency of extreme high and low flow events in the twentieth century. The most extreme dry and wet years in the instrumental record (1943-2000) were not the most extreme of the past 400-years reconstructed for the three rivers (1600-2000), yet both instrumental record years did rank in the five most extreme of the streamflow reconstructions as a whole. These findings suggest a high level of natural variability in the hydro-climatic conditions of the region, where extremes characterized the twentieth century. This information is particularly useful when evaluating and improving a wide variety of water management models that apply to water resources that are sensitive to agricultural and hydropower industries.

A New Holocene Lake Sediment Archive from Samoa (Tropical South Pacific) Reveals Millennial Scale Changes in Hydroclimate.

NASA Astrophysics Data System (ADS)

Sear, D. A.; Hassall, J. D.; Langdon, P. G.; Croudace, I. W. C.; Maloney, A. E.; Sachs, J. P.

2015-12-01

El Niño-Southern Oscillation (ENSO) is the strongest source of interannual climate variability on the planet. Its behaviour leads to major hydro-climate impacts around the world, including flooding, drought, and altering cyclone frequency. Simulating ENSO behaviour is difficult using climate models, as it is a complex non-linear system, and hence predicting its future variability under changing climate is challenging. Using palaeoclimate data thus allows an insight into long-term ENSO behaviour against a range of different forcings throughout the Holocene. To date long, coherent, high resolution records from lake sediment archives have been limited to the Pacific Rim. We present new data from the closed crater Lake Lanoto'o, on Upolu Island, Samoa, located within the tropical South Pacific. The lake sediment record extends back into the early Holocene with an average sedimentation rate 0.4mm a-1. We demonstrate a strong correspondence between precipitation at the study site and measures of the Southern Oscillation Index (SOI)1. We compare geochemical proxies of precipitation to a long-term reconstruction of the SOI2. The resulting proxy SOI record extends over the last 9000 years, revealing scales of change in ENSO that match those recorded from sites located on the Pacific rim3,4. A major period of La-Nina dominance occurs around 4.5ka BP before abruptly switching to El-Nino dominance around 3.2ka. Thereafter, phases of El-Nino - La Nina dominance, alternate every c. 400yrs. The results point to prolonged phases of enhanced or reduced precipitation - conditions that may influence future population resilience to climate change, and may also have been triggers for the colonisation of more remote eastern Polynesia. 1. http://www.cgd.ucar.edu/cas/catalog/climind/SOI.signal.annstd.ascii. 2. Yan, H. et al. (2011) Nature Geoscience, 4, p.611. 3. Conroy J. L. et al. (2008) Quaternary Science Reviews, 27, p.1166 4. Moy, C. M. et al. (2002) Nature, 420, p.162

Can tree-ring isotopes (δ18O and δ13C) improve our understanding of hydroclimate variability in the Columbia River Basin?

NASA Astrophysics Data System (ADS)

Csank, A. Z.; Wise, E.; McAfee, S. A.

2015-12-01

The trajectory of incoming storms from the Pacific Ocean has a strong impact on hydroclimate in the Pacific Northwest. Shifts between zonal and meridional flow are a key influence on drought and pluvial regimes in both the PNW and the western United States as a whole. Circulation-dependent variability in the isotopic composition of precipitation can be recorded and potentially reconstructed using δ18O records derived from tree-rings. Here we present isotopic records of δ18O and δ13C from ponderosa pine (Pinus ponderosa) for the period 1950-2013 from six sites located in the lee of the Cascades in eastern Washington. Because of the orientation of the Cascades, zonal flow will result in an intensified rain shadow whereas meridional flow allows moisture to penetrate at a lower elevation leading to a lower rainout effect. This means zonal flow results in drier conditions in eastern Washington and the converse for meridional flow. We hypothesized that more depleted precipitation δ18O values will occur with periods of more zonal flow across the PNW and will be recorded by trees at our sites. Results show a strong relationship between our δ18O chronologies and winter precipitation (R = -0.50; p<0.001). δ13C chronologies from the same trees showed a relationship to prior fall/winter (pOct-pDec) precipitation (R = -0.46; p<0.005) suggesting a possible link to antecedent moisture conditions. With a focus on years with clear zonal and meridional flow regimes, we regressed the tree-ring δ18O anomaly against the instrumental record of total precipitation and compared the residual series to records of storm track for the period 1978-2008, and we found a detectable signal where the most depleted δ18O was generally associated with zonal flow and the most enriched δ18O with meridional flow. However, there are still some years where the relationship is unclear. Further work is aimed at understanding these anomalous years and extending our record beyond the instrumental period.

Climate variations of Central Asia on orbital to millennial timescales.

PubMed

Cheng, Hai; Spötl, Christoph; Breitenbach, Sebastian F M; Sinha, Ashish; Wassenburg, Jasper A; Jochum, Klaus Peter; Scholz, Denis; Li, Xianglei; Yi, Liang; Peng, Youbing; Lv, Yanbin; Zhang, Pingzhong; Votintseva, Antonina; Loginov, Vadim; Ning, Youfeng; Kathayat, Gayatri; Edwards, R Lawrence

2016-11-11

The extent to which climate variability in Central Asia is causally linked to large-scale changes in the Asian monsoon on varying timescales remains a longstanding question. Here we present precisely dated high-resolution speleothem oxygen-carbon isotope and trace element records of Central Asia's hydroclimate variability from Tonnel'naya cave, Uzbekistan, and Kesang cave, western China. On orbital timescales, the supra-regional climate variance, inferred from our oxygen isotope records, exhibits a precessional rhythm, punctuated by millennial-scale abrupt climate events, suggesting a close coupling with the Asian monsoon. However, the local hydroclimatic variability at both cave sites, inferred from carbon isotope and trace element records, shows climate variations that are distinctly different from their supra-regional modes. Particularly, hydroclimatic changes in both Tonnel'naya and Kesang areas during the Holocene lag behind the supra-regional climate variability by several thousand years. These observations may reconcile the apparent out-of-phase hydroclimatic variability, inferred from the Holocene lake proxy records, between Westerly Central Asia and Monsoon Asia.

Climate variations of Central Asia on orbital to millennial timescales

PubMed Central

Cheng, Hai; Spötl, Christoph; Breitenbach, Sebastian F. M.; Sinha, Ashish; Wassenburg, Jasper A.; Jochum, Klaus Peter; Scholz, Denis; Li, Xianglei; Yi, Liang; Peng, Youbing; Lv, Yanbin; Zhang, Pingzhong; Votintseva, Antonina; Loginov, Vadim; Ning, Youfeng; Kathayat, Gayatri; Edwards, R. Lawrence

2016-01-01

The extent to which climate variability in Central Asia is causally linked to large-scale changes in the Asian monsoon on varying timescales remains a longstanding question. Here we present precisely dated high-resolution speleothem oxygen-carbon isotope and trace element records of Central Asia’s hydroclimate variability from Tonnel’naya cave, Uzbekistan, and Kesang cave, western China. On orbital timescales, the supra-regional climate variance, inferred from our oxygen isotope records, exhibits a precessional rhythm, punctuated by millennial-scale abrupt climate events, suggesting a close coupling with the Asian monsoon. However, the local hydroclimatic variability at both cave sites, inferred from carbon isotope and trace element records, shows climate variations that are distinctly different from their supra-regional modes. Particularly, hydroclimatic changes in both Tonnel’naya and Kesang areas during the Holocene lag behind the supra-regional climate variability by several thousand years. These observations may reconcile the apparent out-of-phase hydroclimatic variability, inferred from the Holocene lake proxy records, between Westerly Central Asia and Monsoon Asia. PMID:27833133

Tropical Indo-Pacific hydroclimate response to North Atlantic forcing during the last deglaciation as recorded by a speleothem from Sumatra, Indonesia

NASA Astrophysics Data System (ADS)

Wurtzel, Jennifer B.; Abram, Nerilie J.; Lewis, Sophie C.; Bajo, Petra; Hellstrom, John C.; Troitzsch, Ulrike; Heslop, David

2018-06-01

Abrupt changes in Atlantic Meridional Overturning Circulation are known to have affected the strength of the Indian and Asian Monsoons during glacial and deglacial climate states. However, there is still much uncertainty around the hydroclimate response of the Indo-Pacific Warm Pool (IPWP) region to abrupt climate changes in the North Atlantic. Many studies suggest a mean southward shift in the intertropical convergence zone (ITCZ) in the IPWP region during phases of reduced Atlantic meridional overturning, however, existing proxies have seasonal biases and conflicting responses, making it difficult to determine the true extent of North Atlantic forcing in this climatically important region. Here we present a precisely-dated, high-resolution record of eastern Indian Ocean hydroclimate variability spanning the last 16 ky (thousand years) from δ18O measurements in an aragonite-calcite speleothem from central Sumatra. This represents the western-most speleothem record from the IPWP region. Precipitation arrives year-round at this site, with the majority sourced from the local tropical eastern Indian Ocean and two additional long-range seasonal sources associated with the boreal and austral summer monsoons. The Sumatran speleothem demonstrates a clear deglacial structure that includes 18O enrichment during the Younger Dryas and 18O depletion during the Bølling-Allerød, similar to the pattern seen in speleothems of the Asian and Indian monsoon realms. The speleothem δ18O changes at this site are best explained by changes in rainfall amount and changes in the contributions from different moisture pathways. Reduced rainfall in Sumatra during the Younger Dryas is most likely driven by reductions in moisture transport along the northern or southern monsoon transport pathways to Sumatra. Considered with other regional proxies, the record from Sumatra suggests the response of the IPWP to North Atlantic freshwater forcing is not solely driven by southward shifts of the ITCZ, but also a reduction in moisture transport along both monsoon pathways.

Architecture of collapse: regime shift and recovery in an hierarchically structured marine ecosystem.

PubMed

Daskalov, Georgi M; Boicenco, Laura; Grishin, Alexandre N; Lazar, Luminita; Mihneva, Vesselina; Shlyakhov, Vladislav A; Zengin, Mustafa

2017-04-01

By the late 20th century, a series of events or 'natural experiments', for example the depletion of apex predators, extreme eutrophication and blooms of invasive species, had suggested that the Black Sea could be considered as a large ecosystem 'laboratory'. The events resulted in regime shifts cascading through all trophic levels, disturbing ecosystem functioning and damaging the water environment. Causal pathways by which the external (hydroclimate, overfishing) and internal (food web interactions) drivers provoke regime shifts are investigated. Statistical data analyses supported by an interpretative framework based on hierarchical ecosystem theory revealed mechanisms of hierarchical incorporation of environmental factors into the ecosystem. Evidence links Atlantic teleconnections to Black Sea hydroclimate, which together with fishing shapes variability in fish stocks. The hydroclimatic signal is conveyed through the food web via changes in productivity at all levels, to planktivorous fish. Fluctuating fish abundance is believed to induce a lagged change in competitor jelly plankton that cascades down to phytoplankton and influences water quality. Deprived of the stabilising role of apex predators, the Black Sea's hierarchical ecosystem organisation is susceptible to both environmental and anthropogenic stresses, and increased fishing makes fish stock collapses highly probable. When declining stocks are confronted with burgeoning fishing effort associated with the inability of fishery managers and decision-makers to adapt rapidly to changes in fish abundance, there is overfishing and stock collapse. Management procedures are ineffective at handling complex phenomena such as ecosystem regime shifts because of the shortage of suitable explanatory models. The proposed concepts and models reported here relate the hydroclimate, overfishing and invasive species to shifts in ecosystem functioning and water quality, unravelling issues such as the causality of ecosystem interactions and mechanisms and offering potential for finding ways to reverse regime shifts. We advocate a management approach aiming at restoring ecosystem hierarchy that might mitigate the costly consequences of regime shifts. © 2016 John Wiley & Sons Ltd.

Global hydrobelts: improved reporting scale for water-related issues?

NASA Astrophysics Data System (ADS)

Meybeck, M.; Kummu, M.; Dürr, H. H.

2012-08-01

Questions related to water such as its availability, water needs or stress, or management, are mapped at various resolutions at the global scale. They are reported at many scales, mostly along political or continental boundaries. As such, they ignore the fundamental heterogeneity of the hydroclimate and the natural boundaries of the river basins. Here, we describe the continental landmasses according to eight global-scale hydrobelts strictly limited by river basins, defined at a 30' (0.5°) resolution. The belts were defined and delineated, based primarily on the annual average temperature (T) and runoff (q), to maximise interbelt differences and minimise intrabelt variability. The belts were further divided into 29 hydroregions based on continental limits. This new global puzzle defines homogeneous and near-contiguous entities with similar hydrological and thermal regimes, glacial and postglacial basin histories, endorheism distribution and sensitivity to climate variations. The Mid-Latitude, Dry and Subtropical belts have northern and southern analogues and a general symmetry can be observed for T and q between them. The Boreal and Equatorial belts are unique. The hydroregions (median size 4.7 Mkm2) contrast strongly, with the average q ranging between 6 and 1393 mm yr-1 and the average T between -9.7 and +26.3 °C. Unlike the hydroclimate, the population density between the North and South belts and between the continents varies greatly, resulting in pronounced differences between the belts with analogues in both hemispheres. The population density ranges from 0.7 to 0.8 p km-2 for the North American Boreal and some Australian hydroregions to 280 p km-2 for the Asian part of the Northern Mid-Latitude belt. The combination of population densities and hydroclimate features results in very specific expressions of water-related characteristics in each of the 29 hydroregions. Our initial tests suggest that hydrobelt and hydroregion divisions are often more appropriate for water-relative global analysis and reporting than conventional continental or political divisions.

Improving Forecasts for Water Management

NASA Astrophysics Data System (ADS)

Arumugam, Sankar; Wood, Andy; Rajagopalan, Balaji; Schaake, John

2014-01-01

Recent advances in seasonal to interannual hydroclimate predictions provide an opportunity for developing a proactive approach toward water management. This motivated a recent AGU Chapman Conference (see program details at http://chapman.agu.org/watermanagement/). Approximately 85 participants from the United States, Oceania, Asia, Europe, and South America presented and discussed the current state of successes, challenges, and opportunities in seasonal to interannual hydroclimate forecasts and water management, and a number of key messages emerged.

Dominance of climate warming effects on recent drying trends over wet monsoon regions

NASA Astrophysics Data System (ADS)

Park, Chang-Eui; Jeong, Su-Jong; Ho, Chang-Hoi; Park, Hoonyoung; Piao, Shilong; Kim, Jinwon; Feng, Song

2017-09-01

Understanding changes in background dryness over land is key information for adapting to climate change because of its critical socioeconomic consequences. However, causes of continental dryness changes remain uncertain because various climate parameters control dryness. Here, we verify dominant climate variables determining dryness trends over continental eastern Asia, which is characterized by diverse hydroclimate regimes ranging from arid to humid, by quantifying the relative effects of changes in precipitation, solar radiation, wind speed, surface air temperature, and relative humidity on trends in the aridity index based on observed data from 189 weather stations for the period of 1961-2010. Before the early 1980s (1961-1983), change in precipitation is a primary condition for determining aridity trends. In the later period (1984-2010), the dominant climate parameter for aridity trends varies according to the hydroclimate regime. Drying trends in arid regions are mostly explained by reduced precipitation. In contrast, the increase in potential evapotranspiration due to increased atmospheric water-holding capacity, a secondary impact of warming, works to increase aridity over the humid monsoon region despite an enhanced water supply and relatively less warming. Our results show significant drying effects of warming over the humid monsoon region in recent decades; this also supports the drying trends over warm and water-sufficient regions in future climate.

Temperature-precipitation relationship of the Common Era in northern Europe

NASA Astrophysics Data System (ADS)

Luoto, Tomi P.; Nevalainen, Liisa

2018-05-01

Due to the lack of knowledge on dynamics of the North Atlantic Oscillation (NAO) prior to the last millennium, synchronized records of air temperature and precipitation variability are needed to understand large-scale drivers of the hydroclimate. Here, we use completely synchronized paleolimnological proxy-based records of air temperature and effective precipitation from two Scandinavian lakes with ˜2000-year sediment profiles. We show that the relationship between air temperature and precipitation (T/P ratio) is synchronous in both study sites throughout the records suggesting warm and dry conditions at ˜300-1100 CE and cold and wet conditions at ˜1200-1900 CE. Owing to the significantly increased air temperatures, the most recent T/P ratio has again turned positive. During the first millennium of the Common Era, the T/P mimics patterns in Southern Oscillation index, whereas the second millennium shows response to the NAO index but is also concurrent with solar irradiance shifts. Since our T/P reconstruction is mostly linked with the NAO, we propose the T/P ratio as an indicator of the NAO. Our results from the coherent records provide first-time knowledge on the long-term temperature-precipitation relationship in Northern Europe that increase understanding of the comprehensive hydroclimate system in the region and the NAO dynamics also further back in time.

Hydroclimate Forecasts in Ethiopia: Benefits, Impediments, and Ways Forward

NASA Astrophysics Data System (ADS)

Block, P. J.

2014-12-01

Numerous hydroclimate forecast models, tools, and guidance exist for application across Ethiopia and East Africa in the agricultural, water, energy, disasters, and economic sectors. This has resulted from concerted local and international interdisciplinary efforts, yet little evidence exists of rapid forecast uptake and use. We will review projected benefits and gains of seasonal forecast application, impediments, and options for the way forward. Specific case studies regarding floods, agricultural-economic links, and hydropower will be reviewed.

Late Holocene Lake Level Fluctuations at Laguna Arapa, Peru and Connections to Human Demography

NASA Astrophysics Data System (ADS)

Hillman, A. L.; Abbott, M. B.; Werne, J. P.; Arkush, E.; Thompson, L. G.; Ferland, T.; Holmes, E.; Puhnaty, C.; Woods, A.

2016-12-01

The relationship between variations in hydroclimate and human demography on the Peruvian Altiplano has significant implications for understanding how people in the past have adapted to changes in freshwater resources. To investigate these human-environmental interactions, this project presents a 2,000 year sediment record from Laguna Arapa, a large lake that is <20 km NW of Lake Titicaca. Using sedimentology and stratigraphy as well as a suite of organic geochemical proxies including fecal 5β-stanols and leaf waxes (long chain n-alkanoic acids), we aim to tie together proxies of human population with indicators of regional hydroclimate. Preliminary results of sedimentology and stratigraphy show notable transitions from sand to silt to clay, suggesting rising lake level sequences at 500 and 700 AD. The last 1,300 years of sediment are characterized by alternating layers of organic rich material with abundant charcoal and black inorganic clay, suggesting intermittent periods of aridity and/or anthropogenic fire-setting. These layers are particularly frequent during the Medieval Climate Anomaly, which was characterized by dry and warm conditions. These results agree well with other records of hydroclimate from regional lakes as well as accumulation rate and temperature from the Quelccaya ice cap. Organic geochemical work is currently in progress and shows promise for linking together proxies of human demography with hydroclimate to understand the relationship between human settlement and climate change.

Simulations of Western North American Hydroclimate during the Little Ice Age and Medieval Climate Anomaly

NASA Astrophysics Data System (ADS)

Simon, S. M.; Mann, M. E.; Steinman, B. A.; Feng, S.; Zhang, Y.; Miller, S. K.

2013-12-01

Despite the immense impact that large, modern North American droughts, such as those of the 1930s and 1950s, have had on economic, social, aquacultural, and agricultural systems, they are smaller in duration and magnitude than the multidecadal megadroughts that affected North America, in particular the western United States, during the Medieval Climate Anomaly (MCA, ~ 900-1300 AD) and the Little Age (LIA, ~1450-1850 AD). Although various proxy records have been used to reconstruct the timing of these MCA and LIA megadroughts in the western United States, there still exists great uncertainty in the magnitude and spatial coherence of such droughts in the Pacific Northwest region, especially on decadal to centennial timescales. This uncertainty motivates the following study to establish a causal link between the climate forcing that induced these megadroughts and the spatiotemporal response of regional North American hydroclimates to this forcing. This study seeks to establish a better understanding of the influence of tropical Pacific and North Atlantic SSTs on North American drought during the MCA and LIA. We force NCAR's Community Atmospheric Model version 5.1.1 (CAM 5) with prescribed proxy-reconstructed tropical Pacific and North Atlantic SST anomalies from the MCA and LIA, in order to investigate the influence that these SST anomalies had on the spatiotemporal patterns of drought in North America. To isolate the effects of individual ocean basin SSTs on the North American climate system, the model experiments use a variety of SST permutations in the tropical Pacific and North Atlantic basin as external forcing. In order to quantify the spatiotemporal response of the North American climate system to these SST forcing permutations, temperature and precipitation data derived from the MCA and LIA model experiments are compared to lake sediment isotope and tree ring-based hydroclimate reconstructions from the Pacific Northwest. The spatiotemporal temperature and precipitation patterns from the model experiments indicate that in the Pacific Northwest, the MCA and LIA were anomalously wet and dry periods, respectively, a finding that is largely supported by the lake sediment records. This pattern contrasts with the dry MCA/wet LIA pattern diagnosed in model experiments for the U.S Southwest and indicated by tree ring-based proxy data. Thus, the CAM 5 model experiments confirm the wet/dry dipole pattern suggested by proxy data for the western U.S. during the MCA and LIA and highlights the role that the natural variability of tropical Pacific and North Atlantic SSTs played in driving this spatiotemporal climate pattern and its related teleconnections.

Hydroclimate variability and regional atmospheric circulation over the past 1,350 years reconstructed from Lake Ohau, New Zealand

NASA Astrophysics Data System (ADS)

Roop, H. A.; Levy, R. H.; Vandergoes, M.; Dunbar, G. B.; Howarth, J. D.; Lorrey, A.; Phipps, S. J.

2016-12-01

Comprehensive understanding of natural climate-system dynamics requires high-resolution paleoclimate records extending beyond the instrumental period. This is particularly the case for the sparsely-instrumented Southern Hemisphere mid-latitudes, where the timing and amplitude of regional and hemispheric-scale climatic events are poorly constrained. Here we present a 1,350-year record of hydroclimatic variability and regional circulation derived from an annually laminated sediment record from Lake Ohau, South Island, New Zealand (44.23°S, 169.85°E). The climate of New Zealand is influenced by climatological patterns originating in both the tropics (e.g. El-Niño-Southern Oscillation, Interdecadal Pacific Oscillation) and the Antarctic (Southern Annular Mode, SAM). Utilizing the annually resolved Lake Ohau hydroclimate record in combination with a tree-ring record of summer temperature from Oroko Swamp, New Zealand (Cook et al., 2002), we generate a circulation index for the Western South Island of New Zealand. This index utilizes the temperature and precipitation anomalies defined by the Regional Climate Regime Classification scheme for New Zealand to assign synoptic scale circulation patterns to 25-year intervals from 900-2000 AD. This circulation index shows significant periods of change, most notably 835 - 985 AD when northerly airflow dominated and from 1385 - 1710 AD when strong southerly airflow persisted. Comparisons with regional SAM and ENSO reconstructions show that dry, warm conditions at Lake Ohau are consistently associated with strengthened tropical teleconnections to New Zealand and a positive SAM, while cold and wet conditions are driven by increased southerly airflow and negative phase SAM. A persistent negative SAM dominates the Little Ice Age (LIA; 1385-1710 AD) interval in the Western South Island. This same period coincides with the Northern Hemisphere LIA.

Pan-Continental Droughts in North America over the Last Millennium

NASA Technical Reports Server (NTRS)

Cook, Benjamin I.; Smerdon, Jason E.; Seager, Richard; Cook, Edward R.

2014-01-01

Regional droughts are common in North America, but pan-continental droughts extending across multiple regions, including the 2012 event, are rare relative to single-region events. Here, the tree-ring-derived North American Drought Atlas is used to investigate drought variability in four regions over the last millennium, focusing on pan-continental droughts. During the Medieval Climate Anomaly (MCA), the central plains (CP), Southwest (SW), and Southeast (SE) regions experienced drier conditions and increased occurrence of droughts and the Northwest (NW) experienced several extended pluvials. Enhanced MCA aridity in the SW and CP manifested as multidecadal megadroughts. Notably, megadroughts in these regions differed in their timing and persistence, suggesting that they represent regional events influenced by local dynamics rather than a unified, continental-scale phenomena. There is no trend in pan-continental drought occurrence, defined as synchronous droughts in three or more regions. SW, CP, and SE (SW+CP+SE) droughts are the most common, occurring in 12 percent of all years and peaking in prevalence during the twelfth and thirteenth centuries; patterns involving three other regions occur in about 8 percent of years. Positive values of the Southern Oscillation index (La Nina conditions) are linked to SW, CP, and SE (SW+CP+SE) droughts and SW, CP, and NW (SW+CP+NW) droughts, whereas CP, NW, and SE (CP+NW+SE) droughts are associated with positive values of the Pacific decadal oscillation and Atlantic multidecadal oscillation. While relatively rare, pan-continental droughts are present in the paleo record and are linked to defined modes of climate variability, implying the potential for seasonal predictability. Assuming stable drought teleconnections, these events will remain an important feature of future North American hydroclimate, possibly increasing in their severity in step with other expected hydroclimate responses to increased greenhouse gas forcing.

Varve-based Reconstruction of Seasonal Hydroclimate from Nar Gölü, Turkey over the last 2.6 ka BP

NASA Astrophysics Data System (ADS)

Primmer, N.; Jones, M.; Metcalfe, S. E.; Eastwood, W.; Brauer, A.; Roberts, C. N.

2017-12-01

In south-west Asia, the wet-dry seasonality and semi-arid climatology increases societal vulnerability to drought. Long, continuous records of such droughts from the region are therefore important to put recent extremes in context, to benchmark natural variability in water availability. We present the longest annual record of south-west Asian climate to date, spanning the entirety of the Common Era. We reconstruct seasonal hydrological change from a climatically sensitive lake, Nar Gölü, Turkey over the past 2,589 years using varve sedimentology. Organic-calcareous varve deposition is driven by the climatic wet-dry seasonality, where varve microfacies analysis has developed an inter- and intra-annual record of the resultant limnological variability. Calibration using modern meteorological data identified that the March-May evaporation/precipitation ratio as the primary control on carbonate sublayer thickness. Combining these analyses with previous stable isotope, pollen and diatom records from the same cores further develops a holistic environmental record of palaeoseasonality able to gauge past and present hydrology, including drought severity. Two threshold hydrological changes to the spring growing season are well-dated at 535 and 1406 AD, thus coinciding with the onset of the Late Antiquity Little Ice Age (LALIA) and Little Ice Age (LIA) respectively. Carbonate mineralogy indicates generally fresher water conditions during the intermediary 871-year long period, with an inferred dry period at 850 AD possibly marking the start of regional, long-term aridification. By reconstructing high resolution hydroclimate, this well constrained annual record of past water availability provides a unique context for understanding climate change and its potential impact in this vulnerable region.

Drought in the northern Bahamas from 3300 to 2500 years ago

NASA Astrophysics Data System (ADS)

van Hengstum, Peter J.; Maale, Gerhard; Donnelly, Jeffrey P.; Albury, Nancy A.; Onac, Bogdan P.; Sullivan, Richard M.; Winkler, Tyler S.; Tamalavage, Anne E.; MacDonald, Dana

2018-04-01

Intensification and western displacement of the North Atlantic Subtropical High (NASH) is projected for this century, which can decrease Caribbean and southeastern American rainfall on seasonal and annual timescales. However, additional hydroclimate records are needed from the northern Caribbean to understand the long-term behavior of the NASH, and better forecast its future behavior. Here we present a multi-proxy sinkhole lake reconstruction from a carbonate island that is proximal to the NASH (Abaco Island, The Bahamas). The reconstruction indicates the northern Bahamas experienced a drought from ∼3300 to ∼2500 Cal yrs BP, which coincides with evidence from other hydroclimate and oceanographic records (e.g., Africa, Caribbean, and South America) for a synchronous southern displacement of the Intertropical Convergence Zone and North Atlantic Hadley Cell. The specific cause of the hydroclimate change in the northeastern Caribbean region from ∼3300 to 2500 Cal yrs BP was probably coeval southern or western displacement of the NASH, which would have increased northeastern Caribbean exposure to subsiding air from higher altitudes.

Finding "Models" in Clouds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Leung, Ruby

2017-05-01

Internationally recognized Climate Scientist Ruby Leung is a cloud gazer. But rather than looking for shapes, Ruby’s life’s calling is to develop regional atmospheric models to better predict and understand the effects of global climate change at scales relevant to humans and the environment. Ruby’s accomplishments include developing novel methods for modeling mountain clouds and precipitation in climate models, and improving understanding of hydroclimate variability and change. She also has led efforts to develop regional climate modeling capabilities in the Weather Research and Forecasting model that is widely adopted by scientists worldwide. Ruby is part of a team of PNNLmore » researchers studying the impacts of global warming.« less

Climatic Controls on Forest Productivity in Western North America; Variability, Covariability, and Projected Change

NASA Astrophysics Data System (ADS)

Hawkins, L. R.; Rupp, D. E.; Li, S.; Mote, P.; Sparrow, S.; Massey, N.

2016-12-01

The forests of western North America serve as a carbon sink sequestering carbon and slowing the rise of CO2 in the atmosphere. Though still positive, the rate of net carbon uptake has been in decline over the past two decades. Regional drought has been shown to slow forest productivity and net carbon uptake despite warmer temperatures and longer growing seasons. With drought conditions projected to increase in frequency and severity under climate change there is concern that these forests' capacity as an effective carbon sink will continue to decrease in the future. To investigate how changes in regional hydroclimate may affect future carbon uptake in western US forests we dynamically downscaled global climate simulations using a 25-km resolution regional climate model HadRM3P with the land surface scheme MOSES2. We generated a 100-member ensemble of simulations for an historical period (1985-2015) and mid-21st century period (2030-2060) under Representative Concentration Pathway 8.5. We evaluated the effects of regional changes in atmospheric moisture demand, seasonality of water supply, and water stress on forest productivity and carbon uptake. We investigated how these changes in hydroclimate interact with the relaxing of temperature controls. This work can inform future adaptation efforts through improving our understanding of climatic controls on forest carbon sequestration.

Tree-ring indicators of rainfall and streamflow for the Ili-Balkhash Basin, Central Asia since CE 1560

NASA Astrophysics Data System (ADS)

Chen, Feng; Yuan, Yujiang; Yu, Shulong

2017-09-01

We reconstructed previous July - current April total precipitation in the upper Ili-Balkhash Basin of Central Asia, using a transfer equation based on the correlation between regional tree-ring width series and local precipitation data. Dry periods were identified from 1586-1612, 1637-1669, 1695-1721, 1759-1782, 1804-1864, 1907-1930 and 1974-1993, while wet periods occurred from 1560-1585, 1613-1636, 1670-1694, 1722-1758, 1783-1803, 1865-1906, 1931-1973 and 1994-2006. Spatial correlation analysis indicates that our precipitation reconstruction is broadly representative of precipitation in the entire Ili-Balkhash Basin. The precipitation timeseries is also strongly related to streamflow measurements, revealing that variations in precipitation in the upper Ili-Balkhash Basin have a dramatic influence on streamflow into Lake Balkhash. The precipitation reconstruction also compares well with various streamflow reconstructions from the Tien Shan, and exhibits an increasing streamflow trend in the 1980s through 2000s. Spectral analysis showed significant 60-, 33-, 11-, 2.8- and 2.1-year cycles over the past 447 years. Our 447-year precipitation reconstruction provides the basis for comparing past and present hydroclimate changes, which will be important for detection and attribution of hydroclimate variation in the Ili-Balkhash Basin.

Climate Change Impact Assessment of Hydro-Climate in Southern Peninsular Malaysia

NASA Astrophysics Data System (ADS)

Ercan, A.; Ishida, K.; Kavvas, M. L.; Chen, Z. R.; Jang, S.; Amin, M. Z. M.; Shaaban, A. J.

2017-12-01

Impacts of climate change on the hydroclimate of the coastal region in the south of Peninsular Malaysia in the 21st century was assessed by means of a regional climate model utilizing an ensemble of 15 different future climate realizations. Coarse resolution Global Climate Models' future projections covering four emission scenarios based on Coupled Model Intercomparison Project phase 3 (CMIP3) datasets were dynamically downscaled to 6 km resolution over the study area. The analyses were made in terms of rainfall, air temperature, evapotranporation, and soil water storage.

Incorporating palaeoclimate data into water security planning and decision making - a case study from southeast Queensland, Australia

NASA Astrophysics Data System (ADS)

Kiem, Anthony; Vance, Tessa; Tozer, Carly; Roberts, Jason

2017-04-01

Decision makers in the water sector need to deal with existing hydroclimatic variability and uncertainty about future changes to climate and catchment conditions. Identifying solutions for hydroclimatic risk adaptation strategies that are both optimal and robust in the presence of variability and uncertainty presents a difficult challenge. A major reason for this challenge is the fact that the instrumental record in Australia is short ( 60-130 years) and fails to encompass enough climate variability to allow the calculation of robust statistics around the baseline risk of extreme events (e.g. multi-year droughts, decadal periods with clustering of major flood events). This climate variability is documented pre-1900 in palaeoclimate records from sources such as corals, tree-rings, freshwater and marine sediments. Despite being remote from Queensland, a high resolution and highly correlated palaeoclimate record from the Law Dome ice cores in Antarctica (Vance et al. 2015) is also now available and has identified eight mega-droughts (lasting from 5-39 years) during 1000-2009 AD. Most importantly, the palaeoclimate information confirms that the post-1900 instrumental period (i.e. the period on which all water resources infrastructure, policy, operation rules and strategies is based) does not capture the full range of variability that has occurred. Other work also clearly shows that, out to 2050 at least, impacts associated with natural variability significantly exceed even the worst-case climate change scenarios (i.e. obtained from Global Climate Models run under the highest emission scenarios). This presentation will demonstrate how the Law Dome ice cores from Antarctica have been used to produce a highly accurate, 1000 year, annual and seasonal resolution, hydroclimate reconstruction (i.e. precipitation and streamflow) for the southeast Queensland region of Australia. We will then show how the palaeoclimate data has been incorporated into the South East Queensland Regional Stochastic Model (SEQRSM) of catchment hydrology to (a) demonstrate the utility of a palaeoclimate proxy approach in producing more robust estimates of hydroclimatic risk under climate variability and change; (b) gain improved insights into the characteristics (e.g. location, duration, frequency, magnitude, spatial extent, sequencing) of hydroclimate extremes for water security planning and (c) deliver optimised solutions for hydroclimatic risk adaptation strategies to water managers (e.g. optimal and sustainable supply of water to meet current and future urban requirements and also to nearby catchments to support irrigation for dairy, vegetable and forage crops).

Late Quaternary Hydroclimate of Arid Northeastern Mexico: Response of Millennial-scale Global Climate Change and the Atlantic Warm Pool

NASA Astrophysics Data System (ADS)

Roy, P. D.; Shanahan, T. M.; Sánchez Zavala, J. L.; Lozano-SantaCruz, R.; Vera-Vera, G.

2017-12-01

Model projections suggest that drought-prone northeastern Mexico could experience an increase of more than 2 ºC in mean annual temperature and precipitation could decrease at least by 10-20% over the 21st century. The combination of drought and warmth would enhance the dryness of this water-stressed region in the coming decades. However, because of the lack of long continuous records from the region, little is known about the past controls on climate variability in northeast Mexico. In order to better understand the susceptibility of this climatically sensitive but data-poor region, we present a new multi-proxy record of past hydrological changes from paleo-lacustrine deposits in the Sandia Basin ( 24°N) over the last 32 cal ka BP. We reconstruct runoff from changes in the abundance of Al-bearing clastic minerals and local hydrological changes from the oxygen isotope composition of lacustrine carbonates, as well as gypsum/calcite abundances. During the cooler Heinrich Stadials (HS3, HS2 and HS1) and Younger Dryas, the basin received less runoff and the lake was more saline, though hydrological conditions varied significantly throughout these stadial events. The wettest interval in the record occurred coincident with the Bølling-Allerød (B/A) interstadial. Arid conditions returned during the Holocene, with low sedimentation rates, reduced proxy runoff indicators, and enhanced gypsum deposition suggesting this was the driest interval of the last 30 ka. Our observations are consistent with a growing number of records from across both northeastern Mexico and the southern Great Plains suggesting dry conditions associated with North Atlantic stadials and a sudden but transient shift to wetter conditions accompanying the strengthening of the overturning circulation during the B/A. We will evaluate the possible influence of Atlantic Warm Pool on hydroclimate of the region by comparing the different proxy records to the sea-surface temperature of Gulf of Mexico, Caribbean Sea and tropical Atlantic Ocean.

20th-Century Climate Change over Africa: Seasonal Variation in Hydroclimate Trends and Sahara Desert Extent

NASA Astrophysics Data System (ADS)

Nigam, S.; Thomas, N. P.

2017-12-01

Twentieth-century trends in seasonal temperature and precipitation over the African continent are analyzed from observational data sets and historical climate simulations. Given the agricultural economy of the continent, a seasonal perspective is adopted as it is more pertinent than an annual-average one which can mask off-setting but agriculturally-sensitive seasonal hydroclimate variations. Examination of linear trends in seasonal surface air temperature (SAT) shows that heat stress has increased in several regions, including Sudan and Northern Africa where largest SAT trends occur in the warm season. Broadly speaking, the northern continent has warmed more than the southern one in all seasons. Precipitation trends are varied but notable declining trends are found in the countries along the Gulf of Guinea, especially in the source region of Niger river in West Africa, and in the Congo river basin. Rainfall over the African Great Lakes - one of the largest freshwater repositories - has however increased. We show that the Sahara Desert has expanded significantly over the 20th century - by 12-20% depending on the season. The desert expanded southward in summer, reflecting retreat of the northern edge of the Sahel rainfall belt; and to the north in winter, indicating potential impact of the widening of the Tropics. Specific mechanisms driving the expansion in each season are investigated. Finally, this observational analysis is used to evaluate the state-of-the-art climate models from a comparison of the 20th-century hydroclimate trends with those manifest in historical climate simulations. The evaluation shows that modeling regional hydroclimate change over the Africa continent remains challenging.

Past and future drought in Mongolia.

PubMed

Hessl, Amy E; Anchukaitis, Kevin J; Jelsema, Casey; Cook, Benjamin; Byambasuren, Oyunsanaa; Leland, Caroline; Nachin, Baatarbileg; Pederson, Neil; Tian, Hanqin; Hayles, Laia Andreu

2018-03-01

The severity of recent droughts in semiarid regions is increasingly attributed to anthropogenic climate change, but it is unclear whether these moisture anomalies exceed those of the past and how past variability compares to future projections. On the Mongolian Plateau, a recent decade-long drought that exceeded the variability in the instrumental record was associated with economic, social, and environmental change. We evaluate this drought using an annual reconstruction of the Palmer Drought Severity Index (PDSI) spanning the last 2060 years in concert with simulations of past and future drought through the year 2100 CE. We show that although the most recent drought and pluvial were highly unusual in the last 2000 years, exceeding the 900-year return interval in both cases, these events were not unprecedented in the 2060-year reconstruction, and events of similar duration and severity occur in paleoclimate, historical, and future climate simulations. The Community Earth System Model (CESM) ensemble suggests a drying trend until at least the middle of the 21st century, when this trend reverses as a consequence of elevated precipitation. Although the potential direct effects of elevated CO 2 on plant water use efficiency exacerbate uncertainties about future hydroclimate trends, these results suggest that future drought projections for Mongolia are unlikely to exceed those of the last two millennia, despite projected warming.

Past and future drought in Mongolia

PubMed Central

Hessl, Amy E.; Anchukaitis, Kevin J.; Jelsema, Casey; Cook, Benjamin; Byambasuren, Oyunsanaa; Leland, Caroline; Nachin, Baatarbileg; Pederson, Neil; Tian, Hanqin; Hayles, Laia Andreu

2018-01-01

The severity of recent droughts in semiarid regions is increasingly attributed to anthropogenic climate change, but it is unclear whether these moisture anomalies exceed those of the past and how past variability compares to future projections. On the Mongolian Plateau, a recent decade-long drought that exceeded the variability in the instrumental record was associated with economic, social, and environmental change. We evaluate this drought using an annual reconstruction of the Palmer Drought Severity Index (PDSI) spanning the last 2060 years in concert with simulations of past and future drought through the year 2100 CE. We show that although the most recent drought and pluvial were highly unusual in the last 2000 years, exceeding the 900-year return interval in both cases, these events were not unprecedented in the 2060-year reconstruction, and events of similar duration and severity occur in paleoclimate, historical, and future climate simulations. The Community Earth System Model (CESM) ensemble suggests a drying trend until at least the middle of the 21st century, when this trend reverses as a consequence of elevated precipitation. Although the potential direct effects of elevated CO2 on plant water use efficiency exacerbate uncertainties about future hydroclimate trends, these results suggest that future drought projections for Mongolia are unlikely to exceed those of the last two millennia, despite projected warming. PMID:29546236

Winter-to-Summer Precipitation Phasing in Southwestern North America: A Multi-Century Perspective from Paleoclimatic Model-Data Comparisons

NASA Technical Reports Server (NTRS)

Coats, Sloan; Smerdon, Jason E.; Seager, Richard; Griffin, Daniel; Cook, Benjamin I.

2015-01-01

The phasing of winter-to-summer precipitation anomalies in the North American monsoon (NAM) region 2 (113.25 deg W-107.75 deg W, 30 deg N-35.25 deg N-NAM2) of southwestern North America is analyzed in fully coupled simulations of the Last Millennium and compared to tree ring reconstructed winter and summer precipitation variability. The models simulate periods with in-phase seasonal precipitation anomalies, but the strength of this relationship is variable on multidecadal time scales, behavior that is also exhibited by the reconstructions. The models, however, are unable to simulate periods with consistently out-of-phase winter-to-summer precipitation anomalies as observed in the latter part of the instrumental interval. The periods with predominantly in-phase winter-to-summer precipitation anomalies in the models are significant against randomness, and while this result is suggestive of a potential for dual-season drought on interannual and longer time scales, models do not consistently exhibit the persistent dual-season drought seen in the dendroclimatic reconstructions. These collective findings indicate that model-derived drought risk assessments may underestimate the potential for dual-season drought in 21st century projections of hydroclimate in the American Southwest and parts of Mexico.

Implications of changing water cycle for the performance and yield characteristics of the multi-purpose Beas Reservoir in India

NASA Astrophysics Data System (ADS)

Adeloye, A. J.; Ojha, C. S.; Soundharajan, B.; Remesan, R.

2013-12-01

There is considerable change in both the spatial and temporal patterns of monsoon rainfall in India, with implications for water resources availability and security. 'Mitigating the Impacts of Climate Change on India Agriculture' (MICCI) is one of five on-going scientific efforts being sponsored as part of the UK-NERC/India-MOES Changing Water Cycle (South Asia) initiative to further the understanding of the problem and proffer solutions that are robust and effective. This paper focuses on assessing the implications of projected climate change on the yield and performance characteristics of the Pong Reservoir on the Beas River, Himachal Pradesh, India. The Pong serves both hydropower and irrigation needs and is therefore strategic for the socio-economic well-being of the region as well as sustaining the livelihoods of millions of farmers that rely on it for irrigation. Simulated baseline and climate-change perturbed hydro-climate scenarios developed as part of a companion Work Package of MICCI formed the basis of the analysis. For both of these scenarios, reservoir analyses were carried out using the Sequent Peak Algorithm (SPA) and Pong's existing level of releases to derive rule curves for the reservoir. These rule curves then formed the basis of further reservoir behaviour simulations in WEAP and the resulting performance of the reservoir was summarised in terms of reliability, resilience, vulnerability and sustainability. The whole exercise was implemented within a Monte Carlo framework for the benefit of characterising the variability in the assessments. The results show that the rule curves developed using future hydro-climate are significantly changed from the baseline in that higher storages will be required to be maintained in the Pong in the future to achieve reliable performance. As far as the overall performance of the reservoir is concerned, future reliability (both time-based and volume-based) is not significantly different from the baseline, provided the future simulations adopt the future rule curves. This is, however, not the case with the resilience, with the future hydro-climate resulting in a less resilient system when compared with the baseline. The resilience is the ability of the system to recover from a hydrological failure; consequently, lower resilience for the future systems is an indication that longer, continuous failure periods are likely with implications for the two purposes of the reservoir. For example, extended periods of water scarcity that may result from a low resilient system will mean that crops are likely to experience longer periods of water stress with implications for crop yields. In such situations, better operational practices that manage the available water through hedging and irrigation water scheduling will be required. Other interventions may include the introduction of water from other sources, e.g. groundwater.

Final Technical Report for DOE Award SC0006616

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robertson, Andrew

2015-08-01

This report summarizes research carried out by the project "Collaborative Research, Type 1: Decadal Prediction and Stochastic Simulation of Hydroclimate Over Monsoonal Asia. This collaborative project brought together climate dynamicists (UCLA, IRI), dendroclimatologists (LDEO Tree Ring Laboratory), computer scientists (UCI), and hydrologists (Columbia Water Center, CWC), together with applied scientists in climate risk management (IRI) to create new scientific approaches to quantify and exploit the role of climate variability and change in the growing water crisis across southern and eastern Asia. This project developed new tree-ring based streamflow reconstructions for rivers in monsoonal Asia; improved understanding of hydrologic spatio-temporal modesmore » of variability over monsoonal Asia on interannual-to-centennial time scales; assessed decadal predictability of hydrologic spatio-temporal modes; developed stochastic simulation tools for creating downscaled future climate scenarios based on historical/proxy data and GCM climate change; and developed stochastic reservoir simulation and optimization for scheduling hydropower, irrigation and navigation releases.« less

Characterizing Transitions Between Decadal States of the Tropical Pacific using State Space Reconstruction

NASA Astrophysics Data System (ADS)

Ramesh, N.; Cane, M. A.

2017-12-01

The complex coupled ocean-atmosphere system of the Tropical Pacific generates variability on timescales from intraseasonal to multidecadal. Pacific Decadal Variability (PDV) is among the key drivers of global climate, with effects on hydroclimate on several continents, marine ecosystems, and the rate of global mean surface temperature rise under anthropogenic greenhouse gas forcing. Predicting phase shifts in the PDV would therefore be highly useful. However, the small number of PDV phase shifts that have occurred in the observational record pose a substantial challenge to developing an understanding of the mechanisms that underlie decadal variability. In this study, we use a 100,000-year unforced simulation from an intermediate-complexity model of the Tropical Pacific region that has been shown to produce PDV comparable to that in the real world. We apply the Simplex Projection method to the NINO3 index from this model to reconstruct a shadow manifold that preserves the topology of the true attractor of this system. We find that the high- and low-variance phases of PDV emerge as a pair of regimes in a 3-dimensional state space, and that the transitions between decadal states lie in a highly predictable region of the attractor. We then use a random forest algorithm to develop a physical interpretation of the processes associated with these highly-predictable transitions. We find that transitions to low-variance states are most likely to occur approximately 2.5 years after an El Nino event, and that ocean-atmosphere variables in the southeastern Tropical Pacific play a crucial role in driving these transitions.

Regional hydro-climatic impacts of contemporary Amazonian deforestation

NASA Astrophysics Data System (ADS)

Khanna, Jaya

More than 17% of the Amazon rainforest has been cleared in the past three decades triggering important climatological and societal impacts. This thesis is devoted to identifying and explaining the regional hydroclimatic impacts of this change employing multidecadal satellite observations and numerical simulations providing an integrated perspective on this topic. The climatological nature of this study motivated the implementation and application of a cloud detection technique to a new geostationary satellite dataset. The resulting sub daily, high spatial resolution, multidecadal time series facilitated the detection of trends and variability in deforestation triggered cloud cover changes. The analysis was complemented by satellite precipitation, reanalysis and ground based datasets and attribution with the variable resolution Ocean-Land-Atmosphere-Model. Contemporary Amazonian deforestation affects spatial scales of hundreds of kilometers. But, unlike the well-studied impacts of a few kilometers scale deforestation, the climatic response to contemporary, large scale deforestation is neither well observed nor well understood. Employing satellite datasets, this thesis shows a transition in the regional hydroclimate accompanying increasing scales of deforestation, with downwind deforested regions receiving 25% more and upwind deforested regions receiving 25% less precipitation from the deforested area mean. Simulations robustly reproduce these shifts when forced with increasing deforestation alone, suggesting a negligible role of large-scale decadal climate variability in causing the shifts. Furthermore, deforestation-induced surface roughness variations are found necessary to reproduce the observed spatial patterns in recent times illustrating the strong scale-sensitivity of the climatic response to Amazonian deforestation. This phenomenon, inconsequential during the wet season, is found to substantially affect the regional hydroclimate in the local dry and parts of transition seasons, hence occurring in atmospheric conditions otherwise less conducive to thermal convection. Evidence of this phenomenon is found at two large scale deforested areas considered in this thesis. Hence, the 'dynamical' mechanism, which affects the seasons most important for regional ecology, emerges as an impactful convective triggering mechanism. The phenomenon studied in this thesis provides context for thinking about the climate of a future, more patchily forested Amazonia, by articulating relationships between climate and spatial scales of deforestation.

Recent Responses of Western North American Forests and Hydroclimate to Pacific Storm Track Position and Intensity

NASA Astrophysics Data System (ADS)

Dannenberg, M. P.; Wise, E.

2017-12-01

Much of the precipitation delivered to western North America arrives during the October to March cool season via midlatitude Pacific storm tracks, which may shift in the future due to climate change. Using historical climate, tree-ring, and remote sensing data, we assessed the sensitivity of western North American hydroclimate and ecosystems to the position and intensity of cool-season Pacific storm tracks. From 1980-2014, mean annual cool-season storm tracks entered western North America between approximately 41°N to 53°N, with substantial interannual variability in both the position and intensity of the storm tracks. We examined relationships between storm tracks and two hydroclimatic variables: the cool-season standardized precipitation-evapotranspiration index and April snow water equivalent. We also assessed how historical storm track variability affected ecosystems using forest growth estimates from a large tree-ring network as well as land surface phenology and wildfire estimates from AVHRR and Landsat, respectively. Cool-season moisture supply and snowpack responded strongly to storm track position, with positive correlations to storm track latitude in eastern Alaska and northwestern Canada but negative correlations in the northwestern U.S. These hydroclimatic impacts were largely driven by the latitudinal position of storm tracks during the "shoulder" seasons (i.e., autumn and early spring). Ecosystems of the western U.S. tended to be greener and more productive following winters with south-shifted storm tracks, while Canadian ecosystems were greener in years when the cool-season storm track was shifted to the north. On average, larger areas of the northwestern U.S. were burned by moderate to high severity wildfires when storm tracks were displaced north, and the average burn area per fire also tended to be higher in years with north-shifted storm tracks. Assuming that these historical relationships continue to hold under future climate scenarios, our results suggest that projected long-term shifts of Pacific storm tracks over the 21st century would likely alter hydroclimatic and ecological regimes in western North America, particularly in the northwestern U.S., where moisture supply and ecosystem processes are highly sensitive to the position of cool-season storm tracks.

Millennial-scale variability in south-east Australian hydroclimate between 30,000 and 10,000 years ago

NASA Astrophysics Data System (ADS)

Falster, Georgina; Tyler, Jonathan; Grant, Katharine; Tibby, John; Turney, Chris; Löhr, Stefan; Jacobsen, Geraldine; Kershaw, A. Peter

2018-07-01

Global climate variability during the late Quaternary is commonly investigated within the framework of the 'bipolar seesaw' pattern of asynchronous temperature variations in the northern and southern polar latitudes. The terrestrial hydrological response to this pattern in south-eastern Australia is not fully understood, as continuous, high-resolution, well-dated proxy records for the hydrological cycle in the region are sparse. Here we present a well-dated, highly resolved record of moisture balance spanning 30000-10000 calendar years before present (30-10 ka BP), based on x-ray fluorescence and organic carbon isotope (δ13COM) measurements of a sedimentary sequence from Lake Surprise in south-eastern Australia. The data provide a locally coherent record of the hydrological cycle. Elevated Si (reflecting windblown quartz and clays), and relatively high δ13COM, indicate an extended period of relative aridity between 28 and 18.5 ka BP, interrupted by millennial-scale episodes of decreased Si and δ13COM, suggesting increased moisture balance. This was followed by a rapid deglacial shift to low Si and δ13COM at 18.5 ka BP, indicative of wetter conditions. We find that these changes are coeval with other records from south-eastern Australia and New Zealand, and use a Monte Carlo Empirical Orthogonal Function approach to extract a common trend from three high-resolution records. Our analyses suggest that drivers of the regional hydrological cycle have varied on multi-millennial time scales, in response to major shifts in global atmosphere-ocean dynamics during the last glacial-interglacial transition. Southern Ocean processes were the dominant control on hydroclimate during glacial times, via a strong influence of cold sea surface temperatures on moisture uptake and delivery onshore. Following the last deglaciation (around 18 ka BP), the southward migration of cold Southern Ocean fronts likely resulted in the establishment of conditions more like those of the present day. Millennial-scale variability in records from the region is dominated by a persistent ca. 2300-year periodicity, consistent with other records across the Southern Hemisphere mid-latitudes; however, this pervasive periodicity is not obviously linked to the 'bipolar seesaw' and the mechanism remains equivocal.

Oxygen isotope values of tree ring α-cellulose as a proxy of hydroclimate variability in arid regions

NASA Astrophysics Data System (ADS)

Dodd, J. P.; Freimuth, E. J.; Olson, E. J.; Diefendorf, A. F.

2015-12-01

One of the main goals of tree ring isotope studies is to reconstruct climate-driven variations in the source water and antecedent precipitation; however, evaporation in the soil and leaves can significantly modify the isotope values of the source water. This is particularly the case in arid environments where evaporative effects are perhaps the most significant unknown variable when attempting to reconstruct regional-scale hydroclimate variations from tree ring isotope proxies. To quantify the effects of extreme aridity on α-cellulose δ18O values, we measured the oxygen isotope values of groundwater, xylem water, leaf water, and tree ring α-cellulose in an endemic species of drought-resistant trees (Prosopis tamarugo) from different microenvironments throughout the Atacama Desert of Northern Chile. Average annual precipitation is <5 mm/yr, and groundwater is the primary water source for P. tamarugo trees in the region. Groundwater δ18O values at the sample locations range from -6.7 to -9.7‰, and xylem water δ18O values record a systematic increase (ave. Δ18Ox-gw =+1.3‰; 2σ =1.0‰). Leaf waters are significantly affected by evaporative enrichment with a range of δ18O values from 7 to 23‰. This range most likely reflects a number of physiological and environmental conditions including tree size, canopy development, and sample time (i.e. morning vs. evening). However, despite the large variation in leaf water δ18O values, the average difference between the α-cellulose and groundwater is very consistent (Δ18Oc-gw = +39.7‰; 2σ =1.3‰). P. tamarugo samples were collected in austral spring, when tree growth was at its maximum; therefore, any seasonal variations in plant physiology not captured with this dataset will have a limited impact on cellulose production. These data demonstrate that despite the variable evaporative enrichment of 18O in the leaf water, the α-cellulose δ18O values provide a remarkably consistent record of variations in groundwater δ18O values in this extremely arid environment.

Dynamic response of peatbank moss communities to hydroclimate over the last 2000 years in the western Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Stelling, J.; Yu, Z.; Beilman, D. W.

2016-12-01

The western Antarctic Peninsula experienced rapid warming in late half of the 20th century in part due to a positive phase of the Southern Annular Mode (SAM) causing poleward expansion of the southern westerly wind belt that brings warmer and moister air to the peninsula. However, we do not know how coastal terrestrial ecosystems have responded to changes in temperature and hydroclimate. Here we present a paleoecological and geochemical record of ecosystem history derived from late Holocene peatbank deposits on Litchfield Island (64°46'S; 64°06'W) to reconstruct terrestrial response to temperature and hydroclimate fluctuations. Chronology of our 80-cm-long peat core from the north-facing slope is constrained by 11 AMS 14C dates covering the last 2500 years. Our macrofossil results show that relative abundance of the two dominant moss species fluctuates between <10 and 90%. Furthermore, the δ13C values of bulk peat range from -26.4 to -22.1‰ that mostly reflects species relative abundance change through time. The periods with C:N values of <20—lower than the expected C:N values (40 to 80) of fresh moss plants—corresponds with intervals containing abundant fine debris (>50%), indicating greater decomposition and selective removal of carbon from peat. Our record shows that periods where moss dominance shifts to Polytrichum, a dry and cold tolerant moss, peat decomposition increases, and coincides with periods of negative SAM. Conversely, dominance shifts to Chorisodontium, a less drought tolerant moss, with decomposition decreased during periods of strong positive SAM. This study demonstrates that ecosystem structure and geochemical signature within these moss peatbanks is sensitive to regional moisture change that can potentially be used to reconstruct shifts in hydroclimate and possibly atmospheric circulation.

A robust null hypothesis for the potential causes of megadrought in western North America

NASA Astrophysics Data System (ADS)

Ault, T.; St George, S.; Smerdon, J. E.; Coats, S.; Mankin, J. S.; Cruz, C. C.; Cook, B.; Stevenson, S.

2017-12-01

The western United States was affected by several megadroughts during the last 1200 years, most prominently during the Medieval Climate Anomaly (MCA: 800 to 1300 CE). A null hypothesis is developed to test the possibility that, given a sufficiently long period of time, these events are inevitable and occur purely as a consequence of internal climate variability. The null distribution of this hypothesis is populated by a linear inverse model (LIM) constructed from global sea-surface temperature anomalies and self-calibrated Palmer Drought Severity Index data for North America. Despite being trained only on seasonal data from the late 20th century, the LIM produces megadroughts that are comparable in their duration, spatial scale, and magnitude as the most severe events of the last 12 centuries. The null hypothesis therefore cannot be rejected with much confidence when considering these features of megadrought, meaning that similar events are possible today, even without any changes to boundary conditions. In contrast, the observed clustering of megadroughts in the MCA, as well as the change in mean hydroclimate between the MCA and the 1500-2000 period, are more likely to have been caused by either external forcing or by internal climate variability not well sampled during the latter half of the Twentieth Century. Finally, the results demonstrate the LIM is a viable tool for determining whether paleoclimate reconstructions events should be ascribed to external forcings, "out of sample" climate mechanisms, or if they are consistent with the variability observed during the recent period.

Spatial δ18Osw-SSS relationship across the western tropical Pacific Ocean

NASA Astrophysics Data System (ADS)

Thompson, D. M.; Conroy, J. L.; Wyman, A.; Read, D.

2017-12-01

Dynamic hydroclimate processes across the western tropical Pacific lead to strong spatial and temporal variability in δ18Osw and sea-surface salinity (SSS) across the western Pacific. Corals in this region have therefore provided key information about past SSS variability, as δ18Osw contributes strongly to coral δ18O across this region. However, uncertainties in the δ18Osw-SSS relationship across space and time often limit quantitative SSS reconstructions from such coral records. Recent work demonstrates considerable variability in the δ18Osw-SSS relationship across the Pacific, which may lead to over- or under-estimation of the contribution of SSS to coral δ18O, particularly across the western tropical Pacific (Conroy et al. 2017). Here we assess the spatial δ18Osw-SSS relationship across the dynamic western tropical Pacific, capitalizing on a transit between Subic Bay, Philippines and Townsville, Australia aboard the International Ocean Discovery program's JOIDES Resolution. Water samples and weather conditions were collected 3 times daily (6:00, 12:00, 18:00) en route, resulting in a network of 47 samples spaced at semi-regular 130-260 km intervals across the western Pacific from 14°N to 18°S. The route also crossed near long-term δ18Osw monitoring sites at Papua New Guinea and Palau (Conroy et al. 2017), allowing us to compare the spatial and temporal δ18Osw-SSS relationships at these sites and test the space-for-time assumption. We present the δ18Osw-SSS relationship across this region, compare the relationship across space and time, and discuss the implications of our results for SSS reconstructions from coral δ18O.

Assessing the risk persistent drought using climate model simulations and paleoclimate data

USGS Publications Warehouse

Ault, Toby R.; Cole, Julia E.; Overpeck, Jonathan T.; Pederson, Gregory T.; Meko, David M.

2014-01-01

Projected changes in global rainfall patterns will likely alter water supplies and ecosystems in semiarid regions during the coming century. Instrumental and paleoclimate data indicate that natural hydroclimate fluctuations tend to be more energetic at low (multidecadal to multicentury) than at high (interannual) frequencies. State-of-the-art global climate models do not capture this characteristic of hydroclimate variability, suggesting that the models underestimate the risk of future persistent droughts. Methods are developed here for assessing the risk of such events in the coming century using climate model projections as well as observational (paleoclimate) information. Where instrumental and paleoclimate data are reliable, these methods may provide a more complete view of prolonged drought risk. In the U.S. Southwest, for instance, state-of-the-art climate model projections suggest the risk of a decade-scale megadrought in the coming century is less than 50%; the analysis herein suggests that the risk is at least 80%, and may be higher than 90% in certain areas. The likelihood of longer-lived events (>35 yr) is between 20% and 50%, and the risk of an unprecedented 50-yr megadrought is nonnegligible under the most severe warming scenario (5%–10%). These findings are important to consider as adaptation and mitigation strategies are developed to cope with regional impacts of climate change, where population growth is high and multidecadal megadrought—worse than anything seen during the last 2000 years—would pose unprecedented challenges to water resources in the region.

A Large-Scale, High-Resolution Hydrological Model Parameter Data Set for Climate Change Impact Assessment for the Conterminous US

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oubeidillah, Abdoul A; Kao, Shih-Chieh; Ashfaq, Moetasim

2014-01-01

To extend geographical coverage, refine spatial resolution, and improve modeling efficiency, a computation- and data-intensive effort was conducted to organize a comprehensive hydrologic dataset with post-calibrated model parameters for hydro-climate impact assessment. Several key inputs for hydrologic simulation including meteorologic forcings, soil, land class, vegetation, and elevation were collected from multiple best-available data sources and organized for 2107 hydrologic subbasins (8-digit hydrologic units, HUC8s) in the conterminous United States at refined 1/24 (~4 km) spatial resolution. Using high-performance computing for intensive model calibration, a high-resolution parameter dataset was prepared for the macro-scale Variable Infiltration Capacity (VIC) hydrologic model. The VICmore » simulation was driven by DAYMET daily meteorological forcing and was calibrated against USGS WaterWatch monthly runoff observations for each HUC8. The results showed that this new parameter dataset may help reasonably simulate runoff at most US HUC8 subbasins. Based on this exhaustive calibration effort, it is now possible to accurately estimate the resources required for further model improvement across the entire conterminous United States. We anticipate that through this hydrologic parameter dataset, the repeated effort of fundamental data processing can be lessened, so that research efforts can emphasize the more challenging task of assessing climate change impacts. The pre-organized model parameter dataset will be provided to interested parties to support further hydro-climate impact assessment.« less

El Nino-Induced Tropical Ocean/Land Energy Exchange in MERRA-2 and M2AMIP

NASA Technical Reports Server (NTRS)

Bosilovich, Michael G.; Robertson, Franklin R.

2017-01-01

Studies have shown the correlation and connection of surface temperatures across the globe, ocean and land, related to Tropical SSTs especially El Nino. This climate variability greatly influences regional weather and hydroclimate extremes (e.g. drought and flood). In this paper, we evaluate the relationship of temperatures across the tropical oceans and continents in MERRA-2, and also in a newly developed MERRA-2 AMIP ensemble simulation (M2AMIP). M2AMIP uses the same model and spatial resolution as MERRA-2, producing the same output diagnostics over 10 ensemble members. Composite El Nino temperature data are compared with observations to evaluate the land/sea contrast, variations and phase relationship. The temperature variations are related to surface heat fluxes and the atmospheric temperatures and transport, to identify the processes that lead to the lagged redistribution of heat in the tropics and beyond. Discernable cloud, radiation and data assimilation changes accompany the onset of El Nino affecting continental regions through the progression to and following the peak values. While the model represents these variations in general, regional strengths and weaknesses can be identified.

The Caspian Sea Catchment influenced by Atlantic Teleconnections in CESM1.2.2 and Observations

NASA Astrophysics Data System (ADS)

Nandini, S. D.; Prange, M.; Schulz, M.

2017-12-01

The Caspian Sea (CS) is the world's largest inland sea and located within a closed (endorheic) drainage basin [ 37°-47N, 47°-54°E]. It has undergone dynamic variations (>3 m) during the past century with huge impacts on the economy, ecosystem and livelihood of coastal people. The origin of these variations as well as future changes are disputable. Here, we examine the impact of the major seasonal North Atlantic teleconnection patterns, the North Atlantic Oscillation (NAO) and the East Atlantic pattern (EA) on Caspian hydroclimate variability from 1850-2100 CE. Five Numerical experiments at different atmospheric grid resolutions (2° and 1°) and atmospheric model versions (CAM4 and CAM5) are carried out with the coupled Community Earth System Model (CESM1.2.2). Results reveal the 1° CESM1.2.2 CAM5 captures DJF NAO (46.5%) and EA (13.4%), agreeing well with observational data (1850-2000). The DJF NAO has a strong influence on the DJF temperature, rainfall and evaporation minus precipitation (E-P) over the Caspian sub-basins (Volga, Ural, Terek and Kura). Furthermore, 1° model climate projections (2020-2100 CE) are performed with different Representative Concentration Pathways (RCP4.5 and RCP8.5) to examine likely changes in the NAO and EA and their influence on the Caspian catchment. The NAO under the RCP4.5 and RCP8.5 scenarios remains the leading mode with the highest variance and influences E-P with increased precipitation over the Volga basin and increased evaporation over the Caspian Sea. The above canceling effects act on the hydroclimate variability in the Caspian sub-basins. Moreover, it is indicated that no substantial change is predicted in the CSL by the year 2100. Keywords: North Atlantic Oscillation (NAO), CESM1.2.2 resolutions, Evaporation minus Precipitation (E-P), RCP4.5, RCP8.5

Increased Amazon freshwater discharge during late Heinrich Stadial 1

NASA Astrophysics Data System (ADS)

Crivellari, Stefano; Chiessi, Cristiano Mazur; Kuhnert, Henning; Häggi, Christoph; da Costa Portilho-Ramos, Rodrigo; Zeng, Jing-Ying; Zhang, Yancheng; Schefuß, Enno; Mollenhauer, Gesine; Hefter, Jens; Alexandre, Felipe; Sampaio, Gilvan; Mulitza, Stefan

2018-02-01

The temporal succession of changes in Amazonian hydroclimate during Heinrich Stadial 1 (HS1) (ca. 18-14.7 cal ka BP) is currently poorly resolved. Here we present HS1 records based on isotope, inorganic and organic geochemistry from a marine sediment core influenced by the Amazon River discharge. Our records offer a detailed reconstruction of the changes in Amazonian hydroclimate during HS1, integrated over the basin. We reconstructed surface water hydrography using stable oxygen isotopes (δ18O) and Mg/Ca-derived paleotemperatures from the planktonic foraminifera Globigerinoides ruber, as well as salinity changes based on stable hydrogen isotope (δD) of palmitic acid. We also analyzed branched and isoprenoid tetraether concentrations, and compared them to existing bulk sediment ln(Fe/Ca) data and vegetation reconstruction based on stable carbon isotopes from n-alkanes, in order to understand the relationship between continental precipitation, vegetation and sediment production. Our results indicate a two-phased HS1 (HS1a and HS1b). During HS1a (18-16.9 cal ka BP), a first sudden increase of sea surface temperatures (SST) in the western equatorial Atlantic correlated with the slowdown of the Atlantic Meridional Overturning Circulation (AMOC) and the associated southern hemisphere warming phase of the bipolar seesaw. This phase was also characterized by an increased delivery of terrestrial material. During HS1b (16.9-14.8 cal ka BP), a decrease in terrestrial input was, however, associated with a marked decline of seawater δ18O and palmitic acid δD. Both isotopic proxies independently indicate a drop in sea surface salinity (SSS). A number of records under the influence of the North Brazil Current, in contrast, indicate increases in SST and SSS resulting from a weakened AMOC during HS1. Our records thus suggest that the expected increase in SSS due to the AMOC slowdown was overridden by a two-phased positive precipitation anomaly in Amazonian hydroclimate.

Internal ocean-atmosphere variability drives megadroughts in Western North America.

PubMed

Coats, S; Smerdon, J E; Cook, B I; Seager, R; Cook, E R; Anchukaitis, K J

2016-09-28

Multidecadal droughts that occurred during the Medieval Climate Anomaly represent an important target for validating the ability of climate models to adequately characterize drought risk over the near-term future. A prominent hypothesis is that these megadroughts were driven by a centuries-long radiatively forced shift in the mean state of the tropical Pacific Ocean. Here we use a novel combination of spatiotemporal tree-ring reconstructions of Northern Hemisphere hydroclimate to infer the atmosphere-ocean dynamics that coincide with megadroughts over the American West, and find that these features are consistently associated with ten-to-thirty year periods of frequent cold El Niño Southern Oscillation conditions and not a centuries-long shift in the mean of the tropical Pacific Ocean. These results suggest an important role for internal variability in driving past megadroughts. State-of-the art climate models from the Coupled Model Intercomparison Project phase 5, however, do not simulate a consistent association between megadroughts and internal variability of the tropical Pacific Ocean, with implications for our confidence in megadrought risk projections.

Early- to Mid-Holocene hydroclimate shifts in tropical East Africa: the multi-proxy sediment record from Lake Rutundu, Kenya

NASA Astrophysics Data System (ADS)

De Cort, Gijs; Creutz, Mike; Barao, Lucia; Conley, Daniel; Haug, Gerald; Bodé, Samuel; Blaauw, Maarten; Engstrom, Dan; Verschuren, Dirk

2015-04-01

Following the generally arid conditions of the Last Glacial Maximum (LGM), a large part of the African continent experienced the Early to Mid-Holocene as a much more humid period than today. This so-called African Humid Period (AHP) coincided with high summertime insolation over the Northern Hemisphere subtropics, causing invigorated monsoons to create moist conditions over the northern parts of the continent. Similarly, equatorial and even low-latitude southeastern Africa experienced a wetter climate due to the post-glacial increase in atmospheric greenhouse gasses ultimately leading to altered Atlantic and Indian Ocean monsoon dynamics. The timing and abruptness of the onset and ending of the AHP in the different regions of the continent have been the subject of major discussion. On the other hand, shorter-lived climate fluctuations within the AHP have received much less attention, due to a scarcity of well-dated, high-resolution African paleoclimate records spanning the entire Holocene. In this study we used the sediment record of Lake Rutundu, a high-altitude crater lake on Mount Kenya, to document multidecadal to millennial-scale hydroclimate variability on the East African equator from the LGM to the present. A multiproxy approach combining core-surface scanning techniques (magnetic susceptibility, X-ray fluorescence) and close-interval bulk-sediment analyses (organic matter and biogenic Si content, grain size, organic δ15N and δ13C) resulted in a high-resolution record firmly anchored in time by an age model based on 210Pb dating and sixteen calibrated radiocarbon ages. This new Lake Rutundu hydroclimate record confirms that moister conditions following the LGM returned to East Africa ca.16 kyr BP, and it contains a perfectly timed Younger Dryas episode (12.8-11.5 kyr BP) of intermittent drought. We find that the Early- to Mid-Holocene period, which in African records is often described as uniformly wet, was in fact punctuated by three distinct, century-scale drought episodes. The first of these provides robust evidence that the 8.2 kyr cooling event, well-known from high northern latitudes, impacted tropical East Africa's moisture balance as well. The two other drought episodes, centered at c.6.5 and 5.5 kyr BP, punctuate the mid-Holocene drying which eventually ended the AHP in this region around 4 kyr BP.

Lake Qinghai sediment geochemistry linked to hydroclimate variability since the last glacial

NASA Astrophysics Data System (ADS)

Jin, Zhangdong; An, Zhisheng; Yu, Jimin; Li, Fuchun; Zhang, Fei

2015-08-01

Geochemistry of basin sediments from semi-arid regions is valuable to understand past hydroclimatic changes. Here, we investigate the links of sedimentary geochemistry (Rb, Sr, Ca/Zr, TOC, and %CaCO3), carbonate mineralogy and ostracod shell δ18O of Lake Qinghai, a basin proximal to major dust production centers at mid-latitudes of the Northern Hemisphere, to changes in depositional conditions and hydroclimate during the past 32 ka. Surface lacustrine sediments are characterized by low-Rb, high-Sr, low-Rb/Sr, high-%CaCO3 and high-Ca/Zr values, in contrast to the chemical compositions of eolian loess (high-Rb, low-Sr, high-Rb/Sr, low-%CaCO3, and low-Ca/Zr). A direct comparison of soluble Ca and Sr in two short cores with instrumental water discharge data suggests that lacustrine precipitates in Lake Qinghai are dominated by authigenic aragonite formed under Ca2+-limited water conditions, and that the accumulation rate of aragonite dominantly depends on solute fluxes into the lake during the rainy seasons (late May to September). Our high-resolution down-core records show that sediments during the last glacial (∼32-19.8 ka) had high-Rb, low-Sr, low-%CaCO3, and low-Ca/Zr, indicating eolian dust (loess) accumulation in a desiccated basin under dry glacial conditions, further supported by grain size and pollen results. This type of sedimentation was maintained during the last deglacial (∼19.8-11.5 ka), but interrupted by episodic lacustrine precipitates with high-Sr, high-%CaCO3, high-Ca/Zr, and low-Rb. At ∼11.5 ka, sedimentary Rb/Sr, Ca/Zr, %CaCO3 and TOC show dramatic and permanent changes, implying an abrupt shift in the atmospheric circulation at the onset of the Holocene in the Lake Qinghai region. Lacustrine precipitates have persisted throughout the Holocene with a maximum during the early to mid-Holocene (∼10.5-8.0 ka). Since ∼8.0 ka, the gradual and significant decreases in aragonite and Sr accumulations in tandem with increasing dust deposit and more positive ostracod δ18O may be linked to a weakening of Asian summer monsoons during the mid-to-late Holocene. Overall, our records appear to show a high sensitivity of sediment development and geochemistry in Lake Qinghai to the regional hydroclimate changes since the last glacial.

Modeling Source Water TOC Using Hydroclimate Variables and Local Polynomial Regression.

PubMed

Samson, Carleigh C; Rajagopalan, Balaji; Summers, R Scott

2016-04-19

To control disinfection byproduct (DBP) formation in drinking water, an understanding of the source water total organic carbon (TOC) concentration variability can be critical. Previously, TOC concentrations in water treatment plant source waters have been modeled using streamflow data. However, the lack of streamflow data or unimpaired flow scenarios makes it difficult to model TOC. In addition, TOC variability under climate change further exacerbates the problem. Here we proposed a modeling approach based on local polynomial regression that uses climate, e.g. temperature, and land surface, e.g., soil moisture, variables as predictors of TOC concentration, obviating the need for streamflow. The local polynomial approach has the ability to capture non-Gaussian and nonlinear features that might be present in the relationships. The utility of the methodology is demonstrated using source water quality and climate data in three case study locations with surface source waters including river and reservoir sources. The models show good predictive skill in general at these locations, with lower skills at locations with the most anthropogenic influences in their streams. Source water TOC predictive models can provide water treatment utilities important information for making treatment decisions for DBP regulation compliance under future climate scenarios.

Water isotope variability across single rainfall events in the tropical Pacific

NASA Astrophysics Data System (ADS)

Cobb, K. M.; Moerman, J. W.; Ellis, S. A.; Bennett, L.; Bosma, C.; Hitt, N. T.

2017-12-01

Water isotopologues provide a powerful diagnostic tool for probing the dynamical processes involved in the initiation and evolution of tropical convective events, yet water isotope observations rarely meet the temporal resolution required to resolve such processes. Here we present timeseries of rainfall oxygen and hydrogen isotopologues across over 30 individual convective events sampled at 1- to 5-minute intervals at both terrestrial (Gunung Mulu National Park, 4N, 115W) and maritime (Kiritimati Island, 2N, 157W) sites located in the equatorial Pacific. The sites are the loci of significant paleoclimate research that employ water isotopologues to reconstruct a variety of climatic parameters of interest over the last century, in the case of coral d18O, to hundreds of thousands of years before present, in the case of stalagmite d18O. As such, there is significant scientific value in refining our understanding of water isotope controls at these particular sites. Our results illustrate large, short-term excursions in water isotope values that far exceed the signals recovered in daily timeseries of rainfall isotopologues from the sites, illustrating the fundamental contribution of mesoscale processes in driving rainfall isotope variability. That said, the cross-event profiles exhibit a broad range of trajectories, even for events collected at the same time of day on adjoining days. Profiles collected at different phases of the 2015-2017 strong El Nino-Southern Oscillation cycle also exhibit appreciable variability. We compare our observations to hypothetical profiles from a 1-dimensional model of each rainfall event, as well as to output from 4-dimensional isotope-equipped, ocean-atmosphere coupled models of rainfall isotope variability in the tropical Pacific. We discuss the implications of our findings for the interpretation of water isotope-based reconstructions of hydroclimate in the tropics.

Holocene Climate, Fire and Vegetation Change Inferred from Lacustrine Proxies in the Tropical Andes, Laguna Yanacocha, SE Peru

NASA Astrophysics Data System (ADS)

Axford, Y.; Isaacson, M.; Matthews-Bird, F.; Schellinger, G. C.; Carrio, C. L.; Kelly, M. A.; Lowell, T. V.; Beal, S. A., Jr.; Stroup, J. S.; Tapia, P. M.

2016-12-01

We present a 12,000-year long paleoenvironmental reconstruction from a small high-elevation lake in southeastern Peru. Climate and environmental change are inferred from chironomid species assemblages, charcoal abundance, size and morphology, and the abundance of some important pollen and spore types (Poaceae, Asteraceae, Isoetes). We employ a new chironomid training set developed for tropical South America (Matthews-Bird et al. 2016) to interpret shifts in chironomid assemblages. The sedimentary record from Yanacocha was first discussed by Beal et al. (2014), who reconstructed Hg deposition and measured metals, biogenic silica and loss-on-ignition through the Holocene. Additional downcore proxies are presented by Stroup et al. (this meeting). Yanacocha sits at 4910 m asl and less than 2 km from Quelccaya Ice Cap (QIC), but the lake's watershed has been topographically isolated from glacier meltwater since 12.3 ka. We compare our inferences from biological proxies with independent constraints on paleoclimate derived from published reconstructions of QIC fluctuations. Previous studies found that temperature was the primary driver of late Holocene fluctuations of QIC (e.g., Stroup et al. 2014), but records from the broader region indicate the Holocene also saw major changes in hydroclimate. Most modern precipitation at Yanacocha derives from the Amazon Basin to the east, and El Niño years are associated with drier conditions. Holocene sediments at Yanacocha likely thus record both changes in temperature and hydroclimate. Vegetation was sparse and no charcoal was preserved prior to 11.7 ka, whereas the early Holocene saw the highest overall pollen concentrations of the entire record and the onset of charcoal preservation. An increase in charcoal abundance, decrease in pollen concentrations, and shifts in vegetation and chironomid assemblages at Yanacocha suggest drier conditions from 9 to 3.5 ka, consistent with widespread regional evidence for early to middle Holocene aridity. One sample at 8.4 ka contains uniquely abundant charcoal, Poaceae and Asteraceae, possibly recording a brief (<500 yr) and uniquely dramatic dry event at that time. Shifts in chironomid assemblages, including a major shift centered on 1000 AD, indicate a variable climate through the late Holocene.

Investigating late Holocene variations in hydroclimate and the stable isotope composition of precipitation using southern South American peatlands: an hypothesis

NASA Astrophysics Data System (ADS)

Daley, T. J.; Mauquoy, D.; Chambers, F. M.; Street-Perrott, F. A.; Hughes, P. D. M.; Loader, N. J.; Roland, T. P.; van Bellen, S.; Garcia-Meneses, P.; Lewin, S.

2012-09-01

Ombrotrophic raised peatlands provide an ideal archive for integrating late Holocene records of variations in hydroclimate and the estimated stable isotope composition of precipitation with recent instrumental measurements. Modern measurements of mean monthly surface air temperature, precipitation, and δD and δ18O-values in precipitation from the late twentieth and early twenty-first centuries provide a short but invaluable record with which to investigate modern relationships between these variables, thereby enabling improved interpretation of the peatland palaeodata. Stable isotope data from two stations in the Global Network for Isotopes in Precipitation (GNIP) from southern South America (Punta Arenas, Chile and Ushuaia, Argentina) were analysed for the period 1982 to 2008 and compared with longer-term meteorological data from the same locations (1890 to present and 1931 to present, respectively). δD and δ18O-values in precipitation have exhibited quite different trends in response to local surface air temperature and precipitation amount. At Punta Arenas, there has been a marked increase in the seasonal difference between summer and winter δ18O-values. A decline in the deuterium excess of summer precipitation at this station was associated with a general increase in relative humidity at 1000 mb over the surface of the Southeast Pacific Ocean, believed to be the major vapour source for the local precipitation. At Ushuaia, a fall in δ18O-values was associated with an increase in the mean annual amount of precipitation. Both records are consistent with a southward retraction and increase in zonal wind speed of the austral westerly wind belt. These regional differences, observed in response to a known driver, should be detectable in peatland sites close to the GNIP stations. Currently, insufficient data with suitable temporal resolution are available to test for these regional differences over the last 3000 yr. Existing peatland palaeoclimate data from two sites near Ushuaia, however, provide evidence for changes in the late Holocene that are consistent with the pattern observed in modern observations.

Developing a Validated Long-Term Satellite-Based Albedo Record in the Central Alaska Range to Improve Regional Hydroclimate Reconstructions

NASA Astrophysics Data System (ADS)

Kreutz, K. J.; Godaire, T. P.; Burakowski, E. A.; Winski, D.; Campbell, S. W.; Wang, Z.; Sun, Q.; Hamilton, G. S.; Birkel, S. D.; Wake, C. P.; Osterberg, E. C.; Schaaf, C.

2015-12-01

Mountain glaciers around the world, particularly in Alaska, are experiencing significant surface mass loss from rapid climatic shifts and constitute a large proportion of the cryosphere's contribution to sea level rise. Surface albedo acts as a primary control on a glacier's mass balance, yet it is difficult to measure and quantify spatially and temporally in steep, mountainous settings. During our 2013 field campaign in Denali National Park to recover two surface to bedrock ice cores, we used an Analytical Spectral Devices (ASD) FieldSpec4 Standard Resolution spectroradiometer to measure incoming solar radiation, outgoing surface reflectance and optical grain size on the Kahiltna Glacier and at the Kahiltna Base Camp. A Campbell Scientific automatic weather station was installed on Mount Hunter (3900m) in June 2013, complementing a longer-term (2008-present) station installed at Kahiltna Base Camp (2100m). Use of our in situ data aids in the validation of surface albedo values derived from Moderate Resolution Imaging Spectroradiometer (MODIS) and Landsat satellite imagery. Comparisons are made between ASD FieldSpec4 ground measurements and 500m MODIS imagery to assess the ability of MODIS to capture the variability of surface albedo across the glacier surface. The MODIS MCD43A3 BRDF/Albedo Product performs well at Kahiltna Base Camp (<5% difference from ASD shortwave broadband data), but low biases in MODIS albedo (10-28% relative to ASD data) appear to occur along the Kahiltna Glacier due to the snow-free valley walls being captured in the 500m MODIS footprint. Incorporating Landsat imagery will strengthen our interpretations and has the potential to produce a long-term (1982-present) validated satellite albedo record for steep and mountainous terrain. Once validation is complete, we will compare the satellite-derived albedo record to the Denali ice core accumulation rate, aerosol records (i.e. volcanics and biomass burning), and glacier mass balance data. This research will ultimately contribute to an improved understanding of the relationship between glacier albedo, surface processes, and regional glacier hydroclimate.

African hydroclimatic variability during the last 2000 years

NASA Astrophysics Data System (ADS)

Nash, David J.; De Cort, Gijs; Chase, Brian M.; Verschuren, Dirk; Nicholson, Sharon E.; Shanahan, Timothy M.; Asrat, Asfawossen; Lézine, Anne-Marie; Grab, Stefan W.

2016-12-01

The African continent is characterised by a wide range of hydroclimate regimes, ranging from humid equatorial West Africa to the arid deserts in the northern and southern subtropics. The livelihoods of much of its population are also vulnerable to future climate change, mainly through variability in rainfall affecting water resource availability. A growing number of data sources indicate that such hydroclimatic variability is an intrinsic component of Africa's natural environment. This paper, co-authored by members of the PAGES Africa 2k Working Group, presents an extensive assessment and discussion of proxy, historical and instrumental evidence for hydroclimatic variability across the African continent, spanning the last two millennia. While the African palaeoenvironmental record is characterised by spatially disjunctive datasets, with often less-than-optimal temporal resolution and chronological control, the available evidence allows the assessment of prominent spatial patterns of palaeomoisture variability through time. In this study, we focus sequentially on data for six major time windows: the first millennium CE, the Medieval Climate Anomaly (900-1250 CE), the Little Ice Age (1250-1750 CE), the end of the LIA (1750-1850 CE), the Early Modern Period (1850-1950), and the period of recent warming (1950 onwards). This results in a continent-wide synthesis of regional moisture-balance trends through history, allowing consideration of possible driving mechanisms, and suggestions for future research.

Unstable relationships between tree ring δ18O and climate variables over southwestern China: possible impacts from increasing central Pacific SSTs

NASA Astrophysics Data System (ADS)

An, Wenling; Liu, Xiaohong; Hou, Shugui; Zeng, Xiaomin; Sun, Weizhen; Wang, Wenzhi; Wang, Yu; Xu, Guobao; Ren, Jiawen

2018-05-01

In this study, we investigated the potential influence of central and eastern Pacific sea surface temperatures (SSTs) on the unstable relationship between earlywood δ18O and climatic factors in the southwestern China from 1902 to 2005. The results show that the strength of the climate signals recorded in the earlywood δ18O series has declined since the late 1970s. This reduction in signal strength may have been caused by the changes in the local hydroclimate, which is associated with the increasing SSTs in the central Pacific Ocean over recent decades. Alongside these increasing SSTs in the central Pacific, southwestern China has experienced more droughts, as well as more severe droughts through the late spring and early summer during the central Pacific (CP) El Niño years than during the eastern Pacific (EP) El Niño years in recent decades. This increased drought frequency may have weakened the response of earlywood δ18O to climate variables.

Hydroclimate changes across the Amazon lowlands over the past 45,000 years

NASA Astrophysics Data System (ADS)

Wang, Xianfeng; Edwards, R. Lawrence; Auler, Augusto S.; Cheng, Hai; Kong, Xinggong; Wang, Yongjin; Cruz, Francisco W.; Dorale, Jeffrey A.; Chiang, Hong-Wei

2017-01-01

Reconstructing the history of tropical hydroclimates has been difficult, particularly for the Amazon basin—one of Earth’s major centres of deep atmospheric convection. For example, whether the Amazon basin was substantially drier or remained wet during glacial times has been controversial, largely because most study sites have been located on the periphery of the basin, and because interpretations can be complicated by sediment preservation, uncertainties in chronology, and topographical setting. Here we show that rainfall in the basin responds closely to changes in glacial boundary conditions in terms of temperature and atmospheric concentrations of carbon dioxide. Our results are based on a decadally resolved, uranium/thorium-dated, oxygen isotopic record for much of the past 45,000 years, obtained using speleothems from Paraíso Cave in eastern Amazonia; we interpret the record as being broadly related to precipitation. Relative to modern levels, precipitation in the region was about 58% during the Last Glacial Maximum (around 21,000 years ago) and 142% during the mid-Holocene epoch (about 6,000 years ago). We find that, as compared with cave records from the western edge of the lowlands, the Amazon was widely drier during the last glacial period, with much less recycling of water and probably reduced plant transpiration, although the rainforest persisted throughout this time.

Hydroclimate changes across the Amazon lowlands over the past 45,000 years.

PubMed

Wang, Xianfeng; Edwards, R Lawrence; Auler, Augusto S; Cheng, Hai; Kong, Xinggong; Wang, Yongjin; Cruz, Francisco W; Dorale, Jeffrey A; Chiang, Hong-Wei

2017-01-11

Reconstructing the history of tropical hydroclimates has been difficult, particularly for the Amazon basin-one of Earth's major centres of deep atmospheric convection. For example, whether the Amazon basin was substantially drier or remained wet during glacial times has been controversial, largely because most study sites have been located on the periphery of the basin, and because interpretations can be complicated by sediment preservation, uncertainties in chronology, and topographical setting. Here we show that rainfall in the basin responds closely to changes in glacial boundary conditions in terms of temperature and atmospheric concentrations of carbon dioxide. Our results are based on a decadally resolved, uranium/thorium-dated, oxygen isotopic record for much of the past 45,000 years, obtained using speleothems from Paraíso Cave in eastern Amazonia; we interpret the record as being broadly related to precipitation. Relative to modern levels, precipitation in the region was about 58% during the Last Glacial Maximum (around 21,000 years ago) and 142% during the mid-Holocene epoch (about 6,000 years ago). We find that, as compared with cave records from the western edge of the lowlands, the Amazon was widely drier during the last glacial period, with much less recycling of water and probably reduced plant transpiration, although the rainforest persisted throughout this time.

Tree-ring reconstructions of hydroclimatic variability in the Upper Colorado River Basin

NASA Astrophysics Data System (ADS)

Hidalgo-Leon, Hugo

Three major sources of improvements in tree-ring analysis and reconstruction of hydroclimatic variables are presented for the Upper Colorado River Basin (UCRB) in the southwestern U.S.: (1) Cross validation statistics are used for identifying optimal reconstruction models based on different alternatives of PCA-based regression. Results showed that a physically-consistent parsimonious model with low mean square error can be obtained by using strict rules for principal component selection and cross validation statistics. The improved methods were used to produce a ˜500 year high-resolution reconstruction of the UCRB's streamflow and compared with results of a previous reconstruction based on traditional procedures. (2) Tree-species' type was found to be a factor for determining chronology selection from dendrohydroclimatic models. The relative sensitivity of six tree species (Pinus edulis, Pseudotsuga menziesii, Pinus ponderosa, Pinus flexilis, Pinus aristata, and Picea engelmanni) to hydroclimatic extreme variations was determined using contingency table scores of tree-ring growth (at different lags) against hydroclimatic observations. Pinus edulis and Pseudotsuga menziesii were found to be the species most sensitive to low water. Results showed that tree-rings are biased towards greater sensitivity to hot-dry conditions and less responsive to cool-moist conditions. Resulted also showed higher streamflow response scores compared to precipitation implying a good integration and persistence representation of the basin through normal hydrological processes. (3) Previous reconstructions on the basin used data extending only up to 1963. This is an important limitation since hydroclimatic records from 1963 to the present show significantly different variation than prior to 1963. The changes are caused by variations in the strength of forcing mechanisms from the Pacific Ocean. A comparative analysis of the influence of North Pacific variation and El Nino/Southern Oscillation (ENSO) showed that the responses of Tropical and North Pacific forcing in UCRB's hydroclimate are different for annual precipitation and total streamflow and that these relationships have changed at decadal time scales. Furthermore, most of the few tree-rings available up to 1985, present the same shifts as the hydroclimatic variables studied. To capture the full range of variability observed in instrumental data is necessary to collect new tree-ring samples.

Climate change impact on hydroclimate regimes and extremes over Andean basins in the central-southern Chile

NASA Astrophysics Data System (ADS)

Bozkurt, Deniz; Rojas, Maisa; Valdivieso, Jonás; Falvey, Mark

2015-04-01

We have assessed the impact of projected increases in temperature and decreased precipitation on variability and potential changes in hydroclimate regimes and extremes over Andean basins in the central-southern Chile (~30-40S). The altitude of the southern Andes in the study area has an average altitude of 5000 m in the north that decreases to 3000 m at the southern edge. Climatically the region has a Mediterranean-like climate with mainly winter precipitation that gradually increases southwards, from around 300 mm/yr to 1000 mm/yr. The region is home to most of the population in Chile (~10 mil. inhabitants), it has fertile and productive agriculture land, as well as hydro-electrical power plants. During the 20th Century the region has experienced a decreasing precipitation trend imbedded in important interannual and decadal scale variability. We have used gridded observed daily precipitation and temperatures to drive and validate the VIC macro-scale model over the region of interest at 0.25 x 0.25 degree resolution. Historical (1960-2005) and projected (RCP8.5, 2006-2099) daily precipitation and temperatures from 28 CMIP5 models are adjusted via a transfer function based on the gridded observed daily precipitation and temperature data. Adjusted time series are then used to drive the VIC model in order to present climate change projections. The hydrological model simulations foresee that drying is robust in the models and total annual runoff will decrease in the future (40-45% by the end of the century). Center timing of runoff tends to shift to earlier days (3-5 weeks by the end of the century). In some areas over the Andes winter runoff is projected to increase due to upward movement of zero isotherm. Moreover, reductions in the amount of snowpack and accelerated snowmelt lead to more pronounced increase in winter evapotranspiration over the same areas. The simulated 12-months Standardized Runoff Index (SRI) clearly shows severe persistent hydrological droughts without (or a few) wet spell interruptions by the end of the century. On the other hand, probability density function of annual maximum runoff over high elevations (>1000 m) and higher interannual variability of 3-months SRI indicate a possible increase in the probability of flood events.

Ecohydrological change and variability over western North America from the Last Glacial Maximum to the near term future: The known, the unknown and the known unknown

NASA Astrophysics Data System (ADS)

Seager, R.; Mankin, J. S.; Cook, B.; Scheff, J.; Smerdon, J. E.; Coats, S.; Williams, P.

2017-12-01

Hydroclimate variability and change in western North America from the last glacial to the near future is reviewed focusing on non-orbital-induced variations. The motivating factor is model projections of intensifying aridity in southwestern North America as a consequence of rising greenhouse gases. Future change will be considered in the context of changes in precipitation, evaporative demand and CO2 and from perspectives of surface hydroclimate and ecological response. Current earth system models project increasing aridity in terms of standard drought measures and declining soil moisture quite robustly as a consequence of declining precipitation (in the interior southwest) and rising evaporative demand (everywhere). However, the same models project rising net primary production, leaf area index and evapotranspiration as the effects on plants of increasing CO2 outweigh the effects of increased water stress. There are reasons to be cautious about the realism of this modeled response but it poses a future with a competition between ecosystems and humans (dependent on soil moisture and runoff) for available water. Looking back over the last millennium with the aid of near hemispheric tree ring drought reconstructions we show that the driving role the tropical Pacific and tropical North Atlantic Oceans have in orchestrating the sequence of western droughts and pluvials extends to the Medieval megadroughts. These famed severe and extended droughts, still visible in the landscape today, were most likely caused by internal atmosphere-ocean variability including frequent, but not anomalously recurrent, La Nina-conditions accompanied by persistent warm shifts in the tropical North Atlantic. Passing over early and mid-Holocene climates that were strongly influenced by orbitally-forcing, we turn to Last Glacial Maximum climates. According to lake records the LGM was moist across western North America while pollen records show a mix of wetter-looking and less lush ("drier-looking") vegetation. Using earth system models it is shown that these records are consistent with a climatic shift to a wetter "greenhouse anti-analog" climate but one in which vegetation is stressed by low levels of CO2. These distant data provide limited support for model projections of a drier-but-greener future for the American West.

Natural and anthropogenic land cover change and its impact on the regional climate and hydrological extremes over Sanjiangyuan region

NASA Astrophysics Data System (ADS)

Ji, P.; Yuan, X.

2017-12-01

Located in the northern Tibetan Plateau, Sanjiangyuan is the headwater region of the Yellow River, Yangtze River and Mekong River. Besides climate change, natural and human-induced land cover change (e.g., Graze for Grass Project) is also influencing the regional hydro-climate and hydrological extremes significantly. To quantify their impacts, a land surface model (LSM) with consideration of soil moisture-lateral surface flow interaction and quasi-three-dimensional subsurface flow, is used to conduct long-term high resolution simulations driven by China Meteorological Administration Land Data Assimilation System forcing data and different land cover scenarios. In particular, the role of surface and subsurface lateral flows is also analyzed by comparing with typical one-dimensional models. Lateral flows help to simulate soil moisture variability caused by topography at hyper-resolution (e.g., 100m), which is also essential for simulating hydrological extremes including soil moisture dryness/wetness and high/low flows. The LSM will also be coupled with a regional climate model to simulate the effect of natural and anthropogenic land cover change on regional climate, with particular focus on the land-atmosphere coupling at different resolutions with different configurations in modeling land surface hydrology.

Development and Evaluation of Season-ahead Precipitation and Streamflow Predictions for Sectoral Management in Western Ethiopia

NASA Astrophysics Data System (ADS)

Block, P. J.; Alexander, S.; WU, S.

2017-12-01

Skillful season-ahead predictions conditioned on local and large-scale hydro-climate variables can provide valuable knowledge to farmers and reservoir operators, enabling informed water resource allocation and management decisions. In Ethiopia, the potential for advancing agriculture and hydropower management, and subsequently economic growth, is substantial, yet evidence suggests a weak adoption of prediction information by sectoral audiences. To address common critiques, including skill, scale, and uncertainty, probabilistic forecasts are developed at various scales - temporally and spatially - for the Finchaa hydropower dam and the Koga agricultural scheme in an attempt to promote uptake and application. Significant prediction skill is evident across scales, particularly for statistical models. This raises questions regarding other potential barriers to forecast utilization at community scales, which are also addressed.

North Atlantic forcing of tropical Indian Ocean climate.

PubMed

Mohtadi, Mahyar; Prange, Matthias; Oppo, Delia W; De Pol-Holz, Ricardo; Merkel, Ute; Zhang, Xiao; Steinke, Stephan; Lückge, Andreas

2014-05-01

The response of the tropical climate in the Indian Ocean realm to abrupt climate change events in the North Atlantic Ocean is contentious. Repositioning of the intertropical convergence zone is thought to have been responsible for changes in tropical hydroclimate during North Atlantic cold spells, but the dearth of high-resolution records outside the monsoon realm in the Indian Ocean precludes a full understanding of this remote relationship and its underlying mechanisms. Here we show that slowdowns of the Atlantic meridional overturning circulation during Heinrich stadials and the Younger Dryas stadial affected the tropical Indian Ocean hydroclimate through changes to the Hadley circulation including a southward shift in the rising branch (the intertropical convergence zone) and an overall weakening over the southern Indian Ocean. Our results are based on new, high-resolution sea surface temperature and seawater oxygen isotope records of well-dated sedimentary archives from the tropical eastern Indian Ocean for the past 45,000 years, combined with climate model simulations of Atlantic circulation slowdown under Marine Isotope Stages 2 and 3 boundary conditions. Similar conditions in the east and west of the basin rule out a zonal dipole structure as the dominant forcing of the tropical Indian Ocean hydroclimate of millennial-scale events. Results from our simulations and proxy data suggest dry conditions in the northern Indian Ocean realm and wet and warm conditions in the southern realm during North Atlantic cold spells.

Past Peatland Distribution as an Indicator of Hydroclimate and Temperature

NASA Astrophysics Data System (ADS)

Treat, C. C.; Jones, M.; Lacourse, T.; Payne, R.; Peteet, D. M.; Sannel, B.; Stelling, J.; Talbot, J.; Williams, C. J.; Kleinen, T.; Grosse, G.; Yu, Z.; Finkelstein, S. A.; Broothaerts, N.; Dommain, R.; Kuhry, P.; Lähteenoja, O.; Dalton, A.; Notebaert, B.; Swindles, G. T.; Tarnocai, C.; Verstraeten, G.; Xia, Z.; Brovkin, V.

2016-12-01

Peatlands, wetlands with > 30 cm of organic sediment, cover more than 3 x 106 km2 of the earth surface and have been accumulating carbon and sediments throughout the Holocene. The location of peatland formation and accumulation has been dynamic over time, as peat formation in areas like Alaska and the West Siberian Lowlands preceded peat formation in Fennoscandia and Eastern North America due to more favorable climate for peat formation. Using the geographic distribution of peatlands in the past can indicate general climatic conditions, including hydroclimate, given that the underlying geology is well understood. Peatlands form under a variety of climatic conditions and landscape positions but do not persist under arid conditions, instead requiring either humid conditions or cold temperatures. However, peatlands may have existed in the past in areas not currently suitable for peatland formation and persistence, but where peats can be found at depth within the sediment column. Here we map the locations of histic paleosols, relict peat, and buried peats since the Last Glacial Maximum using a compilation of sites from previous studies. We compare these records of past peatland distribution to present-day peatland distribution. We evaluate regional differences in timing of peatland development in these buried peatlands to the development of extant peatlands. Finally, we compare the timing of past peatland extent to the to modeled paleoclimate during the Quaternary. In addition to implications for paleoclimate, these past peatlands are not well accounted for in present-day soil carbon stocks but could be an important component of deep soil carbon pools.

Trend and variability in western and central Africa streamflow, and major drivers of variability between 1950 and 2005

NASA Astrophysics Data System (ADS)

Dieppois, B.; Sidibe, M.; Mahe, G. M.; Paturel, J. E.; Anifowose, B. A.; Lawler, D.; Amoussou, E.

2017-12-01

Unprecedented drought episodes that struck western and central Africa between the late 1960s and 1980s, triggered many studies investigating rainfall variability and its impacts on water resources and food production systems. However, most studies were focused at the catchment scale. In this study, we aim at investigating the key large-scale controls determining and modulating climate-river flows relationships at the subcontinental scale between 1950 and 2005. Using the first complete monthly streamflow data set (1950-2005) over western and central Africa, streamflow trend and variability are seasonally assessed at this subcontinental scale and compared to those observed in other hydroclimatic variables (precipitation, temperature and potential evapotranspiration). Long-term trends and variability in streamflow are mainly consistent with trends in rainfall. In particular, the recent post-1990s partial recovery in Sahel rainfall could have, at least partially, positively impacted river flows (e.g. the Senegal and Niger rivers). However, these relationships may have been moderated by: i) changes in land use; and ii) contributions from groundwater resources. In addition, the time-evolution of river flows is shown to be primarily driven by very strong decadal fluctuations, which can be interpreted as modulations in the baseflow, as determined using multi-temporal trend and continuous wavelet analysis. These decadal fluctuations, which are also significantly detected in rainfall, are likely related to large-scale sea-surface temperature (SST) anomaly patterns (such as the tropical Atlantic SST variability, the Atlantic Multidecadal Oscillation, the Interdecadal Pacific Oscillation and the Pacific Decadal Oscillation), which are together modulating the West African monsoon. Furthermore, influences of the catchment properties (e.g. size, vegetation and land use cover, soil properties, direction of stream flow across climate zones) on these decadal fluctuations in river flows have been examined. This study therefore aims to improve the ability of current global to regional climate models to simulate such ranges of variability and understand regional hydroclimate, as a means for improving the development of future scenarios for water resources in western and central Africa.

Precipitation Changes Throughout the South Pacific Convergence Zone During the Last 2000 Years

NASA Astrophysics Data System (ADS)

Maloney, A. E.; Nelson, D. B.; Sachs, J. P.

2016-12-01

The South Pacific Convergence Zone (SPCZ) is the southern hemisphere's most prominent precipitation feature extending 3000km southeastwards from Papua New Guinea to French Polynesia. Seasonal and interannual variability in SPCZ rainfall is well characterized by satellite data, however an understanding of this feature prior to the instrumental record is lacking. Rainfall in the western tropical Pacific is difficult to reconstruct due to a dearth of archives that are both high-resolution and continuous. Here we present molecular fossil hydroclimate reconstructions from the last 2000 years. The hydrogen isotopic composition of the algal lipid biomarker dinosterol was measured in 10 freshwater lake sediment cores from 7 lakes on 4 islands in Vanuatu, the Solomon Islands, and Wallis and Futuna. Coretop δ2Hdinosterol values were well correlated with satellite-derived rainfall rates, providing a transfer function for deriving precipitation rates from sedimentary δ2Hdinosterol values. The Vanuatu and Wallis records indicate that the south-western portion of the SPCZ was driest during the transition from the Medieval Warm Period (MWP) to the Little Ice Age (LIA) (1200-1400 CE) with rainfall rates as low as 2mm/day compare to more typical values of 4mm/day. Conversely, the central SPCZ (Solomon Islands) experienced the driest conditions ( 5mm/day) during the MWP (600-1200 CE) and has maintained high ( 9mm/day) rainfall rates since the LIA. The tropical water cycle influences global climate and these quantitative precipitation records are important for understanding SPCZ natural variability.

Tree Rings Show Recent High Summer-Autumn Precipitation in Northwest Australia Is Unprecedented within the Last Two Centuries

PubMed Central

O'Donnell, Alison J.; Cook, Edward R.; Palmer, Jonathan G.; Turney, Chris S. M.; Page, Gerald F. M.; Grierson, Pauline F.

2015-01-01

An understanding of past hydroclimatic variability is critical to resolving the significance of recent recorded trends in Australian precipitation and informing climate models. Our aim was to reconstruct past hydroclimatic variability in semi-arid northwest Australia to provide a longer context within which to examine a recent period of unusually high summer-autumn precipitation. We developed a 210-year ring-width chronology from Callitris columellaris, which was highly correlated with summer-autumn (Dec–May) precipitation (r = 0.81; 1910–2011; p < 0.0001) and autumn (Mar–May) self-calibrating Palmer drought severity index (scPDSI, r = 0.73; 1910–2011; p < 0.0001) across semi-arid northwest Australia. A linear regression model was used to reconstruct precipitation and explained 66% of the variance in observed summer-autumn precipitation. Our reconstruction reveals inter-annual to multi-decadal scale variation in hydroclimate of the region during the last 210 years, typically showing periods of below average precipitation extending from one to three decades and periods of above average precipitation, which were often less than a decade. Our results demonstrate that the last two decades (1995–2012) have been unusually wet (average summer-autumn precipitation of 310 mm) compared to the previous two centuries (average summer-autumn precipitation of 229 mm), coinciding with both an anomalously high frequency and intensity of tropical cyclones in northwest Australia and the dominance of the positive phase of the Southern Annular Mode. PMID:26039148

Tree Rings Show Recent High Summer-Autumn Precipitation in Northwest Australia Is Unprecedented within the Last Two Centuries.

PubMed

O'Donnell, Alison J; Cook, Edward R; Palmer, Jonathan G; Turney, Chris S M; Page, Gerald F M; Grierson, Pauline F

2015-01-01

An understanding of past hydroclimatic variability is critical to resolving the significance of recent recorded trends in Australian precipitation and informing climate models. Our aim was to reconstruct past hydroclimatic variability in semi-arid northwest Australia to provide a longer context within which to examine a recent period of unusually high summer-autumn precipitation. We developed a 210-year ring-width chronology from Callitris columellaris, which was highly correlated with summer-autumn (Dec-May) precipitation (r = 0.81; 1910-2011; p < 0.0001) and autumn (Mar-May) self-calibrating Palmer drought severity index (scPDSI, r = 0.73; 1910-2011; p < 0.0001) across semi-arid northwest Australia. A linear regression model was used to reconstruct precipitation and explained 66% of the variance in observed summer-autumn precipitation. Our reconstruction reveals inter-annual to multi-decadal scale variation in hydroclimate of the region during the last 210 years, typically showing periods of below average precipitation extending from one to three decades and periods of above average precipitation, which were often less than a decade. Our results demonstrate that the last two decades (1995-2012) have been unusually wet (average summer-autumn precipitation of 310 mm) compared to the previous two centuries (average summer-autumn precipitation of 229 mm), coinciding with both an anomalously high frequency and intensity of tropical cyclones in northwest Australia and the dominance of the positive phase of the Southern Annular Mode.

The progressive aridification of southwest North America: The what, the why, the when and the how (Invited)

NASA Astrophysics Data System (ADS)

Seager, R.; Liu, H.; Henderson, N.; Kushnir, Y.; Ting, M.; Cook, B.; Nakamura, J.

2013-12-01

The latest generation of global coupled climate models from the Coupled Model Intercomparison Project Five (CMIP5), much anticipated after the prior CMIP3 models projected the southwest of North America to transition in the near term to a more arid climate, turned out to be a case of deja-vu all over again. While suggesting that northern California might get more midwinter precipitation, overall the CMIP5 models, like their CMIP3 precursors, project that the interior southwest of the U.S., most of Mexico, Texas and the southern Plains, will progressively transition to a more arid climate with reduced precipitation and increased potential evapotranspiration driving a reduction in soil moisture and streamflow. An about 10% reduction of Colorado River flow for the 2021-2040 period relative to the last half of the 20th Century appears a good ball park number to motivate adaptation efforts. Here we will present new detailed analyses of Reanalysis and CMIP5 model moisture budgets to determine the causes of the projected aridification. The role of moisture convergences by the mean and transient flows will be addressed as well as the dynamical causes of the shifts in atmospheric circulation that contribute to drying or locally offset it. The hydroclimate history of the West for the past few decades will also be examined for evidence that model projected aridification is in progress or cannot currently be detected amidst the large natural variability of hydroclimate in the region. But it will be cautioned that waiting for statistical significance might be as fruitful as Waiting for Godot while, during the wait, the southwest will already have transitioned into a troublingly drier climate with serious impacts on people, societies, ecosystems and agriculture.

Placing the Common Era in a Holocene context: millennial to centennial patterns and trends in the hydroclimate of North America over the past 2000 years

NASA Astrophysics Data System (ADS)

Shuman, Bryan N.; Routson, Cody; McKay, Nicholas; Fritz, Sherilyn; Kaufman, Darrell; Kirby, Matthew E.; Nolan, Connor; Pederson, Gregory T.; St-Jacques, Jeannine-Marie

2018-05-01

A synthesis of 93 hydrologic records from across North and Central America, and adjacent tropical and Arctic islands, reveals centennial to millennial trends in the regional hydroclimates of the Common Era (CE; past 2000 years). The hydrological records derive from materials stored in lakes, bogs, caves, and ice from extant glaciers, which have the continuity through time to preserve low-frequency ( > 100 year) climate signals that may extend deeper into the Holocene. The most common pattern, represented in 46 (49 %) of the records, indicates that the centuries before 1000 CE were drier than the centuries since that time. Principal component analysis indicates that millennial-scale trends represent the dominant pattern of variance in the southwestern US, northeastern US, mid-continent, Pacific Northwest, Arctic, and tropics, although not all records within a region show the same direction of change. The Pacific Northwest and the southernmost tier of the tropical sites tended to dry toward present, as many other areas became wetter than before. In 22 records (24 %), the Medieval Climate Anomaly period (800-1300 CE) was drier than the Little Ice Age (1400-1900 CE), but in many cases the difference was part of the longer millennial-scale trend, and, in 25 records (27 %), the Medieval Climate Anomaly period represented a pluvial (wet) phase. Where quantitative records permitted a comparison, we found that centennial-scale fluctuations over the Common Era represented changes of 3-7 % in the modern interannual range of variability in precipitation, but the accumulation of these long-term trends over the entirety of the Holocene caused recent centuries to be significantly wetter, on average, than most of the past 11 000 years.

How do Changes in Hydro-Climate Conditions Alter the Risk of Infection With Fasciolosis?

NASA Astrophysics Data System (ADS)

Beltrame, L.; Dunne, T.; Rose, H.; Walker, J.; Morgan, E.; Vickerman, P.; Wagener, T.

2017-12-01

Fasciolosis is a widespread parasitic disease of livestock and is emerging as a major zoonosis. Since the parasite and its intermediate host live and develop in the environment, risk of infection is directly affected by climatic-environmental conditions. Changes in disease prevalence, seasonality and distribution have been reported in recent years and attributed to altered temperature and rainfall patterns, raising concerns about the effects of climate change in the future. Therefore, it is urgent to understand how changes in climate-environmental drivers may alter the dynamics of disease risk in a quantitative way, to guide parasite control strategies and interventions in the coming decades. In a previous work, we developed and tested a novel mechanistic hydro-epidemiological model for Fasciolosis, which explicitly represents the parasite life-cycle in connection with key environmental processes, allowing to capture the impact of previously unseen conditions. In this study, we use the new mechanistic model to assess the sensitivity of infection rates to changes in climate-environmental factors. This is challenging as processes underlying disease transmission are complex and interacting, and may have contrasting effects on the parasite life-cycle stages. To this end, we set up a sensitivity analysis framework to investigate in a structured way which factors play a key role in controlling the magnitude, timing and spread of infection, and how the sensitivity of disease risk varies in time and space. Moreover, we define synthetic scenarios to explore the space of possible variability of the hydro-climate drivers and investigate conditions that lead to critical levels of infection. The study shows how the new model combined with the sensitivity analysis framework can support decision-making, providing useful information for disease management.

Can Regional Climate Models be used in the assessment of vulnerability and risk caused by extreme events?

NASA Astrophysics Data System (ADS)

Nunes, Ana

2015-04-01

Extreme meteorological events played an important role in catastrophic occurrences observed in the past over densely populated areas in Brazil. This motived the proposal of an integrated system for analysis and assessment of vulnerability and risk caused by extreme events in urban areas that are particularly affected by complex topography. That requires a multi-scale approach, which is centered on a regional modeling system, consisting of a regional (spectral) climate model coupled to a land-surface scheme. This regional modeling system employs a boundary forcing method based on scale-selective bias correction and assimilation of satellite-based precipitation estimates. Scale-selective bias correction is a method similar to the spectral nudging technique for dynamical downscaling that allows internal modes to develop in agreement with the large-scale features, while the precipitation assimilation procedure improves the modeled deep-convection and drives the land-surface scheme variables. Here, the scale-selective bias correction acts only on the rotational part of the wind field, letting the precipitation assimilation procedure to correct moisture convergence, in order to reconstruct South American current climate within the South American Hydroclimate Reconstruction Project. The hydroclimate reconstruction outputs might eventually produce improved initial conditions for high-resolution numerical integrations in metropolitan regions, generating more reliable short-term precipitation predictions, and providing accurate hidrometeorological variables to higher resolution geomorphological models. Better representation of deep-convection from intermediate scales is relevant when the resolution of the regional modeling system is refined by any method to meet the scale of geomorphological dynamic models of stability and mass movement, assisting in the assessment of risk areas and estimation of terrain stability over complex topography. The reconstruction of past extreme events also helps the development of a system for decision-making, regarding natural and social disasters, and reducing impacts. Numerical experiments using this regional modeling system successfully modeled severe weather events in Brazil. Comparisons with the NCEP Climate Forecast System Reanalysis outputs were made at resolutions of about 40- and 25-km of the regional climate model.

Water isotope tracers of tropical hydroclimate in a warming world

NASA Astrophysics Data System (ADS)

Konecky, B. L.; Noone, D.; Nusbaumer, J. M.; Cobb, K. M.; Di Nezio, P. N.; Otto-Bliesner, B. L.

2016-12-01

The tropical water cycle is projected to undergo substantial changes under a warming climate, but direct meteorological observations to contextualize these changes are rare prior to the 20th century. Stable oxygen and hydrogen isotope ratios (δ18O, δD) of environmental waters preserved in geologic archives are increasingly being used to reconstruct terrestrial rainfall over many decades to millions of years. However, a rising number of new, modern-day observations and model simulations have challenged previous interpretations of these isotopic signatures. This presentation systematically evaluates the three main influences on the δ18O and δD of modern precipitation - rainfall amount, cloud type, and moisture transport - from terrestrial stations throughout the tropics, and uses this interpretive framework to understand past changes in terrestrial tropical rainfall. Results indicate that cloud type and moisture transport have a larger influence on modern δ18O and δD of tropical precipitation than previously believed, indicating that isotope records track changes in cloud characteristics and circulation that accompany warmer and cooler climate states. We use our framework to investigate isotopic records of the land-based tropical rain belt during the Last Glacial Maximum, the period of warming following the Little Ice Age, and the 21st century. Proxy and observational data are compared with water isotope-enabled simulations with the Community Earth System Model in order to discuss how global warming and cooling may influence tropical terrestrial hydroclimate.

On the role of circulation changes in future Northern Hemisphere hydroclimate change

NASA Astrophysics Data System (ADS)

Seager, R.; Ting, M.; Simpson, I.; Shaw, T.

2015-12-01

The "dry-get-drier, wet-get-wetter", otherwise known as "rich-get-richer, poor-get-poorer" concept of the hydrological cycle response to rising greenhouse gases was a major advance in terms of perception of climate change in the research community and the winder public. It provides a good description of hydroclimate change in many regions but especially over the oceans. Here there is a clear divide between wet regions, with positive precipitation minus evaporation (P-E), and dry regions with negative P-E. However over land, long term P-E is either zero or positive and balanced by streamflow and it is not so simple to divide between wet and dry regions. What is more, the simple wet-get-wetter, dry-get-drier paradigm is based only on thermodynamics with rising humidity causing increased amplitude of moisture convergence and moisture divergence and, hence, larger variations in P-E. It is now being realized more and more that changes in atmospheric circulation can also drive changes in moisture convergence/divergence and that a full explanation of hydrological cycle change requires attention to circulation change. This will be illustrated with reference to North America and the Mediterranean region. In both case changes in the mean circulation are important drivers of regional hydroclimate change. Model-projected North American hydroclimate change in winter is strongly influenced by a lengthening of the zonal scale of intermediate-scale stationary waves forced by extratropical heating. Wetting at the west coast, drying in the interior southwest and wetting at the US east coast are stronger in models that have a climatological wave field that exaggerates these waves than in models that have more realistic amplitude wave fields. Intense Mediterranean region drying in both summer and winter is also explained in part by shifts towards regional high pressure that, as of now, have not been fully explained. In neither southwest North America nor the Mediterranean, despite the importance of storm systems in delivering moisture to the regions, is projected drying caused by reduced transient eddy moisture convergence. Instead thermodynamic drying and mean flow changes share the responsibility for shifting the regions to drier, more water-stressed, climates.

A multi-proxy record of Holocene hydroclimate change from a windward montane wetland, Molokai, Hawaii

NASA Astrophysics Data System (ADS)

Beilman, D. W.; Kallstrom, R.; Elison Timm, O.; Nichols, J. E.; Massa, C.

2016-12-01

A core raised from a windward mountain bog on the Island of Molokai, Hawaii was studied to reconstruct changes in hydroclimate and ecosystem response. The 250-cm radiocarbon-dated profile shows that formation of peat (organic matter greater than 90% and bulk density below 0.2 g cm-3) began around 10,000 years ago, in response to wetter conditions needed to waterlog and stabilize soil organic matter, and has continued through the Holocene. A previously-published pollen record from this site has no chronological information, but suggests that the dominant forest species have been present throughout but varied substantially in their relative abundance over Holocene time. The stable carbon isotope value of organic matter (δ13COM) showed a pattern of increasingly more-positive values from 10,000 to 8000 years ago, consistent with decreased stomatal conductance in woody vegetation and an early Holocene drying trend. An overall Holocene decrease in rainfall over the Pacific near Hawaii is also observed in transient model simulations forced by insolation, greenhouse gases and ice. Between 4000 and 2000 years ago, more-negative δ13COM values and a maximum in organic carbon accumulation suggest a period of somewhat wetter climate that seems to have ended around 2,000 years ago. The distribution and abundance of leaf wax compounds including alkyl lipids in the profile suggests a lower relative abundance of woody species 8000 to 3000 years ago and a shift towards more woody inputs preceding the arrival of humans. Taken together, evidence from this windward location shows an overall decrease in rainfall during the Holocene in general agreement with other Hawaii proxy data and model simulations. But these new data also show important millennial-scale changes in hydroclimate and ecosystem responses. Comparison to proxy records at leeward Hawaii locations revealed an onset of peat formation at around the same time at a similar elevation in the early Holocene, but both similarities and differences in hydroclimate trends, and overall complex pattern relative to reconstructions of Holocene El Nino variation, suggesting influence of both tropical and extratropical Pacific circulation.

Long-term Hydroclimate and Pacific Salmon Population Linkages Across a Headwater-to-Coast Continuum in Northern British Columbia, Canada: A Perspective From Multiple Tree-Ring Proxy Records

NASA Astrophysics Data System (ADS)

Welsh, C.; Smith, D. J.; Edwards, T.; Prowse, T.

2016-12-01

Ongoing climate change is expected to have lasting impacts on the runoff behaviour of rivers in northern British Columbia, Canada. Of particular concern is the loss of mountain snowpack and greater rainfall totals altering hydrograph characteristics. Sustained deviations in seasonal streamflow will pose significant challenges for effective watershed management. These ongoing changes highlight the importance of improving our understanding of the long-term biophysical linkages between the storage and release of water and downstream freshwater ecosystems. Such integrated research is particularly relevant to fisheries management as fluctuations in populations of Pacific salmon represent a complex and management-relevant biophysical issue in northern Canada. Unfortunately, hydroclimate and salmon productivity records in this region are sparse and of short duration, constraining our understanding of the impact of climate-induced hydrologic changes and biological responses to the last century. Proxy records derived from tree-rings provide annually or seasonally resolved data and have played a prominent role in attempts to establish how hydroclimate has varied in the past. The objective of my doctoral research is to reconstruct the prehistoric hydroclimate and salmon population trends in the Skeena, Nass and Stikine Watersheds using multiple tree-ring proxies to investigate the long-term biophysical linkages extending across a headwater-to-coast continuum in northern British Columbia, Canada. Ring-width, wood density and stable isotope chronologies using a number of mid-to high-elevation tree species will be constructed across each basin and sub-basin area for the purposes of reconstrucing the predominent temperature and precipiation signature that influence streamflow. Preliminary tree-ring δ18O and δ13C-isotope results indicate a strong negative association with mean monthly relative humidity values, suggesting a physiological control by moisture loss. The results of this study highlight the importance of combining several tree-ring parameters and species in order to strengthen streamflow reconstructions. This study is ongoing and has an estimated completion timeframe of spring 2018.

Insight to forcing of late Quaternary climate change from aeolian dust archives in eastern Australia

NASA Astrophysics Data System (ADS)

McGowan, H. A.; Marx, S.; Soderholm, J.; Denholm, J.; Petherick, L.

2010-12-01

The Australian continent is the largest source of dust in the Southern Hemisphere. Historical dust emissions records display inter-annual variability in response to the El Niño Southern Oscillation (ENSO) phenomenon and inter-decadal variability which has been linked to the Pacific Decadal Oscillation (PDO). These reflect change in hydrometeorology of the continents two major dust source regions, the Murray-Darling Basin and the Lake Eyre Basin. The historical records do not allow longer term variability of ENSO and the PDO and their influence on Australia to be quantified. Importantly, sub-Milankovitch centennial to multi-millennial scale climate cycles and their impacts are not represented in the historical records. In this paper we present summary results from the analysis of two aeolain dust records spanning 7 ka and 45 ka. These were developed from ombrotrophic mire and lacustrine sediment cores collected from the Australian Alps and southeast Queensland. Both sites are located in the southeast Australian dust transport pathway and provide rare insight to forcings of climate variability and its impacts on eastern Australia through the late Quaternary. Age controls for the cores were established using 14C and 210Pb dating [McGowan et al. 2008, 2010]. The cores were sliced into 2 to 5 mm segments with a sub-sample of each segment combusted at 450°C for 12 hrs to destroy organic material and allow recovery of mineral dust. Geochemical fingerprinting of the < 90 µm fraction of the dust was used to determine provenance and to account for contamination by fluvial and/or colluvial sediments [Marx et al. 2005]. Analysis of the dust records, proxy for hydrometeorology, identified tropical ocean teleconnections, variability of solar irradiance and change in ocean deep water circulation as the principal causes of inter-decadal to centennial scale climate cycles and change. Predictions of future climate must consider these forcings so that in water scarce regions of Australia the effect on the hydroclimate is incorporated into the design of water allocation policy and infrastructure, and the management of environmental systems. Comparison with ice core records from Greenland and Antarctica indicate both synchronicity of global climate variability and the impact of forcings originating from the North Hemisphere. These results highlight the potential for adverse impacts on the climate of Australia by disturbance to North Atlantic Ocean circulation. References Marx, S. K., et al. 2005: Provenance of long travelled dust determined with ultra trace element composition: A pilot study with samples from New Zealand glaciers. Earth Surf. Processes Landforms, 30, 699-716. McGowan, H.A., et al. 2008: An ultra-high resolution record of aeolian sedimentation during the late Quaternary from eastern Australia. Palaeogeogr. Palaeoclimatol. Palaeoecol., 265(3-4), 171-181. McGowan, H. A., et al. 2010: Evidence of solar and tropical ocean forcing of hydroclimate cycles in southeastern Australia for the past 6500 years. Geophys. Res. Lett., 37, L10705, doi:10.1029/2010GL042918.

Landslide Hazard from Coupled Inherent and Dynamic Probabilities

NASA Astrophysics Data System (ADS)

Strauch, R. L.; Istanbulluoglu, E.; Nudurupati, S. S.

2015-12-01

Landslide hazard research has typically been conducted independently from hydroclimate research. We sought to unify these two lines of research to provide regional scale landslide hazard information for risk assessments and resource management decision-making. Our approach couples an empirical inherent landslide probability, based on a frequency ratio analysis, with a numerical dynamic probability, generated by combining subsurface water recharge and surface runoff from the Variable Infiltration Capacity (VIC) macro-scale land surface hydrologic model with a finer resolution probabilistic slope stability model. Landslide hazard mapping is advanced by combining static and dynamic models of stability into a probabilistic measure of geohazard prediction in both space and time. This work will aid resource management decision-making in current and future landscape and climatic conditions. The approach is applied as a case study in North Cascade National Park Complex in northern Washington State.

Persistent multi-scale fluctuations shift European hydroclimate to its millennial boundaries.

PubMed

Markonis, Y; Hanel, M; Máca, P; Kyselý, J; Cook, E R

2018-05-02

In recent years, there has been growing concern about the effect of global warming on water resources, especially at regional and continental scales. The last IPCC report on extremes states that there is medium confidence about an increase on European drought frequency during twentieth century. Here we use the Old World Drought Atlas palaeoclimatic reconstruction to show that when Europe's hydroclimate is examined under a millennial, multi-scale perspective, a significant decrease in dryness can be observed since 1920 over most of central and northern Europe. On the contrary, in the south, drying conditions have prevailed, creating an intense north-to-south dipole. In both cases, hydroclimatic conditions have shifted to, and in some regions exceeded, their millennial boundaries, remaining at these extreme levels for the longest period of the 1000-year-long record.

Warm & wet or warm & dry? - A tree-ring based drought reconstruction from the European lowlands with emphasis on the medieval climate anomaly

NASA Astrophysics Data System (ADS)

Scharnweber, Tobias; Heinrich, Ingo; van der Maaten, Ernst; Heußner, Karl-Uwe; Wilmking, Martin

2016-04-01

Recent advances in reconstructing natural drought variability in Europe, such as the 'Old world drought atlas' (Cook et al., 2015), have sharpened our picture of historical hydroclimatic variability. However, our knowledge lacks high spatial resolution, especially for the northern non-arid regions. For example, it is still under debate if the so called medieval climate anomaly (MCA; ~950-1300 AD), a period of warm temperatures comparable to the contemporary warm phase, was likewise accompanied by increased drought occurrence, or, on the contrary, was rather wet (e.g. Kress et al., 2014). Here, we present a new millennial long drought reconstruction based on a unique dataset of tree rings from historical and modern beech wood from the northeastern European lowlands. Beech has a stable and strong regional summer drought signal over the calibration period of instrumental data (r>0.7 with drought index PDSI over 1900-2010) which, in contrast to other species such as oak, is consistent irrespective of the site/soil conditions the trees grew in. It can be assumed that during medieval times beech wood was available locally and not traded long distances. This strongly reduces the possibility that the new reconstruction mixes different signals of the possibly high spatial variability of precipitation. The extremely high replication of our chronology for the period 1000-1300 AD (peak in town foundations in NE-Germany) with more than 600 series enables a direct comparison with the well replicated recent period 1800-2010. In contrast to the results of Kress et al. (2014) for the Swiss Alps, but in accordance with the 'Old world drought atlas', our first results point at a rather dry and warm MCA in NE-Germany. In addition they support the observation that the hydroclimate of the twentieth century was highly variable compared with the last millennium. References Cook ER, Seager R, Kushnir Y, et al. (2015) Old World megadroughts and pluvials during the Common Era. Science advances 1(10), e1500561. Kress A, Hangartner S, Bugmann H, et al. (2014) Swiss tree rings reveal warm and wet summers during medieval times. Geophysical Research Letters 41(5), 1732-1737.

Hydropower in Southeast United States, -a Hydroclimatological Perspective

NASA Astrophysics Data System (ADS)

Engstrom, J.

2016-12-01

Hydropower is unique among renewable energy sources for the ability to store its fuel (water) in reservoirs. The relationship between discharge, macro-scale drivers, and production is complex since production depends not only on water availability, but also upon decisions made by the institution owning the facility that has to consider many competing interests including economics, drinking water supply, recreational uses, etc. This analysis shows that the hydropower plants in Southeast U.S. (AL, GA, NC, SC, and TN) exhibit considerable year to year variability in production. Although the hydroclimatology of the Southeast U.S. has been analyzed partially, no previous study has linked the region's hydroelectricity production to any reported causes of interannual hydroclimatological variability, as has been completed in other regions. Due to the current short-term hydroelectricity production forecasts, the water resource is not optimized from a hydropower perspective as electricity generating potential is not maximized. The results of this study highlight the amount of untapped hydroelectricity that could be produced if long term hydroclimate and large-scale climate drivers were considered in production forecasts.

Drivers of long-term precipitation and runoff variability in the southeastern USA

NASA Astrophysics Data System (ADS)

Engström, Johanna; Waylen, Peter

2018-02-01

The hydroclimatology of the southeastern USA (AL, GA, NC, SC, and TN) is analyzed from a holistic perspective, including multiple climate drivers. Monthly precipitation modeled by the PRISM group and runoff data (1952-2011) from 18 basins are analyzed using a single-field based principal component's analysis. Results indicate that the Atlantic Multidecadal Oscillation and El Niño-Southern Oscillation are the main atmospheric drivers of hydroclimate variability in the region, sometimes operating at several months' lag. Their influence is the strongest in the fall through spring, which corresponds with the dry season in the southern parts of the study area thereby increasing pressure on already limited water resources. The Arctic Oscillation, North Atlantic Oscillation, and Pacific-North American patterns vary on shorter-term bases, and also show a significant, but temporally more sporadic influence. Insight is also brought to the ongoing discussion, confirming the disassociation of the Arctic and North Atlantic Oscillation. Findings can be used in water resources forecasting, giving an indication of expected water volumes several months ahead.

Latest Pleistocene to Holocene hydroclimates from Lake Elsinore, California

NASA Astrophysics Data System (ADS)

Kirby, Matthew E.; Feakins, Sarah J.; Bonuso, Nicole; Fantozzi, Joanna M.; Hiner, Christine A.

2013-09-01

The hydroclimate of the southwestern United States (US) region changed abruptly during the latest Pleistocene as the continental ice sheets over North America retreated from their most southerly extent. To investigate the nature of this change, we present a new record from Lake Elsinore, located 36 km inland from the Pacific Ocean in Southern California and evaluate it in the context of records across the coastal and interior southwest United States, including northwest Mexico. The sediment core recovered from Lake Elsinore provides a continuous sequence with multi-decadal resolution spanning 19-9 ka BP. Sedimentological and geochemical analyses reveal hydrologic variability. In particular, sand and carbonate components indicate abrupt changes at the Oldest Dryas (OD), Bølling-Allerød (BA), and Younger Dryas (YD) transitions, consistent with the timing in Greenland. Hydrogen isotope analyses of the C28n-alkanoic acids from plant leaf waxes (δDwax) reveal a long term trend toward less negative values across 19-9 ka BP. δDwax values during the OD suggest a North Pacific moisture source for precipitation, consistent with the dipping westerlies hypothesis. We find no isotopic evidence for the North American Monsoon reaching as far west as Lake Elsinore; therefore, we infer that wet/dry changes in the coastal southwest were expressed through winter-season precipitation, consistent with modern climatology. Comparing Lake Elsinore to other southwest records (notably Cave of Bells and Fort Stanton) we find coincident timing of the major transitions (OD to BA, BA to YD) and hydrologic responses during the OD and BA. The hydrologic response, however, varied during the YD consistent with a dipole between the coastal and interior southwest. The coherent pattern of hydrologic responses across the interior southwest US and northwest Mexico during the OD (wet), the BA (drier), and YD (wet) follows changes in the Atlantic Meridional Overturning Circulation, presumably via its combined influence on North Pacific winter storm tracks and the extent/magnitude of the North American Monsoon. In contrast, Lake Elsinore and the coastal southwest experiences a deglacial drying trend punctuated by abrupt change at the OD to BA and BA to YD transitions. This trend tracks rising greenhouse gases through the deglacial, with an apparent southward shift in westerly moisture sources adjusting to the retreating ice sheet.

Tree Ring Chronologies in Mexico and Dendroclimatic and Ecological Applications

NASA Astrophysics Data System (ADS)

Villanueva-Diaz, J.; Cerano-Paredes, J.; Stahle, D. W.; Therrell, M. D.; Luckman, B. H.

2007-05-01

The understanding of historic hydroclimate variability is basic to determine the impact of atmospheric circulatory patterns and to plan for a proper management of limited water resources and ecosystem conservation purposes. The objective of this study was to develop a network of tree-ring chronologies for climate reconstruction and to analyze the influence of the ENSO warm phase in northern Mexico by using the Tropical Rainfall Index. Climatic sensitive tree-ring chronologies were developed in mountain ranges and riparian ecosystems of the Sierras Madre Oriental and Occidental, and central Mexico. A grid of over 30 new Douglas-fir, baldcypress, and pinyon pine chronologies were developed and seasonal winter-spring and summer precipitation reconstructions have been produced for northern and central Mexico. The seasonal winter-spring precipitation reconstructions extended 353 years (1450 - 2002) and 530 years (1472 - 2002) for Chihuahua, 228 years (1765 - 1993) and 504 years (1500 - 2003) for Durango, 602 years (1400 - 2002) for Nuevo Leon, 522 years (1474 - 1995) for Tamaulipas; and 342 years (1659 - 2001) and 410 years (1595 - 2004) for Coahuila. Some of the low frequency events were specific for each reconstruction, but common low frequency events (decadal resolution) were present in most of the reconstructions; specific cases are the droughts of the 1780s, 1810s, 1860s, 1870s, 1950s, and 1990s; and the wet episodes of the 1820s, 1830s, and 1890s.Trends in dry or wet periods were disrupted by above or below normal precipitation as affected by the ENSO phenomena, especially in the winter- spring period when this circulatory pattern produced in times abundant rains in northern Mexico. However, the ENSO influence on winter-spring precipitation has fluctuated through time. Cold fronts and hurricanes impacting the Gulf of Mexico may explain some of the hydrological behavior detected for northeastern Mexico. These results indicate that winter-spring hydroclimate variability in northern Mexico is influenced by a range of atmospheric circulatory patterns, and a greater grid of tree-ring chronologies should be developed to better explain climatic variability in this region. Currently, a couple of summer precipitation reconstructions have been developed and others are in process, but future research will focus on this issue. Summer rainfall represents over 70% of the annual precipitation in Mexico and provides water for agriculture, forest productivity, and other uses. On the other hand, fire frequency and forest dynamic studies are in process for restoration and conservation purposes.

An Early Pleistocene high-resolution paleoclimate reconstruction from the West Turkana (Kenya) HSPDP drill site

NASA Astrophysics Data System (ADS)

Stockhecke, Mona; Beck, Catherine; Brown, Erik T.; Cohen, Andrew; Deocampo, Daniel M.; Feibel, Craig S.; Pelletier, Jon D.; Rabideaux, Nathane M.; Sier, Mark

2016-04-01

The Hominin Sites and Paleolakes Drilling Project (HSPDP), and the related Olorgesailie Drilling Project (ODP), recovered ~2 km of drill core since 2012. At the HSPDP West Turkana Kaitio (WTK) site a 216 m-long core that covers the Early Pleistocene time window (1.3 to 1.87 Ma) during which hominids first expanded out of Africa and marine records document reorganization of tropical climate and the development of the strong Walker circulation. WTK carries particular interest for paleoclimate and paleoenvironmental reconstructions as it is located only 2.5 km from the location of one of the most complete hominin skeletons ever recovered (Nariokotome Boy). XRF core scanning data provide a means of evaluating records of past environmental conditions continuously and at high resolution. However, the record contains complex lithologies reflecting repeated episodes of inundation and desiccation along a dynamic lake margin. Here we present a methodological approach to address the highly variable lithostratigraphy of the East African records to establish comprehensive paleoclimate timeseries. The power spectrum of the presented hydroclimate record peaks at Milankovitch cycles, qualifying HSPDP drill cores from the Turkana Basin to be used as high-resolution Early Pleistocene paleoclimate archive. Comparing these data with marine climate reconstructions sheds light into athmospheric processes and continental climate dynamics.

Advances in global mountain geomorphology

NASA Astrophysics Data System (ADS)

Slaymaker, Olav; Embleton-Hamann, Christine

2018-05-01

Three themes in global mountain geomorphology have been defined and reinforced over the past decade: (a) new ways of measuring, sensing, and analyzing mountain morphology; (b) a new emphasis on disconnectivity in mountain geomorphology; and (c) the emergence of concerns about the increasing influence of anthropogenic disturbance of the mountain geomorphic environment, especially in intertropical mountains where population densities are higher than in any other mountain region. Anthropogenically induced hydroclimate change increases geomorphic hazards and risks but also provides new opportunities for mountain landscape enhancement. Each theme is considered with respect to the distinctiveness of mountain geomorphology and in relation to important advances in research over the past decade. The traditional reliance on the high energy condition to define mountain geomorphology seems less important than the presence of unique mountain landforms and landscapes and the distinctive ways in which human activity and anthropogenically induced hydroclimate change are transforming mountain landscapes.

Eastern South African hydroclimate over the past 270,000 years

NASA Astrophysics Data System (ADS)

Simon, Margit H.; Ziegler, Martin; Bosmans, Joyce; Barker, Stephen; Reason, Chris J. C.; Hall, Ian R.

2015-12-01

Processes that control the hydrological balance in eastern South Africa on orbital to millennial timescales remain poorly understood because proxy records documenting its variability at high resolution are scarce. In this work, we present a detailed 270,000 year-long record of terrestrial climate variability in the KwaZulu-Natal province based on elemental ratios of Fe/K from the southwest Indian Ocean, derived from X-ray fluorescence core scanning. Eastern South African climate variability on these time scales reflects both the long-term effect of regional insolation changes driven by orbital precession and the effects associated with high-latitude abrupt climate forcing over the past two glacial-interglacial cycles, including millennial-scale events not previously identified. Rapid changes towards more humid conditions in eastern South Africa as the Northern Hemisphere entered phases of extreme cooling were potentially driven by a combination of warming in the Agulhas Current and shifts of the subtropical anticyclones. These climate oscillations appear coherent with other Southern Hemisphere records but are anti-phased with respect to the East Asian Monsoon. Numerical modelling results reveal that higher precipitation in the KwaZulu-Natal province during precession maxima is driven by a combination of increased local evaporation and elevated moisture transport into eastern South Africa from the coast of Mozambique.

Eastern South African hydroclimate over the past 270,000 years.

PubMed

Simon, Margit H; Ziegler, Martin; Bosmans, Joyce; Barker, Stephen; Reason, Chris J C; Hall, Ian R

2015-12-21

Processes that control the hydrological balance in eastern South Africa on orbital to millennial timescales remain poorly understood because proxy records documenting its variability at high resolution are scarce. In this work, we present a detailed 270,000 year-long record of terrestrial climate variability in the KwaZulu-Natal province based on elemental ratios of Fe/K from the southwest Indian Ocean, derived from X-ray fluorescence core scanning. Eastern South African climate variability on these time scales reflects both the long-term effect of regional insolation changes driven by orbital precession and the effects associated with high-latitude abrupt climate forcing over the past two glacial-interglacial cycles, including millennial-scale events not previously identified. Rapid changes towards more humid conditions in eastern South Africa as the Northern Hemisphere entered phases of extreme cooling were potentially driven by a combination of warming in the Agulhas Current and shifts of the subtropical anticyclones. These climate oscillations appear coherent with other Southern Hemisphere records but are anti-phased with respect to the East Asian Monsoon. Numerical modelling results reveal that higher precipitation in the KwaZulu-Natal province during precession maxima is driven by a combination of increased local evaporation and elevated moisture transport into eastern South Africa from the coast of Mozambique.

Eastern South African hydroclimate over the past 270,000 years

PubMed Central

Simon, Margit H.; Ziegler, Martin; Bosmans, Joyce; Barker, Stephen; Reason, Chris J.C.; Hall, Ian R.

2015-01-01

Processes that control the hydrological balance in eastern South Africa on orbital to millennial timescales remain poorly understood because proxy records documenting its variability at high resolution are scarce. In this work, we present a detailed 270,000 year-long record of terrestrial climate variability in the KwaZulu-Natal province based on elemental ratios of Fe/K from the southwest Indian Ocean, derived from X-ray fluorescence core scanning. Eastern South African climate variability on these time scales reflects both the long-term effect of regional insolation changes driven by orbital precession and the effects associated with high-latitude abrupt climate forcing over the past two glacial-interglacial cycles, including millennial-scale events not previously identified. Rapid changes towards more humid conditions in eastern South Africa as the Northern Hemisphere entered phases of extreme cooling were potentially driven by a combination of warming in the Agulhas Current and shifts of the subtropical anticyclones. These climate oscillations appear coherent with other Southern Hemisphere records but are anti-phased with respect to the East Asian Monsoon. Numerical modelling results reveal that higher precipitation in the KwaZulu-Natal province during precession maxima is driven by a combination of increased local evaporation and elevated moisture transport into eastern South Africa from the coast of Mozambique. PMID:26686943

Comparable hydrogen isotopic fractionation of plant leaf wax n-alkanoic acids in arid and humid subtropical ecosystems

NASA Astrophysics Data System (ADS)

Gao, Li; Zheng, Mei; Fraser, Matthew; Huang, Yongsong

2014-02-01

Leaf wax hydrogen isotope proxies have been widely used to reconstruct past hydrological changes. However, published reconstructions have given little consideration for the potentially variable hydrogen isotopic fractionation relative to precipitation (ɛwax-p) under different climate and environmental settings. Chief among various potential factors controlling fractionation is relative humidity, which is known to strongly affect oxygen isotopic ratios of plant cellulose, but its effect on hydrogen isotopic fractionation of leaf waxes is still ambiguous. Analyses of lake surface sediments and individual modern plants have provided valuable information on the variability of ɛwax-p, but both approaches have significant limitations. Here, we present an alternative method to obtain the integrated, time-resolved ecosystem-level ɛwax-p values, by analyzing modern aerosol samples collected weekly from arid (Arizona lowlands) and humid subtropical (Atlanta, Georgia) environments during the main growth season. Because aerosol samples mainly reflect regional leaf wax resources, the extreme contrast in the hydroclimate and associated vegetation assemblages between our study sites allows us to rigorously assess the impact of relative humidity and associated vegetation assemblages on leaf wax hydrogen isotopic fractionation. We show there is only minor difference (mostly <10‰) in the mean ɛwax-p values in the two end-member environments. One possible explanation is that the positive isotopic effects of low relative humidity are offset by progressive replacement of trees with grasses that have a more negative apparent fractionation. Our results represent an important step toward quantitative interpretation of leaf wax hydrogen isotopic records.

Reconstructed storm tracks reveal three centuries of changing moisture delivery to North America

PubMed Central

Wise, Erika K.; Dannenberg, Matthew P.

2017-01-01

Moisture delivery to western North America is closely linked to variability in the westerly storm tracks of midlatitude cyclones, which are, in turn, modified by larger-scale features such as the El Niño–Southern Oscillation system. Instrumental and modeling data suggest that extratropical storm tracks may be intensifying and shifting poleward due to anthropogenic climate change, but it is difficult to separate recent trends from natural variability because of the large amount of decadal and longer variation in storm tracks and their limited instrumental record. We reconstruct cool-season, midlatitude Pacific storm-track position and intensity from 1693 to 1995 CE using existing tree-ring chronologies along with a network of newly developed chronologies from the U.S. Pacific Northwest, where small variations in storm-track position can have a major influence on hydroclimate patterns. Our results show high interannual-to-multidecadal variability in storm-track position and intensity over the past 303 years, with spectral signatures characteristic of tropical and northern Pacific influences. Comparison with reconstructions of precipitation and tropical sea surface temperature confirms the relationship between shifting drought patterns in the Pacific Northwest and storm-track variability through time and demonstrates the long-term influence of El Niño. These results allow us to place recent storm-track changes in the context of decadal and multidecadal fluctuations across the long-term record, showing that recent changes in storm-track intensity likely represent a warming-related increase amplified by natural decadal variability. PMID:28630900

Reconstructed storm tracks reveal three centuries of changing moisture delivery to North America.

PubMed

Wise, Erika K; Dannenberg, Matthew P

2017-06-01

Moisture delivery to western North America is closely linked to variability in the westerly storm tracks of midlatitude cyclones, which are, in turn, modified by larger-scale features such as the El Niño-Southern Oscillation system. Instrumental and modeling data suggest that extratropical storm tracks may be intensifying and shifting poleward due to anthropogenic climate change, but it is difficult to separate recent trends from natural variability because of the large amount of decadal and longer variation in storm tracks and their limited instrumental record. We reconstruct cool-season, midlatitude Pacific storm-track position and intensity from 1693 to 1995 CE using existing tree-ring chronologies along with a network of newly developed chronologies from the U.S. Pacific Northwest, where small variations in storm-track position can have a major influence on hydroclimate patterns. Our results show high interannual-to-multidecadal variability in storm-track position and intensity over the past 303 years, with spectral signatures characteristic of tropical and northern Pacific influences. Comparison with reconstructions of precipitation and tropical sea surface temperature confirms the relationship between shifting drought patterns in the Pacific Northwest and storm-track variability through time and demonstrates the long-term influence of El Niño. These results allow us to place recent storm-track changes in the context of decadal and multidecadal fluctuations across the long-term record, showing that recent changes in storm-track intensity likely represent a warming-related increase amplified by natural decadal variability.

Understanding the Asian summer monsoon response to greenhouse warming: the relative roles of direct radiative forcing and sea surface temperature change

NASA Astrophysics Data System (ADS)

Li, Xiaoqiong; Ting, Mingfang

2017-10-01

Future hydroclimate projections from state-of-the-art climate models show large uncertainty and model spread, particularly in the tropics and over the monsoon regions. The precipitation and circulation responses to rising greenhouse gases involve a fast component associated with direct radiative forcing and a slow component associated with sea surface temperature (SST) warming; the relative importance of the two may contribute to model discrepancies. In this study, regional hydroclimate responses to greenhouse warming are assessed using output from coupled general circulation models in the Coupled Model Intercomparison Project-Phase 5 (CMIP5) and idealized atmospheric general circulation model experiments from the Atmosphere Model Intercomparison Project. The thermodynamic and dynamic mechanisms causing the rainfall changes are examined using moisture budget analysis. Results show that direct radiative forcing and SST change exert significantly different responses both over land and ocean. For most part of the Asian monsoon region, the summertime rainfall changes are dominated by the direct CO2 radiative effect through enhanced monsoon circulation. The response to SST warming shows a larger model spread compared to direct radiative forcing, possibly due to the cancellation between the thermodynamical and dynamical components. While the thermodynamical response of the Asian monsoon is robust across the models, there is a lack of consensus for the dynamical response among the models and weak multi-model mean responses in the CMIP5 ensemble, which may be related to the multiple physical processes evolving on different time scales.

Disentangling Seasonality and Mean Annual Precipitation in the Indo-Pacific Warm Pool: Insights from Coupled Plant Wax C and H Isotope Measurements

NASA Astrophysics Data System (ADS)

Galy, V.; Oppo, D.; Dubois, N.; Arbuszewski, J. A.; Mohtadi, M.; Schefuss, E.; Rosenthal, Y.; Linsley, B. K.

2016-12-01

There is ample evidence suggesting that rainfall distribution across the Indo-Pacific Warm Pool (IPWP) - a key component of the global climate system - has substantially varied over the last deglaciation. Yet, the precise nature of these hydroclimate changes remains to be elucidated. In particular, the relative importance of variations in precipitation seasonality versus annual precipitation amount is essentially unknown. Here we use a set of surface sediments from the IPWP covering a wide range of modern hydroclimate conditions to evaluate how plant wax stable isotope composition records rainfall distribution in the area. We focus on long chain fatty acids, which are exclusively produced by vascular plants living on nearby land and delivered to the ocean by rivers. We relate the C (δ13C) and H (δD) isotope composition of long chain fatty acids preserved in surface sediments to modern precipitation distribution and stable isotope composition in their respective source area. We show that: 1) δ13C values reflect vegetation distribution (in particular the relative abundance of C3 and C4 plants) and are primarily recording precipitation seasonality (Dubois et al., 2014) and, 2) once corrected for plant fractionation effects, δD values reflect the amount-weighted average stable isotope composition of precipitation and are primarily recording annual precipitation amounts. We propose that combining the C and H isotope composition of long chain fatty acids thus allows independent reconstructions of precipitation seasonality and annual amounts in the IPWP. The practical implications for reconstructing past hydroclimate in the IPWP will be discussed.

Land surface water cycles observed with satellite sensors

NASA Technical Reports Server (NTRS)

Nghiem, Son V.; Njoku, E. G.; Brakenridge, G. R.; Kim, Y.

2005-01-01

Acceleration of the global water cycle may lead to increased global precipitation, faster evaporation and a consequent exacerbation of hydrologic extreme. In the U.S. national assessment of the potential consequences of climate variability and change, two GCMs (CGCM1 and HadCM2) show a large increase in precipitation in the future over the southwestern U.S. particularly during winter (Felzer and Heard, 1999). Increased precipitation potentially has important impacts on agricultural and water use in the southeast U.S. (Hatch et al., 1999) and in the central Great Plains (Nielsen, 1997). A hurricane model predicts a 40% precipitation increase for severe hurricanes affecting southeastern Florida, which provokes substantially greater flooding that could negate most of the benefits of present water-management practices in this basin (Gutowski et al., 1994). Thus, it is important to observe the hydroclimate on a continuous longterm basis to address the question of increased precipitation in the enhanced water cycle.

Relative Contributions of Mean-State Shifts and ENSO-Driven Variability to Precipitation Changes in a Warming Climate

NASA Technical Reports Server (NTRS)

Bonfils, Celine J. W.; Santer, Benjamin D.; Phillips, Thomas J.; Marvel, Kate; Leung, L. Ruby; Doutriaux, Charles; Capotondi, Antonietta

2015-01-01

El Niño-Southern Oscillation (ENSO) is an important driver of regional hydroclimate variability through far-reaching teleconnections. This study uses simulations performed with coupled general circulation models (CGCMs) to investigate how regional precipitation in the twenty-first century may be affected by changes in both ENSO-driven precipitation variability and slowly evolving mean rainfall. First, a dominant, time-invariant pattern of canonical ENSO variability (cENSO) is identified in observed SST data. Next, the fidelity with which 33 state-of-the-art CGCMs represent the spatial structure and temporal variability of this pattern (as well as its associated precipitation responses) is evaluated in simulations of twentieth-century climate change. Possible changes in both the temporal variability of this pattern and its associated precipitation teleconnections are investigated in twenty-first-century climate projections. Models with better representation of the observed structure of the cENSO pattern produce winter rainfall teleconnection patterns that are in better accord with twentieth-century observations and more stationary during the twenty-first century. Finally, the model-predicted twenty-first-century rainfall response to cENSO is decomposed into the sum of three terms: 1) the twenty-first-century change in the mean state of precipitation, 2) the historical precipitation response to the cENSO pattern, and 3) a future enhancement in the rainfall response to cENSO, which amplifies rainfall extremes. By examining the three terms jointly, this conceptual framework allows the identification of regions likely to experience future rainfall anomalies that are without precedent in the current climate.

Relative Contributions of Mean-State Shifts and ENSO-Driven Variability to Precipitation Changes in a Warming Climate

NASA Technical Reports Server (NTRS)

Bonfils, Celine J. W.; Santer, Benjamin D.; Phillips, Thomas J.; Marvel, Kate; Leung, L. Ruby; Doutriaux, Charles; Capotondi, Antonietta

2015-01-01

The El Nino-Southern Oscillation (ENSO) is an important driver of regional hydroclimate variability through far-reaching teleconnections. This study uses simulations performed with Coupled General Circulation Models (CGCMs) to investigate how regional precipitation in the 21st century may be affected by changes in both ENSO-driven precipitation variability and slowly-evolving mean rainfall. First, a dominant, time-invariant pattern of canonical ENSO variability (cENSO) is identified in observed SST data. Next, the fidelity with which 33 state-of-the-art CGCMs represent the spatial structure and temporal variability of this pattern (as well as its associated precipitation responses) is evaluated in simulations of 20th century climate change. Possible changes in both the temporal variability of this pattern and its associated precipitation teleconnections are investigated in 21st century climate projections. Models with better representation of the observed structure of the cENSO pattern produce winter rainfall teleconnection patterns that are in better accord with 20th century observations and more stationary during the 21st century. Finally, the model-predicted 21st century rainfall response to cENSO is decomposed into the sum of three terms: 1) the 21st century change in the mean state of precipitation; 2) the historical precipitation response to the cENSO pattern; and 3) a future enhancement in the rainfall response to cENSO, which amplifies rainfall extremes. By examining the three terms jointly, this conceptual framework allows the identification of regions likely to experience future rainfall anomalies that are without precedent in the current climate.

Abrupt Atmospheric Methane Increases Associated With Hudson Strait Heinrich Events

NASA Astrophysics Data System (ADS)

Rhodes, R.; Brook, E.; Chiang, J. C. H.; Blunier, T.; Maselli, O. J.; McConnell, J. R.; Romanini, D.; Severinghaus, J. P.

2015-12-01

The drivers of abrupt climate change during the Last Glacial Period are not well understood. While Dansgaard-Oeschger (DO) cycles are thought to be linked to variations in the strength of the Atlantic Meridional Ocean Circulation (AMOC), it is not clear how or if Heinrich Events—extensive influxes of icebergs into the North Atlantic Ocean that impacted global climate and biogeochemistry—are related. An enduring problem is the difficultly in dating iceberg rafted debris deposits that typically lack foraminifera. Here we present an ultra-high resolution record of methane from the West Antarctic Ice Sheet Divide ice core at unprecedented, continuous temporal resolution from 67.2-9.8 ka BP, which we propose constrains the timing of Heinrich events. Our methane record essentially mirrors Greenland ice core stable isotope variability across D-O events, except during Heinrich stadials 1, 2, 4 and 5. Partway through these stadials only, methane increases abruptly and rapidly, as at the onset of a D-O event but Greenland temperature exhibits no equivalent response. Speleothem records exhibit signatures of drought in the Northern extra-tropics and intensified monsoonal activity over South America at these times. We use a simple heuristic model to propose that cold air temperatures and extensive sea ice in the North, resulting from Heinrich events, caused extreme reorganization of tropical hydroclimate. This involved curtailment of the seasonal northerly migration of tropical rain belts, leading to intensification of rainfall over Southern Hemisphere tropical wetlands, thus allowing production of excess methane relative to a 'normal' Greenland stadial. We note that this mechanism can operate if AMOC is already in a slowed state when a Heinrich event occurs, as paleo-evidence suggests it was. Heinrich events and associated sea ice cover would therefore act to prolong the duration of this AMOC state. Our findings place the big four Heinrich events of Hudson Strait origin firmly within ice core chronologies and suggest that their impacts on AMOC and tropical hydroclimate persisted for 740-1520 yr.

Placing the Common Era in a Holocene context: Millennial to centennial patterns and trends in the hydroclimate of North America over the past 2000 years

USGS Publications Warehouse

Shuman, Bryan; Routson, Cody C.; McKay, Nicholas P.; Fritz, Sherilyn; Kaufman, Darrell S.; Kirby, Matthew; Nolan, Connor; Pederson, Gregory T.; St. Jacques, Jeannine-Marie

2018-01-01

A synthesis of 93 hydrologic records from across North and Central America, and adjacent tropical and Arctic islands, reveals centennial to millennial trends in the regional hydroclimates of the Common Era (CE; past 2000 years). The hydrological records derive from materials stored in lakes, bogs, caves, and ice from extant glaciers, which have the continuity through time to preserve low-frequency ( > 100 year) climate signals that may extend deeper into the Holocene. The most common pattern, represented in 46 (49 %) of the records, indicates that the centuries before 1000 CE were drier than the centuries since that time. Principal component analysis indicates that millennial-scale trends represent the dominant pattern of variance in the southwestern US, northeastern US, mid-continent, Pacific Northwest, Arctic, and tropics, although not all records within a region show the same direction of change. The Pacific Northwest and the southernmost tier of the tropical sites tended to dry toward present, as many other areas became wetter than before. In 22 records (24 %), the Medieval Climate Anomaly period (800–1300 CE) was drier than the Little Ice Age (1400–1900 CE), but in many cases the difference was part of the longer millennial-scale trend, and, in 25 records (27 %), the Medieval Climate Anomaly period represented a pluvial (wet) phase. Where quantitative records permitted a comparison, we found that centennial-scale fluctuations over the Common Era represented changes of 3–7 % in the modern interannual range of variability in precipitation, but the accumulation of these long-term trends over the entirety of the Holocene caused recent centuries to be significantly wetter, on average, than most of the past 11 000 years.

Past and future impact of North Atlantic teleconnection patterns on the hydroclimate of the Caspian catchment area in CESM1.2.2 and observations

NASA Astrophysics Data System (ADS)

Nandini, Sri

2017-04-01

The Caspian Sea level has undergone dramatic variations of more than 3 m during the past century with important implications for the life of coastal people, economy and the ecosystem. The origin of these variations as well as future changes in the Caspian water budget are still a matter of debate. In this study, we examine the influence of the major seasonal North Atlantic teleconnection patterns, the North Atlantic Oscillation (NAO), the East Atlantic pattern (EA), the Scandinavian pattern (SCA), and the North Sea Caspian Pattern (NCP), on Caspian hydroclimate variability from 1850-2000 CE. Numerical experiments at different atmospheric grid resolutions (2° and 1°) are carried out with the coupled Community Earth System Model (CESM1.2.2). We test model skills under different resolutions through validation against observational data by various statistical methods (Empirical Orthogonal Functions, Taylor diagrams, linear regressions and Spearman rank correlation). Results reveal the strongest simulated signal in winter (DJF) with high explained variances for 1° CESM1.2.2 NAO (39%) and EA (15.7%), similar to observational data. The model is unable to reproduce the SCA pattern in the third EOF, which is found in the observations. The modelled NAO has a strong influence on winter temperature and rainfall over the Caspian catchment area. A strong winter NCP induces above-average 2-meter temperatures over north Caspian region and lower-than-normal precipitation over the eastern Caspian sea. Our study suggests that the 1° version of CESM1.2.2 (with CAM5 atmosphere physics) shows adequate performance with respect to teleconnection maps during the historical period. Lastly, 1° model climate projections (2005-2100 CE) are performed with different Representative Concentration Pathways (RCP 4.5 and RCP 8.5) to examine potential changes in the teleconnection patterns and their influence on the Caspian region.

The Challenge of Simulating the Regional Climate over Florida

NASA Astrophysics Data System (ADS)

Misra, V.; Mishra, A. K.

2015-12-01

In this study we show that the unique geography of the peninsular Florida with close proximity to strong mesoscale surface ocean currents among other factors warrants the use of relatively high resolution climate models to project Florida's hydroclimate. In the absence of such high resolution climate models we highlight the deficiencies of two relatively coarse spatial resolution CMIP5 models with respect to the warm western boundary current of the Gulf Stream. As a consequence it affects the coastal SST and the land-ocean contrast, affecting the rainy summer seasonal precipitation accumulation over peninsular Florida. We also show this through two sensitivity studies conducted with a regional coupled ocean atmosphere model with different bathymetries that dislocate and modulate the strength of the Gulf Stream that locally affects the SST in the two simulations. These studies show that a stronger and more easterly displaced Gulf Stream produces warmer coastal SST's along the Atlantic coast of Florida that enhances the precipitation over peninsular Florida relative to the other regional climate model simulation. However the regional model simulations indicate that variability of wet season rainfall variability in peninsular Florida becomes less dependent on the land-ocean contrast with a stronger Gulf Stream current.

Tropical Pacific forcing on decadal-to-centennial NAO-dominated precipitation variability in northern Mediterranean over the past 6500 years

NASA Astrophysics Data System (ADS)

Hu, H. M.; Shen, C. C.; Michel, V.; Jiang, X.; Mii, H. S.; Wang, Y.; Valensi, P.

2017-12-01

We present a multi-annual-resolved absolute-dated stalagmite-inferred precipitation record, with age precision as good as ±2 years, from northern Italy, to reflect North Atlantic Oscillation (NAO) dynamics since 6.5 ka (thousand years ago, before 1950 C.E.). Our record features millennial precipitation fluctuations punctuated by several centennial-scale drought periods centered at 5.6, 6.2, 4.2, 3.0 and 2.3 ka. The phase relationship with previous NAO-sensitive records suggests a multi-millennial southward migration of the northern Westerlies and enhanced NAO variability from the middle- to late-Holocene. We also found the multi-decadal to centennial rainfall amount could dramatically vary within few decades, possibly affecting ancient Mediterranean civilizations. Concurrence between northern Mediterranean precipitation and western tropical Pacific sea surface temperature records suggests the remote forcing on this NAO-dominated rainfall. We argue that the irregular NAO change nowadays could be related to high frequency of El Niño-Southern Oscillation events and might cause an inevitable abrupt hydroclimate change and irreparable impacts on the regional human society in the near future.

Quantifying Risks in the Global Water-Food-Climate Nexus in the Coming Decades: An Integrated Modeling Approach

NASA Astrophysics Data System (ADS)

Schlosser, C. A.; Strzepek, K.; Arndt, C.; Gueneau, A.; Cai, Y.; Gao, X.; Robinson, S.; Sokolov, A. P.; Thurlow, J.

2011-12-01

The growing need for risk-based assessments of impacts and adaptation to regional climate change calls for the quantification of the likelihood of regional outcomes and the representation of their uncertainty. Moreover, our global water resources include energy, agricultural and environmental systems, which are linked together as well as to climate. With the prospect of potential climate change and associated shifts in hydrologic variation and extremes, the MIT Integrated Global Systems Model (IGSM) framework, in collaboration with UNU-WIDER, has enhanced its capabilities to model impacts (or effects) on the managed water-resource systems. We first present a hybrid approach that extends the MIT Integrated Global System Model (IGSM) framework to provide probabilistic projections of regional climate changes. This procedure constructs meta-ensembles of the regional hydro-climate, combining projections from the MIT IGSM that represent global-scale uncertainties with regionally resolved patterns from archived climate-model projections. From these, a river routing and water-resource management module allocates water among irrigation, hydropower, urban/industrial, and in-stream uses and investigate how society might adapt water resources due to shifts in hydro-climate variations and extremes. These results are then incorporated into economic models allowing us to consider the implications of climate for growth, land use, and development prospects. In this model-based investigation, we consider how changes in the regional hydro-climate over major river basins in southern Africa, Vietnam, as well as the United States impact agricultural productivity and water-management systems, and whether adaptive strategies can cope with the more severe climate-related threats to growth and development. All this is cast under a probabilistic description of regional climate changes encompassed by the IGSM framework.

­Orbital-scale variations in Indo-Pacific hydroclimate during the mid- to late Pleistocene from Lake Towuti, Indonesia

NASA Astrophysics Data System (ADS)

Russell, J. M.; Vogel, H.; Bijaksana, S.; Melles, M.

2016-12-01

The Indo-Pacific region plays a critical role in the Earth's climate system. Changes in local insolation, greenhouse gas concentrations, ice volume, and local sea level are all hypothesized to exert a dominant control on Indo-Pacific hydroclimate, yet existing records from the region are generally short and exhibit fundamental differences in orbital-scale patterns that limit our understanding of the regional climate responses to orbital-scale forcings. In 2015 we conducted an ICDP drilling program on Lake Towuti, located near the equator in central Indonesia, one of the only terrestrial sedimentary archives in the region that continuously spans multiple glacial-interglacial cycles. We recovered over 1,000 meters of core including cores though the entire sediment sequence to bedrock. Previously published organic geochemical reconstructions of vegetation from relatively short, 60 kyr long piston from Lake Towuti exhibit strong drying during the Last Glacial Maximum, indicating that central Indonesian hydroclimate is sensitive to forcing from high-latitude ice-sheets. New, inorganic geochemical and mineralogical reconstructions of lake level also indicate a strong half-precessional climate signal during the last 60 kyr in which lake level highstands occur during austral and boreal summer insolation maxima, suggesting that equatorial rainfall varies in response to remote (likely subtropical) insolation forcing of the Asian monsoons. However, the short length of these records limits our understanding of the regional hydroclimatic response to the full range of global climate boundary conditions experienced during the late Quaternary. This presentation will discuss results from the last 60 kyr and present new geochemical reconstructions from the upper 100 m of core from Lake Towuti, dated using magnetic paleointensity, tephrachronology, and optically-stimulated luminescence to span the last 500 kyr BP.

Forecasting Western U.S. Snowpack

NASA Astrophysics Data System (ADS)

Kapnick, S. B.; Yang, X.; Vecchi, G. A.; Delworth, T. L.; Gudgel, R.; Malyshev, S.; Milly, C.; Shevliakova, E.; Underwood, S.; Margulis, S. A.

2017-12-01

Cold season mountain snow accumulation in the western United States plays a critical role in regional hydroclimate and water supply. While climate projections provide estimates of future snowpack loss by the end of the century and weather forecasts provide predictions of weather conditions and hazards out to two weeks, less progress has been made for snow predictions at seasonal timescales (months to 2 years), particularly beyond 6 months. Utilizing observations, climate indices, and a suite of global climate models, we demonstrate our dynamical system's feasibility of seasonal snowpack predictions and quantify the limits of predictive skill more than 2 seasons in advance for snowpack—snow that accumulates on the ground in the mountains. Our ability to predict snowpack is reliant on both temperature and precipitation prediction skill modulating both the amount of frozen precipitation that falls and how much snow accumulates and stays on the ground throughout the season. We will quantify prediction skill and outline areas necessary for the future advancement of seasonal hydroclimate prediction.

Predicting regime shifts in flow of the Colorado River

USGS Publications Warehouse

Gangopadhyay, Subhrendu; McCabe, Gregory J.

2010-01-01

The effects of continued global warming on water resources are a concern for water managers and stake holders. In the western United States, where the combined climatic demand and consumptive use of water is equal to or greater than the natural supply of water for some locations, there is growing concern regarding the sustainability of future water supplies. In addition to the adverse effects of warming on water supply, another issue for water managers is accounting for, and managing, the effects of natural climatic variability, particularly persistently dry and wet periods. Analyses of paleo-reconstructions of Upper Colorado River basin (UCRB) flow demonstrate that severe sustained droughts, and persistent pluvial periods, are a recurring characteristic of hydroclimate in the Colorado River basin. Shifts between persistently dry and wet regimes (e.g., decadal to multi-decadal variability (D2M)) have important implications for water supply and water management. In this study paleo-reconstructions of UCRB flow are used to compute the risks of shifts between persistently wet and dry regimes given the length of time in a specific regime. Results indicate that low frequency variability of hydro-climatic conditions and the statistics that describe this low frequency variability can be useful to water managers by providing information about the risk of shifting from one hydrologic regime to another. To manage water resources in the future water managers will have to understand the joint hydrologic effects of natural climate variability and global warming. These joint effects may produce future hydrologic conditions that are unprecedented in both the instrumental and paleoclimatic records.

Influence of internal variability on population exposure to hydroclimatic changes

NASA Astrophysics Data System (ADS)

Mankin, Justin S.; Viviroli, Daniel; Mekonnen, Mesfin M.; Hoekstra, Arjen Y.; Horton, Radley M.; E Smerdon, Jason; Diffenbaugh, Noah S.

2017-04-01

Future freshwater supply, human water demand, and people’s exposure to water stress are subject to multiple sources of uncertainty, including unknown future pathways of fossil fuel and water consumption, and ‘irreducible’ uncertainty arising from internal climate system variability. Such internal variability can conceal forced hydroclimatic changes on multi-decadal timescales and near-continental spatial-scales. Using three projections of population growth, a large ensemble from a single Earth system model, and assuming stationary per capita water consumption, we quantify the likelihoods of future population exposure to increased hydroclimatic deficits, which we define as the average duration and magnitude by which evapotranspiration exceeds precipitation in a basin. We calculate that by 2060, ∽31%-35% of the global population will be exposed to >50% probability of hydroclimatic deficit increases that exceed existing hydrological storage, with up to 9% of people exposed to >90% probability. However, internal variability, which is an irreducible uncertainty in climate model predictions that is under-sampled in water resource projections, creates substantial uncertainty in predicted exposure: ∽86%-91% of people will reside where irreducible uncertainty spans the potential for both increases and decreases in sub-annual water deficits. In one population scenario, changes in exposure to large hydroclimate deficits vary from -3% to +6% of global population, a range arising entirely from internal variability. The uncertainty in risk arising from irreducible uncertainty in the precise pattern of hydroclimatic change, which is typically conflated with other uncertainties in projections, is critical for climate risk management that seeks to optimize adaptations that are robust to the full set of potential real-world outcomes.

Dynamic downscaling over western Himalayas: Impact of cloud microphysics schemes

NASA Astrophysics Data System (ADS)

Tiwari, Sarita; Kar, Sarat C.; Bhatla, R.

2018-03-01

Due to lack of observation data in the region of inhomogeneous terrain of the Himalayas, detailed climate of Himalayas is still unknown. Global reanalysis data are too coarse to represent the hydroclimate over the region with sharp orography gradient in the western Himalayas. In the present study, dynamic downscaling of the European Centre for Medium-Range Weather Forecast (ECMWF) Reanalysis-Interim (ERA-I) dataset over the western Himalayas using high-resolution Weather Research and Forecast (WRF) model has been carried out. Sensitivity studies have also been carried out using convection and microphysics parameterization schemes. The WRF model simulations have been compared against ERA-I and available station observations. Analysis of the results suggests that the WRF model has simulated the hydroclimate of the region well. It is found that in the simulations that the impact of convection scheme is more during summer months than in winter. Examination of simulated results using various microphysics schemes reveal that the WRF single-moment class-6 (WSM6) scheme simulates more precipitation on the upwind region of the high mountain than that in the Morrison and Thompson schemes during the winter period. Vertical distribution of various hydrometeors shows that there are large differences in mixing ratios of ice, snow and graupel in the simulations with different microphysics schemes. The ice mixing ratio in Morrison scheme is more than WSM6 above 400 hPa. The Thompson scheme favors formation of more snow than WSM6 or Morrison schemes while the Morrison scheme has more graupel formation than other schemes.

Relating Climate Change Risks to Water Supply Planning Assumptions: Recent Applications by the U.S. Bureau of Reclamation (Invited)

NASA Astrophysics Data System (ADS)

Brekke, L. D.

2009-12-01

Presentation highlights recent methods carried by Reclamation to incorporate climate change and variability information into water supply assumptions for longer-term planning. Presentation also highlights limitations of these methods, and possible method adjustments that might be made to address these limitations. Reclamation was established more than one hundred years ago with a mission centered on the construction of irrigation and hydropower projects in the Western United States. Reclamation’s mission has evolved since its creation to include other activities, including municipal and industrial water supply projects, ecosystem restoration, and the protection and management of water supplies. Reclamation continues to explore ways to better address mission objectives, often considering proposals to develop new infrastructure and/or modify long-term criteria for operations. Such studies typically feature operations analysis to disclose benefits and effects of a given proposal, which are sensitive to assumptions made about future water supplies, water demands, and operating constraints. Development of these assumptions requires consideration to more fundamental future drivers such as land use, demographics, and climate. On the matter of establishing planning assumptions for water supplies under climate change, Reclamation has applied several methods. This presentation highlights two activities where the first focuses on potential changes in hydroclimate frequencies and the second focuses on potential changes in hydroclimate period-statistics. The first activity took place in the Colorado River Basin where there was interest in the interarrival possibilities of drought and surplus events of varying severity relevant to proposals on new criteria for handling lower basin shortages. The second activity occurred in California’s Central Valley where stakeholders were interested in how projected climate change possibilities translated into changes in hydrologic and water supply statistics relevant to a long-term federal Endangered Species Act consultation. Projected climate change possibilities were characterized by surveying a large ensemble of climate projections for change in period climate-statistics and then selecting a small set of projections featuring a bracketing set of period-changes relative to the those from the complete ensemble. Although both methods served the needs of their respective planning activities, each has limited applicability for other planning activities. First, each method addresses only one climate change aspect and not the other. Some planning activities may need to consider potential changes in both period-statistics and frequencies. Second, neither method addresses CMIP3 projected changes in climate variability. The first method bases frequency possibilities on historical information while the second method only surveys CMIP3 projections for change in period-mean and then superimposes those changes on historical variability. Third, artifacts of CMIP3 design lead to interpretation challenges when implementing the second method (e.g., inconsistent projection initialization, model-dependent expressions of multi-decadal variability). Presentation summarizes these issues and also potential method adjustments to address them when defining planning assumptions for water supplies.

Assessing Changes in Precipitation and Impacts on Groundwater in Southeastern Brazil using Regional Hydroclimate Reconstruction

NASA Astrophysics Data System (ADS)

Nunes, A.; Fernandes, M.; Silva, G. C., Jr.

2017-12-01

Aquifers can be key players in regional water resources. Precipitation infiltration is the most relevant process in recharging the aquifers. In that regard, understanding precipitation changes and impacts on the hydrological cycle helps in the assessment of groundwater availability from the aquifers. Regional modeling systems can provide precipitation, near-surface air temperature, together with soil moisture at different ground levels from coupled land-surface schemes. More accurate those variables are better the evaluation of the precipitation impact on the groundwater. Downscaling of global reanalysis very often employs regional modeling systems, in order to give more detailed information for impact assessment studies at regional scales. In particular, the regional modeling system, Satellite-enhanced Regional Downscaling for Applied Studies (SRDAS), might improve the accuracy of hydrometeorological variables in regions with spatial and temporal scarcity of in-situ observations. SRDAS combines assimilation of precipitation estimates from gauge-corrected satellite-based products with spectral nudging technique. The SRDAS hourly outputs provide monthly means of atmospheric and land-surface variables, including precipitation, used in the calculations of the hydrological budget terms. Results show the impact of changes in precipitation on groundwater in the aquifer located near the southeastern coastline of Brazil, through the assessment of the water-cycle terms, using a hydrological model during dry and rainy periods found in the 15-year numerical integration of SRDAS.

Sinking Jelly-Carbon Unveils Potential Environmental Variability along a Continental Margin

PubMed Central

Lebrato, Mario; Molinero, Juan-Carlos; Cartes, Joan E.; Lloris, Domingo; Mélin, Frédéric; Beni-Casadella, Laia

2013-01-01

Particulate matter export fuels benthic ecosystems in continental margins and the deep sea, removing carbon from the upper ocean. Gelatinous zooplankton biomass provides a fast carbon vector that has been poorly studied. Observational data of a large-scale benthic trawling survey from 1994 to 2005 provided a unique opportunity to quantify jelly-carbon along an entire continental margin in the Mediterranean Sea and to assess potential links with biological and physical variables. Biomass depositions were sampled in shelves, slopes and canyons with peaks above 1000 carcasses per trawl, translating to standing stock values between 0.3 and 1.4 mg C m2 after trawling and integrating between 30,000 and 175,000 m2 of seabed. The benthopelagic jelly-carbon spatial distribution from the shelf to the canyons may be explained by atmospheric forcing related with NAO events and dense shelf water cascading, which are both known from the open Mediterranean. Over the decadal scale, we show that the jelly-carbon depositions temporal variability paralleled hydroclimate modifications, and that the enhanced jelly-carbon deposits are connected to a temperature-driven system where chlorophyll plays a minor role. Our results highlight the importance of gelatinous groups as indicators of large-scale ecosystem change, where jelly-carbon depositions play an important role in carbon and energy transport to benthic systems. PMID:24367499

Reconstructions of Columbia River streamflow from tree-ring chronologies in the Pacific Northwest, USA

USGS Publications Warehouse

Littell, Jeremy; Pederson, Gregory T.; Gray, Stephen T.; Tjoelker, Michael; Hamlet, Alan F.; Woodhouse, Connie A.

2016-01-01

We developed Columbia River streamflow reconstructions using a network of existing, new, and updated tree-ring records sensitive to the main climatic factors governing discharge. Reconstruction quality is enhanced by incorporating tree-ring chronologies where high snowpack limits growth, which better represent the contribution of cool-season precipitation to flow than chronologies from trees positively sensitive to hydroclimate alone. The best performing reconstruction (back to 1609 CE) explains 59% of the historical variability and the longest reconstruction (back to 1502 CE) explains 52% of the variability. Droughts similar to the high-intensity, long-duration low flows observed during the 1920s and 1940s are rare, but occurred in the early 1500s and 1630s-1640s. The lowest Columbia flow events appear to be reflected in chronologies both positively and negatively related to streamflow, implying low snowpack and possibly low warm-season precipitation. High flows of magnitudes observed in the instrumental record appear to have been relatively common, and high flows from the 1680s to 1740s exceeded the magnitude and duration of observed wet periods in the late-19th and 20th Century. Comparisons between the Columbia River reconstructions and future projections of streamflow derived from global climate and hydrologic models show the potential for increased hydrologic variability, which could present challenges for managing water in the face of competing demands

Abrupt lake-level changes in the Rocky Mountains and surrounding regions since the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Shuman, B. N.; Serravezza, M.

2016-12-01

The paleohydrologic record of western North America since the last glacial maximum reveals a wide range of hydroclimatic variability and distinctive patterns associated with abrupt climate changes. To evaluate the sequence of abrupt hydroclimatic shifts and centennial-to-millennial hydrologic variability in western North America over the past 17 ka, we reconstruct lake-level histories from two high-elevation lakes in the Beartooth and Bighorn Mountains. The lakes represent the headwaters of the Missouri River drainage in northern Wyoming, but also have the potential to capture regional hydroclimate variability that links the northern Rocky Mountains to the mid-continent, Pacific Northwest, and the Great Basin. We first discuss the stratigraphic record of lake-level changes in small mid-latitude lakes and then use ground-penetrating radar (GPR) and sediment cores to track the elevations of shoreline sediments within the lakes through time. We compare the stratigraphies to the records from four other lakes in Wyoming and Colorado, and find widespread evidence for a Terminal Pleistocene Drought from 15-11 ka, an early Holocene humid period from 11-8 ka, and a period of severe mid-Holocene aridity from 8-5.7 ka. The northern Wyoming lakes also provide evidence of high levels before ca. 15 ka, including rapid hydroclimatic changes at ca. 16.8 ka during Heinrich Event 1. We place the changes in a broad context by summarizing and mapping water-level changes from 107 additional, previously studied lakes. Important patterns include 1) extensive drying across the western U.S. after 15 ka; 2) coherent sub-regional differences during the Younger Dryas and Pleistocene-Holocene transition; 3) a north-south contrast from 9-6 ka consistent with a northward shift in storm tracks as the influence of the Laurentide Ice Sheet diminished; and 4) rapid increases in effective moisture across much of western North America from 6-4 ka.

Detection and attribution of climate change at regional scale: case study of Karkheh river basin in the west of Iran

NASA Astrophysics Data System (ADS)

Zohrabi, Narges; Goodarzi, Elahe; Massah Bavani, Alireza; Najafi, Husain

2017-11-01

This research aims at providing a statistical framework for detection and attribution of climate variability and change at regional scale when at least 30 years of observation data are available. While extensive research has been done on detecting significant observed trends in hydroclimate variables and attribution to anthropogenic greenhouse gas emissions in large continents, less attention has been paid for regional scale analysis. The latter is mainly important for adaptation to climate change in different sectors including but not limited to energy, agriculture, and water resources planning and management, and it is still an open discussion in many countries including the West Asian ones. In the absence of regional climate models, an informative framework is suggested providing useful insights for policymakers. It benefits from general flexibility, not being computationally expensive, and applying several trend tests to analyze temporal variations in temperature and precipitation (gradual and step changes). The framework is implemented for a very important river basin in the west of Iran. In general, some increasing and decreasing trends of the interannual precipitation and temperature have been detected. For precipitation annual time series, a reducing step was seen around 1996 compared with the gradual change in most of the stations, which have not experience a dramatical change. The range of natural forcing is found to be ±76 % for precipitation and ±1.4 °C for temperature considering a two-dimensional diagram of precipitation and temperature anomalies from 1000-year control run of global climate model (GCM). Findings out of applying the proposed framework may provide useful insights into how to approach structural and non-structural climate change adaptation strategies from central governments.

Land Use Induced Hydroclimatic Variability Over Large Deforested Areas in Southern Amazon Rainforest

NASA Astrophysics Data System (ADS)

Khanna, J.; Medvigy, D.

2017-12-01

Contemporary Amazonian deforestation, which occurs at scales of a few hundreds of kilometers, has been found to induce systematic changes in the regional dry season precipitation. The replacement of rough forest with smooth pasture induces a low level atmospheric convergence and uplift in the downwind and divergence and subsidence in the upwind deforested areas. The resulting precipitation change is about ±30% of the deforested area mean in the two regions respectively. Compared with the increase in non-precipitating cloudiness triggered by small scale clearings prevalent in the early phases of deforestation, this `dynamical mesoscale circulation' can have regional ecological impacts by altering precipitation seasonality and in turn ecosystem dynamics. However, the seasonality and variability of this phenomenon hasn't been studied. Using observations and numerical simulations this study investigates the relationships between the dynamical mechanism and the local- and continental-scale atmospheric conditions to understand the physical controls on this phenomenon on the inter-annual, inter-seasonal and daily time scales. We find that the strength of the dynamical mechanism is controlled mostly by regional scale thermal and dynamical conditions of the boundary layer and not the continental and global scale atmospheric state. The lifting condensation level (thermodynamic control) and wind speed (dynamic control) within the boundary layer have the largest and positive correlations with the dipole strength, which is true although not always significant across time scales. Due to this dependence it is found to be strongest during parts of the year when the atmosphere is relatively stable. Hence, overall this phenomenon is found to be the prevalent convective triggering mechanism during the dry and parts of transition seasons (especially spring), significantly affecting the hydroclimate during this period.

Satellite-Enhanced Dynamical Downscaling of Extreme Events

NASA Astrophysics Data System (ADS)

Nunes, A.

2015-12-01

Severe weather events can be the triggers of environmental disasters in regions particularly susceptible to changes in hydrometeorological conditions. In that regard, the reconstruction of past extreme weather events can help in the assessment of vulnerability and risk mitigation actions. Using novel modeling approaches, dynamical downscaling of long-term integrations from global circulation models can be useful for risk analysis, providing more accurate climate information at regional scales. Originally developed at the National Centers for Environmental Prediction (NCEP), the Regional Spectral Model (RSM) is being used in the dynamical downscaling of global reanalysis, within the South American Hydroclimate Reconstruction Project. Here, RSM combines scale-selective bias correction with assimilation of satellite-based precipitation estimates to downscale extreme weather occurrences. Scale-selective bias correction is a method employed in the downscaling, similar to the spectral nudging technique, in which the downscaled solution develops in agreement with its coarse boundaries. Precipitation assimilation acts on modeled deep-convection, drives the land-surface variables, and therefore the hydrological cycle. During the downscaling of extreme events that took place in Brazil in recent years, RSM continuously assimilated NCEP Climate Prediction Center morphing technique precipitation rates. As a result, RSM performed better than its global (reanalysis) forcing, showing more consistent hydrometeorological fields compared with more sophisticated global reanalyses. Ultimately, RSM analyses might provide better-quality initial conditions for high-resolution numerical predictions in metropolitan areas, leading to more reliable short-term forecasting of severe local storms.

Relative contributions of mean-state shifts and ENSO-driven variability to precipitation changes in a warming climate

DOE PAGES

Bonfils, Celine J. W.; Santer, Benjamin D.; Phillips, Thomas J.; ...

2015-12-18

The El Niño–Southern Oscillation (ENSO) is an important driver of regional hydroclimate variability through far-reaching teleconnections. This study uses simulations performed with coupled general circulation models (CGCMs) to investigate how regional precipitation in the twenty-first century may be affected by changes in both ENSO-driven precipitation variability and slowly evolving mean rainfall. First, a dominant, time-invariant pattern of canonical ENSO variability (cENSO) is identified in observed SST data. Next, the fidelity with which 33 state-of-the-art CGCMs represent the spatial structure and temporal variability of this pattern (as well as its associated precipitation responses) is evaluated in simulations of twentieth-century climate change.more » Possible changes in both the temporal variability of this pattern and its associated precipitation teleconnections are investigated in twenty-first-century climate projections. Models with better representation of the observed structure of the cENSO pattern produce winter rainfall teleconnection patterns that are in better accord with twentieth-century observations and more stationary during the twenty-first century. Finally, the model-predicted twenty-first-century rainfall response to cENSO is decomposed into the sum of three terms: 1) the twenty-first-century change in the mean state of precipitation, 2) the historical precipitation response to the cENSO pattern, and 3) a future enhancement in the rainfall response to cENSO, which amplifies rainfall extremes. Lastly, by examining the three terms jointly, this conceptual framework allows the identification of regions likely to experience future rainfall anomalies that are without precedent in the current climate.« less

Two Centuries of Climate Variability From a Gulf of Papua Coral Confirms a Coherent, Widespread Multidecadal Signal

NASA Astrophysics Data System (ADS)

Cole, J. E.; Lough, J.; Reed, E. V.; Schrag, D. P.

2016-12-01

The Indo-Pacific warm pool is intimately involved with large-scale climate variability on seasonal to secular time scales. The lack of long instrumental observations in this region has motivated paleoclimatic analyses using diverse proxy data sources. We present here new multicentury paleoclimate records from a Gulf of Papua coral that capture past variability with a Pacific-wide signature. We have developed stable isotope, Sr/Ca, skeletal density, and luminescence data from a coral core recovered at Bramble Cay, Australia (9°S, 144°E). The geochemical records span CE 1775-1993 and are dominated by low-frequency (decade-century scale) variability that is consistent with records from other proxies in the same region, and with other coral records from far-flung sites across the southwest Pacific. Unlike in many Pacific coral records, we observe no strong trend towards warmer conditions. Although skeletal density bands are clearly visible, they show inconsistent seasonal phasing with the geochemical tracers of sea surface temperature (SST; Sr/Ca and oxygen isotope content), and skeletal density does not correlate with these tracers on longer time scales. In this coral, density banding must be controlled by a more complex mix of internal and/or external factors. Luminescent banding and reconstructed salinity provide similar histories, suggesting a common hydroclimatic signal with significant variability at periods of decades and longer. The strong low-frequency behavior in these new climate records of SST and hydroclimate, from a remote region of the Indo-Pacific, confirms an important source of internal climate variability, on a poorly documented time scale, from a region with far-reaching climatic importance.

Validating modeled soil moisture with in-situ data for agricultural drought monitoring in West Africa

NASA Astrophysics Data System (ADS)

McNally, A.; Yatheendradas, S.; Jayanthi, H.; Funk, C. C.; Peters-Lidard, C. D.

2011-12-01

The declaration of famine in Somalia on July 21, 2011 highlights the need for regional hydroclimate analysis at a scale that is relevant for agropastoral drought monitoring. A particularly critical and robust component of such a drought monitoring system is a land surface model (LSM). We are currently enhancing the Famine Early Warning Systems Network (FEWS NET) monitoring activities by configuring a custom instance of NASA's Land Information System (LIS) called the FEWS NET Land Data Assimilation System (FLDAS). Using the LIS Noah LSM, in-situ measurements, and remotely sensed data, we focus on the following question: How can Noah be best parameterized to accurately simulate hydroclimate variables associated with crop performance? Parameter value testing and validation is done by comparing modeled soil moisture against fortuitously available in-situ soil moisture observations in the West Africa. Direct testing and application of the FLDAS over African agropastoral locations is subject to some issues: [1] In many regions that are vulnerable to food insecurity ground based measurements of precipitation, evapotranspiration and soil moisture are sparse or non-existent, [2] standard landcover classes (e.g., the University of Maryland 5 km dataset), do not include representations of specific agricultural crops with relevant parameter values, and phenologies representing their growth stages from the planting date and [3] physically based land surface models and remote sensing rain data might still need to be calibrated or bias-corrected for the regions of interest. This research aims to address these issues by focusing on sites in the West African countries of Mali, Niger, and Benin where in-situ rainfall and soil moisture measurements are available from the African Monsoon Multidisciplinary Analysis (AMMA). Preliminary results from model experiments over Southern Malawi, validated with Normalized Difference Vegetation Index (NDVI) and maize yield data, show that the ability to detect a drought signal in modeled soil moisture and actual evapotranspiration was sensitive to parameters like minimum stomatal resistance, green vegetation fraction, and minimum threshold for transpiration stress. In addition to improving our understanding and representation of the land surface physics in agropastoral drought, this study moves us closer to confidently validating LSM estimates with remotely sensed data (e.g. MODIS NDVI), essential in regions that lack ground based measurements. Ultimately, these improved information products serve to better inform decision makers about seasonal food production and anticipate the need for relief, as well as guide climate change adaptation strategies, potentially saving millions of lives.

Hydroclimate of the Spring Mountains and Sheep Range, Clark County, Nevada

USGS Publications Warehouse

Moreo, Michael T.; Senay, Gabriel B.; Flint, Alan L.; Damar, Nancy A.; Laczniak, Randell J.; Hurja, James

2014-01-01

Precipitation, potential evapotranspiration, and actual evapotranspiration often are used to characterize the hydroclimate of a region. Quantification of these parameters in mountainous terrains is difficult because limited access often hampers the collection of representative ground data. To fulfill a need to characterize ecological zones in the Spring Mountains and Sheep Range of southern Nevada, spatially and temporally explicit estimates of these hydroclimatic parameters are determined from remote-sensing and model-based methodologies. Parameter-elevation Regressions on Independent Slopes Model (PRISM) precipitation estimates for this area ranges from about 100 millimeters (mm) in the low elevations of the study area (700 meters [m]) to more than 700 mm in the high elevations of the Spring Mountains (> 2,800 m). The PRISM model underestimates precipitation by 7–15 percent based on a comparison with four high‑elevation precipitation gages having more than 20 years of record. Precipitation at 3,000-m elevation is 50 percent greater in the Spring Mountains than in the Sheep Range. The lesser amount of precipitation in the Sheep Range is attributed to partial moisture depletion by the Spring Mountains of eastward-moving, cool-season (October–April) storms. Cool-season storms account for 66–76 percent of annual precipitation. Potential evapotranspiration estimates by the Basin Characterization Model range from about 700 mm in the high elevations of the Spring Mountains to 1,600 mm in the low elevations of the study area. The model realistically simulates lower potential evapotranspiration on northeast-to-northwest facing slopes compared to adjacent southeast-to-southwest facing slopes. Actual evapotranspiration, estimated using a Moderate Resolution Imaging Spectroradiometer based water-balance model, ranges from about 100 to 600 mm. The magnitude and spatial variation of simulated, actual evapotranspiration was validated by comparison to PRISM precipitation. Estimated groundwater recharge, computed as the residual of precipitation depleted by actual evapotranspiration, is within the range of previous estimates. A climatic water deficit dataset and aridity-index-based climate zones are derived from precipitation and evapotranspiration datasets. Climate zones range from arid in the lower elevations of the study area to humid in small pockets on north- to northeast-facing slopes in the high elevations of the Spring Mountains. Correlative analyses between hydroclimatic variables and mean ecosystem elevations indicate that the climatic water deficit is the best predictor of ecosystem distribution (R2 = 0.92). Computed water balances indicate that substantially more recharge is generated in the Spring Mountains than in the Sheep Range. A geospatial database containing compiled and developed hydroclimatic data and other pertinent information accompanies this report.

An Overview of Synoptic and Mesoscale Factors Contributing to the Disastrous Atlanta Flood of 2009

EPA Science Inventory

If IPCC (2007) projections are accurate, the frequency and severity of extreme hydroclimate events (e.g., droughts, floods) will likely increase in response to the acceleration in the water cycle. Additionally, a majority of the population lives in urban areas, and by 2030 this ...

The Role of Soil Water and Land Feedbacks in Decadal Drought in Western North America

NASA Astrophysics Data System (ADS)

Langford, S.; Chikamoto, Y.; Noone, D. C.

2013-12-01

Western North America is susceptible to severe impacts of megadroughts, as evidenced by tree-core or lake sediment records. Future predictions suggest that this region will become more arid, with further consequences for water resources. Understanding the mechanisms of drought variability and persistence in western North America is critical for the eventual development of effective forecasting methods. The ocean is expected to be the main source of decadal memory in the system as the atmosphere varies on a much shorter timescale. The ocean's role in driving the low-frequency variability of the system is potentially predictable. However, low-frequency precipitation anomalies in western North America can occur in the absence of ocean feedbacks. Sea surface temperature anomalies in the north Pacific Ocean only account for around 20 per cent of the low-frequency winter precipitation in California in the CMIP5 historical runs. This is not sufficient to use the skill of global coupled models in predicting ocean conditions ahead of time to successfully forecast the possibility of long-term drought in western North America. Megadroughts therefore may be generated by unpredictable atmospheric noise, or persisted by other sources of low-frequency variability such as land processes and feedbacks. Snowpack in western North America is a crucial water resource for the surrounding communities, storing the winter precipitation for use later in the year. Likewise, soil moisture integrates the precipitation signal; the time scale depends on the depth and characteristics of the soil. Water storage and related variables are more predictable on longer timescales than precipitation, as measured by anomaly correlation for hindcasts compared to a 'perfect model' control run with CESM1.0.3. The importance of antecedent land conditions in persisting megadroughts in western North America is explored with ensemble simulations of CESM1.0.3, where the atmosphere is perturbed at the initiation and peak of a megadrought in the control run. Numerical experiments are used to test land-atmosphere feedbacks or memory sources, highlighting the sensitivity of megadrought initiation, persistence and termination to these antecedent conditions. The model results confirm the importance of land processes in projections of future decadal hydroclimate.

The fractal-multifractal method and temporal resolution: Application to precipitation and streamflow

NASA Astrophysics Data System (ADS)

Maskey, M.; Puente, C. E.; Sivakumar, B.

2017-12-01

In the past, we have established that the deterministic fractal-multifractal (FM) method is a promising geometric tool to analyze hydro-climatic variables, such as precipitation, river flow, and temperature. In this study, we address the issue of temporal resolution to advance the suitability and usefulness of the FM approach in hydro-climate. Specifically, we elucidate the evolution of FM geometric parameters as computed at different time scales ranging from a day to a month (30-day) in increments of a day. For this purpose, both rainfall and river discharge records at Sacramento, California gathered over a year are encoded at different time scales. The analysis reveals that: (a) the FM approach yields faithful encodings of both kinds of data sets at the resolutions considered with reasonably small errors; and (b) the "best" FM parameters ultimately converge when the resolution is increased, thus allowing visualizing both hydrologic attributes. By addressing the scalability of the geometric patterns, these results further advance the suitability of the FM approach.

Precipitation changes in the western tropical Pacific over the past millennium

USGS Publications Warehouse

Richey, Julie; Sachs, Julian P.

2016-01-01

Palau is linked to both meridional movement of the Intertropical Convergence Zone (ITCZ) and changes in the Pacific Walker Circula- tion (PWC) associated with the El Niño–Southern Oscillation. Thus, Palau’s hydroclimate should be sensitive to mean shifts in the ITCZ and PWC on decadal to centennial time scales. Using compound- specific hydrogen isotope ratios (δ2H) of dinosterol in lake sediments, we generated a decadal-resolution proxy record of hydroclimatic variability in Palau spanning the past 800 yr. Results indicate a dry- ing trend during the Little Ice Age in Palau, consistent with a south- ward displacement of the ITCZ. In addition to the secular drying trend, there are persistent large (~20‰) multi-decadal to centennial oscillations in the δ2H record, the most recent of which indicates an abrupt shift to drier conditions in the mid-1970s that coincides with a decadal-scale negative shift in the Southern Oscillation Index.

Trend and variability in western and central Africa streamflow, and their relation to climate variability between 1950 and 2010

NASA Astrophysics Data System (ADS)

Sidibe, Moussa; Dieppois, Bastien; Mahé, Gil; Paturel, Jean-Emmanuel; Rouché, Nathalie; Amoussou, Ernest; Anifowose, Babatunde; Lawler, Damian

2017-04-01

Unprecedented drought episodes that struck western and central Africa between the late 1960s and 1980s. This triggered many studies investigating rainfall variability and its impacts on food production systems. However, most studies were focused at the catchment scale. In this study, we examine how rainfall variability has impacted on river flow at the subcontinental scale between 1950 and 2010, as well as the key large-scale controls on this relationship. For the first time, we establish a complete, gap-filled, monthly streamflow data set, which extends from 1950 to 2010, over the western and central African region. To achieve this, we used linear regression modelling across and between 600 flow gauging stations (see initial database information at http://www.hydrosciences.fr/sierem/index_en.htm). Streamflow trend and variability are then seasonally assessed at this subcontinental scale and compared to those observed in three different rainfall data sets (i.e. CRU TS3.24, GPCC V7, IRD-HSM). Long-term trends and variability in streamflow are mainly consistent with trends in rainfall. However, these relationships may have been moderated by: i) changes in land use; and ii) contributions from groundwater resources. In particular, we note that the recent post 1990s partial recovery in Sahel rainfall could have, at least partially, positively impacted river flows (e.g. the Senegal and Niger rivers). Using multi-temporal trend and continuous wavelet analysis, the time-evolution of western and central African river flows are analysed, and are all characterized by very strong decadal fluctuations, which can be interpreted as modulations in the baseflow. These decadal fluctuations, which are also significantly detected in rainfall, are likely related to large-scale sea-surface temperature (SST) anomaly patterns, such as the tropical Atlantic SST variability, the Atlantic Multidecadal Oscillation, the Interdecadal Pacific Oscillation and/or the Pacific Decadal Oscillation. Furthermore, hitherto-poorly understood hydroclimatic processes related to these teleconnections at decadal timescales will be examined in this study. Influences of the catchment properties (e.g. size, shape, vegetation and landuse cover, soil type, ground-water level, direction of stream flow across climate zones) on these decadal fluctuations in river flows will also be assessed. This study therefore aims to improve the ability of current regional and global climate models to simulate such ranges of variability, to significantly improve regional hydroclimate understanding, as a means for improving the development of future scenarios for water resources in western and central Africa.

Climate change and growth scenarios for California wildfire

Treesearch

A.L. Westerling; B.P. Bryant; H.K. Preisler; T.P. Holmes; H.G. Hildalgo; T. Das; S.R. Shrestha

2011-01-01

Large wildfire occurrence and burned area are modeled using hydroclimate and landsurface characteristics under a range of future climate and development scenarios. The range of uncertainty for future wildfire regimes is analyzed over two emissions pathways (the Special Report on Emissions Scenarios [SRES] A2 and B1 scenarios); three global climate models (Centre...

Rainy Day: A Remote Sensing-Driven Extreme Rainfall Simulation Approach for Hazard Assessment

NASA Astrophysics Data System (ADS)

Wright, Daniel; Yatheendradas, Soni; Peters-Lidard, Christa; Kirschbaum, Dalia; Ayalew, Tibebu; Mantilla, Ricardo; Krajewski, Witold

2015-04-01

Progress on the assessment of rainfall-driven hazards such as floods and landslides has been hampered by the challenge of characterizing the frequency, intensity, and structure of extreme rainfall at the watershed or hillslope scale. Conventional approaches rely on simplifying assumptions and are strongly dependent on the location, the availability of long-term rain gage measurements, and the subjectivity of the analyst. Regional and global-scale rainfall remote sensing products provide an alternative, but are limited by relatively short (~15-year) observational records. To overcome this, we have coupled these remote sensing products with a space-time resampling framework known as stochastic storm transposition (SST). SST "lengthens" the rainfall record by resampling from a catalog of observed storms from a user-defined region, effectively recreating the regional extreme rainfall hydroclimate. This coupling has been codified in Rainy Day, a Python-based platform for quickly generating large numbers of probabilistic extreme rainfall "scenarios" at any point on the globe. Rainy Day is readily compatible with any gridded rainfall dataset. The user can optionally incorporate regional rain gage or weather radar measurements for bias correction using the Precipitation Uncertainties for Satellite Hydrology (PUSH) framework. Results from Rainy Day using the CMORPH satellite precipitation product are compared with local observations in two examples. The first example is peak discharge estimation in a medium-sized (~4000 square km) watershed in the central United States performed using CUENCAS, a parsimonious physically-based distributed hydrologic model. The second example is rainfall frequency analysis for Saint Lucia, a small volcanic island in the eastern Caribbean that is prone to landslides and flash floods. The distinct rainfall hydroclimates of the two example sites illustrate the flexibility of the approach and its usefulness for hazard analysis in data-poor regions.

Effect of Technology Driven Agricultural Land Use Change on Regional Hydroclimate

NASA Astrophysics Data System (ADS)

Arritt, R. W.; Sines, T. R.; Groisman, P. Y.; Gelder, B. K.

2017-12-01

During the mid-20th century motorized equipment replaced work animals in the central U.S. This led to a 95% decrease in farmland for producing oats, which had mostly been used as feed for horses. Much of this land was converted to more profitable crops such as soybeans and maize. The same period also saw a strong shift of the central U.S. precipitation intensity spectrum toward heavier events. Was this a coincidence, or is there a causal relationship? We investigate possible connections between this technology-driven land use change and regional hydroclimate by performing multi-decadal simulations over the central U.S. using the WRF-ARW regional climate model coupled with the Community Land Model (CLM 4.5). Cropland planted in maize, soybean, winter wheat, small grains (which includes oats and spring wheat), and other C3 and C4 crops were reconstructed on a decade by decade basis from 1940-2010 using county-level crop data. These crop distributions were used as land surface boundary conditions for two multi-decadal regional climate simulations, one with 1940s land use and another with modern (circa 2010) land use. Modern land use produced a shift in the simulated daily precipitation intensity spectrum toward heavy events, with higher frequencies of heavy precipitation amounts and lower frequencies of light amounts compared to 1940s land use. The results suggest that replacement of work animals by mechanized transport led to land use changes that produced about 10-30% of the observed trend toward more intense precipitation over the central United States. We therefore recommend that policy- and technology-driven changes in crop type be taken into account when projecting future climate and water resources.

Hemispherically Asymmetric Volcanic Forcing of Tropical Hydroclimate During the Last Millennium

NASA Technical Reports Server (NTRS)

Colose, Christopher M.; Legrande, Allegra N.; Vuille, Mathias

2016-01-01

Volcanic aerosols exert the most important natural radiative forcing of the last millennium. State-of-the-art paleoclimate simulations of this interval are typically forced with diverse spatial patterns of volcanic forcing, leading to different responses in tropical hydroclimate. Recently, theoretical considerations relating the intertropical convergence zone (ITCZ) position to the demands of global energy balance have emerged in the literature, allowing for a connection to be made between the paleoclimate simulations and recent developments in the understanding of ITCZ dynamics. These energetic considerations aid in explaining the well-known historical, paleoclimatic, and modeling evidence that the ITCZ migrates away from the hemisphere that is energetically deficient in response to asymmetric forcing. Here we use two separate general circulation model (GCM) suites of experiments for the last millennium to relate the ITCZ position to asymmetries in prescribed volcanic sulfate aerosols in the stratosphere and related asymmetric radiative forcing. We discuss the ITCZ shift in the context of atmospheric energetics and discuss the ramifications of transient ITCZ migrations for other sensitive indicators of changes in the tropical hydrologic cycle, including global streamflow. For the first time, we also offer insight into the large-scale fingerprint of water isotopologues in precipitation (delta sup 18 Op) in response to asymmetries in radiative forcing. The ITCZ shifts away from the hemisphere with greater volcanic forcing. Since the isotopic composition of precipitation in the ITCZ is relatively depleted compared to areas outside this zone, this meridional precipitation migration results in a large-scale enrichment (depletion) in the isotopic composition of tropical precipitation in regions the ITCZ moves away from (toward). Our results highlight the need for careful consideration of the spatial structure of volcanic forcing for interpreting volcanic signals in proxy records and therefore in evaluating the skill of Common Era climate model output.

Potential for tree rings to reveal spatial patterns of past drought variability across western Australia

NASA Astrophysics Data System (ADS)

O'Donnell, Alison J.; Cook, Edward R.; Palmer, Jonathan G.; Turney, Chris S. M.; Grierson, Pauline F.

2018-02-01

Proxy records have provided major insights into the variability of past climates over long timescales. However, for much of the Southern Hemisphere, the ability to identify spatial patterns of past climatic variability is constrained by the sparse distribution of proxy records. This is particularly true for mainland Australia, where relatively few proxy records are located. Here, we (1) assess the potential to use existing proxy records in the Australasian region—starting with the only two multi-century tree-ring proxies from mainland Australia—to reveal spatial patterns of past hydroclimatic variability across the western third of the continent, and (2) identify strategic locations to target for the development of new proxy records. We show that the two existing tree-ring records allow robust reconstructions of past hydroclimatic variability over spatially broad areas (i.e. > 3° × 3°) in inland north- and south-western Australia. Our results reveal synchronous periods of drought and wet conditions between the inland northern and southern regions of western Australia as well as a generally anti-phase relationship with hydroclimate in eastern Australia over the last two centuries. The inclusion of 174 tree-ring proxy records from Tasmania, New Zealand and Indonesia and a coral record from Queensland did not improve the reconstruction potential over western Australia. However, our findings suggest that the addition of relatively few new proxy records from key locations in western Australia that currently have low reconstruction skill will enable the development of a comprehensive drought atlas for the region, and provide a critical link to the drought atlases of monsoonal Asia and eastern Australia and New Zealand.

A land data assimilation system for sub-Saharan Africa food and water security applications

PubMed Central

McNally, Amy; Arsenault, Kristi; Kumar, Sujay; Shukla, Shraddhanand; Peterson, Pete; Wang, Shugong; Funk, Chris; Peters-Lidard, Christa D.; Verdin, James P.

2017-01-01

Seasonal agricultural drought monitoring systems, which rely on satellite remote sensing and land surface models (LSMs), are important for disaster risk reduction and famine early warning. These systems require the best available weather inputs, as well as a long-term historical record to contextualize current observations. This article introduces the Famine Early Warning Systems Network (FEWS NET) Land Data Assimilation System (FLDAS), a custom instance of the NASA Land Information System (LIS) framework. The FLDAS is routinely used to produce multi-model and multi-forcing estimates of hydro-climate states and fluxes over semi-arid, food insecure regions of Africa. These modeled data and derived products, like soil moisture percentiles and water availability, were designed and are currently used to complement FEWS NET’s operational remotely sensed rainfall, evapotranspiration, and vegetation observations. The 30+ years of monthly outputs from the FLDAS simulations are publicly available from the NASA Goddard Earth Science Data and Information Services Center (GES DISC) and recommended for use in hydroclimate studies, early warning applications, and by agro-meteorological scientists in Eastern, Southern, and Western Africa. PMID:28195575

A land data assimilation system for sub-Saharan Africa food and water security applications

USGS Publications Warehouse

McNally, Amy; Arsenault, Kristi; Kumar, Sujay; Shukla, Shraddhanand; Peterson, Pete; Wang, Shugong; Funk, Chris; Peters-Lidard, Christa; Verdin, James

2017-01-01

Seasonal agricultural drought monitoring systems, which rely on satellite remote sensing and land surface models (LSMs), are important for disaster risk reduction and famine early warning. These systems require the best available weather inputs, as well as a long-term historical record to contextualize current observations. This article introduces the Famine Early Warning Systems Network (FEWS NET) Land Data Assimilation System (FLDAS), a custom instance of the NASA Land Information System (LIS) framework. The FLDAS is routinely used to produce multi-model and multi-forcing estimates of hydro-climate states and fluxes over semi-arid, food insecure regions of Africa. These modeled data and derived products, like soil moisture percentiles and water availability, were designed and are currently used to complement FEWS NET’s operational remotely sensed rainfall, evapotranspiration, and vegetation observations. The 30+ years of monthly outputs from the FLDAS simulations are publicly available from the NASA Goddard Earth Science Data and Information Services Center (GES DISC) and recommended for use in hydroclimate studies, early warning applications, and by agro-meteorological scientists in Eastern, Southern, and Western Africa.

A land data assimilation system for sub-Saharan Africa food and water security applications.

PubMed

McNally, Amy; Arsenault, Kristi; Kumar, Sujay; Shukla, Shraddhanand; Peterson, Pete; Wang, Shugong; Funk, Chris; Peters-Lidard, Christa D; Verdin, James P

2017-02-14

Seasonal agricultural drought monitoring systems, which rely on satellite remote sensing and land surface models (LSMs), are important for disaster risk reduction and famine early warning. These systems require the best available weather inputs, as well as a long-term historical record to contextualize current observations. This article introduces the Famine Early Warning Systems Network (FEWS NET) Land Data Assimilation System (FLDAS), a custom instance of the NASA Land Information System (LIS) framework. The FLDAS is routinely used to produce multi-model and multi-forcing estimates of hydro-climate states and fluxes over semi-arid, food insecure regions of Africa. These modeled data and derived products, like soil moisture percentiles and water availability, were designed and are currently used to complement FEWS NET's operational remotely sensed rainfall, evapotranspiration, and vegetation observations. The 30+ years of monthly outputs from the FLDAS simulations are publicly available from the NASA Goddard Earth Science Data and Information Services Center (GES DISC) and recommended for use in hydroclimate studies, early warning applications, and by agro-meteorological scientists in Eastern, Southern, and Western Africa.

Spatio-temporal examination of precipitation isotopes from the North American monsoon in Arizona, New Mexico, and Utah from 2014 to 2017

NASA Astrophysics Data System (ADS)

Tulley-Cordova, C. L.; Bowen, G. J.

2017-12-01

A significant summertime feature of climate in the southwestern United States (US) is the North American monsoon (NAM), also known as the Mexican monsoon, Arizona monsoon, and the southwestern United States monsoon. NAM is a crucial contributor to total annual precipitation in the Four Corners region of the US. Modern investigation of NAM in this region using stable isotopes has been poorly studied. This study characterizes the spatio-temporal changes of NAM based on stable isotopic results from 40 sites, located within the boundaries of the Navajo Nation, in Arizona, New Mexico, and Utah from 2014 to 2017. Sample collections were collected monthly at each site from May to October. Examination of temporal trends of precipitation revealed strong monthly and interannual changes; spatial analysis showed weak large-scale relationships across the study area. Analysis of stable isotopes in precipitation, surface, ground, and spring waters can be used to interpret the isotopic differences in the modern hydro-climate of the Navajo Nation and Colorado Plateau to help predict future hydro-climate changes and its implications on future water resources.

Data Descriptor: A Land Data Assimilation System for Sub-Saharan Africa Food and Water Security Applications

NASA Technical Reports Server (NTRS)

McNally, Amy; Arsenault, Krist; Kumar, Sujay; Shukla, Shraddhanand; Peter, Pete; Wang, Shugong; Funk, Chris; Peters-Lidard, Christa D.; Verdin, James

2017-01-01

Seasonal agricultural drought monitoring systems, which rely on satellite remote sensing and land surface models (LSMs), are important for disaster risk reduction and famine early warning. These systems require the best available weather inputs, as well as a long-term historical record to contextualize current observations. This article introduces the Famine Early Warning Systems Network (FEWS NET) Land Data Assimilation System (FLDAS), a custom instance of the NASA Land Information System (LIS) framework. The FLDAS is routinely used to produce multi-model and multi-forcing estimates of hydro-climate states and fluxes over semi-arid, food insecure regions of Africa. These modeled data and derived products, like soil moisture percentiles and water availability, were designed and are currently used to complement FEWSNETs operational remotely sensed rainfall, evapotranspiration, and vegetation observations. The 30+ years of monthly outputs from the FLDAS simulations are publicly available from the NASA Goddard Earth Science Data and Information Services Center (GES DISC) and recommended for use in hydroclimate studies, early warning applications, and by agro-meteorological scientists in Eastern, Southern, and Western Africa.

A land data assimilation system for sub-Saharan Africa food and water security applications

NASA Astrophysics Data System (ADS)

McNally, Amy; Arsenault, Kristi; Kumar, Sujay; Shukla, Shraddhanand; Peterson, Pete; Wang, Shugong; Funk, Chris; Peters-Lidard, Christa D.; Verdin, James P.

2017-02-01

Seasonal agricultural drought monitoring systems, which rely on satellite remote sensing and land surface models (LSMs), are important for disaster risk reduction and famine early warning. These systems require the best available weather inputs, as well as a long-term historical record to contextualize current observations. This article introduces the Famine Early Warning Systems Network (FEWS NET) Land Data Assimilation System (FLDAS), a custom instance of the NASA Land Information System (LIS) framework. The FLDAS is routinely used to produce multi-model and multi-forcing estimates of hydro-climate states and fluxes over semi-arid, food insecure regions of Africa. These modeled data and derived products, like soil moisture percentiles and water availability, were designed and are currently used to complement FEWS NET's operational remotely sensed rainfall, evapotranspiration, and vegetation observations. The 30+ years of monthly outputs from the FLDAS simulations are publicly available from the NASA Goddard Earth Science Data and Information Services Center (GES DISC) and recommended for use in hydroclimate studies, early warning applications, and by agro-meteorological scientists in Eastern, Southern, and Western Africa.

Late-Holocene hydroclimate and atmospheric circulation variability in southern Patagonia: insights from triple stable isotopes (δ18O, δ13C, δD) of peat bog Sphagnum moss

NASA Astrophysics Data System (ADS)

Xia, Z.; Yu, Z.; Zheng, Y.; Loisel, J.; Huang, Y.

2017-12-01

The Southern Hemisphere Westerly Winds (SHWWs) exert important influences on regional and global climates, but their long-term behaviors and dynamics are still poorly understood but critical for projecting future changes. Here we present a 5,500-year record from a Sphagnum-dominated peat bog located on the lee side of the Andes at 54.2 °S in southern Patagonia—based on plant macrofossils, Sphagnum cellulose δ18O and δ13C, and lipid δD data—to document and understand the variability in hydroclimate and atmospheric circulation. There is a striking negative correlation between cellulose δ18O and the Southern Annular Mode (SAM) index over the last millennium; particularly the 2.5‰ negative shift of δ18O is concurrent with the observed positive trend in the SAM over the recent decades. The interval of Medieval Climate Anomaly (MCA, 850-600 yr BP) is characterized by a 2.5‰ negative shift of δ18O and low δ13C values, while the Little Ice Age (LIA, 500-300 yr BP) is characterized by a 2.5‰ positive shift of δ18O and high δ13C values. Furthermore, we find the largest negative shift of δ18O ( 3‰) at 2,300 yr BP, suggesting a significantly positive shift in the SAM. We interpret high Sphagnum abundance and high cellulose δ13C values to reflect great moss moisture conditions, while cellulose δ18O variations primarily reflect moisture sources and atmospheric circulation. During the positive phase of SAM (e.g., the MCA and recent decades), strengthened SHWWs enhance the rain-shadow effect, resulting in dry climate and 18O-depleted precipitation (low δ18O values) in the study region. During the negative phase of SAM (e.g., the LIA), weakened SHWWs reduce rain-shadow effect, resulting in wet climate and high δ18O values caused by increases in moisture contributions from the southerly and easterly flows that do not experience strong Rayleigh distillation process during air mass transports. Furthermore, coupling cellulose δ18O and lipid δD enables inverse calculation on the deuterium excess to understand the origin of atmospheric moisture. Our results provide new insights into the evolution of the SHWW and SAM during the late Holocene. We also use back-trajectory analysis equipped with moisture uptake algorithm to link moisture sources and trajectories with isotopic composition of precipitation in southern Patagonia.

Eolian and riverine contributions to central-Mediterranean sediments: a high-resolution Holocene record

NASA Astrophysics Data System (ADS)

Wu, Jiawang; Böning, Philipp; Pahnke, Katharina; Tachikawa, Kazuyo; De Lange, Gert

2017-04-01

Circum-Mediterranean climate variability is reflected in sediments deposited and preserved at the Mediterranean seafloor. Alternating depositions of organic-lean marls and organic-rich sapropel sediments in the eastern Mediterranean Sea (EMS) are clearly related to precessional hydroclimate variability. The exact origin for freshwater sources and related changes therein during sapropel formation are still debated. Here, Sr and Nd isotopes and high-resolution elemental ratios from core CP10BC are used to unravel and constrain different eolian and riverine supplies from North Africa and from northern borderlands to the central Mediterranean over the past 9.8 ka. Based on Sr and Nd isotopic and elemental compositions, the provenance for detrital sediments in the Levantine basin can be adequately described using 2-end-members. However, in the central Mediterranean, a three-endmember mixing system is required. The three endmember include Saharan Dust, Aegean/Nile, and Libyan Soil, which respectively represents the eolian supply from North Africa, the riverine inputs from the Aegean/Nile areas, and the riverine and shelf-derived fluxes from the Libyan-Tunisian margin. For the first time, robust and consistent evidence is given for important riverine supplies from the Libyan-Tunisian margin into the central Mediterranean during sapropel S1 time in particular. Considerable amounts of detrital materials and freshwater must have been delivered into the EMS through the fossil river/wadi systems, which were activated by intensified African monsoon precipitation. A west-east comparison of Sr-Nd isotope data between core CP10BC and 4 other cores throughout the EMS shows that, such detrital supplies originated mainly from western Libya and Tunisia, and were transported as far eastward as 25°E while being diluted by an increasing Nile contribution. The Nile contribution to the central-Mediterranean detrital sediment fraction appears to have been negligible. Moreover, elemental proxies (Ti/Al, K/Al, Y/Sc, Ce/Ni, and Zr/Cr) reflect concordant changes in the three endmembers at high resolution. These indicate that enhanced precipitation and associated detrital fluxes must have occurred not only from North Africa but also from the northern EMS borderlands. Changes in the Libyan-Tunisian riverine contribution show a close correspondence with hydroclimate evolution of NW Libya on the one hand, and with prominent riverine contribution from the northern EMS borderlands on the other (Wu et al., 2016). Wu, J., Böning, P., Pahnke, K., Tachikawa, K., De Lange, G.J., 2016. Unraveling North-African riverine and eolian contributions to central Mediterranean sediments during Holocene sapropel S1 formation. Quaternary Science reviews 152, 31-48.

Climate Change Modeling Needs and Efforts for Hydroelectric System Operations in the Pacific Northwest

NASA Astrophysics Data System (ADS)

Pytlak, E.

2014-12-01

This presentation will outline ongoing, multi-year hydroclimate change research between the Columbia River Management Joint Operating Committee (RMJOC), The University of Washington, Portland State University, and their many regional research partners and stakeholders. Climate change in the Columbia River Basin is of particular concern to the Bonneville Power Administration (BPA) and many Federal, Tribal and regional stakeholders. BPA, the U.S. Army Corp of Engineers, and U.S. Bureau of Reclamation, which comprise the RMJOC, conducted an extensive study in 2009-11 using climate change streamflows produced by the University of Washington Climate Impacts Group (CIG). The study reconfirmed that as more winter precipitation in the Columbia Basin falls as rain rather than snow by mid-century, particularly on the U.S. portion of the basin, increased winter runoff is likely, followed by an earlier spring snowmelt peak, followed by less summer flows as seasonal snowmelt diminished earlier in the water year. Since that initial effort, both global and regional climate change modeling has advanced. To take advantage of the new outputs from the Fifth Coupled Model Intercomparison Project (CMIP-5), the RMJOC, through BPA support, is sponsoring new hydroclimate research which considers not only the most recent information from the GCMs, but also the uncertainties introduced by the hydroclimate modeling process itself. Historical streamflows, which are used to calibrate hydrologic models and ascertain their reliability, are subject to both measurement and modeling uncertainties. Downscaling GCMs to a hydrologically useful spatial and temporal resolution introduces uncertainty, depending on the downscaling methods. Hydrologic modeling introduces uncertainties from calibration and geophysical states, some of which, like land surface characteristics, are likely to also change with time. In the upper Columbia Basin, glacier processes introduce yet another source of uncertainty. The latest joint effort attempts to ascertain the relative contributions of these uncertainties in comparison to the uncertainties brought by changing climate itself.

Regional Climate Modeling and Remote Sensing to Characterize Impacts of Civil War Driven Land Use Change on Regional Hydrology and Climate

NASA Astrophysics Data System (ADS)

Maksimowicz, M.; Masarik, M. T.; Brandt, J.; Flores, A. N.

2016-12-01

Land use/land cover (LULC) change directly impacts the partitioning of surface mass and energy fluxes. Regional-scale weather and climate are potentially altered by LULC if the resultant changes in partitioning of surface energy fluxes are extensive enough. Dynamics of land use, particularly those related to the social dimensions of the Earth System, are often simplified or not represented in regional land-atmosphere models. This study explores the role of LULC change on a regional hydroclimate system, focusing on potential hydroclimate changes arising from an extended civil conflict in Mozambique. Civil war from 1977-1992 in Mozambique led to land use change at a regional scale as a result of the collapse of large herbivore populations due to poaching. Since the war ended, farming has increased, poaching was curtailed, and animal populations were reintroduced. In this study LULC in a region encompassing Gorongosa is classified at three instances between 1977 to 2015 using Landsat imagery. We use these derived LULC datasets to inform lower boundary conditions in the Weather Research and Forecasting (WRF) model. To quantify potential hydrometeorological changes arising from conflict-driven land use change, we performed a factorial-like experiment by mixing input LULC maps and atmospheric forcing data from before, during, and after the civil war. Analysis of the Landsat data shows measurable land cover change from 1977-present as tree cover encroached into grasslands. Initial tests show corresponding sensitivities to different LULC schemes within the WRF model. Preliminary results suggest that the war did indeed impact regional hydroclimate in a significant way via its direct and indirect impacts on land-atmosphere interactions. Results of this study suggest that LULC change arising from regional conflicts are a potentially understudied, yet important human process to capture in both regional reanalyses and climate change projections.

Santa Ana Winds of Southern California: Their Climatology and Variability Spanning 6.5 Decades from Regional Dynamical Modelling

NASA Astrophysics Data System (ADS)

Guzman-Morales, J.; Gershunov, A.

2015-12-01

Santa Ana Winds (SAWs) are an integral feature of the regional climate of Southern California/Northern Baja California region. In spite of their tremendous episodic impacts on the health, economy and mood of the region, climate-scale behavior of SAW is poorly understood. In the present work, we identify SAWs in mesoscale dynamical downscaling of a global reanalysis product and construct an hourly SAW catalogue spanning 65 years. We describe the long-term SAW climatology at relevant time-space resolutions, i.e, we developed local and regional SAW indices and analyse their variability on hourly, daily, annual, and multi-decadal timescales. Local and regional SAW indices are validated with available anemometer observations. Characteristic behaviors are revealed, e.g. the SAW intensity-duration relationship. At interdecadal time scales, we find that seasonal SAW activity is sensitive to prominent large-scale low-frequency modes of climate variability rooted in the tropical and north Pacific ocean-atmosphere system that are also known to affect the hydroclimate of this region. Lastly, we do not find any long-term trend in SAW frequency and intensity as previously reported. Instead, we identify a significant long-term trend in SAW behavior whereby contribution of extreme SAW events to total seasonal SAW activity has been increasing at the expense of moderate events. These findings motivate further investigation on SAW evolution in future climate and its impact on wildfires.

Reduction in carbon uptake during turn of the century drought in western North America

USDA-ARS?s Scientific Manuscript database

Fossil fuel emissions aside, temperate North America is a net sink of carbon dioxide at present1–3. Year-to-year variations in this carbon sink are linked to variations in hydroclimate that affect net ecosystem productivity3,4. The severity and incidence of climatic extremes, including drought, have...

Potential role of vegetation dynamics on recent extreme droughts over tropical South America

NASA Astrophysics Data System (ADS)

Wang, G.; Erfanian, A.; Fomenko, L.

2017-12-01

Tropical South America is a drought hot spot. In slightly over a decade (2005-2016), the region encountered three extreme droughts (2005, 2010, and 2016). Recurrent extreme droughts not only impact the region's eco-hydrology and socio-economy, but are also globally important as they can transform the planet's largest rainforest, the Amazon, from a carbon sink to a carbon source. Understanding drought drivers and mechanisms underlying extreme droughts in tropical South America can help better project the fate of the Amazon rainforest in a changing climate. In this study we use a regional climate model (RegCM4.3.4) coupled with a comprehensive land-surface model (CLM4.5) to study the present-day hydroclimate of the region, focusing specifically on what might have caused the frequent recurrence of extreme droughts. In the context of observation natural variability of the global oceanic forcing, we tackle the role of land-atmosphere interactions and ran the model with and without dynamic vegetation to study how vegetation dynamics and carbon-nitrogen cycles may have influenced the drought characteristics. Our results demonstrate skillful simulation of the South American climate in the model, and indicate substantial sensitivity of the region's hydroclimatology to vegetation dynamics. This presentation will compare the role of global oceanic forcing versus regional land surface feedback in the recent recurrent droughts, and will characterize the effects of vegetation dynamics in enhancing the drought severity. Preliminary results on future projections of the regional ecosystem and droughts perspective will be also presented.

Assessing the Role of Climate Variability on Liver Fluke Risk in the UK Through Mechanistic Hydro-Epidemiological Modelling

NASA Astrophysics Data System (ADS)

Beltrame, L.; Dunne, T.; Rose, H.; Walker, J.; Morgan, E.; Vickerman, P.; Wagener, T.

2016-12-01

Liver fluke is a flatworm parasite infecting grazing animals worldwide. In the UK, it causes considerable production losses to cattle and sheep industries and costs farmers millions of pounds each year due to reduced growth rates and lower milk yields. Large part of the parasite life-cycle takes place outside of the host, with its survival and development strongly controlled by climatic and hydrologic conditions. Evidence of climate-driven changes in the distribution and seasonality of fluke disease already exists, as the infection is increasingly expanding to new areas and becoming a year-round problem. Therefore, it is crucial to assess current and potential future impacts of climate variability on the disease to guide interventions at the farm scale and mitigate risk. Climate-based fluke risk models have been available since the 1950s, however, they are based on empirical relationships derived between historical climate and incidence data, and thus are unlikely to be robust for simulating risk under changing conditions. Moreover, they are not dynamic, but estimate risk over large regions in the UK based on monthly average climate conditions, so they do not allow investigating the effects of climate variability for supporting farmers' decisions. In this study, we introduce a mechanistic model for fluke, which represents habitat suitability for disease development at 25m resolution with a daily time step, explicitly linking the parasite life-cycle to key hydro-climate conditions. The model is used on a case study in the UK and sensitivity analysis is performed to better understand the role of climate variability on the space-time dynamics of the disease, while explicitly accounting for uncertainties. Comparisons are presented with experts' knowledge and a widely used empirical model.

Robust multiscale prediction of Po River discharge using a twofold AR-NN approach

NASA Astrophysics Data System (ADS)

Alessio, Silvia; Taricco, Carla; Rubinetti, Sara; Zanchettin, Davide; Rubino, Angelo; Mancuso, Salvatore

2017-04-01

The Mediterranean area is among the regions most exposed to hydroclimatic changes, with a likely increase of frequency and duration of droughts in the last decades and potentially substantial future drying according to climate projections. However, significant decadal variability is often superposed or even dominates these long-term hydrological trend as observed, for instance, in North Italian precipitation and river discharge records. The capability to accurately predict such decadal changes is, therefore, of utmost environmental and social importance. In order to forecast short and noisy hydroclimatic time series, we apply a twofold statistical approach that we improved with respect to previous works [1]. Our prediction strategy consists in the application of two independent methods that use autoregressive models and feed-forward neural networks. Since all prediction methods work better on clean signals, the predictions are not performed directly on the series, but rather on each significant variability components extracted with Singular Spectrum Analysis (SSA). In this contribution, we will illustrate the multiscale prediction approach and its application to the case of decadal prediction of annual-average Po River discharges (Italy). The discharge record is available for the last 209 years and allows to work with both interannual and decadal time-scale components. Fifteen-year forecasts obtained with both methods robustly indicate a prominent dry period in the second half of the 2020s. We will discuss advantages and limitations of the proposed statistical approach in the light of the current capabilities of decadal climate prediction systems based on numerical climate models, toward an integrated dynamical and statistical approach for the interannual-to-decadal prediction of hydroclimate variability in medium-size river basins. [1] Alessio et. al., Natural variability and anthropogenic effects in a Central Mediterranean core, Clim. of the Past, 8, 831-839, 2012.

Modeling the potential of the Northern China forest shelterbelt in improving hydroclimate conditions

Treesearch

Yongqiang Liu; John Stanturf; Houquan Lu

2008-01-01

The forest shelterbelt (afforestation) project in northern China is the most significant ecosystem project initiated in China during the past three decades. It aims to improve and conserve the ecological environment in the project areas. The tree belt stands along the southern edge of the sandy lands, nearly paralleling to the Great Wall. This study used a regional...

Temporal Tendencies of River Discharge of Five Watersheds of Northern Mexico

Treesearch

José Návar; Humberto Hernández; Julio Ríos

2006-01-01

The watersheds of northern Mexico that encompasses the Rio San Pedro, Sinaloa, Nazas, Aguanaval, San Juan, and San Fernando-Soto La Marina are located within the main mountain ranges of northern Mexico and within the zone of large deserts of the boreal hemisphere. The hydro-climate variations, the management of forest soils and land use changes are shaping the supply...

Abrupt response of chemical weathering to Late Quaternary hydroclimate changes in northeast Africa

PubMed Central

Bastian, Luc; Revel, Marie; Bayon, Germain; Dufour, Aurélie; Vigier, Nathalie

2017-01-01

Chemical weathering of silicate rocks on continents acts as a major sink for atmospheric carbon dioxide and has played an important role in the evolution of the Earth’s climate. However, the magnitude and the nature of the links between weathering and climate are still under debate. In particular, the timescale over which chemical weathering may respond to climate change is yet to be constrained at the continental scale. Here we reconstruct the relationships between rainfall and chemical weathering in northeast Africa for the last 32,000 years. Using lithium isotopes and other geochemical proxies in the clay-size fraction of a marine sediment core from the Eastern Mediterranean Sea, we show that chemical weathering in the Nile Basin fluctuated in parallel with the monsoon-related climatic evolution of northeast Africa. We also evidence strongly reduced mineral alteration during centennial-scale regional drought episodes. Our findings indicate that silicate weathering may respond as quickly as physical erosion to abrupt hydroclimate reorganization on continents. Consequently, we anticipate that the forthcoming hydrological disturbances predicted for northeast Africa may have a major impact on chemical weathering patterns and soil resources in this region. PMID:28290474

Abrupt decadal-to-centennial hydroclimate changes in the Mediterranean region since the mid-Holocene

NASA Astrophysics Data System (ADS)

Hu, Hsun-Ming; Shen, Chuan-Chou; Jiang, Xiuyang; Wang, Yongjin; Mii, Horng-Sheng; Michel, Véronique

2016-04-01

A series of severe drought events in the Mediterranean region over the past two decades has posed a threat on both human society and biosystem. Holocene hydrological dynamics can offer valuable clues for understanding future climate and making proper adaption strategy. Here, we present a decadal-resolved stalagmite record documenting various hydroclimatic fluctuations in the north central Mediterranean region since the middle Holocene. The stalagmite δ18O sequence shows dramatic instability, characterized by abrupt shifts between dry and wet conditions <50 years. The timing of regional culture demises, such as the Hittite Kingdom, Mycenaean Greece, Akkadian Empire, Egyptian Old Kingdom, and Uruk, occurred during the drought events, suggesting an important role of climate impact on human civilization. The unstable hydroclimate evolution is related to transferred North Atlantic Oscillation states. Rate of rapid transfer of precipitation patterns, which can be pin-pointed by our good chronology, improves the prediction to future climate changes in North Atlantic region. We also found that a strong correlation between this stalagmite δ18O and sea surface temperatures especially in Pacific Ocean. This agreement suggests a distant interregional climate teleconnection.

Abrupt response of chemical weathering to Late Quaternary hydroclimate changes in northeast Africa.

PubMed

Bastian, Luc; Revel, Marie; Bayon, Germain; Dufour, Aurélie; Vigier, Nathalie

2017-03-14

Chemical weathering of silicate rocks on continents acts as a major sink for atmospheric carbon dioxide and has played an important role in the evolution of the Earth's climate. However, the magnitude and the nature of the links between weathering and climate are still under debate. In particular, the timescale over which chemical weathering may respond to climate change is yet to be constrained at the continental scale. Here we reconstruct the relationships between rainfall and chemical weathering in northeast Africa for the last 32,000 years. Using lithium isotopes and other geochemical proxies in the clay-size fraction of a marine sediment core from the Eastern Mediterranean Sea, we show that chemical weathering in the Nile Basin fluctuated in parallel with the monsoon-related climatic evolution of northeast Africa. We also evidence strongly reduced mineral alteration during centennial-scale regional drought episodes. Our findings indicate that silicate weathering may respond as quickly as physical erosion to abrupt hydroclimate reorganization on continents. Consequently, we anticipate that the forthcoming hydrological disturbances predicted for northeast Africa may have a major impact on chemical weathering patterns and soil resources in this region.

The Importance of the Montreal Protocol in Protecting the Earth's Hydroclimate

NASA Astrophysics Data System (ADS)

Seager, R.; Wu, Y.; Polvani, L. M.

2012-12-01

The 1987 Montreal Protocol regulating emissions of ozone depleting chlorofluorocarbons (CFCs) was motivated primarily by the harm to human health and ecosystems arising from increased exposure to ultraviolet-B (UV-B) radiation associated with depletion from the ozone layer. It is now known that the Montreal Protocol has reduced global warming since CFCs are greenhouse gases (GHGs). In this paper we show that the Montreal Protocol also significantly protects the Earth's hydroclimate, even though this was also not a motivating factor in the decision-making that led to the Protocol. General Circulation Model (GCM) results show that in the coming decade (2020-29), under the 'World Avoided' scenario of no regulations on CFC emissions, the subtropical dry zones would in general get drier, and the middle and high latitude regions wetter. This change is similar, in both pattern and magnitude, to that in the coming decade caused by projected increases in carbon dioxide concentrations. This implies that because of the Montreal Protocol, and the ozone depletion and global warming associated with CFCs thus avoided, the hydrological cycle changes in the coming decade will be significantly less than what they otherwise would have been.

Holocene and Last Interglacial climate of the Faroe Islands from sedimentary leaf wax hydrogen isotopes

NASA Astrophysics Data System (ADS)

Curtin, L.; D'Andrea, W. J.; de Wet, G.; Balascio, N.; Bradley, R. S.

2017-12-01

The climate of the North Atlantic region is extremely sensitive to changes in ocean and atmospheric circulation, and understanding past natural variability in North Atlantic climate provides important context for modern climate change. Here, we present Holocene and Eemian hydrogen isotope (δD) records from leaf waxes preserved in lacustrine sediments from the North Atlantic Faroe Islands and interpret them as a proxy for temperature and hydroclimate variability. In addition to helping to constrain the timing and amplitude of climate evolution during each of these interglacial periods, the data can be used to directly compare Eemian and Holocene climate using the same proxy from the same terrestrial location. Of the leaf waxes measured, the δD values of long-chain and mid-chain n-alkanes showed two different signals, which we interpret to represent leaf water δD values and lake water δD values, respectively. The δD values for long-chain and mid-chain fatty acids were most similar to the mid-chain n-alkanes, and likely represent a mixture of terrestrial and aquatic sources. Leaf wax-inferred δD values of precipitation during the early Holocene (10,000 to 8,000 cal yr BP) are 13‰ enriched compared to the remainder of the Holocene (after 8,000 cal yr BP), which show relatively stable values over time. Inferred lake water δD values decreased slowly over the late Holocene, suggesting a gradual transition to a wetter climate after 4,000 cal yr BP. At 2,000 cal yr BP there was a significant change in the distribution of leaf waxes that suggests a transition from shrubland to grassland, but which pre-dates the pollen evidence for this transition. The last interglacial period has been suggested as an analog for future climate conditions. We found that long-chain alkane δD values from the Eemian are most similar to the earliest Holocene, which corroborate previous pollen studies suggesting a warmer climate at the Faroe Islands during this period.

An Investigation of the Hydroclimate Variability of Eastern Africa

NASA Astrophysics Data System (ADS)

Smith, K. A.; Semazzi, F. H. M.

2015-12-01

The flow of the Victoria Nile, and the productivity of the dams along it, is determined by the level of Lake Victoria, which is primarily dictated by the rainfall and temperature variability over the Lake Victoria Basin. Notwithstanding the indisputable decline of water resources over the lake basin during the Long Rains of March - May, there is a strong indication based on IPCC climate projections that this trend, which has persisted for several decades, will reverse in the next few decades. This phenomenon has come to be known as the Eastern-Central African climate change paradox and could have profound implications on sustainable development for the next few decades in Lake Victoria Basin. The purpose of this study is to investigate the climate variability associated with the East African Climate Change Paradox for the recent decades. This research analyzes observations to understand the sources of variability and potential physical mechanisms related to the decline in precipitation over Eastern Africa. We then investigate the hydrological factors involved in the decline of Lake Victoria levels in the context of the decline in rainfall. While East Africa has been experiencing persistent decline of the Long Rains for multiple decades, this same decline is not seen in annual rainfall. The remaining seasons show an increase in rainfall which is compensating for the decline of the Long Rains. It is possible that the Long Rains season is shifting in such a way that the season starts earlier, in February, and ending sooner. The corresponding annual Lake Victoria levels modeled using observed rainfall do not decline in the recent decades, except when the Long Rains seasonal variability is considered without variability from other seasons. This shift could impact hydroelectric power planning on a monthly or seasonal time scale, and could potentially have a large impact on agriculture, since it would shift the growing season in the region.

The PAGES 2k Network, Phase 3: Themes and Call for Participation

NASA Astrophysics Data System (ADS)

von Gunten, L.; Mcgregor, H. V.; Martrat, B.; St George, S.; Neukom, R.; Bothe, O.; Linderholm, H. W.; Phipps, S. J.; Abram, N.

2017-12-01

The past 2000 years (the "2k" interval) provides critical context for understanding recent anthropogenic forcing of the climate and provides baseline information about the characteristics of natural climate variability. It also presents opportunities to improve the interpretation of proxy observations and to evaluate the climate models used to make future projections. Phases 1 and 2 of the PAGES 2k Network focussed on building regional and global surface temperature reconstructions for terrestrial regions and the oceans, and comparing these with model simulations to identify mechanisms of climate variation on interannual to bicentennial time scales. Phase 3 was launched in May 2017 and aims to address major questions around past hydroclimate, climate processes and proxy uncertainties. Its scientific themes are: Theme 1: "Climate Variability, Modes and Mechanisms"Further understand the mechanisms driving regional climate variability and change on interannual to centennial time scales; Theme 2: "Methods and Uncertainties"Reduce uncertainties in the interpretation of observations imprinted in paleoclimatic archives by environmental sensors; Theme 3: "Proxy and Model Understanding"Identify and analyse the extent of agreement between reconstructions and climate model simulations. Research is organized as a linked network of well-defined projects, identified and led by 2k community members. The 2k projects focus on specific scientific questions aligned with Phase 3 themes, rather than being defined along regional boundaries. New 2k projects can be proposed at any time at http://www.pastglobalchanges.org/ini/wg/2k-network/projects An enduring element of PAGES 2k is a culture of collegiality, transparency, and reciprocity. Phase 3 seeks to stimulate community based projects and facilitate collaboration between researchers from different regions and career stages, drawing on the breadth and depth of the global PAGES 2k community. All PAGES 2k projects also promote best practises in data stewardship for the research community. The network is open to anyone who is interested. If you would like to participate in PAGES 2k or receive updates, please join our mailing list or speak to a coordinating committee member.

Conjunctive management of surface and groundwater resources under projected future climate change scenarios

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mani, Amir; Tsai, Frank T. -C.; Kao, Shih-Chieh

Our study introduces a mixed integer linear fractional programming (MILFP) method to optimize conjunctive use of future surface water and groundwater resources under projected climate change scenarios. The conjunctive management model maximizes the ratio of groundwater usage to reservoir water usage. Future inflows to the reservoirs were estimated from the future runoffs projected through hydroclimate modeling considering the Variable Infiltration Capacity model, and 11 sets of downscaled Coupled Model Intercomparison Project phase 5 global climate model projections. Bayesian model averaging was adopted to quantify uncertainty in future runoff projections and reservoir inflow projections due to uncertain future climate projections. Optimizedmore » conjunctive management solutions were investigated for a water supply network in northern Louisiana which includes the Sparta aquifer. Runoff projections under climate change scenarios indicate that runoff will likely decrease in winter and increase in other seasons. Ultimately, results from the developed conjunctive management model with MILFP indicate that the future reservoir water, even at 2.5% low inflow cumulative probability level, could counterbalance groundwater pumping reduction to satisfy demands while improving the Sparta aquifer through conditional groundwater head constraint.« less

Problems with the North American Monsoon in CMIP/IPCC GCM Precipitation

NASA Astrophysics Data System (ADS)

Schiffer, N. J.; Nesbitt, S. W.

2011-12-01

Successful water management in the Desert Southwest and surrounding areas hinges on anticipating the timing and distribution of precipitation. IPCC AR4 models predict a more arid climate, more extreme precipitation events, and an earlier peak in springtime streamflow in the North American Monsoon region as the area warms. This study aims to assess the summertime skill with which general circulation models (GCMs) simulate precipitation and related dynamics over this region, a necessary precursor to reliable hydroclimate projections. Thirty-year climatologies of several GCMs in the third and fifth Climate Model Intercomparison Projects (CMIP) are statistically evaluated against each other and observed climatology for their skill in representing the location, timing, variability, character, and large-scale forcing of precipitation over the southwestern United States and northwestern Mexico. The results of this study will lend greater credence to more detailed, higher resolution studies, based on the CMIP and IPCC models, of the region's future hydrology. Our ultimate goal is to provide guidance such that decision-makers can plan future water management with more confidence.

Conjunctive management of surface and groundwater resources under projected future climate change scenarios

DOE PAGES

Mani, Amir; Tsai, Frank T. -C.; Kao, Shih-Chieh; ...

2016-06-16

Our study introduces a mixed integer linear fractional programming (MILFP) method to optimize conjunctive use of future surface water and groundwater resources under projected climate change scenarios. The conjunctive management model maximizes the ratio of groundwater usage to reservoir water usage. Future inflows to the reservoirs were estimated from the future runoffs projected through hydroclimate modeling considering the Variable Infiltration Capacity model, and 11 sets of downscaled Coupled Model Intercomparison Project phase 5 global climate model projections. Bayesian model averaging was adopted to quantify uncertainty in future runoff projections and reservoir inflow projections due to uncertain future climate projections. Optimizedmore » conjunctive management solutions were investigated for a water supply network in northern Louisiana which includes the Sparta aquifer. Runoff projections under climate change scenarios indicate that runoff will likely decrease in winter and increase in other seasons. Ultimately, results from the developed conjunctive management model with MILFP indicate that the future reservoir water, even at 2.5% low inflow cumulative probability level, could counterbalance groundwater pumping reduction to satisfy demands while improving the Sparta aquifer through conditional groundwater head constraint.« less

Intensified ENSO-Driven Precipitation Teleconnections in the Future

NASA Astrophysics Data System (ADS)

Bonfils, C.; Santer, B. D.; Phillips, T. J.; Marvel, K.; Leung, L. R.; Doutriaux, C.

2014-12-01

The El Niño-Southern Oscillation (ENSO) is an important driver of regional hydroclimate variability through far-reaching teleconnections. Most climate models project an increase in the frequency of extreme El Niño events under increased greenhouse-gas (GHG) forcing. However, it is unclear how other aspects of ENSO and ENSO-driven teleconnections will evolve in the future. Here, we identify in 20th century sea-surface temperature (SST) observations a time-invariant ENSO-like (ENSOL) pattern that is largely uncontaminated by GHG forcing. We use this pattern to investigate the future precipitation (P) response to ENSO-like SST anomalies. Models that better capture observed ENSOL characteristics produce P teleconnection patterns that are in better accord with observations and more stationary in the 21st century. We decompose the future P response to ENSOL into the sum of three terms: (1) the change in P mean state, (2) the historical P response to ENSOL, and (3) a future enhancement in the P response to ENSOL. In many regions, this last term can aggravate the P extremes associated with ENSO variability. This simple decomposition allows us to identify regions likely to experience ENSOL-induced P changes that are without precedent in the current climate. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Two millennia of Mesoamerican monsoon variability driven by Pacific and Atlantic synergistic forcing

NASA Astrophysics Data System (ADS)

Lachniet, Matthew S.; Asmerom, Yemane; Polyak, Victor; Bernal, Juan Pablo

2017-01-01

The drivers of Mesoamerican monsoon variability over the last two millennia remain poorly known because of a lack of precisely-dated and climate-calibrated proxy records. Here, we present a new high resolution (∼2 yrs) and precisely-dated (± 4 yr) wet season hydroclimate reconstruction for the Mesoamerican sector of the North American Monsoon over the past 2250 years based on two aragonite stalagmites from southwestern Mexico which replicate oxygen isotope variations over the 950-1950 CE interval. The reconstruction is quantitatively calibrated to instrumental rainfall variations in the Basin of Mexico. Comparisons to proxy indices of ocean-atmosphere circulation show a synergistic forcing by the North Atlantic and El Niño/Southern Oscillations, whereby monsoon strengthening coincided with a La Niña-like mode and a negative North Atlantic Oscillation, and vice versa for droughts. Our data suggest that weak monsoon intervals are associated with a strong North Atlantic subtropical high pressure system and a weak Intertropical convergence zone in the eastern Pacific Ocean. Population expansions at three major highland Mexico civilization of Teotihuacan, Tula, and Aztec Tenochtitlan were all associated with drought to pluvial transitions, suggesting that urban population growth was favored by increasing freshwater availability in the semi-arid Mexican highlands, and that this hydroclimatic change was controlled by Pacific and Atlantic Ocean forcing.

North American Megadroughts in the Common Era: Reconstructions and Simulations

NASA Technical Reports Server (NTRS)

Cook, Benjamin I.; Cook, Edward R.; Smerdon, Jason E.; Seager, Richard; Williams, A. Park; Coats, Sloan; Stahle, David W.; Villanueva Diaz, Jose

2016-01-01

During the Medieval Climate Anomaly (MCA), Western North America experienced episodes of intense aridity that persisted for multiple decades or longer. These megadroughts are well documented in many proxy records, but the causal mechanisms are poorly understood. General circulation models (GCMs) simulate megadroughts, but do not reproduce the temporal clustering of events during the MCA, suggesting they are not caused by the time history of volcanic or solar forcing. Instead, GCMs generate megadroughts through (1) internal atmospheric variability, (2) sea-surface temperatures, and (3) land surface and dust aerosol feedbacks. While no hypothesis has been definitively rejected, and no GCM has accurately reproduced all features (e.g., timing, duration, and extent) of any specific megadrought, their persistence suggests a role for processes that impart memory to the climate system (land surface and ocean dynamics). Over the 21st century, GCMs project an increase in the risk of megadrought occurrence through greenhouse gas forced reductions in precipitation and increases in evaporative demand. This drying is robust across models and multiple drought indicators, but major uncertainties still need to be resolved. These include the potential moderation of vegetation evaporative losses at higher atmospheric [CO2], variations in land surface model complexity, and decadal to multidecadal modes of natural climate variability that could delay or advance onset of aridification over the the next several decades. Because future droughts will arise from both natural variability and greenhouse gas forced trends in hydroclimate, improving our understanding of the natural drivers of persistent multidecadal megadroughts should be a major research priority.

Roosevelt Island Climate Evolution Project (RICE): A 65 Kyr ice core record of black carbon aerosol deposition to the Ross Ice Shelf, West Antarctica.

NASA Astrophysics Data System (ADS)

Edwards, Ross; Bertler, Nancy; Tuohy, Andrea; Neff, Peter; Proemse, Bernedette; Feiteng, Wang; Goodwin, Ian; Hogan, Chad

2015-04-01

Emitted by fires, black carbon aerosols (rBC) perturb the atmosphere's physical and chemical properties and are climatically active. Sedimentary charcoal and other paleo-fire records suggest that rBC emissions have varied significantly in the past due to human activity and climate variability. However, few paleo rBC records exist to constrain reconstructions of the past rBC atmospheric distribution and its climate interaction. As part of the international Roosevelt Island Climate Evolution (RICE) project, we have developed an Antarctic rBC ice core record spanning the past ~65 Kyr. The RICE deep ice core was drilled from the Roosevelt Island ice dome in West Antarctica from 2011 to 2013. The high depth resolution (~ 1 cm) record was developed using a single particle intracavity laser-induced incandescence soot photometer (SP2) coupled to an ice core melter system. The rBC record displays sub-annual variability consistent with both austral dry-season and summer biomass burning. The record exhibits significant decadal to millennial-scale variability consistent with known changes in climate. Glacial rBC concentrations were much lower than Holocene concentrations with the exception of several periods of abrupt increases in rBC. The transition from glacial to interglacial rBC concentrations occurred over a much longer time relative to other ice core climate proxies such as water isotopes and suggests . The protracted increase in rBC during the transition may reflected Southern hemisphere ecosystem / fire regime changes in response to hydroclimate and human activity.

Sensitivities and Tipping Points of Power System Operations to Fluctuations Caused by Water Availability and Fuel Prices

NASA Astrophysics Data System (ADS)

O'Connell, M.; Macknick, J.; Voisin, N.; Fu, T.

2017-12-01

The western US electric grid is highly dependent upon water resources for reliable operation. Hydropower and water-cooled thermoelectric technologies represent 67% of generating capacity in the western region of the US. While water resources provide a significant amount of generation and reliability for the grid, these same resources can represent vulnerabilities during times of drought or low flow conditions. A lack of water affects water-dependent technologies and can result in more expensive generators needing to run in order to meet electric grid demand, resulting in higher electricity prices and a higher cost to operate the grid. A companion study assesses the impact of changes in water availability and air temperatures on power operations by directly derating hydro and thermo-electric generators. In this study we assess the sensitivities and tipping points of water availability compared with higher fuel prices in electricity sector operations. We evaluate the impacts of varying electricity prices by modifying fuel prices for coal and natural gas. We then analyze the difference in simulation results between changes in fuel prices in combination with water availability and air temperature variability. We simulate three fuel price scenarios for a 2010 baseline scenario along with 100 historical and future hydro-climate conditions. We use the PLEXOS electricity production cost model to optimize power system dispatch and cost decisions under each combination of fuel price and water constraint. Some of the metrics evaluated are total production cost, generation type mix, emissions, transmission congestion, and reserve procurement. These metrics give insight to how strained the system is, how much flexibility it still has, and to what extent water resource availability or fuel prices drive changes in the electricity sector operations. This work will provide insights into current electricity operations as well as future cases of increased penetration of variable renewable generation technologies such as wind and solar.

Projecting 21st Century Snowpack Trends in the Western United States using Variable-Resolution CESM

NASA Astrophysics Data System (ADS)

Rhoades, A.; Huang, X.; Zarzycki, C. M.; Ullrich, P. A.

2015-12-01

The western USA is integrally reliant upon winter season snowpack, which supplies 3/4 of the region's fresh water and buffers against seasonal aridity on agricultural, ecosystem, and urban water demands. By the end of the 21st century, western USA snowpack (SWE) could decline by 40-70%, snowfall by 25-40%, more winter storms could tend towards rain rather than snow, and the peak timing of snowmelt will shift several weeks earlier in the season. Further, there has been evidence that mountain ranges could face more accelerated warming (elevational dependent warming) due to climate change. These future trends have largely been derived from global climate models (CMIP5) which can't resolve some of the more relatively narrow mountain ranges, like the California Sierra Nevada, in great detail. Therefore, due to the importance of orographic uplift on weather fronts, eastern Pacific sea-surface temperature anomalies, atmospheric river events, and mesoscale convective systems, high-resolution global scale modeling techniques are necessary to properly resolve western USA mountain range climatology. Variable-resolution global climate models (VRGCMs) are a promising next-generation technique to analyze both past and future hydroclimatic trends in the region. VRGCMs serve as a bridge between regional and global models by allowing for high-resolution in areas of interest, eliminate lateral boundary forcings (and resultant model biases), allow for more dynamically inclusive large-scale climate teleconnections, and require smaller simulation times and lower data storage demand (compared to conventional global models). This presentation focuses on validating these next-generation models as well as projecting future climate change scenario impacts on several of the western USA's key hydroclimate metrics (e.g., two-meter surface temperature, snow cover, snow water equivalent, and snowfall) to inform water managers and policy makers and offer resilience to climate change impacts facing the region.

Evidence for Large Hydrologic and Ecologic Variability During the Late Wisconsin in the Coastal Southwest United States (Lake Elsinore, CA)

NASA Astrophysics Data System (ADS)

Kirby, M.; Heusser, L. E.; Scholz, C. A.; Anderson, M.; Rhodes, E. J.; Hiner, C.; Palermo, J. A.; Silveira, E.

2016-12-01

Future climate change is expected to alter the planet's water cycle, thus stressing water resources and ecologic stability. This impact is predicted to be especially significant in arid environments. Unfortunately, continuous, sub-centennially resolved paleo-terrestrial records are rare from arid environments such as the coastal southwest US (cswUS). Lake Elsinore, a pull-apart basin located 90 km SE of Los Angeles CA, is the largest natural lake in the cswUS. Gravity studies indicate nearly 1000 m of sediments occupy the basin. A recent seismic reflection survey imaged the upper 60-80 m of sediment, revealing continuous sediment accumulation. Here, we present a decadal-to-multi-decadal lacustrine sediment core record used to assess the relationship between vegetation (i.e., pollen) and run-off variability (i.e., grain size) during the late Wisconsin (10-32 kyrs BP). In general, the late Wisconsin is characterized by run-off greater than during the Holocene, indicating more frequent winter storms and/or higher intensity precipitation. A notable dry period, however, exists between 25.5-27.5 kyrs BP (Heusser et al., 2015), where lake level regressed but did not desiccate. Modern lake-level - grain size relationships are used to assess paleo-lake levels during this glacial mega-drought. Peak run-off occurs between 14.7 and 19.8 kyrs BP, generally post-dating the global LGM. A two-step decrease in run-off characterize the B-A to YD to Holocene (Kirby et al., 2013). Vegetation shows a fairly strong coupling to the run-off indicator, signifying rapid ecologic responses to changes in regional hydroclimates. This run-off - vegetation coupling is especially relevant to understanding future vegetative responses in the CA Floristic Province Biodiversity Hotspot. Finally, results are compared to potential forcings such as winter-summer insolation, Pacific SSTs, and Atlantic Meridional Overturning Circulation as well as regional paleo-records.

Assessing response of local moisture conditions in central Brazil to variability in regional monsoon intensity using speleothem 87Sr/86Sr values

NASA Astrophysics Data System (ADS)

Wortham, Barbara E.; Wong, Corinne I.; Silva, Lucas C. R.; McGee, David; Montañez, Isabel P.; Troy Rasbury, E.; Cooper, Kari M.; Sharp, Warren D.; Glessner, Justin J. G.; Santos, Roberto V.

2017-04-01

Delineating the controls on hydroclimate throughout Brazil is essential to assessing potential impact of global climate change on water resources and biogeography. An increasing number of monsoon reconstructions from δ18O records provide insight into variations in regional monsoon intensity over the last millennium. The strength, however, of δ18O as a proxy of regional climate limits its ability to reflect local conditions, highlighting the need for comparable reconstructions of local moisture conditions. Here, speleothem 87Sr/86Sr values are developed as a paleo-moisture proxy in central Brazil to complement existing δ18O-based reconstructions of regional monsoon intensity. Speleothem 87Sr/86Sr values are resolved using laser ablation and conventional solution mass spectrometry at high resolution relative to existing (non-δ18O-based) paleo-moisture reconstructions to allow comparisons of centennial variability in paleo-monsoon intensity and paleo-moisture conditions. Variations in speleothem 87Sr/86Sr values from Tamboril Cave are interpreted to reflect varying extents of water interaction with the carbonate host rock, with more interaction resulting in greater evolution of water isotope values from those initially acquired from the soil to those of the carbonate bedrock. Increasing speleothem 87Sr/86Sr values over the last millennium suggest progressively less interaction with the carbonate host rock likely resulting from higher infiltration rates, expected under wetter conditions. Increasingly wetter conditions over the last millennium are consistent with an overall trend of increasing monsoon intensity (decreasing δ18O values) preserved in many existing δ18O records from the region. Such a trend, however, is absent in δ18O records from our site (central Brazil) and Cristal Cave (southeast Brazil), suggesting the existence of divergent (relevant to δ18Oprecip) shifts in the climate patterns within and outside the core monsoon region.

A walk through the hydroclimate network in Yosemite National Park: River chemistry

USGS Publications Warehouse

Peterson, Dave; Smith, Richard; Hager, Stephen

2004-01-01

Visitors to Yosemite National Park (YNP) are fully aware of the weather, snowmelt, waterfalls (Photo 1), and river discharge and river and lake water temperature. They are not, however, thinking about river chemistry because you can’t see, hear, or feel it. So a river chemistry article in Nature Notes needs a familiar background before we break out the instruments.

Impacts of regional land-grab on regional hydroclimate in southeastern Africa via modeling and remote sensing

NASA Astrophysics Data System (ADS)

Maksimowicz, M.; Masarik, M. T.; Brandt, J.; Flores, A. N.

2017-12-01

Land use/land cover (LULC) change directly impacts the partitioning of surface mass and energy fluxes. Regional-scale weather and climate are potentially altered by LULC if the resultant changes in partitioning of surface energy fluxes are significant enough to induce changes in the evolution of the planetary boundary layer and its interaction with the atmosphere above. Dynamics of land use, particularly those related to the social dimensions of the Earth System, are often simplified or not represented in regional land-atmosphere models or Earth System Models. This study explores the role of LULC change on a regional hydroclimate system, focusing on potential hydroclimate changes arising from timber harvesting due to a land grab boom in Mozambique. We also focus more narrowly at quantifying regional impacts on Gorongosa National Park, a nationally important economic and biodiversity resource in southeastern Africa. After nationalizing all land in 1975 after Mozambique gained independence, complex social processes, including an extended low intensity conflict civil war and economic hardships, led to an escalation of land use rights grants to foreign governments. Between 2004 and 2009, large tracts of land were requested for timber. Here we use existing tree cover loss datasets to more accurately represent land cover within a regional weather model. LULC in a region encompassing Gorongosa is updated at three instances between 2001 and 2014 using a tree cover loss dataset. We use these derived LULC datasets to inform lower boundary conditions in the Weather Research and Forecasting (WRF) model. To quantify potential hydrometeorological changes arising from land use change, we performed a factorial-like experiment by mixing input LULC maps and atmospheric forcing data from before, during, and after the land grab. Results suggest that the land grab has impacted microclimate parameters in a significant way via direct and indirect impacts on land-atmosphere interactions. Results of this study suggest that LULC change arising from regional social dynamics are a potentially understudied, yet important human process to capture in both regional reanalyses and climate change projections.

Tropical Hydroclimate Change during Heinrich Stadial 1: An Integrative Proxy-Model Synthesis

NASA Astrophysics Data System (ADS)

Lawman, A. E.; Sun, T.; Shanahan, T. M.; Di Nezio, P. N.; Gomez, K.; Piatrunia, N.; Sun, C.; Wu, X.; Kageyama, M.; Merkel, U.; Otto-Bliesner, B. L.; Abe-Ouchi, A.; Lohmann, G.; Singarayer, J. S.

2017-12-01

We explore the response of tropical climate to abrupt cooling of the North Atlantic (NA) during Heinrich Stadial 1 (HS1) combining paleoclimate proxies with model simulations. A total of 146 published paleoclimate records from tropical locations are used to categorize whether HS1 was wetter, drier, or unchanged relative to a deglacial baseline state. Only records with sufficient resolution to resolve HS1 and sufficient length to characterize the deglacial trend are considered. This synthesis reveals large-scale patterns of hydroclimate change relative to glacial conditions, confirming previously reported weaker Indian summer monsoon, a wetter southern Africa, and drying over the Caribbean. Our synthesis also reveals large-scale drying over the Maritime continent as well as wetter conditions in northern Australia and southern tropical South America. Our reinterpretation of the available proxy data reveals far more complexity and uncertainties for equatorial East Africa, a region that appears to straddle a pattern of dryer conditions to the north and wetter conditions to the south. Overall, these patterns of hydroclimate change depart from a southward shift of the Inter Tropical Convergence Zone (ITCZ), particularly outside the tropical Atlantic. We explore mechanisms driving these changes using a multi-model ensemble of "hosing" simulations performed relative to glacial conditions. The models show robust weakening of the Afro-Asian Monsoon, which we attribute to ventilation of colder mid-latitude air. Not all models simulate the remaining patterns inferred from the proxy data. The best-agreeing models indicate that cooling over the tropical NA and the Caribbean may be essential to communicate the response to the global tropics. This response can induce warming over the tropical South Atlantic via the wind-evaporation-SST feedback, driving wetter conditions in South Africa and tropical South America. Cooling over the Caribbean is communicated to the Pacific over the Central American isthmus resulting in an El Niño-like pattern accompanied by drying over the Maritime Continent - as seen in the proxy data. Together these results show a dominant role for altered tropical SST gradients driving changes in tropical rainfall, and a lesser role for inter-hemispheric shifts in the ITCZ.

Climatic history of the northeastern United States during the past 3000 years

USGS Publications Warehouse

Marlon, Jennifer R.; Pederson, Neil; Nolan, Connor; Goring, Simon; Shuman, Bryan; Robertson, Ann; Booth, Robert K.; Bartlein, Patrick J.; Berke, Melissa A.; Clifford, Michael; Cook, Edward; Dieffenbacher-Krall, Ann; Dietze, Michael C.; Hessl, Amy; Hubeny, J. Bradford; Jackson, Stephen T.; Marsicek, Jeremiah; McLachlan, Jason S.; Mock, Cary J.; Moore, David J. P.; Nichols, Jonathan M.; Peteet, Dorothy M.; Schaefer, Kevin; Trouet, Valerie; Umbanhowar, Charles; Williams, John W.; Yu, Zicheng

2017-01-01

Many ecosystem processes that influence Earth system feedbacks, including vegetation growth, water and nutrient cycling, and disturbance regimes, are strongly influenced by multi-decadal to millennial-scale variations in climate that cannot be captured by instrumental climate observations. Paleoclimate information is therefore essential for understanding contemporary ecosystems and their potential trajectories under a variety of future climate conditions. With the exception of fossil pollen records, there are a limited number of northeastern US (NE US) paleoclimate archives that can provide constraints on its temperature and hydroclimate history. Moreover, the records that do exist have not been considered together. Tree-ring data indicate that the 20th century was one of the wettest of the past 500 years in the eastern US (Pederson et al., 2014), and lake-level records suggest it was one of the wettest in the Holocene (Newby et al., 2014); how such results compare with other available data remains unclear, however. Here we conduct a systematic review, assessment, and comparison of paleotemperature and paleohydrological proxies from the NE US for the last 3000 years. Regional temperature reconstructions are consistent with the long-term cooling trend (1000 BCE–1700 CE) evident in hemispheric-scale reconstructions, but hydroclimate reconstructions reveal new information, including an abrupt transition from wet to dry conditions around 550–750 CE. NE US paleo data suggest that conditions during the Medieval Climate Anomaly were warmer and drier than during the Little Ice Age, and drier than today. There is some evidence for an acceleration over the past century of a longer-term wetting trend in the NE US, and coupled with the abrupt shift from a cooling trend to a warming trend from increased greenhouse gases, may have wide-ranging implications for species distributions, ecosystem dynamics, and extreme weather events. More work is needed to gather paleoclimate data in the NE US, make inter-proxy comparisons, and improve estimates of uncertainty in the reconstructions.

Simulating the impacts of chronic ozone exposure on plant conductance and photosynthesis, and on the regional hydroclimate using WRF/Chem

NASA Astrophysics Data System (ADS)

Li, Jialun; Mahalov, Alex; Hyde, Peter

2016-11-01

The Noah-Multiparameterization land surface model in the Weather Research and Forecasting (WRF) with Chemistry (WRF/Chem) is modified to include the effects of chronic ozone exposure (COE) on plant conductance and photosynthesis (PCP) found from field experiments. Based on the modified WRF/Chem, the effects of COE on regional hydroclimate have been investigated over the continental United States. Our results indicate that the model with/without modification in its current configuration can reproduce the rainfall and temperature patterns of the observations and reanalysis data, although it underestimates rainfall in the central Great Plains and overestimates it in the eastern coast states. The experimental tests on the effects of COE include setting different thresholds of ambient ozone concentrations ([O3]) and using different linear regressions to quantify PCP against the COE. Compared with the WRF/Chem control run (i.e., without considering the effects of COE), the modified model at different experiment setups improves the simulated estimates of rainfall and temperatures in Texas and regions to the immediate north. The simulations in June, July and August of 2007-2012 show that surface [O3] decrease latent heat fluxes (LH) by 10-27 W m-2, increase surface air temperatures (T 2) by 0.6 °C-2.0 °C, decrease rainfall by 0.9-1.4 mm d-1, and decrease runoff by 0.1-0.17 mm d-1 in Texas and surrounding areas, all of which highly depends on the precise experiment setup, especially the [O3] threshold. The mechanism producing these results is that COE decreases the LH and increases sensible heat fluxes, which in turn increases the Bowen ratios and air temperatures. This lowering of the LH also results in the decrease of convective potential and finally decreases convective rainfall. Employing this modified WRF/Chem model in any high [O3] region can improve the understanding of the interactions of vegetation, meteorology, chemistry/emissions, and crop productivity.

WRF model forecasts and their use for hydroclimate monitoring over southern South America

NASA Astrophysics Data System (ADS)

Muller, Omar; Lovino, Miguel; Berbery, E. Hugo

2017-04-01

Weather forecasting and monitoring systems based on regional models are becoming increasingly relevant for decision support in agriculture and water management. This work evaluates the predictive and monitoring capabilities of a system based on WRF model simulations at 15 km grid spacing over a domain that encompasses La Plata Basin (LPB) in southern South America, where agriculture and water resources are essential. The model's skill up to a lead-time of 7 days is evaluated with daily precipitation and 2m temperature in-situ observations. Results show high prediction performance with 7 days lead-time throughout the domain and particularly over LPB, where about 70% of rain and no-rain days are correctly predicted. The scores tend to be better over humid climates than over arid-to-semiarid climates. Compared to the arid-semiarid climate, the humid climate has a higher probability of detection and less false alarms. The ranges of the skill scores are similar to those found over the United States, suggesting that proper choice of parameterizations lead to no loss of performance of the model. Daily mean, minimum and maximum forecast temperatures are highly correlated with observations up to 7 day lead time. The best performance is for daily mean temperature, followed by minimum temperature and a slightly weaker performance for maximum temperature over arid regions. The usefulness of WRF products for hydroclimate monitoring was tested for an unprecedented drought in southern Brazil and for a slightly above normal precipitation season in northeastern Argentina. In both cases the model products reproduce the observed precipitation conditions with consistent impacts on soil moisture, evapotranspiration and runoff. This evaluation validates the model's usefulness to fore-cast weather up to one week and to monitor climate conditions in real time. The scores suggest that the forecast lead-time can be extended into week two, while bias correction methods can reduce part of the systematic errors.

Evidence of thermophilisation and elevation-dependent warming during the Last Interglacial in the Italian Alps.

PubMed

Johnston, V E; Borsato, A; Frisia, S; Spötl, C; Dublyansky, Y; Töchterle, P; Hellstrom, J C; Bajo, P; Edwards, R L; Cheng, H

2018-02-08

Thermophilisation is the response of plants communities in mountainous areas to increasing temperatures, causing an upward migration of warm-adapted (thermophilic) species and consequently, the timberline. This greening, associated with warming, causes enhanced evapotranspiration that leads to intensification of the hydrological cycle, which is recorded by hydroclimate-sensitive archives, such as stalagmites and flowstones formed in caves. Understanding how hydroclimate manifests at high altitudes is important for predicting future water resources of many regions of Europe that rely on glaciers and snow accumulation. Using proxy data from three coeval speleothems (stalagmites and flowstone) from the Italian Alps, we reconstructed both the ecosystem and hydrological setting during the Last Interglacial (LIG); a warm period that may provide an analogue to a near-future climate scenario. Our speleothem proxy data, including calcite fabrics and the stable isotopes of calcite and fluid inclusions, indicate a +4.3 ± 1.6 °C temperature anomaly at ~2000 m a.s.l. for the peak LIG, with respect to present-day values (1961-1990). This anomaly is significantly higher than any low-altitude reconstructions for the LIG in Europe, implying elevation-dependent warming during the LIG. The enhanced warming at high altitudes must be accounted for when considering future climate adaption strategies in sensitive mountainous regions.

Satellite Remote Sensing and the Hydroclimate: Two Specific Examples of Improved Knowledge and Applications

NASA Astrophysics Data System (ADS)

Shepherd, M.; Santanello, J. A., Jr.

2017-12-01

When Explorer 1 launched nearly 60 years ago, it helped usher in a golden age of scientific understanding of arguably the most important planet in our solar system. From its inception NASA and its partners were charged with leveraging the vantagepoint of space to advance knowledge outside and within Earth's atmosphere. Earth is a particularly complex natural system that is increasingly modified by human activities. The hydrological or water cycle is a critical circuit in the Earth system. Its complexity requires novel observations and simulation capability to fully understand it and predict changes. This talk will introduce some of the unique satellite-based observations used for hydroclimate studies. Two specific examples will be presented. The first example explores a relatively new thread of research examining the impact of soil moisture on landfalling and other types of tropical systems. Recent literature suggests that tropical cyclones or large rain-producing systems like the one that caused catastrophic flooding in Louisiana (2016) derive moisture from a "brown ocean" of wet soils or wetlands. The second example summarizes a decade of research on how urbanization has altered the precipitation and land surface hydrology components of the water cycle. With both cases, a multitude of satellite or model-based datesets will be summarized (e.g., TRMM, GPM, SMAP, NLDAS).

Expansion and Contraction of the Indo-Pacific Tropical Rain Belt over the Last Three Millennia.

PubMed

Denniston, Rhawn F; Ummenhofer, Caroline C; Wanamaker, Alan D; Lachniet, Matthew S; Villarini, Gabriele; Asmerom, Yemane; Polyak, Victor J; Passaro, Kristian J; Cugley, John; Woods, David; Humphreys, William F

2016-09-29

The seasonal north-south migration of the intertropical convergence zone (ITCZ) defines the tropical rain belt (TRB), a region of enormous terrestrial and marine biodiversity and home to 40% of people on Earth. The TRB is dynamic and has been shown to shift south as a coherent system during periods of Northern Hemisphere cooling. However, recent studies of Indo-Pacific hydroclimate suggest that during the Little Ice Age (LIA; AD 1400-1850), the TRB in this region contracted rather than being displaced uniformly southward. This behaviour is not well understood, particularly during climatic fluctuations less pronounced than those of the LIA, the largest centennial-scale cool period of the last millennium. Here we show that the Indo-Pacific TRB expanded and contracted numerous times over multi-decadal to centennial scales during the last 3,000 yr. By integrating precisely-dated stalagmite records of tropical hydroclimate from southern China with a newly enhanced stalagmite time series from northern Australia, our study reveals a previously unidentified coherence between the austral and boreal summer monsoon. State-of-the-art climate model simulations of the last millennium suggest these are linked to changes in the structure of the regional manifestation of the atmosphere's meridional circulation.

Expansion and Contraction of the Indo-Pacific Tropical Rain Belt over the Last Three Millennia

PubMed Central

Denniston, Rhawn F.; Ummenhofer, Caroline C.; Wanamaker, Alan D.; Lachniet, Matthew S.; Villarini, Gabriele; Asmerom, Yemane; Polyak, Victor J.; Passaro, Kristian J.; Cugley, John; Woods, David; Humphreys, William F.

2016-01-01

The seasonal north-south migration of the intertropical convergence zone (ITCZ) defines the tropical rain belt (TRB), a region of enormous terrestrial and marine biodiversity and home to 40% of people on Earth. The TRB is dynamic and has been shown to shift south as a coherent system during periods of Northern Hemisphere cooling. However, recent studies of Indo-Pacific hydroclimate suggest that during the Little Ice Age (LIA; AD 1400–1850), the TRB in this region contracted rather than being displaced uniformly southward. This behaviour is not well understood, particularly during climatic fluctuations less pronounced than those of the LIA, the largest centennial-scale cool period of the last millennium. Here we show that the Indo-Pacific TRB expanded and contracted numerous times over multi-decadal to centennial scales during the last 3,000 yr. By integrating precisely-dated stalagmite records of tropical hydroclimate from southern China with a newly enhanced stalagmite time series from northern Australia, our study reveals a previously unidentified coherence between the austral and boreal summer monsoon. State-of-the-art climate model simulations of the last millennium suggest these are linked to changes in the structure of the regional manifestation of the atmosphere’s meridional circulation. PMID:27682252

Expansion and Contraction of the Indo-Pacific Tropical Rain Belt over the Last Three Millennia

NASA Astrophysics Data System (ADS)

Denniston, Rhawn F.; Ummenhofer, Caroline C.; Wanamaker, Alan D.; Lachniet, Matthew S.; Villarini, Gabriele; Asmerom, Yemane; Polyak, Victor J.; Passaro, Kristian J.; Cugley, John; Woods, David; Humphreys, William F.

2016-09-01

The seasonal north-south migration of the intertropical convergence zone (ITCZ) defines the tropical rain belt (TRB), a region of enormous terrestrial and marine biodiversity and home to 40% of people on Earth. The TRB is dynamic and has been shown to shift south as a coherent system during periods of Northern Hemisphere cooling. However, recent studies of Indo-Pacific hydroclimate suggest that during the Little Ice Age (LIA; AD 1400-1850), the TRB in this region contracted rather than being displaced uniformly southward. This behaviour is not well understood, particularly during climatic fluctuations less pronounced than those of the LIA, the largest centennial-scale cool period of the last millennium. Here we show that the Indo-Pacific TRB expanded and contracted numerous times over multi-decadal to centennial scales during the last 3,000 yr. By integrating precisely-dated stalagmite records of tropical hydroclimate from southern China with a newly enhanced stalagmite time series from northern Australia, our study reveals a previously unidentified coherence between the austral and boreal summer monsoon. State-of-the-art climate model simulations of the last millennium suggest these are linked to changes in the structure of the regional manifestation of the atmosphere’s meridional circulation.

The climate continuum revisited

NASA Astrophysics Data System (ADS)

Emile-Geay, J.; Wang, J.; Partin, J. W.

2015-12-01

A grand challenge of climate science is to quantify the extent of natural variability on adaptation-relevant timescales (10-100y). Since the instrumental record is too short to adequately estimate the spectra of climate measures, this information must be derived from paleoclimate proxies, which may harbor a many-to-one, non-linear (e.g. thresholded) and non-stationary relationship to climate. In this talk, I will touch upon the estimation of climate scaling behavior from climate proxies. Two case studies will be presented: an investigation of scaling behavior in a reconstruction of global surface temperature using state-of- the-art data [PAGES2K Consortium, in prep] and methods [Guillot et al., 2015]. Estimating the scaling exponent β in spectra derived from this reconstruction, we find that 0 < β < 1 in most regions, suggesting long-term memory. Overall, the reconstruction-based spectra are steeper than the ones based on an instrumental dataset [HadCRUT4.2, Morice et al., 2012], and those estimated from PMIP3/CMIP5 models, suggesting the climate system is more energetic at multidecadal to centennial timescales than can be inferred from the short instrumental record or from the models developed to reproduce it [Laepple and Huybers, 2014]. an investigation of scaling behavior in speleothems records of tropical hydroclimate. We will make use of recent advances in proxy system modeling [Dee et al., 2015] and investigate how various aspects of the speleothem system (karst dynamics, age uncertainties) may conspire to bias the estimate of scaling behavior from speleothem timeseries. The results suggest that ignoring such complications leads to erroneous inferences about hydroclimate scaling. References Dee, S. G., J. Emile-Geay, M. N. Evans, Allam, A., D. M. Thompson, and E. J. Steig (2015), J. Adv. Mod. Earth Sys., 07, doi:10.1002/2015MS000447. Guillot, D., B. Rajaratnam, and J. Emile-Geay (2015), Ann. Applied. Statist., pp. 324-352, doi:10.1214/14-AOAS794. Laepple, T., and P. Huybers (2014), PNAS, doi: 10.1073/pnas.1412077111. Morice, C. P., J. J. Kennedy, N. A. Rayner, and P. D. Jones (2012), JGR: Atmospheres, 117(D8), doi:10.1029/2011JD017187. PAGES2K Consortium (in prep), A global multiproxy database for temperature reconstructions of the Common Era, Scientific Data.

Regional Variation in Gravel Riverbed Mobility, Controlled by Hydrologic Regime and Sediment Supply

NASA Astrophysics Data System (ADS)

Pfeiffer, Allison M.; Finnegan, Noah J.

2018-04-01

The frequency and intensity of riverbed mobility are of paramount importance to the inhabitants of river ecosystems as well as to the evolution of bed surface structure. Because sediment supply varies by orders of magnitude across North America, the intensity of bedload transport varies by over an order of magnitude. Climate also varies widely across the continent, yielding a range of flood timing, duration, and intermittency. Together, the differences in sediment supply and hydroclimate result in diverse regimes of bed surface stability. To quantitatively characterize this regional variation, we calculate multidecadal time series of estimated bed surface mobility for 29 rivers using sediment transport equations. We use these data to compare predicted bed mobility between rivers and regions. There are statistically significant regional differences in the (a) exceedance probability of bed-mobilizing flows (W* > 0.002), (b) maximum bed mobility, and (c) number of discrete bed-mobilizing events in a year.

Interannual and low-frequency variability of Upper Indus Basin winter/spring precipitation in observations and CMIP5 models

NASA Astrophysics Data System (ADS)

Greene, Arthur M.; Robertson, Andrew W.

2017-12-01

An assessment is made of the ability of general circulation models in the CMIP5 ensemble to reproduce observed modes of low-frequency winter/spring precipitation variability in the region of the Upper Indus basin (UIB) in south-central Asia. This season accounts for about two thirds of annual precipitation totals in the UIB and is characterized by "western disturbances" propagating along the eastward extension of the Mediterranean storm track. Observational data are utilized for for spatiotemporal characterization of the precipitation seasonal cycle, to compute seasonalized spectra and finally, to examine teleconnections, in terms of large-scale patterns in sea-surface temperature (SST) and atmospheric circulation. Annual and lowpassed variations are found to be associated primarily with SST modes in the tropical and extratropical Pacific. A more obscure link to North Atlantic SST, possibly related to the North Atlantic Oscillation, is also noted. An ensemble of 31 CMIP5 models is then similarly assessed, using unforced preindustrial multi-century control runs. Of these models, eight are found to reproduce well the two leading modes of the observed seasonal cycle. This model subset is then assessed in the spectral domain and with respect to teleconnection patterns, where a range of behaviors is noted. Two model families each account for three members of this subset. The degree of within-family similarity in behavior is shown to reflect underlying model differences. The results provide estimates of unforced regional hydroclimate variability over the UIB on interannual and decadal scales and the corresponding far-field influences, and are of potential relevance for the estimation of uncertainties in future water availability.

Drought variation of western Chinese Loess Plateau since 1568 and its linkages with droughts in western North America

NASA Astrophysics Data System (ADS)

Fang, Keyan; Guo, Zhengtang; Chen, Deliang; Linderholm, Hans W.; Li, Jinbao; Zhou, Feifei; Guo, Guoyang; Dong, Zhipeng; Li, Yingjun

2017-12-01

Understanding long-term drought variations in the past can help to evaluate ongoing and future hydroclimate change in the arid western Chinese Loess Plateau (WCLP), a region with increasing demand for water resources due to the increasing population and socioeconomic activities. Here we present a new tree-ring chronology inform the WCLP, which shows coherent interannual variations with tree-ring chronologies from 7 neighboring areas across the WCLP, suggesting a common regional climate control over tree growth. However, considerable differences are observed among their interdecadal variations, which are likely due to growth disturbances at interdecadal timescales. To deal with this issue, we use a frequency based method to develop a composite tree-ring chronology from 401 tree-ring series from these 8 sites, which shows more pronounced interdecadal variability than a chronology developed using traditional methods. The composite tree-ring chronology is used to reconstruct the annual precipitation from previous August to current July from 1568 to 2012, extending about 50 years longer than the previous longest tree-ring reconstruction from the region. The driest epoch of our reconstruction is found in the 1920s-1930s, which matches well with droughts recorded in historical documents. Over the past four centuries, a strong resemblance between drought variability in the WCLP and western North America (WNA) is evident on multidecadal timescales, but this relationship breaks down on timescales shorter than about 50 years.

A northern Australian coral record of seasonal rainfall and terrestrial runoff (1775-1986)

NASA Astrophysics Data System (ADS)

Patterson, E. W.; Cole, J. E.; Vetter, L.; Lough, J.

2017-12-01

Northern Australia is a climatically dynamic region influenced by both the El Niño-Southern Oscillation (ENSO) and the Australian monsoon. However, this region is largely devoid of long climate records with sub-annual resolution. Understanding long-term climate variations is essential to assess how the storm-prone coasts and rainfall-reliant rangelands of northern Australia have been impacted in the past and may be in the future. In this study, we present a continuous multicentury (1775-1986) coral reconstruction of rainfall and hydroclimate in northern Australia, developed from a Porites spp. coral core collected off the coast of Darwin, Northern Territory, Australia. We combined Ba/Ca measurements with luminescence data as tracers of terrestrial erosion and river discharge respectively. Our results show a strong seasonal cycle in Ba/Ca linked to wet austral summers driven by the Australian monsoon. The Ba/Ca record is corroborated by oxygen isotope data from the same coral and indices of regional river discharge and rainfall. Consistently high levels of Ba measured throughout the record further attest to the importance of river influence on this coral. Our record also shows changes in variability and the baseline level of Ba in coastal waters through time, which may be driven in part by historical land-use change, such as damming or agricultural practices. We will additionally use these records to examine decadal to centennial-scale variability in monsoonal precipitation and regional ENSO signals.

Holocene aridification of India

USGS Publications Warehouse

Ponton, C.; Giosan, L.; Eglinton, T.I.; Fuller, D.Q.; Johnson, J.E.; Kumar, P.; Collett, T.S.

2012-01-01

Spanning a latitudinal range typical for deserts, the Indian peninsula is fertile instead and sustains over a billion people through monsoonal rains. Despite the strong link between climate and society, our knowledge of the long-term monsoon variability is incomplete over the Indian subcontinent. Here we reconstruct the Holocene paleoclimate in the core monsoon zone (CMZ) of the Indian peninsula using a sediment core recovered offshore from the mouth of Godavari River. Carbon isotopes of sedimentary leaf waxes provide an integrated and regionally extensive record of the flora in the CMZ and document a gradual increase in aridity-adapted vegetation from ???4,000 until 1,700 years ago followed by the persistence of aridity-adapted plants after that. The oxygen isotopic composition of planktonic foraminifer Globigerinoides ruber detects unprecedented high salinity events in the Bay of Bengal over the last 3,000 years, and especially after 1,700 years ago, which suggest that the CMZ aridification intensified in the late Holocene through a series of sub-millennial dry episodes. Cultural changes occurred across the Indian subcontinent as the climate became more arid after ???4,000 years. Sedentary agriculture took hold in the drying central and south India, while the urban Harappan civilization collapsed in the already arid Indus basin. The establishment of a more variable hydroclimate over the last ca. 1,700 years may have led to the rapid proliferation of water-conservation technology in south India. Copyright 2012 by the American Geophysical Union.

Landslide Hazard Probability Derived from Inherent and Dynamic Determinants

NASA Astrophysics Data System (ADS)

Strauch, Ronda; Istanbulluoglu, Erkan

2016-04-01

Landslide hazard research has typically been conducted independently from hydroclimate research. We unify these two lines of research to provide regional scale landslide hazard information for risk assessments and resource management decision-making. Our approach combines an empirical inherent landslide probability with a numerical dynamic probability, generated by combining routed recharge from the Variable Infiltration Capacity (VIC) macro-scale land surface hydrologic model with a finer resolution probabilistic slope stability model run in a Monte Carlo simulation. Landslide hazard mapping is advanced by adjusting the dynamic model of stability with an empirically-based scalar representing the inherent stability of the landscape, creating a probabilistic quantitative measure of geohazard prediction at a 30-m resolution. Climatology, soil, and topography control the dynamic nature of hillslope stability and the empirical information further improves the discriminating ability of the integrated model. This work will aid resource management decision-making in current and future landscape and climatic conditions. The approach is applied as a case study in North Cascade National Park Complex, a rugged terrain with nearly 2,700 m (9,000 ft) of vertical relief, covering 2757 sq km (1064 sq mi) in northern Washington State, U.S.A.

Improvements to the gridding of precipitation data across Europe under the E-OBS scheme

NASA Astrophysics Data System (ADS)

Cornes, Richard; van den Besselaar, Else; Jones, Phil; van der Schrier, Gerard; Verver, Ge

2016-04-01

Gridded precipitation data are a valuable resource for analyzing past variations and trends in the hydroclimate. Such data also provide a reference against which model simulations may be driven, compared and/or adjusted. The E-OBS precipitation dataset is widely used for such analyses across Europe, and is particularly valuable since it provides a spatially complete, daily field across the European domain. In this analysis, improvements to the E-OBS precipitation dataset will be presented that aim to provide a more reliable estimate of grid-box precipitation values, particularly in mountainous areas and in regions with a relative sparsity of input station data. The established three-stage E-OBS gridding scheme is retained, whereby monthly precipitation totals are gridded using a thin-plate spline; daily anomalies are gridded using indicator kriging; and the final dataset is produced by multiplying the two grids. The current analysis focuses on improving the monthly thin-plate spline, which has overall control on the final daily dataset. The results from different techniques are compared and the influence on the final daily data is assessed by comparing the data against gridded country-wide datasets produced by various National Meteorological Services

Borneo stalagmites reveal climatic excursions associated with Toba ash layers prior to Greenland Stadial 20

NASA Astrophysics Data System (ADS)

Cobb, K. M.; Orland, I. J.; Carolin, S.; Adkins, J. F.; Valley, J. W.; Jersild, A.; LeGrande, A. N.; Colose, C.

2017-12-01

The Toba super-eruption occurred in close association with an abrupt climate transition from Greenland Interstadial (GI-) 20 to Greenland Stadial (GS-) 20, roughly 74 thousand years ago. However, recent attempts to characterize either the regional or global climate response to Toba have been limited by a lack of age control, geographic proximity, and/or convincing marker of the major eruption in most high-resolution paleoclimate archives. Here, we use a suite of micro-scale analytical techniques to evaluate the oxygen isotopic and geochemical composition of multiple stalagmites that grew across the Toba interval in Gunung Mulu National Park, northern Borneo. New timeseries of stalagmite d18O at 50-micron scales across the Toba horizon revleal a large (>1‰), rapid (<200 yr) increase in d18O values within age-error of the 40Ar/39Ar age of the Youngest Toba Tuff (73.9±0.6 ky BP; Storey et al., 2012). We supplement these traditional mass spectrometric measurements with d18O timeseries made on 9-micron spots using the WiscSIMS CAMECA ims 1280 ion microprobe in time-transgressive segments across the Toba horizon in two well-dated stalagmites previously published in Carolin et al., 2013 and Caroline et al., 2014. The SIMS d18O data reveal high-frequency d18O excursions of +2 and -2 per mil during the transition from GI-20 (warm conditions) to Greenland Stadial GS-20 (cool conditions), suggesting that this period was characterized by large fluctuations in regional hydroclimate in the western tropical Pacific, with potentially profound impacts on global atmospheric circulation. We also present results from synchrotron analyses of ash-related elements (S, P, Si, and Al) to resolve the number and relative magnitude of Toba-related eruptions as recorded in several different stalagmites from Borneo, where ash layers likely exceeded 2cm on the overlying terrain. Together, these results indicate that large, rapid ( 10yr-long) environmental changes with marked effects on both the vegetation and hydroclimate above the cave may have been triggered by discrete eruptions of the Toba caldera. We investigate the regional hydroclimate responses to the Toba super-eruption in the isotope-equipped NASA-GISS coupled climate model across a range of eruption sizes, number, and duration.

GEWEX Water and Energy Budget Study

NASA Technical Reports Server (NTRS)

Roads, J.; Bainto, E.; Masuda, K.; Rodell, Matthew; Rossow, W. B.

2008-01-01

Closing the global water and energy budgets has been an elusive Global Energy and Water-cycle Experiment (GEWEX) goal. It has been difficult to gather many of the needed global water and energy variables and processes, although, because of GEWEX, we now have globally gridded observational estimates for precipitation and radiation and many other relevant variables such as clouds and aerosols. Still, constrained models are required to fill in many of the process and variable gaps. At least there are now several atmospheric reanalyses ranging from the early National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) and NCEP/Department of Energy (DOE) reanalyses to the more recent ERA40 and JRA-25 reanalyses. Atmospheric constraints include requirements that the models state variables remain close to in situ observations or observed satellite radiances. This is usually done by making short-term forecasts from an analyzed initial state; these short-term forecasts provide the next guess, which is corrected by comparison to available observations. While this analysis procedure is likely to result in useful global descriptions of atmospheric temperature, wind and humidity, there is no guarantee that relevant hydroclimate processes like precipitation, which we can observe and evaluate, and evaporation over land, which we cannot, have similar verisimilitude. Alternatively, the Global Land Data Assimilation System (GLDAS), drives uncoupled land surface models with precipitation, surface solar radiation, and surface meteorology (from bias-corrected reanalyses during the study period) to simulate terrestrial states and surface fluxes. Further constraints are made when a tuned water balance model is used to characterize the global runoff observational estimates. We use this disparate mix of observational estimates, reanalyses, GLDAS and calibrated water balance simulations to try to characterize and close global and terrestrial atmospheric and surface water and energy budgets to within 10-20% for long term (1986-1995), large-scale global to regional annual means.

Late Holocene Hydrologic Variability in the southeast Mojave Desert using sediments from Ford Lake, California

NASA Astrophysics Data System (ADS)

Leidelmeijer, J.; Kirby, M.; Anderson, W. T., Jr.; Mayer, S. A.; Palermo, J. A.; Stout, C.; Shellhorn, A.; Weisberg, G.; Rangel, H.; Hess, B.

2017-12-01

Most published lacustrine studies located in the Mojave Desert focus on lakes that receive the majority of their water from the Mojave River (e.g., Silver Lake, Cronese Lakes, Soda Lake, etc). Consequently, these Mojave River-fed lake sites record coastal hydroclimatic signals rather than a solely Mojave-only signal. The reason for this signal-disconnect is that the Mojave River is sourced in the San Bernardino Mountains, where annual precipitation is dictated by coastal hydroclimates. Therefore, much remains unknown about how the Mojave Desert changed during the Holocene at sub-millennial time scales. To address this problem and fill in an important geographical gap, we focus on Ford Lake in the southeastern Mojave Desert. Ford Lake is an internally drained, closed basin, and it is completely disconnected from the Mojave River. As a result, it represents one of the first lakes studied in the Mojave Desert with a climate signal that is 100% Mojave. Sediments from Ford Lake provide valuable context for understanding hydroclimatic variability exclusive to the Mojave Desert. To date, two hand-dug 1.5 m trenches (depocenter and littoral zone) and 3 overlapping sediments cores from the lake's depocenter have been sampled. The total core length is 3.55 m and bottomed in coarse alluvium, suggesting we captured the complete lacustrine sediment package. Initial results by Mayer (2016) focused on the most recent 1200 calendar years before present, or the upper 2.16 m. Mayer (2016) found evidence for increased run-off (wetter climate) during the Little Ice Age and reduced run-off (drier climate) during the Medieval Climatic Anomaly. Here, we complete the study, improving age control using sediment charcoal. Grain size, magnetic susceptibility, percent total organic matter, percent total carbonate content, C:N ratios and C and N isotopic analyses are (will be) measured at 1 cm contiguous intervals. The Ford Lake record has been (will be) compared to pre-existing regional records (i.e. Silver Lake, Abbott Lake, Crystal Lake, Zaca Lake, and the Santa Barbara Basin) to determine similarities and differences between coastal and Mojave-only climate. Final results will be compared to existing forcings to examine the cause of late Holocene hydroclimatic changes.

Changes in northeast African hydrology and vegetation associated with Pliocene-Pleistocene sapropel cycles.

PubMed

Rose, Cassaundra; Polissar, Pratigya J; Tierney, Jessica E; Filley, Timothy; deMenocal, Peter B

2016-07-05

East African climate change since the Late Miocene consisted of persistent shorter-term, orbital-scale wet-dry cycles superimposed upon a long-term trend towards more open, grassy landscapes. Either or both of these modes of palaeoclimate variability may have influenced East African mammalian evolution, yet the interrelationship between these secular and orbital palaeoclimate signals remains poorly understood. Here, we explore whether the long-term secular climate change was also accompanied by significant changes at the orbital-scale. We develop northeast African hydroclimate and vegetation proxy data for two 100 kyr-duration windows near 3.05 and 1.75 Ma at ODP Site 967 in the eastern Mediterranean basin, where sedimentation is dominated by eastern Sahara dust input and Nile River run-off. These two windows were selected because they have comparable orbital configurations and bracket an important increase in East African C4 grasslands. We conducted high-resolution (2.5 kyr sampling) multiproxy biomarker, H- and C-isotopic analyses of plant waxes and lignin phenols to document orbital-scale changes in hydrology, vegetation and woody cover for these two intervals. Both intervals are dominated by large-amplitude, precession-scale (approx. 20 kyr) changes in northeast African vegetation and rainfall/run-off. The δ(13)Cwax values and lignin phenol composition record a variable but consistently C4 grass-dominated ecosystem for both intervals (50-80% C4). Precessional δDwax cycles were approximately 20-30‰ in peak-to-peak amplitude, comparable with other δDwax records of the Early Holocene African Humid Period. There were no significant differences in the means or variances of the δDwax or δ(13)Cwax data for the 3.05 and 1.75 Ma intervals studied, suggesting that the palaeohydrology and palaeovegetation responses to precessional forcing were similar for these two periods. Data for these two windows suggest that the eastern Sahara did not experience the significant increase in C4 vegetation that has been observed in East Africa over this time period. This observation would be consistent with a proposed mechanism whereby East African precipitation is reduced, and drier conditions established, in response to the emergence of modern zonal sea surface temperature gradients in the tropical oceans between 3 and 2 Ma.This article is part of the themed issue 'Major transitions in human evolution'. © 2016 The Author(s).

Changes in northeast African hydrology and vegetation associated with Pliocene–Pleistocene sapropel cycles

PubMed Central

Rose, Cassaundra; Polissar, Pratigya J.; Tierney, Jessica E.; Filley, Timothy

2016-01-01

East African climate change since the Late Miocene consisted of persistent shorter-term, orbital-scale wet–dry cycles superimposed upon a long-term trend towards more open, grassy landscapes. Either or both of these modes of palaeoclimate variability may have influenced East African mammalian evolution, yet the interrelationship between these secular and orbital palaeoclimate signals remains poorly understood. Here, we explore whether the long-term secular climate change was also accompanied by significant changes at the orbital-scale. We develop northeast African hydroclimate and vegetation proxy data for two 100 kyr-duration windows near 3.05 and 1.75 Ma at ODP Site 967 in the eastern Mediterranean basin, where sedimentation is dominated by eastern Sahara dust input and Nile River run-off. These two windows were selected because they have comparable orbital configurations and bracket an important increase in East African C4 grasslands. We conducted high-resolution (2.5 kyr sampling) multiproxy biomarker, H- and C-isotopic analyses of plant waxes and lignin phenols to document orbital-scale changes in hydrology, vegetation and woody cover for these two intervals. Both intervals are dominated by large-amplitude, precession-scale (approx. 20 kyr) changes in northeast African vegetation and rainfall/run-off. The δ13Cwax values and lignin phenol composition record a variable but consistently C4 grass-dominated ecosystem for both intervals (50–80% C4). Precessional δDwax cycles were approximately 20–30‰ in peak-to-peak amplitude, comparable with other δDwax records of the Early Holocene African Humid Period. There were no significant differences in the means or variances of the δDwax or δ13Cwax data for the 3.05 and 1.75 Ma intervals studied, suggesting that the palaeohydrology and palaeovegetation responses to precessional forcing were similar for these two periods. Data for these two windows suggest that the eastern Sahara did not experience the significant increase in C4 vegetation that has been observed in East Africa over this time period. This observation would be consistent with a proposed mechanism whereby East African precipitation is reduced, and drier conditions established, in response to the emergence of modern zonal sea surface temperature gradients in the tropical oceans between 3 and 2 Ma. This article is part of the themed issue ‘Major transitions in human evolution’. PMID:27298473

Sedimentary processes in High Arctic lakes (Cape Bounty, Melville Island, Canada): What do sediments really record?

NASA Astrophysics Data System (ADS)

Normandeau, Alexandre; Lamoureux, Scott; Lajeunesse, Patrick; Francus, Pierre

2016-04-01

Lacustrine sedimentary sequences can hold a substantial amount of information regarding paleoenvironments, hydroclimate variability and extreme events, providing critical insights into past climate change. The study of lacustrine sediments is often limited to the analysis of sediment cores from which past changes are inferred. However, studies have provided evidence that the accumulation of sediments in lacustrine basins and their distribution can be affected by a wide range of internal and external forcing mechanisms. It is therefore crucial to have a good knowledge of the factors controlling the transport and distribution of sediments in lakes prior to investigating paleoenvironmental archives. To address this knowledge gap, the Cape Bounty Arctic Watershed Observatory (CBAWO), located on southern Melville Island in the Canadian High Arctic, was initiated in 2003 as a long term monitoring site with the aim of understanding the controls over sediment transport within similar paired watersheds and lakes. The East and West lakes have been monitored each year since 2003 to document the role of hydro-climate variability on water column processes and sediment deposition. Moorings recording water electrical conductivity, temperature, density, dissolved oxygen and turbidity, as well as sediment traps were deployed during the active hydrological period (generally May-July). These data were analyzed in combination with hydrological and climatic data from the watersheds. Additionally, a high-resolution bathymetric and sub-bottom survey was completed in 2015 and allowed imaging the lake floor and sub-surface in great detail. This combination of process and lake morphological data are unique in the Arctic. The morphostratigraphic analysis reveals two highly disturbed lake floors, being widely affected by subaqueous mass movements that were triggered during the last 2000 years. Backscatter intensity maps and the presence of bedforms on each delta foresets indicate that underflows (turbidity currents) generated at the river mouths are frequent and deliver coarse-grained sediments to the deeper waters. According to the 2003-2014 mooring data, no single hydroclimatic process can explain this underflow activity. Spring snowmelt is often responsible for delivering a substantial amount of sediment to the lakes in the form of underflows, while the contribution of summer rainfalls has also been important in some years. However, one of the largest rainfall recorded (100 mm over four days in August 2013) did not trigger a corresponding underflow event in West Lake, confirming that antecedent soil conditions can significantly reduce runoff and suspended sediment concentrations in the rivers. Moreover, high peaks of turbidity were recorded below ice cover, during the winter, a season thought to be inactive in terms of sedimentary processes. Hence, reconciling the range of processes responsible for sediment deposition and that generate both bedforms and subaqueous mass movements are important to developing consistent records and interpretations of sediment deposition in High Arctic lakes.

Terrigenous provenance follows climate variability at IODP Site U1474, southwestern Indian Ocean

NASA Astrophysics Data System (ADS)

Babin, D. P.; Hemming, S. R.; Simon, M.; Hall, I. R.; Franzese, A. M.; Goldstein, S. L.; Cai, Y.; Liu, T.; Johns, M. A.; Tejada, L.; LeVay, L.

2017-12-01

International Ocean Discovery Program (IODP) Expedition 361 `South African Climates' sought records to document the role of the greater Agulhas Current system in global climate variability and southeast African hydroclimate over the past 5 Ma. IODP Site U1474 is located at the headwaters of the fully constituted Agulhas Current. Being close to the southeast African margin, the core location is ideally situated to track variations of terrigenous sediment delivery to the site, which may relate to climatic changes in southern Africa that follow variability in the Agulhas Current heat content. To analyze climate variability, we consider an XRF record for the site in combination with major and trace element chemistry and K-Ar ages from the clay fraction (<2um) plus bulk major element chemistry of 60 shipboard moisture and density samples spanning 4.8 Ma. These data are interpreted with a sea surface temperature (SST) record from Mg/Ca measurements spaced at 40 kyr on the surface dwelling (mixed layer) planktonic foraminifera Globigerinoides ruber. Both long-term trend and precessionally-paced changes in the terrigenous composition are evident. Fe/K ratios from XRF core scanning data are consistent with those previously reported (Simon et al. 2015 Sci. Reports) in a nearby core that spans the last 270 ka. Terrigenous mass accumulation rates are relatively constant at 3 g/cm3/ky from 5-2.5 Ma, then gradually decrease to 2 g/cm3/ky at the top. This declining flux is accompanied by older and more weathered and mafic sources, possibly a result of reduced precipitation in proximal catchments. It is suggested that the relationships between these proxies is explained by a greater relative contribution of sediment supplied from the Limpopo catchment compared to nearby drainage basins such as the Tugela. The SST record shows a cooling trend from the 27 °C average between 4.5-2.5 Ma to 25 °C at 1.0 Ma, followed by high amplitude changes (6 °C changes instead of °3 C) in SST in the 0-1.0 Ma interval, with minimum SST estimates of 21 °C. These changes are consistent with, but could lag behind models predicting aridification in Africa associated with a drop in Indian Ocean temperatures around 3-4 Ma, caused by tectonic changes in the Indonesian Throughflow that shifted its Pacific source waters further north (Cane & Molnar 2001 Science).

Hydroclimatic Controls of the Hydrogen Isotope Composition of n-alkanes in Melaleuca quinquenervia Leaves: Implications for Understanding Past Environmental Change

NASA Astrophysics Data System (ADS)

Henderson, A. C. G.; McInerney, F. A.; Tibby, J.; Barr, C.; Greenway, M.; Marshall, J. C.; McGregor, G. B.

2017-12-01

The hydrogen isotope composition of plant leaf wax n-alkanes (δ2Hwax) have increasingly been used to reconstruct past hydroclimates from across the globe, over a range of timescales. One of the principal controls on δ2Hwax is the δ2H composition of precipitation (δ2Hppt), but δ2Hwax is depleted compared to δ2Hppt because of a fractionation factor (ɛapp) that encompasses both biosynthetic fractionation and environmentally controlled transpiration enrichment of leaf water. A number of studies using lake surface sediments and living plants have helped to constrain ɛapp, which has provided mechanistic understanding of isotope controls of δ2Hwax, but it is clear there are species-specific and environmental differences that might confound the sediment record. Therefore reconstructing past climates using the δ2Hwax of a single species throughout a sedimentary record means we have the potential to isolate the main driver of isotope change: δ2Hppt and give confidence to the palaeoclimate record. Fortunately, the leaves of the evergreen tree Melaleuca quinquenervia have been found preserved in sediment cores recovered from perched lakes on North Stradbroke and Fraser Islands, Queensland, Australia. Here, we examine the potential of using M. quinquenervia δ2Hwax as a tracer of past precipitation by analyzing the δ2H composition of its leaves. We then examine the relationship between climate and δ2Hwax on a quadrennial basis for an 11-year time series (1992-2003) of leaves collected in litter trays from a wetland in Queensland, to explore whether variability in local δ2Hppt is recorded in δ2Hwax.

Linking climate variations with the hydrological cycle over the semi-arid Central Andes of Argentina. Past, present and future, with emphasis on streamflow droughts.

NASA Astrophysics Data System (ADS)

Rivera, Juan Antonio; Araneo, Diego; Penalba, Olga; Villalba, Ricardo

2017-04-01

In the Central Andes of Argentina (CAA, located between 28° and 38°S), an arid to semi-arid region, the irrigation and a variety of socio-economical activities are highly dependent on river streamflows. Permanent and semi-permanent rivers originate mainly from snowmelt and glacier ablation, enabling the development of large agricultural oasis and the construction of numerous dams and reservoirs for irrigation and power generation. Most of its 2.5 million inhabitants and the main economic activities are located in a small irrigated fraction of the territory, where the variations in the timing and amount of water resources largely determine the socio-economic vulnerability of the region. In this context, the links between climatic variability and the hydrological cycle were assessed considering daily streamflow records from 21 streamgauges in the main rivers of the study area. Principal component analysis of annual hydrographs from 1931 to 2015 allowed to discriminate between precipitation- and temperature-related components associated with variations in snow accumulation (51% of variance) and advances/delays of the streamflow annual peak (16% of variance), respectively. The components related to intraseasonal variability account for 7% and 6% of variance, respectively, mixing both precipitation and thermal factors. The contribution of the precipitation-related component was the main driver of the 2010-15 streamflow drought conditions, although the thermal contribution was relevant during specific seasonal drought events. Based on an empirical decomposition methodology we identified the main modes of streamflow drought variability, which are linked to El Niño-Southern Oscillation on interannual time scales and the Pacific Decadal Oscillation (PDO) for the decadal variations. This result shows the influence of the tropical Pacific Ocean in the development of streamflow drought conditions and its relevance for potential predictability of hydroclimatic variations over the region. Nevertheless, recent studies indicate that, besides the contribution of La Niña and PDO signals, anthropogenic climate change could be responsible for the development of regional extreme drought conditions. In fact, reconstruction of CAA hydroclimate based on centennial-long tree-ring records shows a recent declining precipitation trend that is also evident over North Patagonia (38°-45°S) reconstructions, unprecedented in the last 400 years. This decreasing trend can be linked to the broadening of the sub-tropical dry zones as a displacement of the descending arm of the Hadley Cell circulation, a phenomenon likely forced by increased greenhouse gas concentrations, although its underlying mechanisms still not well understood. The assessment of future drought conditions based on a CMIP5 multi-model ensemble forced under two scenarios (RCP4.5 and RCP8.5) shows an expected increase in the number of drought events, with a decrease in the mean drought duration and non-significant changes in mean drought severity, although these results have a high range of uncertainty and are dependent on the future time horizon and selected scenario. Moreover, projected temperature trends will shift the streamflow peak from summer to late spring, in combination with a decrease in snow accumulation that will decrease the annual cycle amplitude. Both factors will likely change the hydroclimate of the semi-arid Andes, calling for new and improved water management practices over the region.

Diagnosing Mechanisms of Oceanic Influence on Sahel Precipitation Variability

NASA Astrophysics Data System (ADS)

Pomposi, Catherine A.

The West African Monsoon (WAM) is a significant component of the global monsoon system and plays a key role in the annual cycle of precipitation in the Sahel region of Africa (10°N to 20°N) during the summer months (July to September). Rainfall in the Sahel varies on timescales ranging from seasons to millennia as a result of changes in the WAM. In the last century, the Sahel experienced a relatively wet period (prior to the 1960s) followed by a period of severe drought (1970s-1980s) with higher-frequency variability superimposed on this low-frequency background signal. Understanding precipitation variability like that which occurred over the 20th Century and its impact on Sahel precipitation is critically important for skillful hydroclimate predictions and disaster preparedness in the region. Previous work has shown that the WAM responds to both internal atmospheric variability and external oceanic forcing. A large fraction of 20th Century Sahel rainfall variability has been linked to nearby and remote oceanic forcing from the Atlantic, Pacific, and Indian Oceans, suggesting that the ocean is the primary driver of variability. However, the mechanisms underlying the influence of sea surface temperature (SST) forcing to land based precipitation and the relative importance of the roles of different basins are not as well understood. To this end, the work completed in this thesis examines the physical mechanisms linking oceanic forcing to recent precipitation variability in the Sahel and identifies them alongside large-scale environmental conditions. A series of moisture budget decomposition studies are performed for the Sahel in order to understand the processes that govern regional hydroclimate variability on decadal and interannual time scales. The results show that the oceanic forcing of atmospheric mass convergence and divergence explains the moisture balance patterns in the region to first order on the timescales considered. On decadal timescales, forcing by the Indian and Atlantic Oceans correlate strongly with precipitation variability. The combination of a warm Indian Ocean and negative gradient across the Atlantic forces anomalous circulation patterns that result in net moisture divergence by the mean and transient flow. Together with negative moisture advection, these processes result in a strong drying of the Sahel during the later part of the 20th Century. Diagnosis of moisture budget and circulation components within the main rainbelt and along the monsoon margins show that changes to the mass convergence are related to the magnitude of precipitation that falls in the region, while the advection of dry air is associated with the maximum latitudinal extent of precipitation. On interannual timescales, results show that warm conditions in the Eastern Tropical Pacific remotely force anomalously dry conditions primarily through affecting the low-troposphere mass divergence field. This behavior is related to increased subsidence over the tropical Atlantic and into the Sahel and an anomalous westward flow of moisture from the continent, both resulting in a coherent drying pattern. The interannual signal is then further explored, particularly in light of the expected link between the El Nino Southern Oscillation and dry conditions in the Sahel, notably unseen during the historic El Nino event of 2015. Motivated by this, recent El Nino years and their precipitation signature in the Sahel along with the associated large-scale environmental conditions are examined. Two different outcomes for Sahel summer season are defined; an anomalously wet or an anomalously dry season coincident with El Nino conditions. The different precipitation patterns are distinguished by increased moisture supply for the wet years, which can be driven by both regional oceanic conditions that favor increased moisture convergence over the continent as well as weaker El Nino forcing. Finally, a series of new idealized SST-forced experiments that explore the causal link between oceanic forcing and the response of convection in the region on daily time resolution are discussed and preliminary results shown. These experiments aim to understand how convection in the Sahel responds to SST forcing using transient model simulations that track the evolving response of the WAM through time, day-by-day, under different oceanic conditions. Preliminary results show the stark differences in seasonal precipitation that occur when anomalies of opposite sign are applied in parts of the Atlantic and Pacific basin. There is also a suggestion of a difference in the timing of the rainy season when the model is run with different SST configurations.

A Precipitation Climatology of the Snowy Mountains, Australia

NASA Astrophysics Data System (ADS)

Theobald, Alison; McGowan, Hamish; Speirs, Johanna

2014-05-01

The precipitation that falls in the Snowy Mountains region of southeastern Australia provides critical water resources for hydroelectric power generation. Water storages in this region are also a major source of agricultural irrigation, environmental flows, and offer a degree of flood protection for some of the major river systems in Australia. Despite this importance, there remains a knowledge gap regarding the long-term, historic variability of the synoptic weather systems that deliver precipitation to the region. This research aims to increase the understanding of long-term variations in precipitation-bearing weather systems resulting in runoff into the Snowy Mountains catchments and reservoirs, and the way in which these are influenced by large-scale climate drivers. Here we present initial results on the development of a climatology of precipitation-bearing synoptic weather systems (synoptic typology), spanning a period of over 100 years. The synoptic typology is developed from the numerical weather model re-analysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF), in conjunction with regional precipitation and temperature data from a network of private gauges. Given the importance of surface, mid- and upper-air patterns on seasonal precipitation, the synoptic typing will be based on a range of meteorological variables throughout the depth of the troposphere, highlighting the importance of different atmospheric levels on the development and steering of synoptic precipitation bearing systems. The temporal and spatial variability of these synoptic systems, their response to teleconnection forcings and their contribution to inflow generation in the headwater catchments of the Snowy Mountains will be investigated. The resulting climatology will provide new understanding of the drivers of regional-scale precipitation variability at inter- and intra-annual timescales. It will enable greater understanding of how variability in synoptic scale atmospheric circulation affects the hydroclimate of alpine environments in southeast Australia - allowing recently observed precipitation declines to be placed in the context of a long-term record spanning at least 100 years. This information will provide further insight into the impacts of predicted anthropogenic climate change and will ultimately lead to more informed water resource management in the Snowy Mountains.

A 150 kyr-long hydroclimate record from Southern California using Searles Lake sediments: initial findings

NASA Astrophysics Data System (ADS)

Stroup, J. S.; Olson, K. J.; McGee, D.; Lowenstein, T. K.; Smoot, J. P.; Janick, J. J.; Lund, S.; Peaple, M.; Chen, C. Y.; Feakins, S. J.; Litwin, R.

2017-12-01

Over decadal to millennial scales, the southwestern U.S has experienced large shifts in hydroclimate ranging from pluvial conditions to extreme droughts. Direct observations, modeling and proxy data suggest precipitation amount and distribution are controlled by multiple factors including the position of the Hadley Cell, strength of the Aleutian Low and North Pacific High, ENSO and the path of winter storm tracks. Sediment records from closed basin lakes provide a means for assessing how hydrologic conditions have responded to past climate changes; however, long (>50 ka) paleoclimate records from lakes are rare and high-resolution age models are challenging to obtain. Searles Lake, in southeastern California, contains a sedimentary record that spans from the Holocene to the Pliocene at high resolution. Previous drill core studies from the basin used stratigraphy and sediment mineralogy to interpret paleoenvironmental changes and have demonstrated that the lake's sediments are able to be precisely dated. These results provide a strong foundation for new high-resolution investigations of the lake sediments. In January 2017, our group collected a new 80 m-long core with the aim of reconstructing hydrologic changes over the last 150 ka at millennial or better resolution. The core was split at the National Lacustrine Core Facility (LacCore) in June. The core contains alternating evaporite layers and finely laminated muds which likely indicate times of dryer and wetter conditions. Despite the challenge of alternating lithologies, core recovery and quality are extremely high. Here, we will present our initial chronological and stratigraphic findings. The core record will be dated using a combination of U/Th, 14C and magnetostratigraphy. We will compare our initial stratigraphic description to the existing Searles Lake literature as well as other records from the region, such as data from Devils Hole. These results provide the framework upon which we will develop detailed stratigraphic and crystallographic interpretations as well as a host of proxy records including leaf waxes, pollen and stable isotopes to advance our understanding of paleoenvironment and paleoclimate.

A multispecies tree ring reconstruction of Potomac River streamflow (950-2001)

NASA Astrophysics Data System (ADS)

Maxwell, R. Stockton; Hessl, Amy E.; Cook, Edward R.; Pederson, Neil

2011-05-01

Mean May-September Potomac River streamflow was reconstructed from 950-2001 using a network of tree ring chronologies (n = 27) representing multiple species. We chose a nested principal components reconstruction method to maximize use of available chronologies backward in time. Explained variance during the period of calibration ranged from 20% to 53% depending on the number and species of chronologies available in each 25 year time step. The model was verified by two goodness of fit tests, the coefficient of efficiency (CE) and the reduction of error statistic (RE). The RE and CE never fell below zero, suggesting the model had explanatory power over the entire period of reconstruction. Beta weights indicated a loss of explained variance during the 1550-1700 period that we hypothesize was caused by the reduction in total number of predictor chronologies and loss of important predictor species. Thus, the reconstruction is strongest from 1700-2001. Frequency, intensity, and duration of drought and pluvial events were examined to aid water resource managers. We found that the instrumental period did not represent adequately the full range of annual to multidecadal variability present in the reconstruction. Our reconstruction of mean May-September Potomac River streamflow was a significant improvement over the Cook and Jacoby (1983) reconstruction because it expanded the seasonal window, lengthened the record by 780 years, and better replicated the mean and variance of the instrumental record. By capitalizing on variable phenologies and tree growth responses to climate, multispecies reconstructions may provide significantly more information about past hydroclimate, especially in regions with low aridity and high tree species diversity.

Reconstructing East African rainfall and Indian Ocean sea surface temperatures over the last centuries using data assimilation

NASA Astrophysics Data System (ADS)

Klein, François; Goosse, Hugues

2018-06-01

The relationship between the East African rainfall and Indian Ocean sea-surface temperatures (SSTs) is well established. The potential interest of this covariance to improve reconstructions of both variables over the last centuries is examined here. This is achieved through an off-line method of data assimilation based on a particle filter, using hydroclimate-related records at four East African sites (Lake Naivasha, Lake Challa, Lake Malawi and Lake Masoko) and SSTs-related records at six oceanic sites spread over the Indian Ocean to constrain the Last Millennium Ensemble of simulations performed by CESM1. Skillful reconstructions of the Indian SSTs and East African rainfall can be obtained based on the assimilation of only one of these variables, when assimilating pseudo-proxy data deduced from the model CESM1. The skill of these reconstructions increases with the number of particles selected in the particle filter, although the improvement becomes modest beyond 99 particles. When considering a more realistic framework, the skill of the reconstructions is strongly deteriorated because of the model biases and the uncertainties of the real proxy-based reconstructions. However, it is still possible to obtain a skillful reconstruction of SSTs over most of the Indian Ocean only based on the assimilation of the six SST-related proxy records selected, as far as a local calibration is applied at all individual sites. This underlines once more the critical role of an adequate integration of the signal inferred from proxy records into the climate models for reconstructions based on data assimilation.

Thermodynamic and Dynamic Causes of Pluvial Conditions During the Last Glacial Maximum in Western North America

NASA Astrophysics Data System (ADS)

Morrill, Carrie; Lowry, Daniel P.; Hoell, Andrew

2018-01-01

During the last glacial period, precipitation minus evaporation increased across the currently arid western United States. These pluvial conditions have been commonly explained for decades by a southward deflection of the jet stream by the Laurentide Ice Sheet. Here analysis of state-of-the-art coupled climate models shows that effects of the Laurentide Ice Sheet on the mean circulation were more important than storm track changes in generating wet conditions. Namely, strong cooling by the ice sheet significantly reduced humidity over land, increasing moisture advection in the westerlies due to steepened humidity gradients. Additionally, the removal of moisture from the atmosphere by mass divergence associated with the subtropical high was diminished at the Last Glacial Maximum compared to present. These same dynamic and thermodynamic factors, working in the opposite direction, are projected to cause regional drying in western North America under increased greenhouse gas concentrations, indicating continuity from past to future in the mechanisms altering hydroclimate.

Statistical U-Th dating results of speleothem from south Europe and the orbital-scale implication

NASA Astrophysics Data System (ADS)

Hu, H. M.

2016-12-01

Reconstructing of hydroclimate in the Mediterranean on an orbital time scale helps improve our understanding of interaction between orbital forcing and north hemisphere climate. We collected 180 speleothem subsamples from Observatoire Cave (Monaco), Prince Cave (south France), Chateaueuf Cave (South France), Arago Cave (South France), and Basura Cave (North Italy) during 2013 to 2015 C.E. Uranium-thorium dating were conducted in the High-Precision Mass Spectrometry and Environment Change Laboratory (HISPEC), National Taiwan University. The results show that most of the speleothem formed during interglacial periods, particularly in marine isotope stage (MIS) 1, 5, and 11. However, only a few speleothem were dated between 180 to 250 thousand years ago (ka). The interval is approximately equivalent to MIS 7, which is a period with contrasting orbital parameters compared to MIS1, 5, and 11. Our statistical dating result implies that the orbital-scale humid/dry condition in southern Europe could be dominantly controlled by orbital forcing.

Identifying sensitive ranges in global warming precipitation change dependence on convective parameters

DOE PAGES

Bernstein, Diana N.; Neelin, J. David

2016-04-28

A branch-run perturbed-physics ensemble in the Community Earth System Model estimates impacts of parameters in the deep convection scheme on current hydroclimate and on end-of-century precipitation change projections under global warming. Regional precipitation change patterns prove highly sensitive to these parameters, especially in the tropics with local changes exceeding 3mm/d, comparable to the magnitude of the predicted change and to differences in global warming predictions among the Coupled Model Intercomparison Project phase 5 models. This sensitivity is distributed nonlinearly across the feasible parameter range, notably in the low-entrainment range of the parameter for turbulent entrainment in the deep convection scheme.more » This suggests that a useful target for parameter sensitivity studies is to identify such disproportionately sensitive dangerous ranges. Here, the low-entrainment range is used to illustrate the reduction in global warming regional precipitation sensitivity that could occur if this dangerous range can be excluded based on evidence from current climate.« less

Identifying sensitive ranges in global warming precipitation change dependence on convective parameters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bernstein, Diana N.; Neelin, J. David

A branch-run perturbed-physics ensemble in the Community Earth System Model estimates impacts of parameters in the deep convection scheme on current hydroclimate and on end-of-century precipitation change projections under global warming. Regional precipitation change patterns prove highly sensitive to these parameters, especially in the tropics with local changes exceeding 3mm/d, comparable to the magnitude of the predicted change and to differences in global warming predictions among the Coupled Model Intercomparison Project phase 5 models. This sensitivity is distributed nonlinearly across the feasible parameter range, notably in the low-entrainment range of the parameter for turbulent entrainment in the deep convection scheme.more » This suggests that a useful target for parameter sensitivity studies is to identify such disproportionately sensitive dangerous ranges. Here, the low-entrainment range is used to illustrate the reduction in global warming regional precipitation sensitivity that could occur if this dangerous range can be excluded based on evidence from current climate.« less

Managing Southeastern US Forests for Increased Water Yield

NASA Astrophysics Data System (ADS)

Acharya, S.; Kaplan, D. A.; Mclaughlin, D. L.; Cohen, M. J.

2017-12-01

Forested lands influence watershed hydrology by affecting water quantity and quality in surface and groundwater systems, making them potentially effective tools for regional water resource planning. In this study, we quantified water use and water yield by pine forests under varying silvicultural management (e.g., high density plantation, thinning, and prescribed burning). Daily forest water use (evapotranspiration, ET) was estimated using continuously monitored soil-moisture in the root-zone at six sites across Florida (USA), each with six plots ranging in forest leaf-area index (LAI). Plots included stands with different rotational ages (from clear-cut to mature pine plantations) and those restored to more historical conditions. Estimated ET relative to potential ET (PET) was strongly associated with LAI, root-zone soil-moisture status, and site hydroclimate; these factors explained 85% of the variation in the ET:PET ratio. Annual water yield (Yw) calculated from these ET estimates and a simple water balance differed significantly among sites and plots (ranging from -0.12 cm/yr to > 100 cm/yr), demonstrating substantive influence of management regimes. LAI strongly influenced Yw in all sites, and a general linear model with forest attributes (LAI and groundcover), hydroclimate, and site characteristics explained >90% of variation in observed Yw. These results can be used to predict water yield changes under different management and climate scenarios and may be useful in the development of payment for ecosystem services approaches that identify water as an important product of forest best management practices.

The Benefits of Past and Current Regional Hydroclimate Projects to the Third Pole Environment (TPE) Water and Energy Exchanges Studies

NASA Astrophysics Data System (ADS)

Benedict, Sam; van Oevelen, Peter

2014-05-01

To improve understanding of the various processes at work on spatial and temporal scales from regional to global the Regional Hydroclimate Projects (RHP's) are established as part of the Global Energy and Water Exchanges (GEWEX)Project to link the regional observations and process understanding to the global scale. This is done through exchange of observations, data, modeling, transferability studies etc. In this presentation the series of RHP's that were underway over North and South America, Europe and Asia continuously from the early 1990's up to the present will be examined, the reasons they were established, how they evolved and how they are evolving or are likely to evolve in the future, with an emphasis on where they can and should benefit similar work proposed for the TPE. The results will be presented in the context of the World Climate Research Programme (WCRP) Grand Challenge related to the development of a water strategy that addresses the issue of past and future changes in Water, in general, and the GEWEX science question on global water resource systems, in particular. This material will address issues associated with how changes in land surface and hydrology influence past and future changes in water availability and security, how new observations lead to improvements in water management and how models become better in global and regional climate predictions and projections of precipitation and how these outcomes relate to the TPE Water and Energy Exchanges Studies.

Ecosystem Processes at the Watershed Scale: Stability and Resilience of Catchment Spatial Structure and Function to Disturbance

NASA Astrophysics Data System (ADS)

Baron, J.; Mast, A.; Clow, D. W.; Wetherbee, G. A.

2014-12-01

Ecohydrological systems evolve spontaneously in response to geologic, hydroclimate and biodiversity drivers. The stability and resilience of these systems to multiple disturbances can be addressed over specific temporal extents, potentially embedded within long term transience in response to geologic or climate change. The limits of ecohydrological resilience of system state in terms of vegetation canopy and soil catenae and the space/time distribution of water, carbon and nutrient cycling is determined by a set of critical feedbacks and potential substitutions of plant functional forms in response to disturbance. The ability of forest systems to return to states functionally similar to states prior to major disturbance, or combinations of multiple disturbances, is a critical question given increasing hydroclimate extremes, biological invasions, and human disturbance. Over the past century, forest landscape ecological patterns appear to have the ability to recover from significant disturbance and re-establish similar hydrological and ecological function in humid, biodiverse regions such as the southern Appalachians, and potentially drier forest ecosystems. Understanding and prediction of past and future long term dynamics requires explicit representation of spatial and temporal feedbacks and dependencies between hydrological, ecosystem and geomorphic processes, and the spatial pattern of species or plant functional type (PFT). Comprehensive models of watershed ecohydrological resilience requires careful balance between the level of process and parameter detail between the interacting components, relative to the structure, organization, space and time scales of the landscape.

Modelling the Influence of Long-Term Hydraulic Conditions on Juvenile Salmon Habitats in AN Upland Scotish River

NASA Astrophysics Data System (ADS)

Fabris, L.; Malcolm, I.; Millidine, K. J.; Buddendorf, B.; Tetzlaff, D.; Soulsby, C.

2015-12-01

Wild Atlantic salmon populations in Scottish rivers constitute an important economic and recreational resource, as well as being a key component of biodiversity. Salmon have very specific habitat requirements at different life stages and their distribution is therefore strongly influenced by a complex suite of biological and physical controls. Previous research has shown that stream hydrodynamics and channel morphology have a strong influence on the distribution and density of juvenile salmon. Here, we utilise a unique 20 year data set of spatially distributed juvenile salmon densities derived from annual electro-fishing surveys in an upland Scottish river. We examine to what extent the spatial and temporal variability of in-stream hydraulics regulates the spatial and temporal variability in the performance and density of juvenile salmon. A 2-D hydraulic model (River2D) is used to simulate water velocity and water depth under different flow conditions for seven different electro-fishing sites. The selected sites represent different hydromorphological environments including plane-bed, step-pool and pool riffle reaches. The bathymetry of each site was characterised using a total station providing an accurate DTM of the bed, and hydraulic simulations were driven by 20 year stream flow records. Habitat suitability curves, based on direct observations during electro-fishing surveys, were produced for a range of hydraulic indices for juvenile salmon. The hydraulic simulations showed marked spatial differences in juvenile habitat quality both within and between reaches. They also showed marked differences both within and between years. This is most evident in extreme years with wet summers when salmon feeding opportunities may be constrained. Integration of hydraulic habitat models, with fish preference curves and the long term hydrological data allows us to assess whether long-term changes in hydroclimate may be affecting juvenile salmonid populations in the study stream.Wild Atlantic salmon populations in Scottish rivers constitute an important economic and recreational resource, as well as being a key component of biodiversity. Salmon have very specific habitat requirements at different life stages and their distribution is therefore strongly influenced by a complex suite of biological and physical controls. Previous research has shown that stream hydrodynamics and channel morphology have a strong influence on the distribution and density of juvenile salmon. Here, we utilise a unique 20 year data set of spatially distributed juvenile salmon densities derived from annual electro-fishing surveys in an upland Scottish river. We examine to what extent the spatial and temporal variability of in-stream hydraulics regulates the spatial and temporal variability in the performance and density of juvenile salmon. A 2-D hydraulic model (River2D) is used to simulate water velocity and water depth under different flow conditions for seven different electro-fishing sites. The selected sites represent different hydromorphological environments including plane-bed, step-pool and pool riffle reaches. The bathymetry of each site was characterised using a total station providing an accurate DTM of the bed, and hydraulic simulations were driven by 20 year stream flow records. Habitat suitability curves, based on direct observations during electro-fishing surveys, were produced for a range of hydraulic indices for juvenile salmon. The hydraulic simulations showed marked spatial differences in juvenile habitat quality both within and between reaches. They also showed marked differences both within and between years. This is most evident in extreme years with wet summers when salmon feeding opportunities may be constrained. Integration of hydraulic habitat models, with fish preference curves and the long term hydrological data allows us to assess whether long-term changes in hydroclimate may be affecting juvenile salmonid populations in the study stream.

First Insights of the Eemian Hydroclimate of the Snowy Mountains, Australia.

NASA Astrophysics Data System (ADS)

Campbell, M.; Wong, H.; McGrath, G. S.; McGowan, H. A.; Callow, J. N.

2016-12-01

Geologic archives from the Last Interglacial (LIG) provide an opportunity to investigate the likely impacts of a future warmer climate on the hydroclimate of regions sensitive to climate change. Here we present early results from the analysis of a stalagmite from the Yarrangobilly Caves complex in Kosciuszko National Park, Australia - a marginal alpine setting believed to be highly susceptible to the impacts of global warming. Five uranium-series dates show that this stalagmite grew continuously from 123.77 - 117.74 ka B.P. Trace element analysis (Mg/Ca and Sr/Ca) shows that Mg/Ca and Sr/Ca correlate at lags of 40 to 100 years during the period 122.21 ka - 120.37 ka (MIS 5e). Wavelet power spectra show significant periodicity at 60 years in both the Sr/Ca and Mg/Ca record during this time. During the period 120.2 ka - 119.8 ka the Sr/Ca record continues to display significant periodicity at 60 years, while similar periodicity at this scale in the Mg/Ca record is limited to 119.7 ka - 119.6 ka. While it has been suggested that Mg/Ca and Sr/Ca must covary and be in phase in order to interpret `wet' vs `dry' proxies (Tremaine & Froelich 2013), others have shown that Mg/Ca and Sr/Ca can move in and out of phase, attributed to wind-blown inputs of Sr (Frumkin & Stein 2004; Li et al. 2005; Cross et al. 2015). It has been suggested that, due to this and other factors that make Sr less likely to be concentrated during prior calcite precipitation, Mg/Ca may be a better indicator of infiltration rates (Steponaitis et al. 2015). The disconnect between Mg/Ca and Sr/Ca in our record suggests that they had different climatic forcings in south-east Australia during the LIG, and the breakdown in the relationship coincides with peak Mg/Ca in the record and peak SST in the Western Pacific (Lea 2004). Periodicity of 60 years is common in the global climate system and is thought to be astronomical in origin. This periodicity is similar also to the penta-decadal (50-70 yr) cycle of the Pacific Decadal Oscillation. Results indicate that this signal dominated the south-eastern Australian climate signal recorded by the stalagmite during the lead up to the height of the LIG. This signal may therefore be significant under a warmer climate as a dominant cycle in the hydroclimate of the Australian Alpine region.

Holocene forest dynamics in central and western Mediterranean: periodicity, spatio-temporal patterns and climate influence.

PubMed

Di Rita, Federico; Fletcher, William J; Aranbarri, Josu; Margaritelli, Giulia; Lirer, Fabrizio; Magri, Donatella

2018-06-12

It is well-known that the Holocene exhibits a millennial-scale climate variability. However, its periodicity, spatio-temporal patterns and underlying processes are not fully deciphered yet. Here we focus on the central and western Mediterranean. We show that recurrent forest declines from the Gulf of Gaeta (central Tyrrhenian Sea) reveal a 1860-yr periodicity, consistent with a ca. 1800-yr climate fluctuation induced by large-scale changes in climate modes, linked to solar activity and/or AMOC intensity. We show that recurrent forest declines and dry events are also recorded in several pollen and palaeohydrological proxy-records in the south-central Mediterranean. We found coeval events also in several palaeohydrological records from the south-western Mediterranean, which however show generally wet climate conditions, indicating a spatio-temporal hydrological pattern opposite to the south-central Mediterranean and suggesting that different expressions of climate modes occurred in the two regions at the same time. We propose that these opposite hydroclimate regimes point to a complex interplay of the prevailing or predominant phases of NAO-like circulation, East Atlantic pattern, and extension and location of the North African anticyclone. At a larger geographical scale, displacements of the ITCZ, modulated by solar activity and/or AMOC intensity, may have also indirectly influenced the observed pattern.

Hydroclimatic influences on seasonal and spatial cholera transmission cycles: Implications for public health intervention in the Bengal Delta

NASA Astrophysics Data System (ADS)

Akanda, Ali Shafqat; Jutla, Antarpreet S.; Alam, Munirul; de Magny, Guillaume Constantin; Siddique, A. Kasem; Sack, R. Bradley; Huq, Anwar; Colwell, Rita R.; Islam, Shafiqul

2011-03-01

Cholera remains a major public health threat in many developing countries around the world. The striking seasonality and annual recurrence of this infectious disease in endemic areas remain of considerable interest to scientists and public health workers. Despite major advances in the ecological and microbiological understanding of Vibrio cholerae, the causative agent of the disease, the role of underlying large-scale hydroclimatic processes in propagating the disease for different seasons and spatial locations is not well understood. Here we show that the cholera outbreaks in the Bengal Delta region are propagated from the coastal to the inland areas and from spring to fall by two distinctly different transmission cycles, premonsoon and postmonsoon, influenced by coastal and terrestrial hydroclimatic processes, respectively. A coupled analysis of the regional hydroclimate and cholera incidence reveals a strong association of the space-time variability of incidence peaks with seasonal processes and extreme climatic events. We explain how the asymmetric seasonal hydroclimatology affects regional cholera dynamics by providing a coastal growth environment for bacteria in spring, while propagating the disease to fall by monsoon flooding. Our findings may serve as the basis for "climate-informed" early warnings and for prompting effective means for intervention and preempting epidemic cholera outbreaks in vulnerable regions.

Late-Holocene vegetation dynamics in response to a changing climate and anthropogenic influences - Insights from stratigraphic records and subfossil trees from southeast Lithuania

NASA Astrophysics Data System (ADS)

Edvardsson, Johannes; Stančikaitė, Miglė; Miras, Yannick; Corona, Christophe; Gryguc, Gražyna; Gedminienė, Laura; Mažeika, Jonas; Stoffel, Markus

2018-04-01

To increase our understanding of long-term climate dynamics and its effects on different ecosystems, palaeoclimatic and long-term botanical reconstructions need to be improved, in particular in underutilized geographical regions. In this study, vegetation, (hydro)climate, and land-use changes were documented at two southeast Lithuanian peatland complexes - Čepkeliai and Rieznyčia - for the Late-Holocene period. The documentation was based on a combination of pollen, plant macrofossils, peat stratigraphic records, and subfossil trees. Our results cover the last two millennia and reveal the existence of moist conditions in Southern Lithuania between 300 and 500 CE and from 950 to 1850 CE. Conversely, changes towards warmer and/or dryer conditions have been recorded in 100, 600, and 750 CE, and since the 1850s. Significant differences with other Baltic proxies prevent deriving a complete and precise long-term reconstruction of past hydroclimatic variability at the regional scale. Yet, our results provide an important cornerstone for an improved understanding of regional climate change, i.e. in a region for which only (i) few detailed palaeobotanical studies exist and which has, in addition, been considered as (ii) an ecologically sensitive region at the interface between the temperate and boreal bioclimatic zones.

Tropical Pacific climate during the Medieval Climate Anomaly: progress and pitfalls

NASA Astrophysics Data System (ADS)

Cobb, K. M.; Westphal, N.; Charles, C.; Sayani, H. R.; Edwards, R. L.; Cheng, H.; Grothe, P. R.; Chen, T.; Hitt, N. T.; O'Connor, G.; Atwood, A. R.

2016-12-01

A vast trove of paleoclimate records indicates that the Medieval Climate Anomaly (MCA; 900-1200AD) was characterized by relative warmth throughout the Northern Hemisphere and significant hydroclimate anomalies - particularly well-resolved over North America - that posed a challenge to human populations. The global-scale nature of the climate anomalies has driven speculation that the tropical Pacific, with its rich spectrum of natural variability and far-reaching impact, may have undergone a prolonged reorganization during the MCA. While some key records from across the tropical Pacific document significant changes in temperature and/or hydrology, a dynamically-consistent picture of the MCA tropical Pacific climate state has proven elusive. In particular, there are few if any robust paleoclimate constraints from the central Pacific, where even modest changes in ocean temperature translate into distinct patterns of global atmospheric teleconnections. Here, we present a new collection of fossil coral multi-proxy records from Christmas Island (2N, 157W) that provide robust constraints on both temperature and hydrological changes during the MCA. We employ both modern coral data, instrumental climate data, and climate model output in developing a framework for quantifying the uncertainties associated with the new fossil coral data. In doing so, we illustrate the clear benefits of modern environmental monitoring campaigns that inform the generation of paleoclimate pseudo-proxies.

Integrating terrestrial through aquatic processing of water, carbon and nitrogen over hot, cold and lukewarm moments in mixed land use catchments

NASA Astrophysics Data System (ADS)

Band, L. E.; Lin, L.; Duncan, J. M.

2017-12-01

A major challenge in understanding and managing freshwater volumes and quality in mixed land use catchments is the detailed heterogeneity of topography, soils, canopy, and inputs of water and biogeochemicals. The short space and time scale dynamics of sources, transport and processing of water, carbon and nitrogen in natural and built environments can have a strong influence on the timing and magnitude of watershed runoff and nutrient production, ecosystem cycling and export. Hydroclimate variability induces a functional interchange of terrestrial and aquatic environments across their transition zone with the temporal and spatial expansion and contraction of soil wetness, standing and flowing water over seasonal, diurnal and storm event time scales. Variation in sources and retention of nutrients at these scales need to be understood and represented to design optimal mitigation strategies. This paper discusses the conceptual framework used to design both simulation and measurement approaches, and explores these dynamics using an integrated terrestrial-aquatic watershed model of coupled water-carbon-nitrogen processes at resolutions necessary to resolve "hot spot/hot moment" phenomena in two well studied catchments in Long Term Ecological Research sites. The potential utility of this approach for design and assessment of urban green infrastructure and stream restoration strategies is illustrated.

The PIRATA Observing System in the Tropical Atlantic: Enhancements and perspectives

NASA Astrophysics Data System (ADS)

Hernandez, Fabrice; Araujo, Moacyr; Bourlès, Bernard; Brandt, Peter; Campos, Edmo; Giordani, Hervé; Lumpkin, Rick; McPhaden, Michael J.; Nobre, Paulo; Saravanan, Ramalingam

2017-04-01

PIRATA (Prediction and Research Moored Array in the Tropical Atlantic) is a multinational program established to improve our knowledge and understanding of ocean-atmosphere variability in the tropical Atlantic, a region that strongly influences the regional hydro-climates and, consequently, the economies of the regions bordering the Atlantic Ocean (e.g. West Africa, North-Eastern Brazil, the West Indies and the United States). PIRATA is motivated not only by fundamental scientific questions but also by societal needs for improved prediction of climatic variability and its impacts. PIRATA, initiated in 1997, is based around an array of moored buoys providing meteorological and oceanographic measurements transmitted in real-time, disseminated via GTS and Global Data Servers. Then, through yearly mooring maintenance, recorded high frequency data are collected and calibrated. The dedicated cruises of yearly maintenance allow complementary acquisition of a large number of measurements along repeated ship track lines and also provide platforms for deployments of other components of the observing system. Several kinds of operations are carried out in collaboration with other international programs. PIRATA provides invaluable data for numerous and varied applications, among which are analyses of climate variability on intraseasonal-to-decadal timescales, equatorial dynamics, mixed-layer temperature and salinity budgets, air-sea fluxes, data assimilation, and weather and climate forecasts. PIRATA is now 20 years old, well established and recognized as the backbone of the tropical Atlantic sustained observing system. Several enhancements have been achieved during recent years, including progressive updating of mooring systems and sensors, also in collaborations with and as a contribution to other programs (such as EU PREFACE and AtlantOS). Recent major accomplishments in terms of air-sea exchanges and climate predictability will be highlighted in this presentation. Future perspectives for the network will also be discussed in the framework of a sustainable Atlantic Ocean Observing System.

Shifting Pacific storm tracks as stressors to ecosystems of western North America.

PubMed

Dannenberg, Matthew P; Wise, Erika K

2017-11-01

Much of the precipitation delivered to western North America arrives during the cool season via midlatitude Pacific storm tracks, which may experience future shifts in response to climate change. Here, we assess the sensitivity of the hydroclimate and ecosystems of western North America to the latitudinal position of cool-season Pacific storm tracks. We calculated correlations between storm track variability and three hydroclimatic variables: gridded cool-season standardized precipitation-evapotranspiration index, April snow water equivalent, and water year streamflow from a network of USGS stream gauges. To assess how historical storm track variability affected ecosystem processes, we derived forest growth estimates from a large network of tree-ring widths and land surface phenology and wildfire estimates from remote sensing. From 1980 to 2014, cool-season storm tracks entered western North America between approximately 41°N and 53°N. Cool-season moisture supply and snowpack responded strongly to storm track position, with positive correlations to storm track latitude in eastern Alaska and northwestern Canada but negative correlations in the northwestern U.S. Ecosystems of the western United States were greener and more productive following winters with south-shifted storm tracks, while Canadian ecosystems were greener in years when the cool-season storm track was shifted to the north. On average, larger areas of the northwestern United States were burned by moderate to high severity wildfires when storm tracks were displaced north, and the average burn area per fire also tended to be higher in years with north-shifted storm tracks. These results suggest that projected shifts of Pacific storm tracks over the 21st century would likely alter hydroclimatic and ecological regimes in western North America, particularly in the northwestern United States, where moisture supply and ecosystem processes are highly sensitive to the position of cool-season storm tracks. © 2017 John Wiley & Sons Ltd.

Hydroclimatic Controls on Agroecosystem Resiliency in the Northern High Plains

NASA Astrophysics Data System (ADS)

Munoz-Arriola, F.; Amaranto, A.; Solomatine, D.; Corzo, G.

2016-12-01

Water-controlled ecosystems play a critical role in sustaining intensive food production. More frequent and intense droughts and extreme precipitation challenge genetic progresses to increase crop yields. This work aims to identify the agroecosystem's resiliency to droughts and extreme precipitation in the Northern High Plains (NHP). NHP is characterized by its extensive use of groundwater to fulfill crop irrigation requirements. Groundwater "subsidizes" water deficits and supports intensification of crop production. However, it is unclear how sensitive are agroecosystems to hydroclimatological variations at large-scale, which may affect water discharge and recharge at basin scale and crop production at field scale. Our objective is to develop diagnostic and prognostic conceptual models for groundwater withdrawals in response to climate variability and consumptive use of water. The present study is located in the irrigated agricultural areas of the NHP. We use observed changes in the water table as tracers to changes natural forcing (i.e. observed precipitation) and anthropogenic water demands (i.e. simulated evapotranspiration) though the development of two different diagnostic/prognostic models using Artificial Neural Network (ANN) and Support Vector Machine (SVM). Water-table data was obtained from the Nebraska Geological Survey, and gridded daily hydroclimatic data from Livneh et al (2015), which together with MODIS-LAI provided the inputs for a Variable Infiltration Capacity model to simulate evapotranspiration at a 1/16th degree resolution. A regionalization procedure based on K-Clustering was applied to precipitation data (1950-2013) to identify areas of common and natural variability. Inconsistent output and input sampling frequencies used a time adaptation algorithm to assist the training of the ANN and SVM models. Results showed that both the ANN and the SVM diagnose and predicted ground water. Selected dry and wet (identified Extreme-Precipitation-Event) years are evaluated to isolate hydroclimate and water management drivers and resilient agroecosystems. This methodology will contribute to identify areas of physical vulnerability and agroecosystem resiliency.

Regional Hydroclimatic Impacts of Contemporary Amazonian Deforestation and Their Spatiotemporal Variability - An Integrated Study Using Remotely Sensed Data and Numerical Tools

NASA Astrophysics Data System (ADS)

Medvigy, D.; Khanna, J.

2016-12-01

The Amazon rainforest has been under deforestation for more than four decades. Recent investigation of the regional hydroclimatic impacts of the past three decades of deforestation has revealed a strong scale-dependence of the atmospheric response to land use change. Contemporary deforestation, affecting spatial scales of a few hundreds of kilometers, has resulted in a spatial redistribution of the local dry season rainfall, with downwind and upwind deforested regions receiving respectively 30% more and 30% less rainfall from the area mean. This phenomenon is attributable to a `dynamical' response of the boundary layer air to a reduction in surface roughness due to deforestation, apparent in both satellite and numerically simulated data. This response is starkly different from a spatially uniform increase in non-precipitating cloudiness triggered by small scale clearings, prevalent in the early phases of deforestation. This study investigates the `generalizability' of the dynamical mechanism to understand its impacts on a continually deforested Amazonia. In particular, we investigate the spatiotemporal variability of the dynamical mechanism. The nature of this investigation demands long time series and large spatial converge datasets of the hydroclimate. As such, satellite imagery of clouds (GridSat) and precipitation (PERSIANN and TRMM) has proven particularly useful in facilitating this analysis. The analysis is further complemented by a reanalysis product (ERA-interim) and numerical simulations (using a variable resolution GCM). Results indicate the presence of the dynamical mechanism during local dry and transition seasons effecting the mean precipitation during this period. Its effect on the transition season precipitation can be important for the local dry season length. The dynamical mechanism also occurs in atmospheric conditions which are otherwise less conducive to thermally triggered convection. Hence, this mechanism, which effects the seasons most important for regional ecology, emerges as a possibly impactful convective triggering mechanism. This study provides context for thinking about the climate of a future, more patchily deforested Amazonia that is more favorable to the dynamical mechanism.

Suwannee River flow variability 1550-2005 CE reconstructed from a multispecies tree-ring network

NASA Astrophysics Data System (ADS)

Harley, Grant L.; Maxwell, Justin T.; Larson, Evan; Grissino-Mayer, Henri D.; Henderson, Joseph; Huffman, Jean

2017-01-01

Understanding the long-term natural flow regime of rivers enables resource managers to more accurately model water level variability. Models for managing water resources are important in Florida where population increase is escalating demand on water resources and infrastructure. The Suwannee River is the second largest river system in Florida and the least impacted by anthropogenic disturbance. We used new and existing tree-ring chronologies from multiple species to reconstruct mean March-October discharge for the Suwannee River during the period 1550-2005 CE and place the short period of instrumental flows (since 1927 CE) into historical context. We used a nested principal components regression method to maximize the use of chronologies with varying time coverage in the network. Modeled streamflow estimates indicated that instrumental period flow conditions do not adequately capture the full range of Suwannee River flow variability beyond the observational period. Although extreme dry and wet events occurred in the gage record, pluvials and droughts that eclipse the intensity and duration of instrumental events occurred during the 16-19th centuries. The most prolonged and severe dry conditions during the past 450 years occurred during the 1560s CE. In this prolonged drought period mean flow was estimated at 17% of the mean instrumental period flow. Significant peaks in spectral density at 2-7, 10, 45, and 85-year periodicities indicated the important influence of coupled oceanic-atmospheric processes on Suwannee River streamflow over the past four centuries, though the strength of these periodicities varied over time. Future water planning based on current flow expectations could prove devastating to natural and human systems if a prolonged and severe drought mirroring the 16th and 18th century events occurred. Future work in the region will focus on updating existing tree-ring chronologies and developing new collections from moisture-sensitive sites to improve understandings of past hydroclimate in the region.

Arctic temperature and moisture trends during the past 2000 years - Progress from multiproxy-paleoclimate data compilations

NASA Astrophysics Data System (ADS)

Kaufman, Darrell; Routson, Cody; McKay, Nicholas; Beltrami, Hugo; Jaume-Santero, Fernando; Konecky, Bronwen; Saenger, Casey

2017-04-01

Instrumental climate data and climate-model projections show that Arctic-wide surface temperature and precipitation are positively correlated. Higher temperatures coincide with greater moisture by: (1) expanding the duration and source area for evaporation as sea ice retracts, (2) enhancing the poleward moisture transport, and (3) increasing the water-vapor content of the atmosphere. Higher temperature also influences evaporation rate, and therefore precipitation minus evaporation (P-E), the climate variable often sensed by paleo-hydroclimate proxies. Here, we test whether Arctic temperature and moisture also correlate on centennial timescales over the Common Era (CE). We use the new PAGES2k multiproxy-temperature dataset along with a first-pass compilation of moisture-sensitive proxy records to calculate century-scale composite timeseries, with a focus on longer records that extend back through the first millennium CE. We present a new Arctic borehole temperature reconstruction as a check on the magnitude of Little Ice Age cooling inferred from the proxy records, and we investigate the spatial pattern of centennial-scale variability. Similar to previous reconstructions, v2 of the PAGES2k proxy temperature dataset shows that, prior to the 20th century, mean annual Arctic-wide temperature decreased over the CE. The millennial-scale cooling trend is most prominent in proxy records from glacier ice, but is also registered in lake and marine sediment, and trees. In contrast, the composite of moisture-sensitive (primarily P-E) records does not exhibit a millennial-scale trend. Determining whether fluctuations in the mean state of Arctic temperature and moisture were in fact decoupled is hampered by the difficulty in detecting a significant trend within the relatively small number of spatially heterogeneous multi-proxy moisture-sensitive records. A decoupling of temperature and moisture would indicate that evaporation had a strong counterbalancing effect on precipitation and/or that shifting circulation patterns overwhelmed any multi-centennial-scale co-variability.

Boreal spring precipitation variability in the cold arid western Himalaya during the last millennium, regional linkages, and socio-economic implications

NASA Astrophysics Data System (ADS)

Yadava, Akhilesh K.; Bräuning, Achim; Singh, Jayendra; Yadav, Ram R.

2016-07-01

Precipitation in the monsoon shadow zone of the western Himalayan region, largely under the influence of mid-latitude westerlies, is the dominant regional socioeconomic driver. Current knowledge of long-term regional precipitation variability is scarce due to spatially and temporally limited weather and high-resolution proxy climate records. We developed the first boreal spring precipitation reconstruction for the western Himalaya covering the last millennium (1030-2011 C.E.). The annually resolved reconstruction is based on a large tree-ring data set of Himalayan cedar (Cedrus deodara) and neoza pine (Pinus gerardiana) from 16 ecologically homogeneous moisture stressed settings in Kinnaur, western Indian Himalaya. The precipitation reconstruction revealed persistent long-term spring droughts from the 12th to early 16th century C.E. and pluvial from the late 16th century C.E. to recent decades. The late 15th and early 16th centuries (1490-1514 C.E.) displayed the driest episode, with precipitation being ∼15% lower than the long-term mean. The early 19th century (1820-1844 C.E.) was the wettest period of the past millennium, with mean precipitation ∼13% above the long-term mean. The reconstructed boreal spring precipitation from the western Himalaya revealed large-scale consistency with hydrological records from westerly dominated regions in Central Asia, indicating synoptic-scale changes in atmospheric circulation during the major part of the Medieval and Little Ice Age periods. Protracted droughts in Central Asia could have caused severe contraction of the regional economy, as indicated by striking coherence of reconstructed drought periods and historic social upheavals and invasions of India from Central and Western Asian invaders. Vulnerability to climatic extremes underpins the need to develop a better understanding of the temporal and spatial variability in regional hydroclimate in order to devise viable water resource management plans.

Impacts of future climate change on river discharge based on hydrological inference: A case study of the Grand River Watershed in Ontario, Canada.

PubMed

Li, Zhong; Huang, Guohe; Wang, Xiuquan; Han, Jingcheng; Fan, Yurui

2016-04-01

Over the recent years, climate change impacts have been increasingly studied at the watershed scale. However, the impact assessment is strongly dependent upon the performance of the climatic and hydrological models. This study developed a two-step method to assess climate change impacts on water resources based on the Providing Regional Climates for Impacts Studies (PRECIS) modeling system and a Hydrological Inference Model (HIM). PRECIS runs provided future temperature and precipitation projections for the watershed under the Intergovernmental Panel on Climate Change SRES A2 and B2 emission scenarios. The HIM based on stepwise cluster analysis is developed to imitate the complex nonlinear relationships between climate input variables and targeted hydrological variables. Its robust mathematical structure and flexibility in predictor selection makes it a desirable tool for fully utilizing various climate modeling outputs. Although PRECIS and HIM cannot fully cover the uncertainties in hydro-climate modeling, they could provide efficient decision support for investigating the impacts of climate change on water resources. The proposed method is applied to the Grand River Watershed in Ontario, Canada. The model performance is demonstrated with comparison to observation data from the watershed during the period 1972-2006. Future river discharge intervals that accommodate uncertainties in hydro-climatic modeling are presented and future river discharge variations are analyzed. The results indicate that even though the total annual precipitation would not change significantly in the future, the inter-annual distribution is very likely to be altered. The water availability is expected to increase in Winter while it is very likely to decrease in Summer over the Grand River Watershed, and adaptation strategies would be necessary. Copyright © 2016 Elsevier B.V. All rights reserved.

Disentangling the role of Natural Variability and Climate Change in the aggravation of Droughts in central Chile

NASA Astrophysics Data System (ADS)

Garreaud, R. D.; Boisier, J. P.; Rondanelli, R. F.

2016-12-01

Among other climate extreme events, droughts (annual rainfall deficit larger than 25%) have punctuated the hydro-climate history of central Chile (30-40°S) with profoundly negative effects on physical (e.g., water storage depletion), ecological (e.g., increase in forest fires) and human systems (e.g., major distress in rural communities). In this presentation we show that intense but short-lived (1 or 2 years long) droughts are associated with anticyclonic (cyclonic) anomalies over the subtropical south Pacific (Amudsen sea), reduced synoptic-scale variability in that area and weakening of the westerly winds impinging the west coast of South America. These large-scale anomalies often occurs in connection with the cold phase of ENSO (La Niña events). Of particular interest is an uninterrupted rainfall deficit since 2010 to date, referred to as the central Chile mega-drought (MD) in virtue of its unprecedented character in term of duration, spatial extent and coincidence with warm air temperatures. The protracted MD shares some of the climate features of the historical events but for the prevalence of near-neutral ENSO years with the exception of 2010 (La Niña) and 2015 (intense El Niño). Thus, we use a suite of fully-coupled and SST-forced climate simulations to disentangle natural and anthropogenic contributions to current mega drought as well as to shed light in the physical link between global climate change and rainfall deficit in central Chile drought. It turns out that anthropogenic climate change accounts for about a third of the drought as it forces SAM towards its positive polarity. The later enhances a dipole of geopotential height over the South Pacific that is conducive to dry conditions in central Chile.

New Insights on Hydro-Climate Feedback Processes over the Tropical Ocean from TRMM

NASA Technical Reports Server (NTRS)

Lau, William K. M.; Wu, H. T.; Li, Xiaofan; Sui, C. H.

2002-01-01

In this paper, we study hydro-climate feedback processes over the tropical oceans, by examining the relationships among large scale circulation and Tropical Rainfall Measuring Mission Microwave Imager-Sea Surface Temperature (TMI-SST), and a range of TRMM rain products including rain rate, cloud liquid water, precipitable water, cloud types and areal coverage, and precipitation efficiency. Results show that for a warm event (1998), the 28C threshold of convective precipitation is quite well defined over the tropical oceans. However, for a cold event (1999), the SST threshold is less well defined, especially over the central and eastern Pacific cold tongue, where stratiform rain occurs at much lower than 28 C. Precipitation rates and cloud liquid water are found to be more closely related to the large scale vertical motion than to the underlying SST. While total columnar water vapor is more strongly dependent on SST. For a large domain, over the eastern Pacific, we find that the areal extent of the cloudy region tends to shrink as the SST increases. Examination of the relationship between cloud liquid water and rain rate suggests that the residence time of cloud liquid water tends to be shorter, associated with higher precipitation efficiency in a warmer climate. It is hypothesized that the reduction in cloudy area may be influenced both by the shift in large scale cloud patterns in response to changes in large scale forcings, and possible increase in the cloud liquid water conversion to rain water in a warmer environment. Results of numerical experiments with the Goddard cloud resolving model to test the hypothesis will be discussed.

Surface-Atmosphere Connections on Titan: A New Window into Terrestrial Hydroclimate

NASA Astrophysics Data System (ADS)

Faulk, Sean

This dissertation investigates the coupling between the large-scale atmospheric circulation and surface processes on Titan, with a particular focus on methane precipitation and its influence on surface geomorphology and hydrology. As the only body in the Solar System with an active hydrologic cycle other than Earth, Titan presents a valuable laboratory for studying principles of hydroclimate on terrestrial planets. Idealized general circulation models (GCMs) are used here to test hypotheses regarding Titan's surface-atmosphere connections. First, an Earth-like GCM simulated over a range of rotation rates is used to evaluate the effect of rotation rate on seasonal monsoon behavior. Slower rotation rates result in poleward migration of summer rain, indicating a large-scale atmospheric control on Titan's observed dichotomy of dry low latitudes and moist high latitudes. Second, a Titan GCM benchmarked against observations is used to analyze the magnitudes and frequencies of extreme methane rainstorms as simulated by the model. Regional patterns in these extreme events correlate well with observed geomorphic features, with the most extreme rainstorms occurring in mid-latitude regions associated with high alluvial fan concentrations. Finally, a planetary surface hydrology scheme is developed and incorporated into a Titan GCM to evaluate the roles of surface flow, subsurface flow, infiltration, and groundmethane evaporation in Titan's climate. The model reproduces Titan's observed surface liquid and cloud distributions, and reaches an equilibrium state with limited interhemispheric transport where atmospheric transport is approximately balanced by subsurface transport. The equilibrium state suggests that Titan's current hemispheric surface liquid asymmetry, favoring methane accumulation in the north, is stable in the modern climate.

How can streamflow and climate-landscape data be used to estimate baseflow mean response time?

NASA Astrophysics Data System (ADS)

Zhang, Runrun; Chen, Xi; Zhang, Zhicai; Soulsby, Chris; Gao, Man

2018-02-01

Mean response time (MRT) is a metric describing the propagation of catchment hydraulic behavior that reflects both hydro-climatic conditions and catchment characteristics. To provide a comprehensive understanding of catchment response over a longer-time scale for hydraulic processes, the MRT function for baseflow generation was derived using an instantaneous unit hydrograph (IUH) model that describes the subsurface response to effective rainfall inputs. IUH parameters were estimated based on the "match test" between the autocorrelation function (ACFs) derived from the filtered base flow time series and from the IUH parameters, under the GLUE framework. Regionalization of MRT was conducted using estimates and hydroclimate-landscape indices in 22 sub-basins of the Jinghe River Basin (JRB) in the Loess Plateau of northwest China. Results indicate there is strong equifinality in determination of the best parameter sets but the median values of the MRT estimates are relatively stable in the acceptable range of the parameters. MRTs vary markedly over the studied sub-basins, ranging from tens of days to more than a year. Climate, topography and geomorphology were identified as three first-order controls on recharge-baseflow response processes. Human activities involving the cultivation of permanent crops may elongate the baseflow MRT and hence increase the dynamic storage. Cross validation suggests the model can be used to estimate MRTs in ungauged catchments in similar regions of throughout the Loess Plateau. The proposed method provides a systematic approach for MRT estimation and regionalization in terms of hydroclimate and catchment characteristics, which is helpful in the sustainable water resources utilization and ecological protection in the Loess Plateau.

Memory of irrigation effects on hydroclimate and its modeling challenge

NASA Astrophysics Data System (ADS)

Chen, Fei; Xu, Xiaoyu; Barlage, Michael; Rasmussen, Roy; Shen, Shuanghe; Miao, Shiguang; Zhou, Guangsheng

2018-06-01

Irrigation modifies land-surface water and energy budgets, and also influences weather and climate. However, current earth-system models, used for weather prediction and climate projection, are still in their infancy stage to consider irrigation effects. This study used long-term data collected from two contrasting (irrigated and rainfed) nearby maize-soybean rotation fields, to study the effects of irrigation memory on local hydroclimate. For a 12 year average, irrigation decreases summer surface-air temperature by less than 1 °C and increases surface humidity by 0.52 g kg‑1. The irrigation cooling effect is more pronounced and longer lasting for maize than for soybean. Irrigation reduces maximum, minimum, and averaged temperature over maize by more than 0.5 °C for the first six days after irrigation, but its temperature effect over soybean is mixed and negligible two or three days after irrigation. Irrigation increases near-surface humidity over maize by about 1 g kg‑1 up to ten days and increases surface humidity over soybean (~ 0.8 g kg‑1) with a similar memory. These differing effects of irrigation memory on temperature and humidity are associated with respective changes in the surface sensible and latent heat fluxes for maize and soybean. These findings highlight great need and challenges for earth-system models to realistically simulate how irrigation effects vary with crop species and with crop growth stages, and to capture complex interactions between agricultural management and water-system components (crop transpiration, precipitation, river, reservoirs, lakes, groundwater, etc.) at various spatial and temporal scales.

Establishing a baseline precipitation and temperature regime for the Guianas from observations and reanalysis data

NASA Astrophysics Data System (ADS)

Bovolo, C. Isabella; Pereira, Ryan; Parkin, Geoff; Wagner, Thomas

2010-05-01

The tropical rainforests of the Guianas, north of the Amazon, are home to several Amerindian communities, hold high levels of biodiversity and, importantly, remain some of the world's most pristine and intact rainforests. Not only do they have important functions in the global carbon cycle, but they regulate the local and regional climate and help generate rain over vast distances. Despite their significance however, the climate and hydrology of this region is poorly understood. It is important to establish the current climate regime of the area as a baseline against which any impacts of future climate change or deforestation can be measured but observed historical climate datasets are generally sparse and of low quality. Here we examine the available precipitation and temperature datasets for the region and derive tentative precipitation and temperature maps focussed on Guyana. To overcome the limitations in the inadequate observational data coverage we also make use of a reanalysis dataset from the European Centre for Medium-range Weather Forecasts (ECMWF). The ECMWF ERA40 dataset comprises a spatially consistent global historical climate for the period 1957-2002 at a ~125 km2 (1.125 degree) resolution at the equator and is particularly valuable for establishing the climate of data-poor areas. Once validated for the area of interest, ERA40 is used to determine the precipitation and temperature regime of the Guianas. Grid-cell by grid-cell analysis provides a complete picture of spatial patterns of averaged monthly precipitation variability across the area, vital for establishing a basis from which to compare any future effects of climate change. This is the first comprehensive study of the recent historical climate and its variability in this area, placing a new hydroclimate monitoring and research program at the Iwokrama International Centre for Rainforest Conservation and Development, Guyana, into the broader climate context. Mean differences (biases) and annual average spatial correlations are examined between modelled ERA40 and observed time series comparing the seasonal cycles and the yearly, monthly and monthly anomaly time series. This is to evaluate if the reanalysis data correctly reproduces the areally averaged observed mean annual precipitation, interannual variability and seasonal precipitation cycle over the region. Results show that reanalysis precipitation for the region compares favourably with areally averaged observations where available, although the model underestimates precipitation in some zones of higher elevation. Also ERA40 data is slightly positively biased along the coast and negatively biased inland. Comparisons between observed and modelled data show that although correlations of annual time series are low (<0.6), correlations of monthly time series reach 0.8 demonstrating that the model captures much of the seasonal variation in precipitation. However correlations between monthly precipitation anomalies, where the averaged seasonal cycle has been removed from the comparison, are lower (< 0.6). As precipitation observations are not assimilated into the reanalysis these results provide a good validation of model performance. The seasonal cycle of precipitation is found to be highly variable across the region. Two wet-seasons (June and December) occur in northern Guyana which relate to the twice yearly passage of the inter-tropical convergence zone whereas a single wet season (April-August) occurs in the savannah zone, which stretches from Venezuela through the southern third of Guyana. The climate transition zone lies slightly north of the distinctive forest-savannah boundary which suggests that the boundary may be highly sensitive to future alterations in climate, such as those due to climate change or deforestation.

Multi-Proxy Evidence for Decoupled Monsoon Intensity and Southeast Asian Precipitation on Orbital and Millennial Timescales

NASA Astrophysics Data System (ADS)

Johnson, K. R.; Griffiths, M. L.; Borsato, A.; Frisia, S.; Bhattacharya, T.; Tierney, J. E.; LeGrande, A. N.; Henderson, G. M.

2017-12-01

Despite significant advances in our understanding of Asian monsoon variability on orbital to millennial timescales, we still know very little about the range and mechanisms of variability in the Southeast Asian monsoon region. To address this need, we have developed a decadally-resolved and replicated speleothem δ18O and δ13C record from Tham Doun Mai Cave in Northern Laos. The record spans the period from 37.7 kyr BP to the present and the age model is constrained by 35 U-Th dates. The orbital and millennial scale δ18O variability is remarkably similar to other Asian speleothem records, with the lowest values observed during the early Holocene summer insolation maxima and clear δ18O increases observed during Heinrich Stadials (HS) 1-3, the Younger Dryas, and the 8.2 kyr event. The strong similarity with Chinese speleothem δ18O records suggests that variations in upstream rainout over the Indian Ocean, Bay of Bengal, and Indian Monsoon region are the dominant control on orbital and millennial scale precipitation δ18O variability across Southeast and East Asia. In contrast to δ18O, TM speleothem δ13C is reflective of local hydroclimate. The δ13C record shows large positive excursions during HS 1-3, suggesting dry conditions during these events. Positive δ13C values during the early Holocene indicate dry conditions in SE Asia were synchronous with increased upstream rainout. This interpretation is further supported by crystal fabric and greyscale analyses, which reflect internal porosity changes likely related to infiltration variability. Compact columnar, translucent calcite is associated with decreased infiltration, and typifies HS events and the early Holocene. The positive δ13C excursions during these periods may then be enhanced by the prolonged degassing associated with slower drip rates. Time-slice simulations conducted with the isotope-enabled GISS Model E further support a dry early Holocene in this region. Model analyses suggest dry conditions in SE Asia during insolation maxima may arise from decreased low-level moisture convergence over the Indo-China Peninsula as precipitation over India and East Asia increases, effectively drawing away moisture from our study site. Nevertheless, the impacts of upstream rainout lead to regionally coherent δ18O decreases across the broad Asian monsoon region.

Influence of the Amazon River on the Nd isotope composition of deep water in the western equatorial Atlantic during the Oligocene-Miocene transition

NASA Astrophysics Data System (ADS)

Stewart, Joseph A.; Gutjahr, Marcus; James, Rachael H.; Anand, Pallavi; Wilson, Paul A.

2016-11-01

Dissolved and particulate neodymium (Nd) are mainly supplied to the oceans via rivers, dust, and release from marine sediments along continental margins. This process, together with the short oceanic residence time of Nd, gives rise to pronounced spatial gradients in oceanic 143Nd/144Nd ratios (εNd). However, we do not yet have a good understanding of the extent to which the influence of riverine point-source Nd supply can be distinguished from changes in mixing between different water masses in the marine geological record. This gap in knowledge is important to fill because there is growing awareness that major global climate transitions may be associated not only with changes in large-scale ocean water mass mixing, but also with important changes in continental hydroclimate and weathering. Here we present εNd data for fossilised fish teeth, planktonic foraminifera, and the Fe-Mn oxyhydroxide and detrital fractions of sediments recovered from Ocean Drilling Project (ODP) Site 926 on Ceara Rise, situated approximately 800 km from the mouth of the River Amazon. Our records span the Mi-1 glaciation event during the Oligocene-Miocene transition (OMT; ∼23 Ma). We compare our εNd records with data for ambient deep Atlantic northern and southern component waters to assess the influence of particulate input from the Amazon River on Nd in ancient deep waters at this site. εNd values for all of our fish teeth, foraminifera, and Fe-Mn oxyhydroxide samples are extremely unradiogenic (εNd ≈ - 15); much lower than the εNd for deep waters of modern or Oligocene-Miocene age from the North Atlantic (εNd ≈ - 10) and South Atlantic (εNd ≈ - 8). This finding suggests that partial dissolution of detrital particulate material from the Amazon (εNd ≈ - 18) strongly influences the εNd values of deep waters at Ceara Rise across the OMT. We conclude that terrestrially derived inputs of Nd can affect εNd values of deep water many hundreds of kilometres from source. Our results both underscore the need for care in reconstructing changes in large-scale oceanic water-mass mixing using sites proximal to major rivers, and highlight the potential of these marine archives for tracing changes in continental hydroclimate and weathering.

The Towuti Drilling Project: A new, long Pleistocene record of Indo-Pacific Climate

NASA Astrophysics Data System (ADS)

Russell, James M.; Vogel, Hendrik; Bijaksana, Satria; Melles, Martin

2016-04-01

Lake Towuti is the largest tectonic lake in Indonesia, and the longest known terrestrial sediment archive in Southeast Asia. Lake Towuti's location in central Indonesia provides an important opportunity to reconstruct long-term changes in terrestrial climate in the Western Pacific warm pool, heart of the El Niño-Southern Oscillation. Lake Towuti has extremely high rates of floral and faunal endemism and is surrounded by one of the most diverse tropical forests on Earth making it a hotspot of Southeast Asian biodiversity. The ultramafic rocks and soils surrounding Lake Towuti provide high concentrations of metals to the lake and its sediments that feed a diverse, exotic microbial community. From May - July, 2015, the Towuti Drilling Project, consisting of more than 30 scientists from eight countries, recovered over 1,000 meters of new sediment core from 3 different drill sites in Lake Towuti, including cores through the entire sediment column to bedrock. These new sediment cores will allow us to investigate the history of rainfall and temperature in central Indonesia, long-term changes in the composition of the region's rainforests and diverse aquatic ecosystems, and the micro-organisms living in Towuti's exotic, metal-rich sediments. The Indo-Pacific region plays a pivotal role in the Earth's climate system, regulating critical atmospheric circulation systems and the global concentration of atmospheric water vapor- the Earth's most important greenhouse gas. Changes in seasonal insolation, greenhouse gas concentrations, ice volume, and local sea level are each hypothesized to exert a dominant control on Indo-Pacific hydroclimate variations through the Pleistocene. Existing records from the region are short and exhibit fundamental differences and complexity in orbital-scale climate patterns that limit our understanding of the regional climate responses to climate boundary conditions. Our sediment cores, which span much of the past 1 million years, allow new tests of these hypotheses. Sediment core logging and lithostratigraphic data document major shifts in sediment composition, including alterations of lake clays and calcareous sediments in the upper ~100m and peats and gravels in the basal units of our records. These data show excellent agreement with major lithological transitions recorded in seismic reflection data, and indicate large changes in lake levels and hydroclimate through the late Quaternary. Prior work on Lake Towuti indicated a dominant control by global ice volume on regional hydroclimate, a hypothesis we now test through the analysis of these new cores. This presentation will review existing records from the region and show the first long geochemical and sedimentological records from Lake Towuti to understand orbital-scale Indo-Pacific hydrologic change during the late Pleistocene.

Galápagos hydroclimate of the Common Era from paired microalgal and mangrove biomarker 2H/1H values

NASA Astrophysics Data System (ADS)

Nelson, Daniel B.; Sachs, Julian P.

2016-03-01

Tropical maritime precipitation affects global atmospheric circulation, influencing storm tracks and the size and location of subtropical deserts. Paleoclimate evidence suggests centuries-long changes in rainfall in the tropical Pacific over the past 2,000 y, but these remain poorly characterized across most of the ocean where long, continuous proxy records capable of resolving decadal-to-centennial climate changes are still virtually nonexistent despite substantial efforts to develop them. Here we apply a new climate proxy based on paired hydrogen isotope ratios from microalgal and mangrove-derived sedimentary lipids in the Galápagos to reconstruct maritime precipitation changes during the Common Era. We show that increased rainfall during the Little Ice Age (LIA) (∼1400-1850 CE) was likely caused by a southward migration of the Intertropical Convergence Zone (ITCZ), and that this shift occurred later than previously recognized, coeval with dynamically linked precipitation changes in South America and the western tropical Pacific. Before the LIA, we show that drier conditions at the onset of the Medieval Warm Period (∼800-1300 CE) and wetter conditions ca. 2 ka were caused by changes in the El Niño/Southern Oscillation (ENSO). Collectively, the large natural variations in tropical rainfall we detect, each linked to a multicentury perturbation of either ENSO-like variability or the ITCZ, imply a high sensitivity of tropical Pacific rainfall to climate forcings.

Climate variability and cultural eutrophication at Walden Pond (Massachusetts, USA) during the last 1800 years.

PubMed

Stager, J Curt; Wiltse, Brendan; Hubeny, J Bradford; Yankowsky, Eric; Nardelli, David; Primack, Richard

2018-01-01

Recent shifts in the ecological condition of Walden Pond, MA, are of potentially wide interest due to the lake's importance as a cultural, historical, and recreational resource in addition to its scientific value as an indicator of local and global environmental change. Algal microfossils in six sediment cores document changes in hydroclimate and trophic status of the lake during the last 1800 years and extend two previous sediment core records of shorter length. Low percentages of planktonic diatoms in the longest cores (WAL-3, WAL-15) indicate shallowing and/or greater water clarity associated with a relatively arid interval during the Medieval Climate Anomaly, ca. A.D. 1150-1300, Cultural eutrophication of the lake since the A.D. 1920s caused diatoms in the genera Asterionella and Synedra to increase in relative abundance at the expense of Cyclotella, Discostella, and the chrysophyte alga Mallomonas allorgei. Percentages of Asterionella and Synedra have remained fairly stable since A.D. 2000 when a previous sediment core study was conducted, but scaled chrysophytes have become more numerous. These findings suggest that, although mitigation efforts have curtailed anthropogenic nutrient inputs to Walden Pond, the lake has not returned to the pre-impact condition described by Henry David Thoreau and may become increasingly vulnerable to further changes in water quality in a warmer and possibly wetter future.

Climate variability and cultural eutrophication at Walden Pond (Massachusetts, USA) during the last 1800 years

PubMed Central

Wiltse, Brendan; Hubeny, J. Bradford; Yankowsky, Eric; Nardelli, David; Primack, Richard

2018-01-01

Recent shifts in the ecological condition of Walden Pond, MA, are of potentially wide interest due to the lake's importance as a cultural, historical, and recreational resource in addition to its scientific value as an indicator of local and global environmental change. Algal microfossils in six sediment cores document changes in hydroclimate and trophic status of the lake during the last 1800 years and extend two previous sediment core records of shorter length. Low percentages of planktonic diatoms in the longest cores (WAL-3, WAL-15) indicate shallowing and/or greater water clarity associated with a relatively arid interval during the Medieval Climate Anomaly, ca. A.D. 1150–1300, Cultural eutrophication of the lake since the A.D. 1920s caused diatoms in the genera Asterionella and Synedra to increase in relative abundance at the expense of Cyclotella, Discostella, and the chrysophyte alga Mallomonas allorgei. Percentages of Asterionella and Synedra have remained fairly stable since A.D. 2000 when a previous sediment core study was conducted, but scaled chrysophytes have become more numerous. These findings suggest that, although mitigation efforts have curtailed anthropogenic nutrient inputs to Walden Pond, the lake has not returned to the pre-impact condition described by Henry David Thoreau and may become increasingly vulnerable to further changes in water quality in a warmer and possibly wetter future. PMID:29617379

A Record of Moisture History in Hawaii since the Arrival of Humans Inferred from Testate Amoebae and Cladocera Fossils Preserved in Bog Sediments

NASA Astrophysics Data System (ADS)

Barrett, K.; Kim, S. H.; Hotchkiss, S.

2015-12-01

Around AD 800, Polynesians arrived on the Hawaiian Islands where they expanded and intensified distinct agricultural practices in the islands' wet and dry regions. Dryland farming productivity in particular would have been sensitive to atmospheric rearrangements of the ENSO and PDO systems that affect rainfall in Hawaii. The few detailed terrestrial paleoclimate records in Hawaii are mainly derived from vegetation proxies (e.g. pollen, seeds, fruits, and plant biomarkers) which are heavily influenced by widespread landscape modification following human arrival. Here we present initial results of an independent paleomoisture proxy: fossil remains of moisture-sensitive testate amoebae (Protozoa: Rhizopoda) and cladocera (water fleas) preserved in continuous bog sediments on Kohala Volcano uplsope of the ancient Kohala agricultural field system, one of the largest dryland field systems in Hawaii. Hydrologic conditions inferred from testate amoebae and cladoceran fossil assemblages correlate with observed decadal moisture regimes in Hawaii and state changes of the PDO system during the last century. Testate ameoabe and cladoceran fossils in older sediments reveal an alternating history of very wet, lake-forming conditions on the bog surface to periods when bog soils were much drier than today's, demonstrating that this method can be paired with vegetation proxies to provide a better understanding of hydroclimate variability in prehistoric Hawaii.

Implications of Water Use and Hydroclimatic Anomalies on the Freshwater Sustainability across the US Sunbelt

NASA Astrophysics Data System (ADS)

Arumugam, S.; Sabo, J. L.; Ruhí, A.; Sinha, T.; Kominoski, J. S.; Hagler, M.; Kunkel, K.; Berglund, E.; Larson, K.; Mahinthakumar, K.

2014-12-01

A synthesis on freshwater sustainability is investigated across the US Sunbelt. Spatio-temporal variability of potential drivers - hydroclimate and water use - influencing the freshwater sustainability are examined both individually as well as collectively by considering the eco-region and 4-digit Hydrologic Unit Code (HUC-4)as the spatial reference for the analysis. A detailed analysis on national water use also indicates a north-south gradient with Frostbelt being more efficient in water use as opposed to the Sunbelt. This basically stems from the understanding of regional cross-differences in public supply consumption per capita which is significantly low in high-income urban counties. National analyses on agricultural water use efficiency (i.e., per-acreage application) also shows sprinkler irrigation and micro-irrigation being the primary drivers of differences in agricultural consumption. Given the well-known hydroclimatic west (arid)-east (humid) gradient across the Sunbelt, the study also evaluates the role of flow anomalies - represented by the changes in magnitude, frequency and timing of extremes (high flows and low flows) and by the changes in seasonality - in influencing native fish diversity patterns, as a proxy for freshwater biodiversity, in virgin basins and in basins influenced by significant storage and pumping. Cross-regional differences in water consumption during and after droughts are also presented in the context of adaptations and policy relevance.

Natural and Anthropogenic Causes of Accelerated Sediment Accumulation Rates in Nehalem Bay Salt Marshes, Oregon

NASA Astrophysics Data System (ADS)

Molino, G. D.; Wheatcroft, R. A.; Peck, E. K.; Brophy, L.

2016-12-01

Vertical sediment accretion in estuarine salt marshes occurs as sediments settle out of the water column and onto marsh soils during periods of tidal inundation - thus accretion is influenced by both relative sea level rise (RSLR) and sediment flux to the estuary. Oregon estuaries are understudied compared to their East and Gulf Coast counterparts, but provide a unique opportunity to disentangle these effects. A broader study in three Oregon estuaries (Peck et al., this session) indicates RSLR as the dominant factor controlling sedimentation rates. Working in Nehalem Bay (northern Oregon coast), replicate sediment cores were taken along several transects across an elevation gradient for analysis of sediment and carbon accumulation using CT scans, gamma detection of Pb-210, X-Ray Fluorescence (XRF) and Loss-on-Ignition (LOI). Preliminary results indicate sediment accumulation rates over the past century are higher than rates seen in other comparable Oregon salt marshes; this is consistent with past studies and preliminary analysis of remote sensing data that show significant horizontal expansion of Nehalem marshes. A number of possible causes for the high sediment accumulation rates - hydroclimate of Nehalem River, extensive timber harvesting, forest fires such as the so-called Tillamook Burns, and diking of adjacent marshes - are being explored.

500-year Reconstructions of Circulation in the Northeastern Pacific and Western North America: Relation to Precipitation and Fire Conditions in California and Precipitation in Hawai'i

NASA Astrophysics Data System (ADS)

Wahl, E. R.; Zorita, E.; Trouet, V.; Diaz, H. F.

2015-12-01

A reconstruction of the position of the North Pacific Jet Stream (NPJ) over the past 500 years is evaluated in relation to dry and wet extremes in California and extremes of Sierra Nevada fire activity. This work represents a unique combination of independent annually-resolved paleoclimate and paleoecological reconstructions in the region. Results indicate that fire and precipitation extremes are both closely linked with NPJ winter position, with characteristic wet/low fire and dry/high fire NPJ spatial features in the Pacific adjacent to western North America. These features are in turn evaluated in 21st century climate model scenarios using transient integrations over the past millennium, the instrumental period, and the 21st century. The reconstruction of NPJ position is driven by an analog process that employs independent paleoclimate field reconstructions to select model states closest to the reconstructions; it is thus logically and scientifically most consistent to use comparable models to evaluate the future in relation to the past. Initial results indicate that relatively wet/low fire regional conditions are reasonably possible in the later 21st century under a high greenhouse gas forcing regime (RCP 8.5), even though temperatures rise significantly. Related hydroclimate research reconstructs a precipitation index for the Hawai'ian Islands (HI-precip) over the past 500 years. A northeastern Pacific sea level pressure index reconstructed using the analog process is employed as the driving variable in a calibration against HI-precip. Initial reconstruction results indicate significant bicentennial spectral power, which includes a long-term drying trend that began around 1850 and continues into the first decades of the 21st century. Related statistical downscaling of climate model output for HI-precip to the end of the 21st century suggests the possibility of continued drying under RCP 8.5.

Patterns of Precipitation and Streamflow Responses to Moisture Fluxes during Atmospheric Rivers

NASA Astrophysics Data System (ADS)

Henn, B. M.; Wilson, A. M.; Asgari Lamjiri, M.; Ralph, M.

2017-12-01

Precipitation from landfalling atmospheric rivers (ARs) have been shown to dominate the hydroclimate of many parts of the world. ARs are associated with saturated, neutrally-stable profiles in the lower atmosphere, in which forced ascent by topography induces precipitation. Understanding the spatial and temporal variability of precipitation over complex terrain during AR-driven precipitation is critical for accurate forcing of distributed hydrologic models and streamflow forecasts. Past studies using radar wind profilers and radiosondes have demonstrated predictability of precipitation rates based on upslope water vapor flux over coastal terrain, with certain levels of moisture flux exhibiting the greatest influence on precipitation. Additionally, these relationships have been extended to show that streamflow in turn responds predictably to upslope vapor flux. However, past studies have focused on individual pairs of profilers and precipitation gauges; the question of how orographic precipitation in ARs is distributed spatially over complex terrain, at different topographic scales, is less well known. Here, we examine profiles of atmospheric moisture transport from radiosondes and wind profilers, against a relatively dense network of precipitation gauges, as well as stream gauges, to assess relationships between upslope moisture flux and the spatial response of precipitation and streamflow. We focus on California's Russian River watershed in the 2016-2017 cool season, when regular radiosonde launches were made at two locations during an active sequence of landfalling ARs. We examine how atmospheric water vapor flux results in precipitation patterns across gauges with different topographic relationships to the prevailing moisture-bearing winds, and conduct a similar comparison of runoff volume response from several unimpaired watersheds in the upper Russian watershed, taking into account antecedent soil moisture conditions that influence runoff generation. Finally, we compare observed spatial patterns of precipitation accumulations to those in a topographically-aided gridded precipitation dataset to understand how atmospheric moisture transport may inform methods to downscale precipitation to high resolution for use in hydrologic modeling.

Isotopes in North American Rocky Mountain Snowpack 1993-2014

NASA Astrophysics Data System (ADS)

Anderson, Lesleigh; Berkelhammer, Max; Mast, M. Alisa

2016-01-01

We present ∼1300 new isotopic measurements (δ18O and δ2H) from a network of snowpack sites in the Rocky Mountains that have been sampled since 1993. The network includes 177 locations where depth-integrated snow samples are collected each spring near peak accumulation. At 57 of these locations snowpack samples were obtained for 10-21 years and their isotopic measurements provide unprecedented spatial and temporal documentation of snowpack isotope values at mid-latitudes. For environments where snowfall accounts for the majority of annual precipitation, snowmelt is likely to have the strongest influence on isotope values retained in proxy archives. In this first presentation of the dataset we (1) describe the basic features of the isotope values in relation to the Global Meteoric Water Line (GMWL), (2) evaluate space for time substitutions traditionally used to establish δ18O-temperature relations, (3) evaluate site-to-site similarities across the network and identify those that are the most regionally representative, (4) examine atmospheric circulation patterns for several years with spatially coherent isotope patterns, and (5) provide examples of the implications this new dataset has for interpreting paleoclimate records (Bison Lake, Colorado and Minnetonka Cave, Idaho). Results indicate that snowpack δ18O is rarely a simple proxy of temperature. Instead, it exhibits a high degree of spatial heterogeneity and temporal variance that reflect additional processes such as vapor transport and post-depositional modification. Despite these complexities we identify consistent climate-isotope patterns and regionally representative locations that serve to better define Holocene hydroclimate estimates and their uncertainty. Climate change has and will affect western U.S. snowpack and we suggest these changes can be better understood and anticipated by oxygen and hydrogen isotope-based reconstructions of Holocene hydroclimate using a process-based understanding of the controls on snowpack isotope ratios.

Drivers of pluvial lake distributions in western North America

NASA Astrophysics Data System (ADS)

Ibarra, D. E.; Oster, J. L.; Winnick, M.; Caves, J. K.; Ritch, A. J.; Chamberlain, C. P.; Maher, K.

2016-12-01

The distribution of large inland lakes in western North America during the Plio-Pleistocene is intimately linked to the regional hydroclimate and moisture delivery dynamics. We investigate the climatological conditions driving terminal basin lakes in western North America during the mid-Pliocene warm period and the latest Pleistocene glacial maximum. Lacustrine deposits and geologic proxies suggest that lakes and wet conditions persisted during both warm and cold periods in the southwest, despite dramatically different global climate, ice sheet configuration and pCO2 levels. We use two complementary methods to quantify the hydroclimate drivers of terminal basin lake levels. First, a quantitative proxy-model comparison is conducted using compilations of geologic proxies and an ensemble of climate models. We utilize archived climate model simulations of the Last Glacial Maximum (21 ka, LGM) and mid-Pliocene (3.3 Ma) produced by the Paleoclimate Modelling Intercomparison Project (PMIP and PlioMIP). Our proxy network is made up of stable isotope records from caves, soils and paleosols, lake deposits and shorelines, glacier chronologies, and packrat middens. Second, we forward model the spatial distribution of lakes in the region using a Budyko framework to constrain the water balance for terminally draining watersheds, and make quantitative comparisons to mapped lacustrine shorelines and outcrops. Cumulatively these two approaches suggest that reduced evaporation and moderate increases in precipitation, relative to modern, drove moderate to large pluvial lakes during the LGM in the Great Basin. In contrast, larger precipitation increases appear to be the primary driver of lake levels during the mid-Pliocene in the southwest, with this spatial difference suggesting a role for El Niño teleconnections. These results demonstrate that during past periods of global change patterns of `dry-gets-drier, wet-gets-wetter' do not hold true for western North America.

Caves, Carbonates and Climate: Karst Landscape Development through Environmental Forcing, Little Cayman Island

NASA Astrophysics Data System (ADS)

Hsia, S.; Ouellette, G., Jr.; Manfrino, C.

2016-12-01

The Cayman Islands are situated in the west-central Caribbean Sea, between Cuba and the Yucatan Peninsula. Little Cayman Island (LCI) is relatively underdeveloped and understudied in comparison to its sister islands, Grand Cayman and Cayman Brac, and hosts less than 200 permanent residents over a 30 square kilometer area. However, like its sister islands, LCI is a small carbonate platform derived from reef building during the Oligocene, Miocene, and Quaternary. The shared geologic history of the Cayman Islands along with minimal human disturbance makes LCI an ideal site to study an island karst landscape. Conduction of field surveys, stratigraphic and petrologic comparisons between primary lithologic formations, and compilation of a geospatial inventory of karst features and lithology of LCI using GIS revealed novel insights into landscape evolution on LCI. In addition to surface karst surveys, several caves on the island were mapped. Cave morphologies suggest that evolution of LCI karst features have been driven by both hydroclimate, as well as salt and freshwater mixing, modulated by sea level fluctuations. These findings are mirrored in the lithology of partially dolomitized Miocene carbonates, which contain paleo-karst fill features and reveal hydroclimate influence, as well as enhanced resistance to dissolution in the present day, ostensibly from submersion in Mg-rich sea waters prior to the Quaternary. These findings shed light on the complex relationship of climate, geology, and karst landscape development on this particular carbonate island. This information is critical in anticipating structural and hydrogeological integrity on LCI under future climate change scenarios and serves as an example of the interplay linking climate and geologic processes to karst landscape development on small carbonate islands.

Hydrologic modeling for monitoring water availability in Africa and the Middle East

NASA Astrophysics Data System (ADS)

McNally, A.; Getirana, A.; Arsenault, K. R.; Peters-Lidard, C. D.; Verdin, J. P.

2015-12-01

Drought impacts water resources required by crops and communities, in turn threatening lives and livelihoods. Early warning systems, which rely on inputs from hydro-climate models, are used to help manage risk and provide humanitarian assistance to the right place at the right time. However, translating advancements in hydro-climate science into action is a persistent and time-consuming challenge: scientists and decision-makers need to work together to enhance the salience, credibility, and legitimacy of the hydrological data products being produced. One organization that tackles this challenge is the Famine Early Warning Systems Network (FEWS NET), which has been using evidence-based approaches to address food security since the 1980s.In this presentation, we describe the FEWS NET Land Data Assimilation System (FLDAS), developed by FEWS NET and NASA hydrologic scientists to maximize the use of limited hydro-climatic observations for humanitarian applications. The FLDAS, an instance of the NASA Land Information System (LIS), is comprised of land surface models driven by satellite rainfall inputs already familiar to FEWS NET food security analysts. First, we evaluate the quality of model outputs over parts of the Middle East and Africa using remotely sensed soil moisture and vegetation indices. We then describe derived water availability indices that have been identified by analysts as potentially useful sources of information. Specifically, we demonstrate how the Baseline Water Stress and Drought Severity Index detect recent water availability crisis events in the Tigris-Euphrates Basin and the Gaborone Reservoir, Botswana. Finally we discuss ongoing work to deliver this information to FEWS NET analysts in a timely and user-friendly manner, with the ultimate goal of integrating these water availability metrics into regular decision-making activities.

Extreme aridity and mild temperatures in the Middle East during the late Little Ice Age indicated by paired coral Sr/Ca and δ18O from the northern Red Sea

NASA Astrophysics Data System (ADS)

Felis, T.; Ionita, M.; Rimbu, N.; Lohmann, G.; Kölling, M.

2016-12-01

Throughout the global deserts, annually resolved reconstructions of temperature that extend the short instrumental record are virtually absent, and proxy records of aridity are difficult to obtain. The Little Ice Age ( 1450-1850) is thought to have been characterized by generally cold conditions in many regions of the globe with little commonality regarding the hydroclimate. However, due to a lack of annually resolved natural archives in the Sahara and Arabian Desert, the precise characteristics of Middle Eastern climate during the Little Ice Age are unknown. Here we show, based on subseasonally resolved proxy records using corals from the northern Red Sea that the Middle East did not experience pronounced cooling during the late Little Ice Age (1751-1850). Instead, it was characterised by an even more arid climate than today. From our coral records and early instrumental data we conclude that Middle Eastern aridity resulted from a blocking-like atmospheric circulation over central Europe that weakened the moist Mediterranean westerlies and favoured the advection of dry continental air from Eurasia. We find that this extreme aridity terminated abruptly between 1850 and 1855 due to an atmospheric circulation change over the European-Middle East area at the end of the Little Ice Age with profound impacts on regional hydroclimate. Our results provide a hydroclimatic perspective on the resettlement of abandoned areas of the historical Fertile Crescent following the Little Ice Age. Furthermore, we speculate such an atmospheric blocking could have prevailed during other North Atlantic-European cold events of the Holocene epoch, and may explain the northern Mesopotamian aridification at 4,200 years ago that is thought to have led to the collapse of ancient civilizations.

Hydro-meteorological trends in the Gidabo catchment of the Rift Valley Lakes Basin of Ethiopia

NASA Astrophysics Data System (ADS)

Belihu, Mamuye; Abate, Brook; Tekleab, Sirak; Bewket, Woldeamlak

2018-04-01

The global and regional variability and changes of climate and stream flows are likely to have significant influence on water resource availability. The magnitude and impacts of climate variability and change differs spatially and temporally. This study examines the long term hydroclimatic changes, analyses of the hydro-climate variability and detect whether there exist significant trend or not in the Gidabo catchment, rift valley lakes basin of Ethiopia. Precipitation, temperature and stream flow time series data were used in monthly, seasonal and annual time scales. The precipitation and temperature data span is between 1982 and 2014 and that of stream flow is between 1976 and 2006. To detect trends the analysis were done by using Mann Kendal (MK), Sen's graphical method and to detect change point using the Pettit test. The comparison of trend analysis between MK trend test and Sen graphical method results depict mostly similar pattern. The annual rainfall trends exhibited a significant decrease by about 12 mm per year in the upstream, which is largely driven by the significant decrease in the peak season rainfall. The Pettit test revealed that the years 1997 and 2007 were the change points. It is noted that the rise of temperature over a catchment might have decreased the availability of soil moisture which resulted in less runoff. The temperature analyses also revealed that the catchment was getting warmer; particularly in the upstream. The minimum temperature trend showed a significant increase about 0.08°c per annum. There is generally a decreasing trend in stream flow. The monthly stream flow also exhibited a decreasing trend in February, March and September. The decline in annual and seasonal rainfall and the increase in temperature lead to more evaporation and directly affecting the stream flow negatively. This trend compounded with the growth of population and increasing demand for irrigation water exacerbates the competing demand for water resources. It thus calls for prudence in devising appropriate intervention in the planning and sustainable development of the basin water resources.

A Continuous Holocene Record of Hydroclimate from Kartchner Cavern, AZ, Supported by Multiyear Dripwater Monitoring

NASA Astrophysics Data System (ADS)

Cole, J. E.; Hlohowskyj, S.; Vetter, L.; King, J.; Casavant, R. R.; Woodhead, J. D.; Drysdale, R.; Truebe, S.; Henderson, G. M.

2017-12-01

In the arid southwest, hydroclimatic variability is critical to natural and human systems. Cave records provide the chance to reconstruct past variations in moisture, including the seasonal hydroclimatic response to known forcings such as the seasonal distribution of insolation. At Kartchner Caverns State Park, AZ, a sample dating to 12,000 years before present reveals a continuous Holocene history of the Southwest monsoon in its stable isotope content. We interpret the large ( 4‰) changes in speleothem d18O in terms of seasonal precipitation balance, based on modern isotope studies. The Kartchner record confirms a shorter ( 6500 yr) reconstruction from the neighboring Cave of the Bells in describing a strong trend of declining monsoon moisture during the Holocene. The Kartchner sample reveals an early Holocene monsoon peak defined by a broad δ18O peak between 7000 and 9000 years ago, following a gradual strengthening from the start of the record. Between 7000-2000 years ago, the monsoon weakened, and the oxygen isotope values show no trend over the past 2000 years. Substantial multidecadal-multicentury variability is present throughout the record. This pattern is consistent with a sensitive response of the Southwest monsoon to orbital forcing of seasonal radiation. A new laser-ICPMS multi-element dataset spans the past 2400 years and adds information to our isotope-based reconstruction. In particular, Ba and Sr highlight intervals of overall wet and dry conditions, complementing the isotopic record of seasonal precipitation distribution. Dripwater monitoring since 2011 at 4 sites in the cave allows us to identify seasonal and interannual controls on the isotopic and elemental variations of dripwater. Drips differ in their isotopic behavior, with some dominated by relatively steady, low (winter) values and others exhibiting highly variable δ18O. This study provides one of the first cave-based reconstructions of the North American monsoon spanning the entire Holocene. The modern dripwater data shed light on how isotopic and elemental signals vary over space and time and create the multivariate climate record preserved in cave calcite.

Palaeo-dust records: A window to understanding past environments

NASA Astrophysics Data System (ADS)

Marx, Samuel K.; Kamber, Balz S.; McGowan, Hamish A.; Petherick, Lynda M.; McTainsh, Grant H.; Stromsoe, Nicola; Hooper, James N.; May, Jan-Hendrik

2018-06-01

Dust entrainment, transport over vast distances and subsequent deposition is a fundamental part of the Earth system. Yet the role and importance of dust has been underappreciated, due largely to challenges associated with recognising dust in the landscape and interpreting its depositional history. Despite these challenges, interest in dust is growing. Technical advances in remote sensing and modelling have improved understanding of dust sources and production, while advances in sedimentology, mineralogy and geochemistry (in particular) have allowed dust to be more easily distinguished within sedimentary deposits. This has facilitated the reconstruction of records of dust emissions through time. A key advance in our understanding of dust has occurred following the development of methods to geochemically provenance (fingerprint) dust to its source region. This ability has provided new information on dust transport pathways, as well as the reach and impact of dust. It has also expanded our understanding of the processes driving dust emissions over decadal to millennial timescales through linking dust deposits directly to source area conditions. Dust provenance studies have shown that dust emission, transport and deposition are highly sensitive to variability in climate. They also imply that dust emissions are not simply a function of the degree of aridity in source areas, but respond to a more complex array of conditions, including sediment availability. As well as recording natural variability, dust records are also shown to sensitively track the impact of human activity. This is reflected by both changing dust emission rates and changing dust chemistry. Specific examples of how dust responds to, and records change, are provided with our work on dust emissions from Australia, the most arid inhabited continent and the largest dust source in the Southern Hemisphere. These case studies show that Australian dust emissions reflect hydro-climate variability, with reorganisation of Australian dust source areas occurring during the mid to late Holocene. Dust emissions are shown to sensitively map the structure of the Last Glacial Maximum in Australia, demonstrating that this period was associated with enhanced, but also variable dust emissions, driven by changing sources area conditions. Finally we show how dust emissions have responded to the arrival of Europeans and the associated onset of broad-scale agriculture across the Australian continent.

Tracking Extra Tropical Cyclones to Explore how the Jet Stream Shifted During The Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Garrett, H.

2016-12-01

The behavior of the jet stream during the last glacial maximum (LGM 21ka) has been the focus of multiple studies but remains highly debated. Proxy data shows that during this time in the United States, the northwest was drier than modern conditions and the southwest was wetter than modern conditions. To explain this there are two competing hypothesis, one which suggests that the jet stream shifted uniformly south and the other which suggests a stronger jet that split shifting both north and south. For this study we used TECA, to reanalyze model out-put, looking at the frequency and patterns of Extra Tropical Cyclones (ETC's), which have been found to be steered by the jet stream. We used the CCSM4 model based on its agreement with proxy data, and compared data from both the LGM and pre-industrial time periods. Initial results show a dramatic shift of ETC's north by about 10º-15º degrees and a decrease in frequency compared to pre-industrial conditions, coupled with a less pronounced southward shift of 5º-10º degrees.This evidence supports the idea that the jet stream split during the LGM. A stronger understanding of jet stream behavior will help to improve future models and prediction capabilities to prepare for hydro-climate change in drought sensitive areas.

Increasing aridity threats to Himalayan alpine ecosystems? A millenial history of hydroclimate from the Tibetan plateau derived from a δ18O tree-ring network

NASA Astrophysics Data System (ADS)

Griessinger, J.

2015-12-01

The Tibetan plateau (TP) plays an important role as an elevated heat source responsible for the establishment of the Asias monsoonal systems. Besides the Indian Summer Monsoon (ISM), also the East Asian Summer Monsoon (EASM) is triggering the regional precipitation regimes during the vegetation period from May to September. Within recent decades, fundamental climate changes on the southeastern part of the TP were detected leading to substantial changes within the regional hydrological budget and affecting local ecosystems. By using a spatial network of multicentennial to 1.5 millenial year old tree-ring δ18O time-series from the southeastern part of the TP, the regional climate history as well as the late Holocene monsoonal variability will be presented. Since the main climatically sensitive periods like the Medieval Warm Period and the Little Ice Age are displayed in all chronologies, their typical hydroclimatological characteristics and impacts will be discussed especially in regard to the recent warming trend on the TP and the responsible climatic triggers. Arising from these results, regional impacts and differences of the proposed hydrological changes will be discussed. In addition, first results of a comparison between proxy-based (δ18O) and model-based (re-analysis datasets) trajectory calculations will be presented, trying to give insights in the origin and impact of air masses for the most striking last three decades on the southeastern part of the TP.

Stochastic simulation and decadal prediction of hydroclimate in the Western Himalayas

NASA Astrophysics Data System (ADS)

Robertson, A. W.; Chekroun, M. D.; Cook, E.; D'Arrigo, R.; Ghil, M.; Greene, A. M.; Holsclaw, T.; Kondrashov, D. A.; Lall, U.; Lu, M.; Smyth, P.

2012-12-01

Improved estimates of climate over the next 10 to 50 years are needed for long-term planning in water resource and flood management. However, the task of effectively incorporating the results of climate change research into decision-making face a ``double conflict of scales'': the temporal scales of climate model projections are too long, while their usable spatial scales (global to planetary) are much larger than those needed for actual decision making (at the regional to local level). This work is designed to help tackle this ``double conflict'' in the context of water management over monsoonal Asia, based on dendroclimatic multi-century reconstructions of drought indices and river flows. We identify low-frequency modes of variability with time scales from interannual to interdecadal based on these series, and then generate future scenarios based on (a) empirical model decadal predictions, and (b) stochastic simulations generated with autoregressive models that reproduce the power spectrum of the data. Finally, we consider how such scenarios could be used to develop reservoir optimization models. Results will be presented based on multi-century Upper Indus river discharge reconstructions that exhibit a strong periodicity near 27 years that is shown to yield some retrospective forecasting skill over the 1700-2000 period, at a 15-yr yield time. Stochastic simulations of annual PDSI drought index values over the Upper Indus basin are constructed using Empirical Model Reduction; their power spectra are shown to be quite realistic, with spectral peaks near 5--8 years.

From Fall to Spring, or Spring to Fall? Seasonal Cholera Transmission Cycles and Implications for Climate Change

NASA Astrophysics Data System (ADS)

Akanda, A. S.; Jutla, A. S.; Huq, A.; Colwell, R.; Islam, S.; WE Reason

2010-12-01

Cholera remains a major public health threat in many developing countries around the world. The striking seasonality and the annual recurrence of this infectious disease in endemic areas continues to be of considerable interest to scientists and public health workers. Despite major advances in the ecological, and microbiological understanding of Vibrio cholerae, the causative agent, the role of underlying macro-scale hydroclimatic processes in propagating the disease in different seasons and years is not well understood. The incidence of cholera in the Bengal Delta region, the ‘native homeland’ of cholera, shows distinct biannual peaks in the southern floodplains, as opposed to single annual peaks in coastal areas and the northern parts of Bangladesh, as well as other cholera-endemic regions in the world. A coupled analysis of the regional hydroclimate and cholera incidence reveals a strong association of the spatio-temporal variability of incidence peaks with seasonal processes and extreme events. At a seasonal scale, the cycles indicate a spring-fall transmission pattern, contrary to the prevalent notion of a fall-spring transmission cycle. We show that the asymmetric seasonal hydroclimatology affects regional cholera dynamics by providing a coastal growth environment for bacteria in spring, while propagating transmission to fall by flooding. This seasonal interpretation of the progression of cholera has important implications, for formulating effective cholera intervention and mitigation efforts through improved water management and understanding the impacts of changing climate patterns on seasonal cholera transmission. (Water Environental Research Education Actionable Solutions Network)

Galápagos hydroclimate of the Common Era from paired microalgal and mangrove biomarker 2H/1H values

PubMed Central

Sachs, Julian P.

2016-01-01

Tropical maritime precipitation affects global atmospheric circulation, influencing storm tracks and the size and location of subtropical deserts. Paleoclimate evidence suggests centuries-long changes in rainfall in the tropical Pacific over the past 2,000 y, but these remain poorly characterized across most of the ocean where long, continuous proxy records capable of resolving decadal-to-centennial climate changes are still virtually nonexistent despite substantial efforts to develop them. Here we apply a new climate proxy based on paired hydrogen isotope ratios from microalgal and mangrove-derived sedimentary lipids in the Galápagos to reconstruct maritime precipitation changes during the Common Era. We show that increased rainfall during the Little Ice Age (LIA) (∼1400–1850 CE) was likely caused by a southward migration of the Intertropical Convergence Zone (ITCZ), and that this shift occurred later than previously recognized, coeval with dynamically linked precipitation changes in South America and the western tropical Pacific. Before the LIA, we show that drier conditions at the onset of the Medieval Warm Period (∼800–1300 CE) and wetter conditions ca. 2 ka were caused by changes in the El Niño/Southern Oscillation (ENSO). Collectively, the large natural variations in tropical rainfall we detect, each linked to a multicentury perturbation of either ENSO-like variability or the ITCZ, imply a high sensitivity of tropical Pacific rainfall to climate forcings. PMID:26976574

Extensive wet episodes in Late Glacial Australia resulting from high-latitude forcings

PubMed Central

Bayon, Germain; De Deckker, Patrick; Magee, John W.; Germain, Yoan; Bermell, Sylvain; Tachikawa, Kazuyo; Norman, Marc D.

2017-01-01

Millennial-scale cooling events termed Heinrich Stadials punctuated Northern Hemisphere climate during the last glacial period. Latitudinal shifts of the intertropical convergence zone (ITCZ) are thought to have rapidly propagated these abrupt climatic signals southward, influencing the evolution of Southern Hemisphere climates and contributing to major reorganisation of the global ocean-atmosphere system. Here, we use neodymium isotopes from a marine sediment core to reconstruct the hydroclimatic evolution of subtropical Australia between 90 to 20 thousand years ago. We find a strong correlation between our sediment provenance proxy data and records for western Pacific tropical precipitations and Australian palaeolakes, which indicates that Northern Hemisphere cooling phases were accompanied by pronounced excursions of the ITCZ and associated rainfall as far south as about 32°S. Comparatively, however, each of these humid periods lasted substantially longer than the mean duration of Heinrich Stadials, overlapping with subsequent warming phases of the southern high-latitudes recorded in Antarctic ice cores. In addition to ITCZ-driven hydroclimate forcing, we infer that changes in Southern Ocean climate also played an important role in regulating late glacial atmospheric patterns of the Southern Hemisphere subtropical regions.

Snowfall less sensitive to warming in Karakoram than in Himalayas due to a unique seasonal cycle

USGS Publications Warehouse

Kapnick, Sarah B.; Delworth, Thomas L.; Ashfaq, Moetasim; Malyshev, Sergey; Milly, Paul C.D.

2014-01-01

The high mountains of Asia, including the Karakoram, Himalayas and Tibetan Plateau, combine to form a region of perplexing hydroclimate changes. Glaciers have exhibited mass stability or even expansion in the Karakoram region1, 2, 3, contrasting with glacial mass loss across the nearby Himalayas and Tibetan Plateau1, 4, a pattern that has been termed the Karakoram anomaly. However, the remote location, complex terrain and multi-country fabric of high-mountain Asia have made it difficult to maintain longer-term monitoring systems of the meteorological components that may have influenced glacial change. Here we compare a set of high-resolution climate model simulations from 1861 to 2100 with the latest available observations to focus on the distinct seasonal cycles and resulting climate change signatures of Asia’s high-mountain ranges. We find that the Karakoram seasonal cycle is dominated by non-monsoonal winter precipitation, which uniquely protects it from reductions in annual snowfall under climate warming over the twenty-first century. The simulations show that climate change signals are detectable only with long and continuous records, and at specific elevations. Our findings suggest a meteorological mechanism for regional differences in the glacier response to climate warming.

Spatiotemporal variability of suspended sediment particle size in a mixed-land-use watershed.

PubMed

Kellner, Elliott; Hubbart, Jason A

2018-02-15

Given existing knowledge gaps, there is a need for research that quantitatively characterizes spatiotemporal variation of suspended sediment particle size distribution (PSD) in contemporary watersheds. A five-year study was conducted in a representative watershed of the central United States utilizing a nested-scale experimental watershed study design, comprising five gauging sites partitioning the catchment into five sub-watersheds. Streamwater grab samples were collected four times per week, at each gauging site, for the duration of the study period (Oct. 2009-Feb. 2014). Samples were analyzed using laser particle diffraction. Significantly different (p<0.05) suspended sediment PSDs were observed at monitoring sites throughout the course of the study. For example, results indicated greater proportions of silt at site #5 (65%), relative to other sites (41, 32, 29, and 43%, for sites #1-#4, respectively). Likewise, results showed greater proportions of sand at sites #2 and #3 (66 and 68%, respectively), relative to other sites (57, 55, and 34%, for sites #1, #4, and #5, respectively). PSD spatial variability was not fully explained by hydroclimate or sub-watershed land use/land cover characteristics. Rather, results were strengthened by consideration of surficial geology (e.g. supply-controlled spatial variation of particle size). PSD displayed consistent seasonality during the study, characterized by peaks in the proportion of sand (and aggregates) during the winter (i.e. 70-90%), and minimums during the summer (i.e. 12-38%); and peaks in the proportion of silt particles in the summer (i.e. 61-88%) and minimums in the winter (i.e. 10-23%). Likely explanations of results include seasonal streamflow differences. Results comprise distinct observations of spatiotemporal variation of PSD, thereby improving understanding of lotic suspended sediment regimes and advancing future management practices in mixed-land-use watersheds. Copyright © 2017 Elsevier B.V. All rights reserved.

An Overview of the NASA Energy and Water cycle Study (NEWS) and the North American Water Program (NAWP)

NASA Astrophysics Data System (ADS)

Houser, P. R.

2014-12-01

NEWS: 10 years ago, NASA established the NASA Energy and Water-cycle Study (NEWS), whose long-term grand challenge is to document and enable improved, observationally based, predictions of water and energy cycle consequences of Earth system variability and change. The NEWS program builds upon existing NASA-supported basic research in atmospheric physics and dynamics, radiation, climate modeling, and terrestrial hydrology. While these NASA programs fund research activities that address individual aspects of the global energy and water cycles, they are not specifically designed to generate a coordinated result. NEWS developed the first coordinated attempt to describe the complete global energy and water cycle using existing and forthcoming satellite and ground based observations, and laying the foundation for essential NEWS developments in model representations of atmospheric energy and water exchange processes. This comprehensive energy and water data analysis program exploited crucial datasets, some requiring complete re-processing, and new satellite measurements. NAWP: Dramatically changing climates has had an indelible impact on North America's water crisis. To decisively address these challenges, we recommend that NAWP coalesce an interdisciplinary, international and interagency effort to make significant contributions to continental- to decision-scale hydroclimate science and solutions. By entraining, integrating and coordinating the vast array of interdisciplinary observational and prediction resources available, NAWP will significantly advance skill in predicting, assessing and managing variability and changes in North American water resources. We adopt three challenges to organize NAWP efforts. The first deals with developing a scientific basis and tools for mitigating and adapting to changes in the water supply-demand balance. The second challenge is benchmarking; to use incomplete and uncertain observations to assess water storage and quality dynamics, and to characterize the information content of water cycle predictions in a way that allows for model improvement. The final challenge is to establish clear pathways to inform water managers, practitioners and decision makers about newly developed tools, observations and research results.

The Mediterranean Sea regime shift at the end of the 1980s, and intriguing parallelisms with other European basins.

PubMed

Conversi, Alessandra; Fonda Umani, Serena; Peluso, Tiziana; Molinero, Juan Carlos; Santojanni, Alberto; Edwards, Martin

2010-05-19

Regime shifts are abrupt changes encompassing a multitude of physical properties and ecosystem variables, which lead to new regime conditions. Recent investigations focus on the changes in ecosystem diversity and functioning associated to such shifts. Of particular interest, because of the implication on climate drivers, are shifts that occur synchronously in separated basins. In this work we analyze and review long-term records of Mediterranean ecological and hydro-climate variables and find that all point to a synchronous change in the late 1980s. A quantitative synthesis of the literature (including observed oceanic data, models and satellite analyses) shows that these years mark a major change in Mediterranean hydrographic properties, surface circulation, and deep water convection (the Eastern Mediterranean Transient). We provide novel analyses that link local, regional and basin scale hydrological properties with two major indicators of large scale climate, the North Atlantic Oscillation index and the Northern Hemisphere Temperature index, suggesting that the Mediterranean shift is part of a large scale change in the Northern Hemisphere. We provide a simplified scheme of the different effects of climate vs. temperature on pelagic ecosystems. Our results show that the Mediterranean Sea underwent a major change at the end of the 1980s that encompassed atmospheric, hydrological, and ecological systems, for which it can be considered a regime shift. We further provide evidence that the local hydrography is linked to the larger scale, northern hemisphere climate. These results suggest that the shifts that affected the North, Baltic, Black and Mediterranean (this work) Seas at the end of the 1980s, that have been so far only partly associated, are likely linked as part a northern hemisphere change. These findings bear wide implications for the development of climate change scenarios, as synchronous shifts may provide the key for distinguishing local (i.e., basin) anthropogenic drivers, such as eutrophication or fishing, from larger scale (hemispheric) climate drivers.

Mode Decomposition Methods for Soil Moisture Prediction

NASA Astrophysics Data System (ADS)

Jana, R. B.; Efendiev, Y. R.; Mohanty, B.

2014-12-01

Lack of reliable, well-distributed, long-term datasets for model validation is a bottle-neck for most exercises in soil moisture analysis and prediction. Understanding what factors drive soil hydrological processes at different scales and their variability is very critical to further our ability to model the various components of the hydrologic cycle more accurately. For this, a comprehensive dataset with measurements across scales is very necessary. Intensive fine-resolution sampling of soil moisture over extended periods of time is financially and logistically prohibitive. Installation of a few long term monitoring stations is also expensive, and needs to be situated at critical locations. The concept of Time Stable Locations has been in use for some time now to find locations that reflect the mean values for the soil moisture across the watershed under all wetness conditions. However, the soil moisture variability across the watershed is lost when measuring at only time stable locations. We present here a study using techniques such as Dynamic Mode Decomposition (DMD) and Discrete Empirical Interpolation Method (DEIM) that extends the concept of time stable locations to arrive at locations that provide not simply the average soil moisture values for the watershed, but also those that can help re-capture the dynamics across all locations in the watershed. As with the time stability, the initial analysis is dependent on an intensive sampling history. The DMD/DEIM method is an application of model reduction techniques for non-linearly related measurements. Using this technique, we are able to determine the number of sampling points that would be required for a given accuracy of prediction across the watershed, and the location of those points. Locations with higher energetics in the basis domain are chosen first. We present case studies across watersheds in the US and India. The technique can be applied to other hydro-climates easily.

Hydrological and depositional processes associated with recent glacier recession in Yanamarey catchment, Cordillera Blanca (Peru).

PubMed

López-Moreno, J I; Valero-Garcés, B; Mark, B; Condom, T; Revuelto, J; Azorín-Molina, C; Bazo, J; Frugone, M; Vicente-Serrano, S M; Alejo-Cochachin, J

2017-02-01

In this study, we investigate changes in the glaciated surface and the formation of lakes in the headwater of the Querococha watershed in Cordillera Blanca (Peru) using 24 Landsat images from 1975 to 2014. Information of glacier retreat was integrated with available climate data, the first survey of recent depositional dynamics in proglacial Yanamarey Lake (4600m a.s.l.), and a relatively short hydrological record (2002-2014) at the outlet of Yanamarey Lake. A statistically significant temperature warming (0.21°C decade -1 for mean annual temperature) has been detected in the region, and it caused a reduction of the glacierized area since 1975 from 3.5 to 1.4km -2 . New small lakes formed in the deglaciated areas, increasing the flooded area from1.8ha in 1976 to 2.8ha in 2014. A positive correlation between annual rates of glacier recession and runoff was found. Sediment cores revealed a high sedimentation rate (>1cmyr -1 ) and two contrasted facies, suggesting a shift toward a reduction of meltwater inputs and higher hydrological variability likely due to an increasing role of precipitation on runoff during the last decades. Despite the age control uncertainties, the main transition likely occurred around 1998-2000, correlating with the end of the phase with maximum warming rates and glacier retreat during the 1980s and 1990s, and the slowing down of expansion of surface lake-covered surface. With this hydrological - paleolimnological approach we have documented the association between recent climate variability and glacier recession and the rapid transfer of hydroclimate signal to depositional and geochemical processes in high elevation Andean environments. This, study also alerts about water quality risks as proglacial lakes act as secondary reservoirs that trap trace and minor elements in high altitude basins. Copyright © 2016 Elsevier B.V. All rights reserved.

Understanding and seasonal forecasting of hydrological drought in the Anthropocene

NASA Astrophysics Data System (ADS)

Yuan, Xing; Zhang, Miao; Wang, Linying; Zhou, Tian

2017-11-01

Hydrological drought is not only caused by natural hydroclimate variability but can also be directly altered by human interventions including reservoir operation, irrigation, groundwater exploitation, etc. Understanding and forecasting of hydrological drought in the Anthropocene are grand challenges due to complicated interactions among climate, hydrology and humans. In this paper, five decades (1961-2010) of naturalized and observed streamflow datasets are used to investigate hydrological drought characteristics in a heavily managed river basin, the Yellow River basin in north China. Human interventions decrease the correlation between hydrological and meteorological droughts, and make the hydrological drought respond to longer timescales of meteorological drought. Due to large water consumptions in the middle and lower reaches, there are 118-262 % increases in the hydrological drought frequency, up to 8-fold increases in the drought severity, 21-99 % increases in the drought duration and the drought onset is earlier. The non-stationarity due to anthropogenic climate change and human water use basically decreases the correlation between meteorological and hydrological droughts and reduces the effect of human interventions on hydrological drought frequency while increasing the effect on drought duration and severity. A set of 29-year (1982-2010) hindcasts from an established seasonal hydrological forecasting system are used to assess the forecast skill of hydrological drought. In the naturalized condition, the climate-model-based approach outperforms the climatology method in predicting the 2001 severe hydrological drought event. Based on the 29-year hindcasts, the former method has a Brier skill score of 11-26 % against the latter for the probabilistic hydrological drought forecasting. In the Anthropocene, the skill for both approaches increases due to the dominant influence of human interventions that have been implicitly incorporated by the hydrological post-processing, while the difference between the two predictions decreases. This suggests that human interventions can outweigh the climate variability for the hydrological drought forecasting in the Anthropocene, and the predictability for human interventions needs more attention.

Species-specific and seasonal differences in chlorophyll fluorescence and photosynthetic light response among three evergreen species in a Madrean sky island mixed conifer forest

NASA Astrophysics Data System (ADS)

Potts, D. L.; Minor, R. L.; Braun, Z.; Barron-Gafford, G. A.

2012-12-01

Unlike the snowmelt-dominated hydroclimate of more northern mountainous regions, the hydroclimate of the Madrean sky islands is characterized by snowmelt and convective storms associated with the North American Monsoon. These mid-summer storms trigger biological activity and are important drivers of primary productivity. For example, at the highest elevations where mixed conifer forests occur, ecosystem carbon balance is influenced by monsoon rains. Whereas these storms' significance is increasingly recognized at the ecosystem scale, species-specific physiological responses to the monsoon are poorly known. Prior to and following monsoon onset, we measured pre-dawn and light-adapted chlorophyll fluorescence as well as photosynthetic light response in southwestern white pine (Pinus strobiformis), ponderosa pine (Pinus ponderosa), and Douglas fir (Pseudotsuga menziesii) in a Madrean sky island mixed conifer forest near Tucson, Arizona. Photochemical quenching (qp), an indicator of the proportion of open PSII reaction centers, was greatest in P. strobiformis and least in P. menziesii and increased in response to monsoon rains (repeated-measures ANOVA; species, F2,14 = 6.17, P = 0.012; time, F2,14= 8.17, P = 0.013). In contrast, non-photochemical quenching (qN), an indicator of heat dissipation ability, was greatest in P. ponderosa and least in P. menziesii, but was not influenced by monsoon onset (repeated-measures ANOVA; species, F2,12 = 4.18, P = 0.042). Estimated from leaf area-adjusted photosynthetic light response curves, maximum photosynthetic rate (Amax) was greatest in P. ponderosa and least in P. menziesii (repeated-measures ANOVA; species, F2,8= 40.8, P = 0.001). Surprisingly, while the monsoon positively influenced Amax among P. ponderosa and P. strobiformis, Amax of P. menziesii declined with monsoon onset (repeated-measures ANOVA; species x time, F2,8 = 13.8, P = 0.002). Calculated as the initial slope of the photosynthetic light response curve, light-use efficiency (AQE) was similar among P. strobiformis and P. ponderosa and least in P. menziesii (repeated-measures ANOVA; species, F2,8 = 13.83, P = 0.002). Across all three species, monsoon onset increased AQE (repeated-measures ANOVA; time, F1,8= 10.04, P = 0.01). Likewise, P. strobiformis and P. ponderosa shared a similar, greater light compensation point than P. menziesii (repeated-measures ANOVA; species, F2,8 = 5.89, P = 0.02). However, across species, monsoon onset did not influence light compensation points. These results support the hypothesis that the monsoon has species-specific effects on evergreen physiological performance and are broadly consistent with predictions of stress tolerance based on species' latitudinal and elevational range distributions. Moreover, with year-to-year rainfall variability predicted to increase under future climate scenarios, species-specific functional traits related to stress tolerance and photosynthesis may promote ecosystem functional resilience in Madrean sky island mixed conifer forests.

Model projections of an imminent transition to a more arid climate in southwestern North America.

PubMed

Seager, Richard; Ting, Mingfang; Held, Isaac; Kushnir, Yochanan; Lu, Jian; Vecchi, Gabriel; Huang, Huei-Ping; Harnik, Nili; Leetmaa, Ants; Lau, Ngar-Cheung; Li, Cuihua; Velez, Jennifer; Naik, Naomi

2007-05-25

How anthropogenic climate change will affect hydroclimate in the arid regions of southwestern North America has implications for the allocation of water resources and the course of regional development. Here we show that there is a broad consensus among climate models that this region will dry in the 21st century and that the transition to a more arid climate should already be under way. If these models are correct, the levels of aridity of the recent multiyear drought or the Dust Bowl and the 1950s droughts will become the new climatology of the American Southwest within a time frame of years to decades.

Holocene record of glacier variability from lake sediments reveals tripartite climate history for Svalbard

NASA Astrophysics Data System (ADS)

van der Bilt, Willem; Bakke, Jostein; Vasskog, Kristian; D`Andrea, William; Bradley, Raymond; Olafsdottir, Sædis

2016-04-01

The Arctic is responding sensitively to ongoing global climate change, warming and moistening faster than any other region on the planet. Holocene proxy paleoclimate time series are increasingly used to put this amplified response in perspective by understanding Arctic climate processes beyond the instrumental period. Glaciers rapidly respond to climate shifts as demonstrated by their current demise around the world. This response has a composite climate signature, marked by shifts in hydroclimate (winter precipitation) as well as (summer) temperature. Attendant changes in glacier size are recorded by variations in glacigenic rock flour that may be deposited in downstream lakes. Here, we present a Holocene reconstruction of glacier activity, based on sediments from Hajeren, a glacier-fed lake on northwest Spitsbergen in the High Arctic Svalbard archipelago. Owing to undisturbed sediments and robust age control, we could resolve variability on a sub-centennial scale. To ensure the accurate detection of glacier activity, we applied a toolbox of physical, magnetic and geochemical proxies in conjunction with multivariate statistics. Our findings indicate a three-stage Holocene climate history for Svalbard, driving by melt water pulses, episodic Atlantic cooling and a decline in orbitally driven summer insolation. Correspondence between inferred advances, including a Holocene glacier maximum around 9.5 ka BP, suggests forcing by the melting LIS during the Early Holocene. Following a late Holocene Thermal Maximum around 7.4 ka BP, glaciers disappeared from the catchment. Glaciers reformed around 4.2 ka BP during the regional onset of the Neoglacial, supporting previous findings. This transition did, however, not mark the onset of persistent glacier activity in the catchment, but a series of centennial-scale cycles of growth and decay, including events around 3.3 and 1.1 ka BP. As orbitally driven insolation declined towards the present, the glaciation threshold progressively lowered. The forcing behind these advances remains elusive, but their agreement with other glacier reconstructions from the region indicates a North Atlantic signature. Prolonged glacier activity commenced after 0.7 ka BP during the Little Ice Age, in agreement with other evidence from Svalbard. Comparatively high reconstructed temperatures during this timeframe suggest that glacier growth was precipitation-driven. Our findings highlight the sensitivity of small glaciers to climate shifts, demonstrating their potential to resolve centennial-scale perturbations. Moreover, this study underlines the value of lake sediments from glacier-fed lakes in understanding Holocene climate in the Arctic.

Paleohydrology of the Polar Urals from the Last Glacial Maximum Through the Holocene

NASA Astrophysics Data System (ADS)

Cowling, O.; Thomas, E.; Svendsen, J. I.; Haflidason, H.

2017-12-01

Paleohydrologic records provide important information concerning the past response of local hydrology to abrupt temperature changes. Arctic hydrology is particularly sensitive to temperature due to feedbacks involving sea ice and ice sheets. The most recent deglacial interval contains multiple abrupt temperature changes, which provide opportunities to study the relationship between temperature, ice sheets, and hydrology. We present a lacustrine δ2Hwax record from Bolshoye Schuchye, in the Polar Ural Mountains, spanning 24.5- 1.3 ka, and interpret hydroclimate conditions at a multi-centennial scale from the Last Glacial Maximum (LGM) through the Holocene. Bolshoye Schuchye's position beyond the reach of local glaciers during the LGM makes it a unique site, since lacustrine paleoclimate records from the Arctic rarely span this entire interval, so Bolshoye Schuchye helps to cover a gap in understanding of paleoclimate. Compound specific analysis of leaf wax hydrogen isotopes (δ2Hwax) is a hydroclimate proxy that can be used to infer moisture source area, transport history, and local aridity. Inferences based on δ2Hwax rely on mechanistic understanding of the process by which hydrogen from meteoric water is incorporated into waxes, and subsequently deposited in lake sediments. The δ2Hwax value of a sample reflects the isotopic composition of precipitation, while also incorporating fractionation that occurs between precipitation and uptake by plants, and biosynthetic fractionation during wax synthesis. Comparisons between different chain length waxes can be used to infer the isotopic composition of terrestrial and aquatic waxes, as terrestrial plants tend to produce longer chain lengths than aquatic macrophytes. The offset between terrestrial and aquatic δ2Hwax, expressed as ɛt-a, indicates differences between the precipitation used by terrestrial plants, and the lake water used by aquatic plants. Significant changes in ɛt-a can represent shifts in local aridity or precipitation seasonality. The record we present from Bolshoye Schuchye gives insights into terrestrial hydrologic changes resulting from rapid temperature shifts since the LGM.

Improving understanding of mixed-land-use watershed suspended sediment regimes: Mechanistic progress through high-frequency sampling.

PubMed

Kellner, Elliott; Hubbart, Jason A

2017-11-15

Given the importance of suspended sediment to biogeochemical functioning of aquatic ecosystems, and the increasing concern of mixed-land-use effects on pollutant loading, there is an urgent need for research that quantitatively characterizes spatiotemporal variation of suspended sediment dynamics in contemporary watersheds. A study was conducted in a representative watershed of the central United States utilizing a nested-scale experimental watershed design, including five gauging sites (n=5) partitioning the catchment into five sub-watersheds. Hydroclimate stations at gauging sites were used to monitor air temperature, precipitation, and stream stage at 30-min intervals during the study (Oct. 2009-Feb. 2014). Streamwater grab samples were collected four times per week, at each site, for the duration of the study (Oct. 2009-Feb. 2014). Water samples were analyzed for suspended sediment using laser particle diffraction. Results showed significant differences (p<0.05) between monitoring sites for total suspended sediment concentration, mean particle size, and silt volume. Total concentration and silt volume showed a decreasing trend from the primarily agricultural upper watershed to the urban mid-watershed, and a subsequent increasing trend to the more suburban lower watershed. Conversely, mean particle size showed an opposite spatial trend. Results are explained by a combination of land use (e.g. urban stormwater dilution) and surficial geology (e.g. supply-controlled spatial variation of particle size). Correlation analyses indicated weak relationships with both hydroclimate and land use, indicating non-linear sediment dynamics. Suspended sediment parameters displayed consistent seasonality during the study, with total concentration decreasing through the growing season and mean particle size inversely tracking air temperature. Likely explanations include vegetation influences and climate-driven weathering cycles. Results reflect unique observations of spatiotemporal variation of suspended sediment particle size class. Such information is crucial for land and water resource managers working to mitigate aquatic ecosystem degradation and improve water resource sustainability in mixed-land-use watersheds globally. Copyright © 2017 Elsevier B.V. All rights reserved.

Isotopes in North American Rocky Mountain snowpack 1993–2014

USGS Publications Warehouse

Anderson, Lesleigh; Max Berkelhammer,; Mast, M. Alisa

2015-01-01

We present ∼1300 new isotopic measurements (δ18O and δ2H) from a network of snowpack sites in the Rocky Mountains that have been sampled since 1993. The network includes 177 locations where depth-integrated snow samples are collected each spring near peak accumulation. At 57 of these locations snowpack samples were obtained for 10–21 years and their isotopic measurements provide unprecedented spatial and temporal documentation of snowpack isotope values at mid-latitudes. For environments where snowfall accounts for the majority of annual precipitation, snowmelt is likely to have the strongest influence on isotope values retained in proxy archives. In this first presentation of the dataset we (1) describe the basic features of the isotope values in relation to the Global Meteoric Water Line (GMWL), (2) evaluate space for time substitutions traditionally used to establish δ18O-temperature relations, (3) evaluate site-to-site similarities across the network and identify those that are the most regionally representative, (4) examine atmospheric circulation patterns for several years with spatially coherent isotope patterns, and (5) provide examples of the implications this new dataset has for interpreting paleoclimate records (Bison Lake, Colorado and Minnetonka Cave, Idaho). Results indicate that snowpack δ18O is rarely a simple proxy of temperature. Instead, it exhibits a high degree of spatial heterogeneity and temporal variance that reflect additional processes such as vapor transport and post-depositional modification. Despite these complexities we identify consistent climate-isotope patterns and regionally representative locations that serve to better define Holocene hydroclimate estimates and their uncertainty. Climate change has and will affect western U.S. snowpack and we suggest these changes can be better understood and anticipated by oxygen and hydrogen isotope-based reconstructions of Holocene hydroclimate using a process-based understanding of the controls on snowpack isotope ratios.

Effect of local hydroclimate on phytoplankton groups in the Charente estuary

NASA Astrophysics Data System (ADS)

Guesdon, Stéphane; Stachowski-Haberkorn, Sabine; Lambert, Christophe; Beker, Beatriz; Brach-Papa, Christophe; Auger, Dominique; Béchemin, Christian

2016-11-01

This study aimed to describe seasonal variations of phytoplankton abundances in relation to the physical and chemical (nutrients and metals) environment under the influence of freshwater input in the Charente river estuary (Marennes-Oléron bay, France) over three years, from 2011 to 2014. Phytoplankton abundances were determined using microscopy and flow cytometry. Considering high frequency temperature and salinity data, breakpoints in each series led to the identification of two local hydroclimatic periods: the first (2011 and early 2012) being warmer and higher in salinity than the second (from spring 2012 to the beginning of 2014). A multiblock PLS analysis highlighted the significant contribution of the physical environment (temperature, salinity and Photosynthetically Active Radiation (PAR)) on phytoplankton abundances. Two partial triadic analyses (PTA) were run in order to visualize seasonal variations of i) phytoplankton groups and ii) nutrients and trace elements, irrespective of spatial gradient: picoeukaryote occurrence showed a difference between year 2011 and the years 2012 and 2013 (as did cadmium, nickel and silica levels). However, both PTA revealed greater differences between year 2013 and the years 2011 and 2012, as shown by occurrences of cryptophytes, dinoflagellates and nanoeukaryotes, as well as copper and phosphate levels. These results showed a shift between the hydroclimate breakpoint and some phytoplankton responses, suggesting that their development and succession might depend on conditions early in the year. Finally, a STATICO analysis was performed on the paired PTA in order to examine the relations of phytoplankton with nutrients and metals more closely. Most phytoplankton groups were represented on the first axis, together with cadmium on the one hand, and nitrates, silica and nickel on the other. This analysis revealed the separation of phytoplankton groups on the second axis that represented phosphates and copper. Hydroclimatic conditions and the nature of freshwater inputs, especially phosphates and copper content, might be key factors driving phytoplankton structure in the Charente estuary.

Spatiotemporal patterns of plant water isotope values from a continental-scale sample network in Europe as a tool to improve hydroclimate proxies

NASA Astrophysics Data System (ADS)

Nelson, D. B.; Kahmen, A.

2016-12-01

The hydrogen and oxygen isotopic composition of water available for biosynthetic processes in vascular plants plays an important role in shaping the isotopic composition of organic compounds that these organisms produce, including leaf waxes and cellulose in leaves and tree rings. Characterizing changes in large scale spatial patterns of precipitation, soil water, stem water, and leaf water isotope values over time is therefore useful for evaluating how plants reflect changes in the isotopic composition of these source waters in different environments. This information can, in turn, provide improved calibration targets for understanding the environmental signals that plants preserve. The pathway of water through this continuum can include several isotopic fractionations, but the extent to which the isotopic composition of each of these water pools varies under normal field conditions and over space and time has not been systematically and concurrently evaluated at large spatial scales. Two season-long sampling campaigns were conducted at nineteen sites throughout Europe over the 2014 and 2015 growing seasons to track changes in the isotopic composition of plant-relevant waters. Samples of precipitation, soil water, stem water, and leaf water were collected over more than 200 field days and include more than 500 samples from each water pool. Measurements were used to validate continent-wide gridded estimates of leaf water isotope values derived from a combination of mechanistic and statistical modeling conducted with temperature, precipitation, and relative humidity data. Data-model comparison shows good agreement for summer leaf waters, and substantiates the incorporation of modeled leaf waters in evaluating how plants respond to hydroclimate changes at large spatial scales. These results also suggest that modeled leaf water isotope values might be used in future studies in similar ecosystems to improve the coverage density of spatial or temporal data.

Pollen-based evidence of extreme drought during the last Glacial (32.6-9.0 ka) in coastal southern California

NASA Astrophysics Data System (ADS)

Heusser, Linda E.; Kirby, Matthew E.; Nichols, Jonathan E.

2015-10-01

High resolution pollen analyses of sediment core LEDC10-1 from Lake Elsinore yield the first well-dated, terrestrial record of sub-centennial-scale ecologic change in coastal southern California between ˜32 and 9 ka. In the Lake Elsinore watershed, the initial, mesic montane conifer forests dominated by Pinus, and Cupressaceae with trace amounts of Abies and Picea were replaced by a sequence of multiple, extended severe mega-droughts between ˜27.5 and ˜25.5 ka, in which halophytic and xerophytic herbs and shrubs occupied an ephemeral lake. This prolonged and extended dry interval, which corresponds with warm waters offshore, imply strengthening of the North Pacific High and persistent below-average winter precipitation. The subsequent, contrasting monotonic occurrence of montane conifers reflects little variation in cold, mesic climate until ˜15 ka. Postglacial development of Quercus woodland and chaparral mark the return to more xeric, warmer conditions at this time. A brief reversal at ˜13.1-˜12.1 ka, as reflected by an expansion of Pinus, is correlative with the Younger Dryas and interrupts development of warm, postglacial climate. Subsequent gradual expansion of xeric vegetation post - Younger Dryas denotes the establishment of a winter hydroclimate regime in coastal southern California that is more similar to modern conditions. Pollen-based reconstructions of temperature and precipitation at Lake Elsinore are generally correlative with pollen-based paleoclimatic reconstructions and foraminifera-based sea surface temperatures from Santa Barbara Basin in marine core ODP 893. The conspicuous absence of the ˜27.5-˜25.5 ka glacial "mega-drought" in the Santa Barbara Basin pollen record highlights the sensitivity of Lake Elsinore to hydroclimate change, and thus, the importance of this new record that indicates that mega-drought can occur during the full glacial when climatic boundary conditions and forcings differed substantially from the present.

How Hydroclimate Influences the Effectiveness of Particle Filter Data Assimilation of Streamflow in Initializing Short- to Medium-range Streamflow Forecasts

NASA Astrophysics Data System (ADS)

Clark, E.; Wood, A.; Nijssen, B.; Clark, M. P.

2017-12-01

Short- to medium-range (1- to 7-day) streamflow forecasts are important for flood control operations and in issuing potentially life-save flood warnings. In the U.S., the National Weather Service River Forecast Centers (RFCs) issue such forecasts in real time, depending heavily on a manual data assimilation (DA) approach. Forecasters adjust model inputs, states, parameters and outputs based on experience and consideration of a range of supporting real-time information. Achieving high-quality forecasts from new automated, centralized forecast systems will depend critically on the adequacy of automated DA approaches to make analogous corrections to the forecasting system. Such approaches would further enable systematic evaluation of real-time flood forecasting methods and strategies. Toward this goal, we have implemented a real-time Sequential Importance Resampling particle filter (SIR-PF) approach to assimilate observed streamflow into simulated initial hydrologic conditions (states) for initializing ensemble flood forecasts. Assimilating streamflow alone in SIR-PF improves simulated streamflow and soil moisture during the model spin up period prior to a forecast, with consequent benefits for forecasts. Nevertheless, it only consistently limits error in simulated snow water equivalent during the snowmelt season and in basins where precipitation falls primarily as snow. We examine how the simulated initial conditions with and without SIR-PF propagate into 1- to 7-day ensemble streamflow forecasts. Forecasts are evaluated in terms of reliability and skill over a 10-year period from 2005-2015. The focus of this analysis is on how interactions between hydroclimate and SIR-PF performance impact forecast skill. To this end, we examine forecasts for 5 hydroclimatically diverse basins in the western U.S. Some of these basins receive most of their precipitation as snow, others as rain. Some freeze throughout the mid-winter while others experience significant mid-winter melt events. We describe the methodology and present seasonal and inter-basin variations in DA-enhanced forecast skill.

The Lake Ohrid Drilling Project: initial interpretations of stable isotope data over the last 640 ka

NASA Astrophysics Data System (ADS)

Lacey, J. H.; Leng, M. J.; Francke, A.; Sloane, H. J.; Milodowski, A. E.; Vogel, H.; Baumgarten, H.; Wagner, B.

2015-12-01

Lake Ohrid (Macedonia/Albania) is an ancient European lake with a unique biodiversity and a site of global significance to study the influence of climate, geological and tectonic events on the biological evolution of taxa. Here, we present oxygen (δ18O) and carbon (δ13C) isotope data on carbonate from sediment cores spanning 640 ka recovered as part of the Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO) project. Previous work on cores from the lake (up to 15 m, <140 ka) indicated that the Total Inorganic Carbon (TIC) content of sediments was highly sensitive to climate change during the last glacial-interglacial cycle, comprising abundant endogenic calcite through interglacials and being almost absent in glacials, apart from discrete bands of early diagenetic authigenic siderite. Isotope measurements on calcite (δ18Oc and δ13Cc) reveal variations both between and within interglacials that suggest the lake has been subject to hydroclimate fluctuations on orbital and millennial timescales. We also measured isotopes on authigenic siderite (δ18Os and δ13Cs) and, with the δ18Oc and δ18Os, reconstruct δ18O of lakewater (δ18Olw). Glacials are observed to have lower δ18Olw when compared to interglacials, most likely due to cooler summer temperatures, a higher proportion of winter precipitation (snowfall), and a reduced inflow from neighbouring Lake Prespa. The isotope data suggest Lake Ohrid experienced a period of overall stability through Marine Isotope Stage (MIS) 15 to 13, highlighting MIS 14 as a particularly warm glacial, and MIS 9 was isotopically freshest. Following MIS 9, the variability between glacial and interglacial δ18Olw is enhanced and the lake became increasingly evaporated through to present day with MIS 5 having the highest average δ18Olw. These findings provide new evidence for long-term climate change in the northern Mediterranean region, which will form the basis to better understand the influence of major environmental events on endemic speciation within the lake.

Mediterranean climate since the Middle Pleistocene: a 640 ka stable isotope record from Lake Ohrid (Albania/Macedonia)

NASA Astrophysics Data System (ADS)

Lacey, J. H.; Leng, M. J.; Francke, A.; Sloane, H. J.; Milodowski, A.; Vogel, H.; Baumgarten, H.; Wagner, B.

2015-08-01

Lake Ohrid (Macedonia/Albania) is an ancient lake with a unique biodiversity and a site of global significance for investigating the influence of climate, geological and tectonic events on the generation of endemic populations. Here, we present oxygen (δ18O) and carbon (δ13C) isotope data on carbonate from the upper ca. 248 m of sediment cores recovered as part of the Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO) project, covering the past 640 ka. Previous studies on short cores from the lake (up to 15 m, < 140 ka) have indicated the Total Inorganic Carbon (TIC) content of sediments to be highly sensitive to climate change over the last glacial-interglacial cycle, comprising abundant endogenic calcite through interglacials and being almost absent in glacials, apart from discrete bands of early diagenetic authigenic siderite. Isotope measurements on endogenic calcite (δ18Oc and δ13Cc) reveal variations both between and within interglacials that suggest the lake has been subject to hydroclimate fluctuations on orbital and millennial timescales. We also measured isotopes on authigenic siderite (δ18Os and δ13Cs) and, with the δ18OCc and δ18Os, reconstruct δ18O of lakewater (δ18Olw) through the 640 ka. Overall, glacials have lower δ18Olw when compared to interglacials, most likely due to cooler summer temperatures, a higher proportion of winter precipitation (snowfall), and a reduced inflow from adjacent Lake Prespa. The isotope stratigraphy suggests Lake Ohrid experienced a period of general stability through Marine Isotope Stage (MIS) 15 to MIS 13, highlighting MIS 14 as a particularly warm glacial, and was isotopically freshest during MIS 9. After MIS 9, the variability between glacial and interglacial δ18Olw is enhanced and the lake became increasingly evaporated through to present day with MIS 5 having the highest average δ18Olw. Our results provide new evidence for long-term climate change in the northern Mediterranean region, which will form the basis to better understand the influence of major environmental events on biological evolution within the lake.

Evaluating Precipitation Elevation Gradients in the Alaska Range using Ice Core and Alpine Weather Station Records

NASA Astrophysics Data System (ADS)

McConnell, E.; Osterberg, E. C.; Winski, D.; Kreutz, K. J.; Wake, C. P.; Campbell, S. W.; Ferris, D. G.; Birkel, S. D.

2016-12-01

Precipitation in Alaska is sensitive to the Aleutian Low (ALow) pressure system and North Pacific sea-surface temperatures, as shown by the increase in Alaskan sub-Arctic precipitation associated with the 1976 shift to the positive phase of the Pacific Decadal Oscillation (PDO). Precipitation in the high-elevation accumulation zones of Alaskan alpine glaciers provides critical mass input for glacial mass balance, which has been declining in recent decades from warmer summer temperatures despite the winter precipitation increase. Twin >1500-year ice cores collected from the summit plateau of Mount Hunter in Denali National Park, Alaska show a remarkable doubling of annual snow accumulation over the past 150 years, with most of the change observed in the winter. Other alpine ice cores collected from the Alaska and Saint Elias ranges show similar snowfall increases over recent decades. However, although Alaskan weather stations at low elevation recorded a 7-38% increase in winter precipitation across the 1976 PDO transition, this increase is not as substantial as that recorded in the Mt. Hunter ice core. Weather stations at high-elevation alpine sites are comparatively rare, and reasons for the enhanced precipitation trends at high elevation in Alaska remain unclear. Here we use Automatic Weather Station data from the Mt. Hunter drill site (3,900 m a.s.l) and from nearby Denali climber's Base Camp (2,195 m a.s.l.) to evaluate the relationships between alpine and lowland Alaskan precipitation on annual, seasonal, and storm-event temporal scales from 2008-2016. Both stations are located on snow and have sonic snow depth sounders to record daily precipitation. We focus on the role of variable ALow and North Pacific High strength in influencing Alaskan precipitation elevational gradients, particularly in association with the extreme 2015-2016 El Niño event, the 2009-2010 moderate El Niño event, and the 2010-2011 moderate La Niña event. Our analysis will improve our paleoclimate interpretations of the 1200-year Mt. Hunter accumulation record, and improve our ability to integrate low-elevation hydroclimate proxies from lake sediment cores.

Shifts of regional hydro-climatic regimes in the warmer future

NASA Astrophysics Data System (ADS)

Kim, H.; Morishita, S.

2016-12-01

It is well known that the global climate is projected to be significantly warmer than pre-industrial period, and, in 2015, it was indicated as 1-degreen increase of global mean temperature that was unprecedented previously. Human-induced additional radiative forcing causes global and regional mean temperature increase and alters energy and water partitioning in the heterogeneous pathway. Budyko proposed a conceptual equation to estimate a climate-induced dryness relating available energy and precipitation, and it has been used broadly in hydrology communities to determine regional hydro-climatic characteristics. In this study, a diagnosis framework is proposed to traced how the regional hydro-climatic regimes are shifted under the warming condition with 4 °C increase of global mean temperature. A database for Policy Decision making for Future climate change (d4PDF) based on a super-ensemble AMIP-style experiment (11,400 model years, totally) with sea surface temperature patterns extracted from six CMIP5 models is used to estimate the probability distribution of the regime shifts maximizing signal-to-noise. It was found that the global future hydro-climate condition shifts slightly to more humid condition comparing to the historical condition, since the increase of precipitation is greater and the increate of net radiation, globally. Very humid regions including tropics and semi-arid regions tend to expand, and Semi-humid and arid-regions tend to shrink. Although the change of global mean state between historical and future climate is not considerable, temporal variability under the warming climate is amplified significantly, and it induces more frequent occurrence of once-in-a-century level drought over large terrestrial regions including Africa, South America, East and Central Asia, Australia, and United States. This analysis will be extended up to the availability (expected as October 2016) of a similar database being produced under the Half a degree Additional warming, Projections, Prognosis and Impacts (HAPPI) project following the Paris Agreement, 2015, to aim to limit the increase in global average temperature to 1.5°C above pre-industrial levels.

A snow cover climatology for the Pyrenees from MODIS snow products

NASA Astrophysics Data System (ADS)

Gascoin, S.; Hagolle, O.; Huc, M.; Jarlan, L.; Dejoux, J.-F.; Szczypta, C.; Marti, R.; Sánchez, R.

2014-11-01

The seasonal snow in the Pyrenees is critical for hydropower production, crop irrigation and tourism in France, Spain and Andorra. Complementary to in situ observations, satellite remote sensing is useful to monitor the effect of climate on the snow dynamics. The MODIS daily snow products (Terra/MOD10A1 and Aqua/MYD10A1) are widely used to generate snow cover climatologies, yet it is preferable to assess their accuracies prior to their use. Here, we use both in situ snow observations and remote sensing data to evaluate the MODIS snow products in the Pyrenees. First, we compare the MODIS products to in situ snow depth (SD) and snow water equivalent (SWE) measurements. We estimate the values of the SWE and SD best detection thresholds to 40 mm water equivalent (we) and 105 mm respectively, for both MOD10A1 and MYD10A1. Kappa coefficients are within 0.74 and 0.92 depending on the product and the variable. Then, a set of Landsat images is used to validate MOD10A1 and MYD10A1 for 157 dates between 2002 and 2010. The resulting accuracies are 97% (κ = 0.85) for MOD10A1 and 96% (κ = 0.81) for MYD10A1, which indicates a good agreement between both datasets. The effect of vegetation on the results is analyzed by filtering the forested areas using a land cover map. As expected, the accuracies decreases over the forests but the agreement remains acceptable (MOD10A1: 96%, κ = 0.77; MYD10A1: 95%, κ = 0.67). We conclude that MODIS snow products have a sufficient accuracy for hydroclimate studies at the scale of the Pyrenees range. Using a gapfilling algorithm we generate a consistent snow cover climatology, which allows us to compute the mean monthly snow cover duration per elevation band. We finally analyze the snow patterns for the atypical winter 2011-2012. Snow cover duration anomalies reveal a deficient snowpack on the Spanish side of the Pyrenees, which seems to have caused a drop in the national hydropower production.

Ensemble Simulation of Sierra Nevada Snowmelt Runoff Using a Regional Climate Modeling Approach

NASA Astrophysics Data System (ADS)

Holtzman, N.; Pavelsky, T.; Wrzesien, M.

2017-12-01

The snowmelt-dominated watersheds on the western slopes of the California Sierra Nevada drain into reservoirs that generate electricity and help irrigate Central Valley farms. At the end of the wet season of each year, around April 1, most of the water that will become runoff in these basins is stored as snow at high elevations. Snow measurements provide a good estimate of the total annual runoff to come. For efficient water management, however, it is also useful to know the timing of runoff. When and how large will the peak flow into a reservoir be, and how fast will the flow decline after it peaks? We address such questions using a coupled regional climate and land surface model, WRF and Noah-MP, to dynamically downscale the North American Regional Reanalysis (NARR) with an ensemble approach. First, we assess several methods of deriving melt-season runoff from WRF. We run WRF for a complete water year, and also test initializing WRF snow from observation-based datasets at the approximate date of peak snow water equivalent. By aggregating the modeled runoffs over the drainage basins of reservoirs and comparing to naturalized flow data, we can assess the basin-scale snow accumulation accuracy of WRF and the other datasets in the Sierra. After choosing a procedure to set the model snow at the end of the wet season, we apply in WRF the melt-season meteorology from 20 different past years of NARR to produce an ensemble of simulations, each with modeled flows into 8 reservoirs spanning the Sierra. We use the ensemble to characterize the likely spread in the timing and magnitude of hydrologic outcomes during the melt season. Probabilistic forecasts can help water-energy systems operate more efficiently. The ensemble also shows the effect of warm-season temperature extremes on flow timing, allowing human systems to prepare for those possibilities. Finally, the ensemble provides a baseline estimate of the maximum variability in runoff timing that could be generated by past conditions. If future runoff patterns consistently exceed the extremes found in the ensemble, nonstationary hydroclimate can be inferred.

Late Pleistocene shifts in Northeast African hydroclimate and the Out-of-Africa migration

NASA Astrophysics Data System (ADS)

Tierney, J. E.; deMenocal, P. B.; Zander, P. D.

2016-12-01

The major "Out-of-Africa" migration of modern humans is hypothesized to have occurred ca. 60,000-80,000 yr BP, with populations crossing the Red Sea via either the Bab al Mandeb strait or the Sinai Peninsula. The role of climatic and environmental pressures in driving the migration has long been a topic of debate. While paleoclimate data from southern East Africa generally show evidence for climatic instability during the Out-Of-Africa interval, no data has been available from northeast Africa, the region from which haplogroup L3, the most common parental lineage for humans outside Africa, dispersed. Here we present leaf wax hydrogen isotope data measured in a marine sediment core that provide a clear picture of how Northeast African climate has varied during the past 200,000 years. The data show that wet periods are generally in-phase with Northern hemisphere summer insolation, with MIS 7a emerging as the wettest "African Humid Period" of the last 200 ka. Interestingly, Stages 5e, 5c, and 5a are comparably wet. Last glacial aridity does not begin in earnest until ca. 75 ka, with an abrupt drop out of mesic Stage 5 conditions followed by a descent into very dry conditions during Stage 4. The timing of this wet-to-dry transition compares well with the estimated timing of Out-of-Africa migration from genetic data, suggesting that climatic deterioration could have been an impetus for early humans to leave northeast Africa.

Evidence of El Niño driven desiccation cycles in a shallow estuarine lake: The evolution and fate of Africa's largest estuarine system, Lake St Lucia

NASA Astrophysics Data System (ADS)

Humphries, M. S.; Green, A. N.; Finch, J. M.

2016-12-01

Projections of an increase in drought frequency and intensity over the next century are expected to have severe implications for a number of globally important coastal ecosystems. In this paper, we present geochemical data from three sediment cores extracted from the main depositional basins of Lake St Lucia, Africa's largest estuarine system. Lake St Lucia is subject to extreme natural variations in salinity. The sedimentary record documents the evolution of the system from a relatively deep-water, open lagoon to a confined, shallow estuarine lake that today is highly sensitive to changes in freshwater supply. This is particularly evident in the northern portions of the system, where the presence of distinct halite-enriched horizons document episodes of prolonged drought. The lateral persistence of these halite layers, as revealed by seismic profiling, point to a system-wide onset of desiccation associated with a major shift in the regional hydroclimate. The most severe drought events identified, which may have lasted several years, occur at 1100 and 1750 cal year BP, and are associated with known peaks in El Niño frequency and intensity. Our analyses suggest that past cycles of desiccation and hyper-salinity have been controlled by climatic changes related to ENSO intensification. This study provides a valuable new record from a key ENSO-sensitive region of the Southern Hemisphere. Our findings have important relevance for understanding ENSO variability across the Indo-Pacific region and the influence exerted on systems sensitive to changes in moisture balance.

Changes in Pore Water Quality After Peatland Restoration: Assessment of a Large-Scale, Replicated Before-After-Control-Impact Study in Finland

NASA Astrophysics Data System (ADS)

Menberu, Meseret Walle; Marttila, Hannu; Tahvanainen, Teemu; Kotiaho, Janne S.; Hokkanen, Reijo; Kløve, Bjørn; Ronkanen, Anna-Kaisa

2017-10-01

Drainage is known to affect peatland natural hydrology and water quality, but peatland restoration is considered to ameliorate peatland degradation. Using a replicated BACIPS (Before-After-Control-Impact Paired Series) design, we investigated 24 peatlands, all drained for forestry and subsequently restored, and 19 pristine control boreal peatlands with high temporal and spatial resolution data on hydroclimate and pore water quality. In drained conditions, total nitrogen (Ntot), total phosphorus (Ptot), and dissolved organic carbon (DOC) in pore water were several-fold higher than observed at pristine control sites, highlighting the impacts of long-term drainage on pore water quality. In general, pore water DOC and Ntot decreased after restoration measures but still remained significantly higher than at pristine control sites, indicating long time lags in restoration effects. Different peatland classes and trophic levels (vegetation gradient) responded differently to restoration, primarily due to altered hydrology and varying acidity levels. Sites that were hydrologically overrestored (inundated) showed higher Ptot, Ntot, and DOC than well-restored or insufficiently restored sites, indicating the need to optimize natural-like hydrological regimes when restoring peatlands drained for forestry. Rich fens (median pH 6.2-6.6) showed lower pore water Ptot, Ntot, and DOC than intermediate and poor peats (pH 4.0-4.6) both before and after restoration. Nutrients and DOC in pore water increased in the first year postrestoration but decreased thereafter. The most important variables related to pore water quality were trophic level, peatland class, water table level, and soil and air temperature.

Coupling a three-dimensional subsurface flow model with a land surface model to simulate stream-aquifer-land interactions

NASA Astrophysics Data System (ADS)

Huang, M.; Bisht, G.; Zhou, T.; Chen, X.; Dai, H.; Hammond, G. E.; Riley, W. J.; Downs, J.; Liu, Y.; Zachara, J. M.

2016-12-01

A fully coupled three-dimensional surface and subsurface land model is developed and applied to a site along the Columbia River to simulate three-way interactions among river water, groundwater, and land surface processes. The model features the coupling of the Community Land Model version 4.5 (CLM4.5) and a massively-parallel multi-physics reactive tranport model (PFLOTRAN). The coupled model (CLM-PFLOTRAN) is applied to a 400m×400m study domain instrumented with groundwater monitoring wells in the Hanford 300 Area along the Columbia River. CLM-PFLOTRAN simulations are performed at three different spatial resolutions over the period 2011-2015 to evaluate the impact of spatial resolution on simulated variables. To demonstrate the difference in model simulations with and without lateral subsurface flow, a vertical-only CLM-PFLOTRAN simulation is also conducted for comparison. Results show that the coupled model is skillful in simulating stream-aquifer interactions, and the land-surface energy partitioning can be strongly modulated by groundwater-river water interactions in high water years due to increased soil moisture availability caused by elevated groundwater table. In addition, spatial resolution does not seem to impact the land surface energy flux simulations, although it is a key factor for accurately estimating the mass exchange rates at the boundaries and associated biogeochemical reactions in the aquifer. The coupled model developed in this study establishes a solid foundation for understanding co-evolution of hydrology and biogeochemistry along the river corridors under historical and future hydro-climate changes.

Increased frequency of ENSO-related hydroclimate extremes in a warming climate

NASA Astrophysics Data System (ADS)

Sun, Q.; Miao, C.; AghaKouchak, A.

2017-12-01

Global warming will likely alter surface warming in tropical Pacific regions, leading to changes in the characteristics of the El Niño Southern Oscillation (ENSO) characteristics and an incresed frequency of extreme ENSO events. The ENSO-related climatic variation and associated impacts will likely be modified in a warmer climatic state. However, little is known about the effect of changes in ENSO teleconnections with regard to future dry and wet conditions over land around the globe, especially outside tropical regions. We used the model simulations of the fifth phase of the Coupled Model Intercomparison Project (CMIP5) for different twenty-first-century emission scenarios (RCP 4.5 and RCP 8.5) to investigate the changes in the ENSO' teleconnection on dry/wet condition over global land. Our results show that 64.64% and 38.12% of 181 river basins studied are expected to experience an increase in the frequency of unusually wet/dry events forced by both ENSO phases under the RCP 4.5 and 8.5, respectively. The anomalous precipitation variability forced by ENSO events will be intensified through a "wet-get-wetter, dry-get-drier" mechanism over west North America, South America, central Asia, and west Asia. More than 850 million people are at risk of exposure to unusually dry/wet events. There is a potential increased risk of high-intensity dry/wet events, with an increase/decrease in the 50-year return level of SPI value for drying/wetting regions. These results have important implications for disaster evaluation and related policies and for appropriate engineering design.

Near-term acceleration of hydroclimatic change in the western U.S.

NASA Astrophysics Data System (ADS)

Ashfaq, Moetasim; Ghosh, Subimal; Kao, Shih-Chieh; Bowling, Laura C.; Mote, Philip; Touma, Danielle; Rauscher, Sara A.; Diffenbaugh, Noah S.

2013-10-01

Given its large population, vigorous and water-intensive agricultural industry, and important ecological resources, the western United States presents a valuable case study for examining potential near-term changes in regional hydroclimate. Using a high-resolution, hierarchical, five-member ensemble modeling experiment that includes a global climate model (Community Climate System Model), a regional climate model (RegCM), and a hydrological model (Variable Infiltration Capacity model), we find that increases in greenhouse forcing over the next three decades result in an acceleration of decreases in spring snowpack and a transition to a substantially more liquid-dominated water resources regime. These hydroclimatic changes are associated with increases in cold-season days above freezing and decreases in the cold-season snow-to-precipitation ratio. The changes in the temperature and precipitation regime in turn result in shifts toward earlier snowmelt, base flow, and runoff dates throughout the region, as well as reduced annual and warm-season snowmelt and runoff. The simulated hydrologic response is dominated by changes in temperature, with the ensemble members exhibiting varying trends in cold-season precipitation over the next three decades but consistent negative trends in cold-season freeze days, cold-season snow-to-precipitation ratio, and 1 April snow water equivalent. Given the observed impacts of recent trends in snowpack and snowmelt runoff, the projected acceleration of hydroclimatic change in the western U.S. has important implications for the availability of water for agriculture, hydropower, and human consumption, as well as for the risk of wildfire, forest die-off, and loss of riparian habitat.

Examining Dynamical Processes of Tropical Mountain Hydroclimate, Particularly During the Wet Season, Through Integration of Autonomous Sensor Observations and Climate Modeling

NASA Astrophysics Data System (ADS)

Hellstrom, R. A.; Fernandez, A.; Mark, B. G.; Covert, J. M.

2016-12-01

Peru is facing imminent water resource issues as glaciers retreat and demand increases, yet limited observations and model resolution hamper understanding of hydrometerological processes on local to regional scales. Much of current global and regional climate studies neglect the meteorological forcing of lapse rates (LRs) and valley and slope wind dynamics on critical components of the Peruvian Andes' water-cycle, and herein we emphasize the wet season. In 2004 and 2005 we installed an autonomous sensor network (ASN) within the glacierized Llanganuco Valley, Cordillera Blanca (9°S), consisting of discrete, cost-effective, automatic temperature loggers located along the valley axis and anchored by two automatic weather stations. Comparisons of these embedded hydrometeorological measurements from the ASN and climate modeling by dynamical downscaling using the Weather Research and Forecasting model (WRF) elucidate distinct diurnal and seasonal characteristics of the mountain wind regime and LRs. Wind, temperature, humidity, and cloud simulations suggest that thermally driven up-valley and slope winds converging with easterly flow aloft enhance late afternoon and evening cloud development which helps explain nocturnal wet season precipitation maxima measured by the ASN. Furthermore, the extreme diurnal variability of along-valley-axis LR, and valley wind detected from ground observations and confirmed by dynamical downscaling demonstrate the importance of realistic scale parameterizations of the atmospheric boundary layer to improve regional climate model projections in mountainous regions. We are currently considering to use intermediate climate models such as ICAR to reduce computing cost and we continue to maintain the ASN in the Cordillera Blanca.

Reconstructed Sediment Mobilization Processes in a Large Reservoir Using Short Sediment Cores

NASA Astrophysics Data System (ADS)

Cockburn, J.; Feist, S.

2014-12-01

Williston Reservoir in northern British Columbia (56°10'31"N, 124°06'33") was formed when the W.A.C. Bennett Dam was created in the late 1960s, is the largest inland body of water in BC and facilitates hydroelectric power generation. Annually the reservoir level rises and lowers with the hydroelectric dam operation, and this combined with the inputs from several river systems (Upper Peace, Finlay, Parsnip, and several smaller creeks) renews suspended sediment sources. Several short-cores retrieved from shallow bays of the Finlay Basin reveal near-annual sedimentary units and distinct patterns related to both hydroclimate variability and the degree to which the reservoir lowered in a particular year. Thin section and sedimentology from short-cores collected in three bays are used to evaluate sediment mobilization processes. The primary sediment sources in each core location is linked to physical inputs from rivers draining into the bays, aeolian contributions, and reworked shoreline deposits as water levels fluctuate. Despite uniform water level lowering across the reservoir, sediment sequences differed at each site, reflecting the local stream inputs. However, distinct organic-rich units, facilitated correlation across the sites. Notable differences in particle size distributions from each core points to important aeolian derived sediment sources. Using these sedimentary records, we can evaluate the processes that contribute to sediment deposition in the basin. This work will contribute to decisions regarding reservoir water levels to reduce adverse impacts on health, economic activities and recreation in the communities along the shores of the reservoir.

A Framework for Effective Use of Hydroclimate Models in Climate-Change Adaptation Planning for Managed Habitats with Limited Hydrologic Response Data.

PubMed

Esralew, Rachel A; Flint, Lorraine; Thorne, James H; Boynton, Ryan; Flint, Alan

2016-07-01

Climate-change adaptation planning for managed wetlands is challenging under uncertain futures when the impact of historic climate variability on wetland response is unquantified. We assessed vulnerability of Modoc National Wildlife Refuge (MNWR) through use of the Basin Characterization Model (BCM) landscape hydrology model, and six global climate models, representing projected wetter and drier conditions. We further developed a conceptual model that provides greater value for water managers by incorporating the BCM outputs into a conceptual framework that links modeled parameters to refuge management outcomes. This framework was used to identify landscape hydrology parameters that reflect refuge sensitivity to changes in (1) climatic water deficit (CWD) and recharge, and (2) the magnitude, timing, and frequency of water inputs. BCM outputs were developed for 1981-2100 to assess changes and forecast the probability of experiencing wet and dry water year types that have historically resulted in challenging conditions for refuge habitat management. We used a Yule's Q skill score to estimate the probability of modeled discharge that best represents historic water year types. CWD increased in all models across 72.3-100 % of the water supply basin by 2100. Earlier timing in discharge, greater cool season discharge, and lesser irrigation season water supply were predicted by most models. Under the worst-case scenario, moderately dry years increased from 10-20 to 40-60 % by 2100. MNWR could adapt by storing additional water during the cool season for later use and prioritizing irrigation of habitats during dry years.

6-kyr record of flood frequency and intensity in the western Mediterranean Alps - Interplay of solar and temperature forcing

NASA Astrophysics Data System (ADS)

Sabatier, Pierre; Wilhelm, Bruno; Ficetola, Gentile Francesco; Moiroux, Fanny; Poulenard, Jérôme; Develle, Anne-Lise; Bichet, Adeline; Chen, Wentao; Pignol, Cécile; Reyss, Jean-Louis; Gielly, Ludovic; Bajard, Manon; Perrette, Yves; Malet, Emmanuel; Taberlet, Pierre; Arnaud, Fabien

2017-08-01

The high-resolution sedimentological and geochemical analysis of a sediment sequence from Lake Savine (Western Mediterranean Alps, France) led to the identification of 220 event layers for the last 6000 years. 200 were triggered by flood events and 20 by underwater mass movements possibly related to earthquakes that occurred in 5 clusters of increase seismicity. Because human activity could influence the flood chronicle, the presence of pastures was reconstructed through ancient DNA, which suggested that the flood chronicle was mainly driven by hydroclimate variability. Weather reanalysis of historical floods allow to identify that mesoscale precipitation events called "East Return" events were the main triggers of floods recorded in Lake Savine. The first part of this palaeoflood record (6-4 kyr BP) was characterized by increases in flood frequency and intensity in phase with Northern Alpine palaeoflood records. By contrast, the second part of the record (i.e., since 4 kyr BP) was phased with Southern Alpine palaeoflood records. These results suggest a palaeohydrological transition at approximately 4 kyr BP, as has been previously described for the Mediterranean region. This may have resulted in a change of flood-prone hydro-meteorological processes, i.e., in the balance between occurrence and intensity of local convective climatic phenomena and their influence on Mediterranean mesoscale precipitation events in this part of the Alps. At a centennial timescale, increases in flood frequency and intensity corresponded to periods of solar minima, affecting climate through atmospheric changes in the Euro-Atlantic sector.

Assessing Covariation of Holocene Monsoon Intensity and Local Moisture Conditions in Eastern and Southwestern Amazon Basin Using Speleothem δ18O and 87Sr/86Sr Values

NASA Astrophysics Data System (ADS)

Ward, B. M.; Wong, C. I.; Novello, V. F.; Silva, L.; McGee, D.; Cheng, H.; Wang, X.; Edwards, R. L.; Cruz, F. W., Sr.; Santos, R. V.

2017-12-01

δ18O records from South America offer insight into past variability of the South American Monsoon System (SAMS). Potential, however, for understanding local moisture conditions is limited as precipitation δ18O is strongly influenced by regional climate dynamics. Here we create Holocene speleothem 87Sr/86Sr records at 200-yr resolution using TIMS methods in the Center for Isotope Geochemistry at Boston College to complement existing Holocene δ18O speleothem records and investigate local moisture conditions above caves located in the eastern Amazon Basin (PAR - 4°S, 55°W) and southwestern Brazil (JAR - 21°S, 56°W). Speleothem 87Sr/86Sr variability is interpreted to reflect differences in the extent of water-rock interaction due to differences in infiltration rates under wet and dry conditions. Drier conditions promote longer residence time, enhanced water-rock interaction, and greater evolution of dripwater 87Sr/86Sr values from an initial isotopic signature acquired from the soil to the signature of the cave host rock. PAR speleothem 87Sr/86Sr values range from 0.71024 to 0.71067 and are bracketed by soil (0.71710 to 0.70956) and bedrock (0.70852 to 0.70899) values. JAR speleothem 87Sr/86Sr values range from 0.71216 to 0.71539 and are greater than bedrock values (0.70825 to 0.71219), although some speleothem values exceed the single analysis conducted of the soil isotopic composition (0.71473). JAR speleothem 87Sr/86Sr values increase from the early to mid Holocene, consistent with increase in local moisture availability associated with intensification of the SAMS suggested by decreasing δ18O values in many records from the region. Speleothem 87Sr/86Sr values at JAR decrease from the mid to late Holocene, consistent with an increase in δ18O values at PAR that suggest a decline in monsoon intensity. 87Sr/86Sr variability at JAR, however, is positively correlated with the δ18O record. Preliminary 87Sr/86Sr results from PAR are only broadly consistent with the JAR 87Sr/86Sr record and exhibit variability that is not obviously consistent with other records in the region. On-going research investigates the conceptual model of Sr-isotopes as a local moisture proxy and the nature of coupling between local and regional Holocene hydroclimate at these sites and additional sites in central and southeast Brazil.

Recent drying of the Fertile Crescent: natural or externally forced?

NASA Astrophysics Data System (ADS)

Kelley, Colin

2014-05-01

There has been a reduction in observed precipitation over the greater Mediterranean region since the middle of the 20th Century. Recent studies suggest that while anthropogenic forcing has already begun to assert itself in recent decades, the preponderance of the winter drying trend is attributable to the large natural multidecadal variability of the North Atlantic Oscillation (NAO), while over the eastern Mediterranean, the anthropogenic, or forced drying signal is more clearly evident. This forced drying is projected to increase during the 21st Century according to the newest global climate models and this aridification would present significant challenges for a region that is already water-stressed. Although the Fertile Crescent is historically known for its agricultural prosperity, the severity and persistence of the recent multiyear drought in Syria, directly prior to the 2011 uprising there, leads us to ask whether this is evidence of emerging global warming influence. This drought exacerbated existing water insecurity, resulting in an agricultural collapse and a mass migration of rural drought refugees to the urban areas in Syria's west. This migration followed the previous influx of Iragi refugees and combined with strong natural population growth to place a severe strain on resources. Here we examine observations of precipitation and temperature, both gridded and stations, along with simulations and projections from the newest global climate models, to estimate the forced contribution to the recent Syrian drought, and assess the uncertainty in future drying according to the models. We find that this region has experienced a long-term downward trend in precipitation, and a concomitant increase in temperature, serving to further dry the soil, and in surface pressure. We find that the shift in the distributions of three-year running means of surface pressure and precipitation due to the forcing make severe events such as the recent Syrian drought several times more likely. Next we examine the moisture budget in the models and compare with the ground truth of atmospheric reanalyses to determine the relative contributions from the mean flow and the transient eddies. We find that the mean and transient patterns of moisture budget change over the eastern Mediterranean under forcing resemble the patterns of the NAO-induced moisture budget anomaly, but that over the greater Mediterranean there are distinct differences. Under forced moisture budget change, as noted in a recent study, the mean flow serves to strongly dry the greater Mediterranean, with a smaller contribution from the transients. For the eastern Mediterranean however, the transients oppose the drying by the mean flow, under climate change and under a positive phase of the NAO. These results suggest that anthropogenically forced drying of the Fertile Crescent may already be underway, primarily through a poleward shift in the mean flow, and represent a step forward toward a better understanding of the mechanisms associated with eastern Mediterranean hydroclimate change and variability and how they compare.

Coral record of variability in the upstream Kuroshio Current during 1953-2004

NASA Astrophysics Data System (ADS)

Li, Xiaohua; Liu, Yi; Hsin, Yi-Chia; Liu, Weiguo; Shi, Zhengguo; Chiang, Hong-Wei; Shen, Chuan-Chou

2017-08-01

The Kuroshio Current (KC), one of the most important western boundary currents in the North Pacific Ocean, strongly affects regional hydroclimate in East Asia and upper ocean thermal structure. Limited by few on-site observations, the responses of the KC to regional and remote climate forcings are still poorly understood. Here we use monthly coral δ18O data to reconstruct a KC transport record with annual to interannual resolution for the interval 1953-2004. The field site is located in southern Taiwan on the western flank of the upstream KC. Increased (reduced) KC transport would generate strong (weak) upwelling, resulting in relatively high (low) local coral δ18O. The upstream KC transport and downstream transport, off Tatsukushi Bay, Japan, covary on interannual and decadal time scales. This suggests common forcings, such as meridional drift of the North Equatorial Current bifurcation, or zonal climatic oscillations in the Pacific. The intensities of KC transport off southeastern and northeastern Taiwan are in phase before 1990 and antiphase after 1990. This difference may be due to a poleward shift of the subtropical western boundary current as a response to global warming.