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Sample records for actual evapotranspiration estimates

  1. Alternate corrections for estimating actual wetland evapotranspiration from potential evapotranspiration

    USGS Publications Warehouse

    Barclay, Shoemaker W.; Sumner, D.M.

    2006-01-01

    Corrections can be used to estimate actual wetland evapotranspiration (AET) from potential evapotranspiration (PET) as a means to define the hydrology of wetland areas. Many alternate parameterizations for correction coefficients for three PET equations are presented, covering a wide range of possible data-availability scenarios. At nine sites in the wetland Everglades of south Florida, USA, the relatively complex PET Penman equation was corrected to daily total AET with smaller standard errors than the PET simple and Priestley-Taylor equations. The simpler equations, however, required less data (and thus less funding for instrumentation), with the possibility of being corrected to AET with slightly larger, comparable, or even smaller standard errors. Air temperature generally corrected PET simple most effectively to wetland AET, while wetland stage and humidity generally corrected PET Priestley-Taylor and Penman most effectively to wetland AET. Stage was identified for PET Priestley-Taylor and Penman as the data type with the most correction ability at sites that are dry part of each year or dry part of some years. Finally, although surface water generally was readily available at each monitoring site, AET was not occurring at potential rates, as conceptually expected under well-watered conditions. Apparently, factors other than water availability, such as atmospheric and stomata resistances to vapor transport, also were limiting the PET rate. ?? 2006, The Society of Wetland Scientists.

  2. Estimating riparian and agricultural actual evapotranspiration by reference evapotranspiration and MODIS Enhanced Vegetation Index

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Dryland river basins frequently support both irrigated agriculture and riparian vegetation and remote sensing methods are needed to monitor water use by both crops and natural vegetation in these districts. We developed a general algorithm for estimating actual evapotranspiration (ETa) based on the ...

  3. Introducing a framework to improve estimation of actual evapotranspiration using MODIS images with SEBAL algorithm

    NASA Astrophysics Data System (ADS)

    Mianabadi, Ameneh; Alizadeh, Amin; Sanaeinejad, Hossein; Ghahraman, Bijan; Davary, Kamran; Coenders-Gerrits, Miriam

    2015-04-01

    To have an accurate estimation of actual evapotranspiration, it is a good idea to use every-day images of MODIS. But under clouded condition, it is difficult to have appropriate images and also it is time-consuming to interpret all those images. Therefore, in this paper, we tried to choose the appropriate images to improve estimation of actual evapotranspiration. For this purpose, we introduced a framework to choose appropriate dates to produce best estimation of actual evapotranspiration. On the other hand, finding the location of dry (hot pixel) and wet (cold pixel) endpoints of evapotranspiration spectrum is so important. We dealt with this problem by employing the statistical procedure for automated selection of cold and hot pixels. We also visually reviewed the location of hot and cold pixels using land cover image to ensure that the most appropriate pixels had been selected. To integrate evapotranspiration over time, the linear and spline interpolation techniques were applied. Also, based on the precipitation rates during 5 days before the date of image and the mean seasonal amount of evapotranspiration, we found a logarithmic equation to produce the best estimation of evapotranspiration during the given time. Results showed that the logarithmic equation could produce more accurate estimation of evapotranspiration rather than linear interpolation.

  4. On the downscaling of actual evapotranspiration maps based on combination of MODIS and landsat-based actual evapotranspiration estimates

    USGS Publications Warehouse

    Singh, Ramesh K.; Senay, Gabriel B.; Velpuri, Naga Manohar; Bohms, Stefanie; Verdin, James P.

    2014-01-01

     Downscaling is one of the important ways of utilizing the combined benefits of the high temporal resolution of Moderate Resolution Imaging Spectroradiometer (MODIS) images and fine spatial resolution of Landsat images. We have evaluated the output regression with intercept method and developed the Linear with Zero Intercept (LinZI) method for downscaling MODIS-based monthly actual evapotranspiration (AET) maps to the Landsat-scale monthly AET maps for the Colorado River Basin for 2010. We used the 8-day MODIS land surface temperature product (MOD11A2) and 328 cloud-free Landsat images for computing AET maps and downscaling. The regression with intercept method does have limitations in downscaling if the slope and intercept are computed over a large area. A good agreement was obtained between downscaled monthly AET using the LinZI method and the eddy covariance measurements from seven flux sites within the Colorado River Basin. The mean bias ranged from −16 mm (underestimation) to 22 mm (overestimation) per month, and the coefficient of determination varied from 0.52 to 0.88. Some discrepancies between measured and downscaled monthly AET at two flux sites were found to be due to the prevailing flux footprint. A reasonable comparison was also obtained between downscaled monthly AET using LinZI method and the gridded FLUXNET dataset. The downscaled monthly AET nicely captured the temporal variation in sampled land cover classes. The proposed LinZI method can be used at finer temporal resolution (such as 8 days) with further evaluation. The proposed downscaling method will be very useful in advancing the application of remotely sensed images in water resources planning and management.

  5. Merging raster meteorological data with low resolution satellite images for improved estimation of actual evapotranspiration

    NASA Astrophysics Data System (ADS)

    Cherif, Ines; Alexandridis, Thomas; Chambel Leitao, Pedro; Jauch, Eduardo; Stavridou, Domna; Iordanidis, Charalampos; Silleos, Nikolaos; Misopolinos, Nikolaos; Neves, Ramiro; Safara Araujo, Antonio

    2013-04-01

    Actual evapotranspiration (ETa) can be estimated using Energy Balance models and remotely sensed data. In particular, satellite images acquired in visible, near and thermal infrared parts of the spectrum have been used with the Surface Energy Balance Algorithm for Land (SEBAL) to estimate actual evapotranspiration. This algorithm is solving the Energy Balance Equation using data from a meteorological station present in the vicinity, and assumes the meteorological conditions homogeneous over the study area. Most often, data from a representative weather station are used. This assumption may lead to substantial errors in areas with high spatial variability in weather parameters. In this paper, the ITA-MyWater algorithms (Integrated Thermodynamic Algorithms for MyWater project), an adaptation of SEBAL was merged together with spatially distributed meteorological data to increase the accuracy of ETa estimations at regional scale using MODIS satellite images. The major changes introduced to migrate from point to raster are that (i) air temperature and relative humidity maps are used for the estimation of the Energy Balance terms, including instantaneous net radiation and soil heat flux and (ii) the variability of wind speed is taken into account to generate maps of the aerodynamic resistance, sensible heat flux and difference between soil and air temperature at the boundary conditions (at dry and wet pixels). The approach was applied in the river basin of Tamega in Portugal, where actual evapotranspiration was estimated for several MODIS 8-day periods from spring to winter of the same year. The raster meteorological maps were produced by the MM5 weather forecast model. Daily reference evapotranspiration was calculated with MOHID LAND model. Using a temporal integration technique and the daily reference evapotranspiration maps, the cumulative evapotranspiration over the MODIS 8-day period was estimated and compared to the global evapotranspiration MODIS product (MOD16A2

  6. Modelling bulk surface resistance from MODIS time series data to estimate actual regional evapotranspiration

    NASA Astrophysics Data System (ADS)

    Autovino, Dario; Minacapilli, Mario; Provenzano, Giuseppe

    2015-04-01

    Estimation of actual evapotraspiration by means of Penman-Monteith (P-M) equation requires the knowledge of the so-called 'bulk surface resistance', rc,act, representing the vapour flow resistance through the transpiring crop and evaporating soil surface. The accurate parameterization of rc,act still represents an unexploited topic, especially in the case of heterogeneous land surface. In agro-hydrological applications, the P-M equation commonly used to evaluate reference evapotranspiration (ET0) of a well-watered 'standardized crop' (grass or alfalfa), generally assumes for the bulk surface resistance a value of 70 s m-1. Moreover, specific crop coefficients have to be used to estimate maximum and/or actual evapotranspiration based on ET0. In this paper, a simple procedure for the indirect estimation of rc,act as function of a vegetation index computed from remote acquisition of Land Surface Temperature (LST), is proposed. An application was carried out in an irrigation district located near Castelvetrano, in South-West of Sicily, mainly cultivated with olive groves, in which actual evapotranspiration fluxes were measured during two years (2010-2011) by an Eddy Covariance flux tower (EC). Evapotranspiration measurements allowed evaluating rc,actbased on the numerical inversion of the P-M equation. In the same study area, a large time series of MODIS LST data, characterized by a spatial resolution of 1x1 km and a time step of 8-days, was also acquired for the period from 2000 to 2014. A simple Vegetation Index Temperatures (VTI), with values ranging from 0 to 1, was computed using normalized LST values. Evapotranspiration fluxes measured in 2010 were used to calibrate the relationship between rc,act and VTI, whereas data from 2011 were used for its validation. The preliminary results evidenced that, for the considered crop, an almost constant value of rc,act, corresponding to about 250 s m-1, can be considered typical of periods in which the crop is well

  7. Estimation of Actual Evapotranspiration by Remote Sensing: Application in Thessaly Plain, Greece

    PubMed Central

    Tsouni, Alexia; Kontoes, Charalabos; Koutsoyiannis, Demetris; Elias, Panagiotis; Mamassis, Nikos

    2008-01-01

    Remote sensing can assist in improving the estimation of the geographical distribution of evapotranspiration, and consequently water demand in large cultivated areas for irrigation purposes and sustainable water resources management. In the direction of these objectives, the daily actual evapotranspiration was calculated in this study during the summer season of 2001 over the Thessaly plain in Greece, a wide irrigated area of great agricultural importance. Three different methods were adapted and applied: the remote-sensing methods by Granger (2000) and Carlson and Buffum (1989) that use satellite data in conjunction with ground meteorological measurements and an adapted FAO (Food and Agriculture Organisation) Penman-Monteith method (Allen at al. 1998), which was selected to be the reference method. The satellite data were used in conjunction with ground data collected on the three closest meteorological stations. All three methods, exploit visible channels 1 and 2 and infrared channels 4 and 5 of NOAA-AVHRR (National Oceanic and Atmospheric Administration - Advanced Very High Resolution Radiometer) sensor images to calculate albedo and NDVI (Normalised Difference Vegetation Index), as well as surface temperatures. The FAO Penman-Monteith and the Granger method have used exclusively NOAA-15 satellite images to obtain mean surface temperatures. For the Carlson-Buffum method a combination of NOAA-14 and NOAA-15 satellite images was used, since the average rate of surface temperature rise during the morning was required. The resulting estimations show that both the Carlson-Buffum and Granger methods follow in general the variations of the reference FAO Penman-Monteith method. Both methods have potential for estimating the spatial distribution of evapotranspiration, whereby the degree of the relative agreement with the reference FAO Penman-Monteith method depends on the crop growth stage. In particular, the Carlson-Buffum method performed better during the first half

  8. Impact of potential and (scintillometer-based) actual evapotranspiration estimates on the performance of a lumped rainfall-runoff model

    NASA Astrophysics Data System (ADS)

    Samain, B.; Pauwels, V. R. N.

    2013-11-01

    Evapotranspiration (ET) plays a key role in hydrological impact studies and operational flood forecasting models as ET represents a loss of water from a catchment. Although ET is a major component of the catchment water balance, the evapotranspiration input for rainfall-runoff models is often simplified in contrast to the detailed estimates of catchment averaged precipitation. In this study, an existing conceptual rainfall-runoff model calibrated for and operational in the Bellebeek catchment in Belgium firstly has been validated and its sensitivity to different available potential ET input has been studied. It has been shown that when applying a calibrated rainfall-runoff model, the model input should be consistent with the input used for the calibration process, not only on the volume of ET, but also on the seasonal pattern. Secondly, estimates of the actual evapotranspiration based on measurements of a large aperture scintillometer (LAS) have been used as model forcing in the rainfall-runoff model. From this analysis, it has been shown that the actual evapotranspiration is a crucial factor in simulating the catchment water balance and the resulting stream flow. Regarding the actual evapotranspiration estimates from the LAS, it has been concluded that they can be considered realistic in summer months. In the months where stable conditions prevail (autumn, winter and (early) spring), an underestimation of the actual evapotranspiration is made, which has an important impact on the catchment's water balance.

  9. Testing two temporal upscaling schemes for the estimation of the time variability of the actual evapotranspiration

    NASA Astrophysics Data System (ADS)

    Maltese, A.; Capodici, F.; Ciraolo, G.; La Loggia, G.

    2015-10-01

    Temporal availability of grapes actual evapotranspiration is an emerging issue since vineyards farms are more and more converted from rainfed to irrigated agricultural systems. The manuscript aims to verify the accuracy of the actual evapotranspiration retrieval coupling a single source energy balance approach and two different temporal upscaling schemes. The first scheme tests the temporal upscaling of the main input variables, namely the NDVI, albedo and LST; the second scheme tests the temporal upscaling of the energy balance output, the actual evapotranspiration. The temporal upscaling schemes were implemented on: i) airborne remote sensing data acquired monthly during a whole irrigation season over a Sicilian vineyard; ii) low resolution MODIS products released daily or weekly; iii) meteorological data acquired by standard gauge stations. Daily MODIS LST products (MOD11A1) were disaggregated using the DisTrad model, 8-days black and white sky albedo products (MCD43A) allowed modeling the total albedo, and 8-days NDVI products (MOD13Q1) were modeled using the Fisher approach. Results were validated both in time and space. The temporal validation was carried out using the actual evapotranspiration measured in situ using data collected by a flux tower through the eddy covariance technique. The spatial validation involved airborne images acquired at different times from June to September 2008. Results aim to test whether the upscaling of the energy balance input or output data performed better.

  10. Actual evapotranspiration estimation by means of airborne and satellite remote sensing data

    NASA Astrophysics Data System (ADS)

    Ciraolo, Giuseppe; D'Urso, Guido; Minacapilli, Mario

    2006-09-01

    During the last the two decades, the scientific community developed detailed mathematical models for simulating land surface energy fluxes and crop evapotranspiration rates by means of a energy balance approach. These models can be applied in large areas and with a spatial distributed approach using surface brightness temperature and some ancillary data retrieved from satellite/airborne remote sensed imagery. In this paper a district scale application in combination with multispectral (LandaSat 7 TM data) and hyperspectral airborne MIVIS data has been carried out to test the potentialities of two different energy balance models to estimate evapotranspiration fluxes from a set of typical Mediterranean crops (wine, olive, citrus). The impact of different spatial and radiometric resolutions of MIVIS (3m x 3m) and LandSat (60m x 60m) on models-derived fluxes has been investigated to understand the roles and the main conceptual differences between the two models which respectively use a "single-layer" (SEBAL) and a "two-layer" (TS) schematisation.

  11. Actual daily evapotranspiration estimated from MERIS and AATSR data over the Chinese Loess Plateau

    NASA Astrophysics Data System (ADS)

    Liu, R.; Wen, J.; Wang, X.; Wang, L.; Tian, H.; Zhang, T. T.; Shi, X. K.; Zhang, J. H.; Lv, Sh. N.

    2010-01-01

    The Chinese Loess Plateau is located in the north of China and has a significant impact on the climate and ecosystem evolvement over the East Asian continent. Estimates of evapotranspiration (ET) at a regional scale are in crucial need for climate studies, weather forecasts, hydrological surveys, ecological monitoring and water resource management. In this research, the ET of the Chinese Loess Plateau was estimated by using an energy balance approach and data collected during the LOess Plateau land-atmosphere interaction pilot EXperiments 2005 (LOPEX05). With the combined data of the Medium Resolution Imaging Spectrometer (MERIS), the Advanced Along-Track Scanning Radiometer (AATSR) and some other variables such as air temperature, crop height and wind speed, the instantaneous net radiation, sensible heat flux and soil heat flux were calculated; the instantaneous latent heat flux was derived as the residual term of energy balance, and then converted to daily ET value by sunshine duration. The calculated daily ET from the model showed a good match with the measurements of the eddy covariance systems deployed in LOPEX05. The minimum relative error of this approach is 9.0%, the cause of the bias was also explored and discussed.

  12. Potential of remote sensing derived soil moisture for the estimation of actual evapotranspiration in cotton ecosystems of Middle Asia

    NASA Astrophysics Data System (ADS)

    Knoefel, Patrick; Conrad, Christopher; Dech, Stefan

    2013-04-01

    Actual evapotranspiration (ETact) is an essential component of the water balance and its determination for larger areas is difficult on regional scale. Here, remote sensing provides a powerful tool to estimate regional actual evapotranspiration to support regional water management. Particularly, in irrigation agriculture of Middle Asia decision makers have to handle limited water availability and to improve the efficiency of their regional water management systems. The growing interest in quantifying regional actual ET for water resource and irrigation management led to the development of numerous methods to estimate ET from remote sensing data. The study is primarily concerned with the irrigation farming of cotton ecosystems in Middle Asia, in particular with the situation within Khorezm Oblast in Uzbekistan. Regional problems of Khorezm Oblast are e.g. high groundwater levels, soil salinity, and non-sustainable use of land and water. The water for irrigation is taken from the Amu Darya River and then canalled to the agricultural fields. The available water in Khorezm depends on the water demand in the upstream regions. Because of this variation and the historical annual shortage of available irrigation water a sustainable use of water is highly important for the regional water management in Khorezm. Cotton is the major crop in Khorezm region. About 46% of the agricultural area was covered with cotton in 2010 and 2011, among the other main crops winter wheat (30%) and rice (5%). The objective of this study was to investigate the potential of satellite derived surface soil moisture for the optimization of the estimated ETact. Actual evapotranspiration in this study is indirectly derived by solving the surface energy balance equation using the surface energy balance algorithm for land (SEBAL). Due to its high temporal resolution MODIS (1km) data is used to provide the input information to solve the equation. The results were compared with measurements of an eddy

  13. Surface energy balance and actual evapotranspiration of the transboundary Indus Basin estimated from satellite measurements and the ETLook model

    NASA Astrophysics Data System (ADS)

    Bastiaanssen, W. G. M.; Cheema, M. J. M.; Immerzeel, W. W.; Miltenburg, I. J.; Pelgrum, H.

    2012-11-01

    The surface energy fluxes and related evapotranspiration processes across the Indus Basin were estimated for the hydrological year 2007 using satellite measurements. The new ETLook remote sensing model (version 1) infers information on actual Evaporation (E) and actual Transpiration (T) from combined optical and passive microwave sensors, which can observe the land-surface even under persistent overcast conditions. A two-layer Penman-Monteith equation was applied for quantifying soil and canopy evaporation. The novelty of the paper is the computation of E and T across a vast area (116.2 million ha) by using public domain microwave data that can be applied under all weather conditions, and for which no advanced input data are required. The average net radiation for the basin was estimated as being 112 Wm-2. The basin average sensible, latent and soil heat fluxes were estimated to be 80, 32, and 0 Wm-2, respectively. The average evapotranspiration (ET) and evaporative fraction were 1.2 mm d-1 and 0.28, respectively. The basin wide ET was 496 ± 16.8 km3 yr-1. Monte Carlo analysis have indicated 3.4% error at 95% confidence interval for a dominant land use class. Results compared well with previously conducted soil moisture, lysimeter and Bowen ratio measurements at field scale (R2 = 0.70; RMSE = 0.45 mm d-1; RE = -11.5% for annual ET). ET results were also compared against earlier remote sensing and modeling studies for various regions and provinces in Pakistan (R2 = 0.76; RMSE = 0.29 mmd-1; RE = 6.5% for annual ET). The water balance for all irrigated areas together as one total system in Pakistan and India (26.02 million ha) show a total ET value that is congruent with the ET value from the ETLook surface energy balance computations. An unpublished validation of the same ETLook model for 23 jurisdictional areas covering the entire Australian continent showed satisfactory results given the quality of the watershed data and the diverging physiographic and climatic

  14. Estimation of actual evapotranspiration using measured and calculated values of bulk surface resistance

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Currently the United Nations-Food and Agriculture Organization (FAO) recommends using the Penman-Monteith method for estimating ET over all other meteorological methods. The principal limitation of using the generalized form of the Penman-Monteith equation is in obtaining accurate values for the bu...

  15. Comparative analysis and validation of remotely sensed estimation of actual evapotranspiration in cotton ecosystems of Middle Asia

    NASA Astrophysics Data System (ADS)

    Knoefel, P.; Falk, U.; Conrad, C.; Dech, S.

    2012-04-01

    Detailed knowledge of land surface fluxes, especially latent and sensible components, is important for monitoring the climate and land surface, and for agriculture applications such as irrigation scheduling and water management. Accurate estimation of evapotranspiration (ET) plays an important role in quantification of the water balance at the watershed, basin, and regional scale for better planning and managing water resources. The growing interest in quantifying regional actual ET for water resource and irrigation management led to the development of numerous methods to estimate ET from remote sensing data. The objective of this study was to compare the performance of the established surface energy balance algorithm for land (SEBAL) approach for estimating the energy balance using input data with different temporal and spatial resolution (Landsat/MODIS). Input data to the model are basically surface reflectance, land use classification and meteorological data of the years 2009 and 2010. The study is primarily concerned with the irrigation farming of cotton ecosystems in Middle Asia, in particular with the situation within Khorezm Oblast in Uzbekistan. Regional problems of Khorezm Oblast are e.g. high groundwater levels, soil salinity, and non sustainable use of land and water. Cotton is the major crop in Khorezm region. About 46% of the agricultural area was covered with cotton in 2009 and 2010, among the other main crops winter wheat (30%) and rice (5%). Due to the low level of precipitation (<100 mm p.a.) irrigation is the only available water source for the crops. The water for irrigation is taken from the Amu Darya River and then canalled to the agricultural fields. The available water in Khorezm depends on the water demand in the upstream regions. Because of this variation and the historical annual shortage of available irrigation water a sustainable use of water is highly important for the regional water management in Khorezm. Input parameters and

  16. Validation of an improved energy balance model to estimate actual evapotranspiration in irrigated cotton ecosystems of Central Asia

    NASA Astrophysics Data System (ADS)

    Knoefel, Patrick; Conrad, Christopher; Falk, Ulrike; Bauer-Marschallinger, Bernhard

    2014-05-01

    The understanding of the hydrological and the energy cycles are essential in order to describe the complex interactions within the climate system of the earth. Being recognized as an essential component of both the water and the energy cycle, reliable estimation of actual evapotranspiration and its spatial distribution is one outstanding challenge in this context. For instance, in irrigation systems of arid regions, artificial locations of evapotranspiration have been created. An in-depth process understanding is of paramount importance, as irrigated agriculture consumes about 70 % of the available freshwater resources worldwide, with a significant but unsatisfyingly quantified impact on the water cycle, especially on regional scale. Moreover, an exact quantification of ET inside these artificial ecosystems enables assessments of crop water consumptions and hence about water use efficiency (WUE). The withdrawal of water for agricultural use in the countries of Central Asia is more than 90%. Khorezm region in Uzbekistan is a case study region for the problems of irrigated agriculture in CA. For Khorezm the seasonal actual ET was calculated for the years 2003 - 2010 using the partly modified surface energy balance algorithm for land (SEBAL). SEBAL was implemented based on MODIS time series to calculate the energy balance components like net radiation (Rn), sensible heat (H), latent heat (LE), and soil heat flux (G). Whilst SEBAL is using an empirical equation for estimating G, a more physically based method was introduced in this study. This method uses microwave soil moisture products (ASAR-SSM and ASCAT-SSM) as additional input information. The modelled energy balance components were intensively validated by field measurements with an eddy covariance system and soil sensors. For turbulent heat fluxes the RMSE is about 40 W/m² for H and 80 W/m² for LE with a coefficient of determination (r²) of 0.64 for H and 0.52 for LE. Soil heat flux estimation could be

  17. Bowen ratio measurements above various vegetation covers and its comparison with actual evapotranspiration estimated by SoilClim model

    NASA Astrophysics Data System (ADS)

    Hlavinka, P.; Trnka, M.; Fischer, M.; Kucera, J.; Mozny, M.; Zalud, Z.

    2010-09-01

    The principle of Bowen ratio is one of the available techniques for measurements of actual evapotranspiration (ETa) as one of essential water balance fractions. The main aims of submitted study were: (i) to compare the water balance of selected crops, (ii) to compare outputs of SoilClim model with observed parameters (including ETa on Bowen ratio basis). The measurements were conducted at two experimental stations in the Czech Republic (Polkovice 49°23´ (N), 17°17´ (E), 205 m a.s.l.; Domanínek 49°32´ (N), 16°15´ (E), 544 m a.s.l.) during the years 2009 and 2010. Together with Bowen ratio the global solar radiation, radiation balance, soil heat flux, volumetric soil moisture and temperature within selected depths, precipitation and wind speed were measured. The measurements were conducted simultaneously above various covers within the same soil conditions: spring barley vs. winter wheat, spring barley vs. winter rape; grass vs. poplars; harvested field after tillage vs. harvested field after cereals without any tillage. The observed parameters from different covers were compared with SoilClim estimates. SoilClim model is modular software for water balance and soil temperature modelling and finally could be used for soil Hydric and Thermic regimes (according to USDA classification) identification. The core of SoilClim is based on modified FAO Penman-Monteith methodology. Submitted study proved the applicability of SoilClim model for ETa, soil moisture within two defined layers and soil temperature (in 0.5 m depth) estimates for various crops, covers, selected soil types and climatic conditions. Acknowledgement: We gratefully acknowledge the support of the Grant Agency of the Czech Republic (no. 521/09/P479) and the project NAZV QI91C054. The study was also supported by Research plan No. MSM6215648905 "Biological and technological aspects of sustainability of controlled ecosystems and their adaptability to climate change".

  18. A coupled remote sensing and simplified surface energy balance approach to estimate actual evapotranspiration from irrigated fields

    USGS Publications Warehouse

    Senay, G.B.; Budde, M.; Verdin, J.P.; Melesse, Assefa M.

    2007-01-01

    Accurate crop performance monitoring and production estimation are critical for timely assessment of the food balance of several countries in the world. Since 2001, the Famine Early Warning Systems Network (FEWS NET) has been monitoring crop performance and relative production using satellite-derived data and simulation models in Africa, Central America, and Afghanistan where ground-based monitoring is limited because of a scarcity of weather stations. The commonly used crop monitoring models are based on a crop water-balance algorithm with inputs from satellite-derived rainfall estimates. These models are useful to monitor rainfed agriculture, but they are ineffective for irrigated areas. This study focused on Afghanistan, where over 80 percent of agricultural production comes from irrigated lands. We developed and implemented a Simplified Surface Energy Balance (SSEB) model to monitor and assess the performance of irrigated agriculture in Afghanistan using a combination of 1-km thermal data and 250m Normalized Difference Vegetation Index (NDVI) data, both from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. We estimated seasonal actual evapotranspiration (ETa) over a period of six years (2000-2005) for two major irrigated river basins in Afghanistan, the Kabul and the Helmand, by analyzing up to 19 cloud-free thermal and NDVI images from each year. These seasonal ETa estimates were used as relative indicators of year-to-year production magnitude differences. The temporal water-use pattern of the two irrigated basins was indicative of the cropping patterns specific to each region. Our results were comparable to field reports and to estimates based on watershed-wide crop water-balance model results. For example, both methods found that the 2003 seasonal ETa was the highest of all six years. The method also captured water management scenarios where a unique year-to-year variability was identified in addition to water-use differences between

  19. A Coupled Remote Sensing and Simplified Surface Energy Balance Approach to Estimate Actual Evapotranspiration from Irrigated Fields

    PubMed Central

    Senay, Gabriel B.; Budde, Michael; Verdin, James P.; Melesse, Assefa M.

    2007-01-01

    Accurate crop performance monitoring and production estimation are critical for timely assessment of the food balance of several countries in the world. Since 2001, the Famine Early Warning Systems Network (FEWS NET) has been monitoring crop performance and relative production using satellite-derived data and simulation models in Africa, Central America, and Afghanistan where ground-based monitoring is limited because of a scarcity of weather stations. The commonly used crop monitoring models are based on a crop water-balance algorithm with inputs from satellite-derived rainfall estimates. These models are useful to monitor rainfed agriculture, but they are ineffective for irrigated areas. This study focused on Afghanistan, where over 80 percent of agricultural production comes from irrigated lands. We developed and implemented a Simplified Surface Energy Balance (SSEB) model to monitor and assess the performance of irrigated agriculture in Afghanistan using a combination of 1-km thermal data and 250-m Normalized Difference Vegetation Index (NDVI) data, both from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. We estimated seasonal actual evapotranspiration (ETa) over a period of six years (2000-2005) for two major irrigated river basins in Afghanistan, the Kabul and the Helmand, by analyzing up to 19 cloud-free thermal and NDVI images from each year. These seasonal ETa estimates were used as relative indicators of year-to-year production magnitude differences. The temporal water-use pattern of the two irrigated basins was indicative of the cropping patterns specific to each region. Our results were comparable to field reports and to estimates based on watershed-wide crop water-balance model results. For example, both methods found that the 2003 seasonal ETa was the highest of all six years. The method also captured water management scenarios where a unique year-to-year variability was identified in addition to water-use differences between

  20. Testing an Energy Balance Model for Estimating Actual Evapotranspiration Using Remotely Sensed Data. [Hannover, West Germany barley and wheat fields

    NASA Technical Reports Server (NTRS)

    Gurney, R. J.; Camillo, P. J.

    1985-01-01

    An energy-balance model is used to estimate daily evapotranspiration for 3 days for a barley field and a wheat field near Hannover, Federal Republic of Germany. The model was calibrated using once-daily estimates of surface temperatures, which may be remotely sensed. The evaporation estimates were within the 95% error bounds of independent eddy correlation estimates for the daytime periods for all three days for both sites, but the energy-balance estimates are generally higher; it is unclear which estimate is biassed. Soil moisture in the top 2 cm of soil, which may be remotely sensed, may be used to improve these evaporation estimates under partial ground cover. Sensitivity studies indicate the amount of ground data required is not excessive.

  1. Fully-automated estimation of actual to potential evapotranspiration in the Everglades using Landsat and air temperature data as inputs to the Vegetation Index-Temperature Trapezoid method

    NASA Astrophysics Data System (ADS)

    Yagci, A. L.; Jones, J. W.

    2014-12-01

    While the greater Everglades contains a vast wetland, evapotranspiration (ET) is a major source of water "loss" from the system. Like other ecosystems, the Everglades is vulnerable to drought. Everglades restoration science and resource management requires information on the spatial and temporal distribution of ET. We developed a fully-automated ET model using the Vegetation Index-Temperature Trapezoid concept. The model was tested and evaluated against in-situ ET observations collected at the Shark River Slough Mangrove Forest eddy-covariance tower in Everglades National Park (Sitename / FLUXNET ID: Florida Everglades Shark River Slough Mangrove Forest / US-Skr). It uses Landsat Surface Reflectance Climate Data from Landsat 5, and Landsat 5 thermal and air temperature data from the Daily Gridded Surface Dataset to output the ratio of actual evapotranspiration (AET) and potential evapotranspiration (PET). When multiplied with a PET estimate, this output can be used to estimate ET at high spatial resolution. Furthermore, it can be used to downscale coarse resolution ET and PET products. Two example outputs covering the agricultural lands north of the major Everglades wetlands extracted from two different dates are shown below along with a National Land Cover Database image from 2011. The irrigated and non-irrigated farms are easily distinguishable from the background (i.e., natural land covers). Open water retained the highest AET/PET ratio. Wetlands had a higher AET/PET ratio than farmlands. The main challenge in this study area is prolonged cloudiness during the growing season.

  2. A coupled remote sensing and the Surface Energy Balance with Topography Algorithm (SEBTA) to estimate actual evapotranspiration under complex terrain

    NASA Astrophysics Data System (ADS)

    Gao, Z. Q.; Liu, C. S.; Gao, W.; Chang, N. B.

    2010-07-01

    Evapotranspiration (ET) may be used as an ecological indicator to address the ecosystem complexity. The accurate measurement of ET is of great significance for studying environmental sustainability, global climate changes, and biodiversity. Remote sensing technologies are capable of monitoring both energy and water fluxes on the surface of the Earth. With this advancement, existing models, such as SEBAL, S_SEBI and SEBS, enable us to estimate the regional ET with limited temporal and spatial scales. This paper extends the existing modeling efforts with the inclusion of new components for ET estimation at varying temporal and spatial scales under complex terrain. Following a coupled remote sensing and surface energy balance approach, this study emphasizes the structure and function of the Surface Energy Balance with Topography Algorithm (SEBTA). With the aid of the elevation and landscape information, such as slope and aspect parameters derived from the digital elevation model (DEM), and the vegetation cover derived from satellite images, the SEBTA can fully account for the dynamic impacts of complex terrain and changing land cover in concert with some varying kinetic parameters (i.e., roughness and zero-plane displacement) over time. Besides, the dry and wet pixels can be recognized automatically and dynamically in image processing thereby making the SEBTA more sensitive to derive the sensible heat flux for ET estimation. To prove the application potential, the SEBTA was carried out to present the robust estimates of 24 h solar radiation over time, which leads to the smooth simulation of the ET over seasons in northern China where the regional climate and vegetation cover in different seasons compound the ET calculations. The SEBTA was validated by the measured data at the ground level. During validation, it shows that the consistency index reached 0.92 and the correlation coefficient was 0.87.

  3. A coupled remote sensing and the Surface Energy Balance with Topography Algorithm (SEBTA) to estimate actual evapotranspiration over heterogeneous terrain

    NASA Astrophysics Data System (ADS)

    Gao, Z. Q.; Liu, C. S.; Gao, W.; Chang, N.-B.

    2011-01-01

    Evapotranspiration (ET) may be used as an ecological indicator to address the ecosystem complexity. The accurate measurement of ET is of great significance for studying environmental sustainability, global climate changes, and biodiversity. Remote sensing technologies are capable of monitoring both energy and water fluxes on the surface of the Earth. With this advancement, existing models, such as SEBAL, S_SEBI and SEBS, enable us to estimate the regional ET with limited temporal and spatial coverage in the study areas. This paper extends the existing modeling efforts with the inclusion of new components for ET estimation at different temporal and spatial scales under heterogeneous terrain with varying elevations, slopes and aspects. Following a coupled remote sensing and surface energy balance approach, this study emphasizes the structure and function of the Surface Energy Balance with Topography Algorithm (SEBTA). With the aid of the elevation and landscape information, such as slope and aspect parameters derived from the digital elevation model (DEM), and the vegetation cover derived from satellite images, the SEBTA can account for the dynamic impacts of heterogeneous terrain and changing land cover with some varying kinetic parameters (i.e., roughness and zero-plane displacement). Besides, the dry and wet pixels can be recognized automatically and dynamically in image processing thereby making the SEBTA more sensitive to derive the sensible heat flux for ET estimation. To prove the application potential, the SEBTA was carried out to present the robust estimates of 24 h solar radiation over time, which leads to the smooth simulation of the ET over seasons in northern China where the regional climate and vegetation cover in different seasons compound the ET calculations. The SEBTA was validated by the measured data at the ground level. During validation, it shows that the consistency index reached 0.92 and the correlation coefficient was 0.87.

  4. A coupled remote sensing and the Surface Energy Balance based algorithms to estimate actual evapotranspiration over the western and southern regions of Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Mahmoud, Shereif H.; Alazba, A. A.

    2016-07-01

    In countries with absolute water scarcity such as the Kingdom of Saudi Arabia (KSA), large-scale actual evapotranspiration estimation is of great concern in water use practices. Herein, spatial and temporal distribution of actual evapotranspiration (AET) in the western and southern regions of KSA during 1992-2014 was estimated using the SEBAL model with field observations. Zonal statistics for each land use-cover type were also identified, in order to understand their effects on water consumption. In addition, daily and seasonal water consumption for major crops was computed. Results revealed a gradual increase in monthly AET values from January to April and subsequent decline from May to December. The maximum monthly AET values were observed for irrigated cropland in southwestern, central, and southeastern regions of Asir Province, central and southwestern regions of Al-Baha Province, central and the plains region of Jazan Province, southern portion of Makkah Province, and limited areas in the northern regions of Madinah Province. The annual AET ranged from 418.8 to 3442.3 mm yr-1. The normal distribution of mean annual AET values ranged from 717 to 1020 mm yr-1. Forty-two percent of the study area had an annual AET that ranged from 717 to 1020 mm yr-1. The second highest range of frequencies was concentrated around 1020-1322 mm yr-1, representing the majority of agricultural land. The consumptive water use of the different land cover types in study area indicated that irrigated cropland which occupied 14.6% of the study area had AET rates much higher than other land uses. Water bodies are the next highest, with forest and shrubland and sparse vegetation slightly lower, and very low AET rates from bare soil. Daily and seasonal water consumption of major cropping systems varied spatially depending on cropping practices and climatic conditions.

  5. Assessing the impact of end-member selection on the accuracy of satellite-based spatial variability models for actual evapotranspiration estimation

    NASA Astrophysics Data System (ADS)

    Long, Di; Singh, Vijay P.

    2013-05-01

    This study examines the impact of end-member (i.e., hot and cold extremes) selection on the performance and mechanisms of error propagation in satellite-based spatial variability models for estimating actual evapotranspiration, using the triangle, surface energy balance algorithm for land (SEBAL), and mapping evapotranspiration with high resolution and internalized calibration (METRIC) models. These models were applied to the soil moisture-atmosphere coupling experiment site in central Iowa on two Landsat Thematic Mapper/Enhanced Thematic Mapper Plus acquisition dates in 2002. Evaporative fraction (EF, defined as the ratio of latent heat flux to availability energy) estimates from the three models at field and watershed scales were examined using varying end-members. Results show that the end-members fundamentally determine the magnitudes of EF retrievals at both field and watershed scales. The hot and cold extremes exercise a similar impact on the discrepancy between the EF estimates and the ground-based measurements, i.e., given a hot (cold) extreme, the EF estimates tend to increase with increasing temperature of cold (hot) extreme, and decrease with decreasing temperature of cold (hot) extreme. The coefficient of determination between the EF estimates and the ground-based measurements depends principally on the capability of remotely sensed surface temperature (Ts) to capture EF (i.e., depending on the correlation between Ts and EF measurements), being slightly influenced by the end-members. Varying the end-members does not substantially affect the standard deviation and skewness of the EF frequency distributions from the same model at the watershed scale. However, different models generate markedly different EF frequency distributions due to differing model physics, especially the limiting edges of EF defined in the remotely sensed vegetation fraction (fc) and Ts space. In general, the end-members cannot be properly determined because (1) they do not

  6. Estimation of total available water in the soil layer by integrating actual evapotranspiration data in a remote sensing-driven soil water balance

    NASA Astrophysics Data System (ADS)

    Campos, Isidro; González-Piqueras, Jose; Carrara, Arnaud; Villodre, Julio; Calera, Alfonso

    2016-03-01

    The total available water (τ) by plants that could be stored in its root soil layer is a key parameter when applying soil water balance models. Since the transpiration rate of a vegetation stand could be the best proxy about the soil water content into the root soil layer, we propose a methodology for estimating τ by using as basic inputs the evapotranspiration rate of the stand and time series of multispectral imagery. This methodology is based on the inverted formulation of the soil water balance model. The inversion of the model was addressed by using an iterative approach, which optimizes the τ parameter to minimize the difference between measured and modeled ET. This methodology was tested for a Mediterranean holm oak savanna (dehesa) for which eddy covariance measurements of actual ET were available. The optimization procedure was performed by using a continuous dataset (in 2004) of daily ET measurements and 16 sets of 8 daily ET measurements, resulting in τ values of 325 and 305 mm, respectively. The use of these τ values in the RSWB model for the validation period (2005-2008) allowed us to estimate dehesa ET with a RMSE = 0.48 mm/day. The model satisfactorily reproduces the water stress process. The sensitivity of τ estimates was evaluated regarding two of the more uncertain parameters in the RSWB model. These parameters are the average fraction of τ that can be depleted from the root zone without producing moisture stress (pτ) and the soil evaporation component. The results of this analysis indicated relatively little influence from the evaporation component and the need for adequate knowledge about pτ for estimating τ.

  7. Evaluation of a Modified SEBAL Algorithm to Estimate Actual Evapotranspiration in Cotton Ecosystems of Central Asia using Microwave and Optical Remote Sensing Data

    NASA Astrophysics Data System (ADS)

    Knoefel, Patrick; Conrad, Christopher

    2015-04-01

    Being recognized as an essential component of both the water and the energy cycle, actual evapotranspiration (ETa) plays in important role in order to describe the complex interactions within the climate system of the Earth. Here, remote sensing is a powerful tool to estimate regional ETa to support the regional water management. For instance, the water withdrawal of the agricultural sector in OECD countries is on average about 44 %, but in the states of Central Asia it achieves more than 90 %. This fact is identified as one of the main reasons for the increasing water scarcity in this region. An accuracy assessment of the methods used for determining ETa is necessary concerning an appropriate use of the model results to support agriculture and irrigation management. Within Central Asia the Khorezm region in Uzbekistan is a case study region for the problems of irrigated agriculture. For Khorezm the seasonal ETa based on MODIS data was calculated for the years 2009 - 2011 using a partly modified surface energy balance algorithm for land (SEBAL). SEBAL was implemented based on MODIS time series to calculate the energy balance components like net radiation (Rn), sensible heat (H), latent heat (LE), and soil heat flux (G). Whilst SEBAL is using an empirical equation for the estimation of G, a more physically based method was introduced in this study. This method uses microwave soil moisture products (ASAR and ASCAT-SSM) as an additional model input. The input parameters and the model results of all energy balance components (Rn, H, LE, and G) were intensively validated by field measurements with an eddy covariance system and soil sensors. The model shows very good performance for Rn with average model efficiency (NSE) of 0.68 and small relative errors (rRMSE) of about 10%. For turbulent heat fluxes good results can be achieved with NSE of 0.31 for H and 0.55 for LE, the rRMSE are about 21% (H) and 18% (LE). Soil heat flux estimation could be improved using the

  8. A new assimilation method with physical mechanism to estimate evapotranspiration

    NASA Astrophysics Data System (ADS)

    Ye, Wen; Xu, Xinyi

    2016-04-01

    The accurate estimation of regional evapotranspiration has been a research hotspot in the field of hydrology and water resources both in domestic and abroad. A new assimilation method with physical mechanism was proposed to estimate evapotranspiration, which was easier to apply. Based on the evapotranspiration (ET) calculating method with soil moisture recurrence relations in the Distributed Time Variant Gain Model (DTVGM) and Ensemble Kalman Filter (EnKF), it constructed an assimilation system for recursive calculation of evapotranspiration in combination with "observation value" by the retrieval data of evapotranspiration through the Two-Layer Remote Sensing Model. By updating the filter in the model with assimilated evapotranspiration, synchronization correction to the model estimation was achieved and more accurate time continuous series values of evapotranspiration were obtained. Through the verification of observations in Xiaotangshan Observatory and hydrological stations in the basin, the correlation coefficient of remote sensing inversion evapotranspiration and actual evapotranspiration reaches as high as 0.97, and the NS efficiency coefficient of DTVGM model was 0.80. By using the typical daily evapotranspiration from Remote Sensing and the data from DTVGM Model, we assimilated the hydrological simulation processes with DTVGM Model in Shahe Basin in Beijing to obtain continuous evapotranspiration time series. The results showed that the average relative error between the remote sensing values and DTVGM simulations is about 12.3%, and for the value between remote sensing retrieval data and assimilation values is 4.5%, which proved that the assimilation results of Ensemble Kalman Filter (EnKF) were closer to the "real" data, and was better than the evapotranspiration simulated by DTVGM without any improvement. Keyword Evapotranspiration assimilation Ensemble Kalman Filter Distributed hydrological model Two-Layer Remote Sensing Model

  9. Establishing seasonal chronicles of actual evapotranspiration under sloping conditions

    NASA Astrophysics Data System (ADS)

    Zitouna Chebbi, R.; Prévot, L.; Jacob, F.; Voltz, M.

    2012-04-01

    Estimation of daily and seasonal actual evapotranspiration (ETa) is strongly needed for hydrological and agricultural purposes. Although the eddy covariance method is well suited for such estimation of land surface fluxes, this method suffers from limitations when establishing long time series. Missing data are often encountered, resulting from bad meteorological conditions, rejection by quality control tests, power failures… Numerous gap fill techniques have been proposed in the literature but there applicability in sloping conditions is not well known. In order to estimate ETa over long periods (agricultural cycle) on crops cultivated in sloping areas, a pluri-annual experiment was conducted in the Kamech catchment, located in North-eastern Tunisia. This Mediterranean site is characterized by a large heterogeneity in topography, soils and crops. Land surface fluxes were measured using eddy covariance systems. Measurements were collected on the two opposite sides of the Kamech V-shaped catchment, within small fields having slopes steeper than 5%. During three different years, four crops were studied: durum wheat, oat, fava bean and pasture. The topography of the catchment and the wind regime induced upslope and downslope flows over the study fields. In this study, we showed that gap filling of the turbulent fluxes (sensible and latent heat) can be obtained through linear regressions against net radiation. To account for the effect of the topography, linear regressions were calibrated by distinguishing upslope and downslope flows. This significantly improved the quality of the reconstructed data over 30 minute intervals. This gap filling technique also improved the energy balance closure at the daily time scale. As a result, seasonal chronicles of daily ETa throughout the growth cycle of the study crops in the Kamech watershed were established, thus providing useful information about the water use of annual crops in a semi-arid rainfed and hilly area.

  10. Divergence of actual and reference evapotranspiration observations for irrigated sugarcane with windy tropical conditions

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Standardized reference evapotranspiration (ET) and ecosystem-specific vegetation coefficients are frequently used to estimate actual ET. However, equations for calculating reference ET have not been well validated in more humid environments. We measured ET (ETEC) using Eddy Covariance (EC) towers a...

  11. A drought index based on actual evapotranspiration from the Bouchet hypothesis

    NASA Astrophysics Data System (ADS)

    Kim, Daeha; Rhee, Jinyoung

    2016-10-01

    Global drought assessment has mainly depended on precipitation-based drought indices that may also take into account potential evapotranspiration (ETp). In this study, we combined the actual evapotranspiration (ETa) estimated from the Bouchet hypothesis and the structure of the Standardized Precipitation-Evapotranspiration Index to develop a fully ET-based drought index, the Standardized Evapotranspiration Deficit Index (SEDI). We found that SEDI, without using precipitation data, produces results that are consistent with the Palmer Drought Severity Index (PDSI) and the Standardized Precipitation Index (SPI) for drought identification in the South-Central United States. We also found a competitive performance of SEDI through comparisons between the Vegetation Health Index with SEDI, PDSI, and SPI. We suggest the high applicability of the SEDI based on the Bouchet hypothesis as an independent drought index for regions with strong land-atmosphere coupling or as an alternative drought index to fully precipitation-dependent indices for assessing agricultural droughts.

  12. Actual evapotranspiration estimation in a Mediterranean mountain region by means of Landsat-5 TM and TERRA/AQUA MODIS imagery and Sap Flow measurements in Pinus sylvestris forest stands.

    NASA Astrophysics Data System (ADS)

    Cristóbal, J.; Poyatos, R.; Ninyerola, M.; Pons, X.; Llorens, P.

    2009-04-01

    Evapotranspiration monitoring has important implications on global and regional climate modelling, as well as in the knowledge of the hydrological cycle and in the assessment of environmental stress that affects forest and agricultural ecosystems. An increase of evapotranspiration while precipitation remains constant, or is reduced, could decrease water availability for natural and agricultural systems and human needs. Consequently, water balance methods, as the evapotranspiration modelling, have been widely used to estimate crop and forest water needs, as well as the global change effects. Nowadays, radiometric measurements provided by Remote Sensing and GIS analysis are the technologies used to compute evapotranspiration at regional scales in a feasible way. Currently, the 38% of Catalonia (NE of the Iberian Peninsula) is covered by forests, and one of the most important forest species is Scots Pine (Pinus sylvestris) which represents the 18.4% of the area occupied by forests. The aim of this work is to model actual evapotranspiration in Pinus sylvestris forest stands, in a Mediterranean mountain region, using remote sensing data, and compare it with stand-scale sap flow measurements measured in the Vallcebre research area (42° 12' N, 1° 49' E), in the Eastern Pyrenees. To perform this study a set of 30 cloud-free TERRA-MODIS images and 10 Landsat-5 TM images of path 198 and rows 31 and 32 from June 2003 to January 2005 have been selected to perform evapotranspiration modelling in Pinus sylvestris forest stands. TERRA/AQUA MODIS images have been downloaded by means of the EOS Gateway. We have selected two different types of products which contain the remote sensing data we have used to model daily evapotranspiration, daily LST product and daily calibrated reflectances product. Landsat-5 TM images have been corrected by means of conventional techniques based on first order polynomials taking into account the effect of land surface relief using a Digital

  13. Actual evapotranspiration estimation in a Mediterranean mountain region by means of Landsat-5 TM and TERRA/AQUA MODIS imagery and Sap Flow measurements in Pinus sylvestris forest stands.

    NASA Astrophysics Data System (ADS)

    Cristóbal, J.; Poyatos, R.; Ninyerola, M.; Pons, X.; Llorens, P.

    2009-04-01

    Evapotranspiration monitoring has important implications on global and regional climate modelling, as well as in the knowledge of the hydrological cycle and in the assessment of environmental stress that affects forest and agricultural ecosystems. An increase of evapotranspiration while precipitation remains constant, or is reduced, could decrease water availability for natural and agricultural systems and human needs. Consequently, water balance methods, as the evapotranspiration modelling, have been widely used to estimate crop and forest water needs, as well as the global change effects. Nowadays, radiometric measurements provided by Remote Sensing and GIS analysis are the technologies used to compute evapotranspiration at regional scales in a feasible way. Currently, the 38% of Catalonia (NE of the Iberian Peninsula) is covered by forests, and one of the most important forest species is Scots Pine (Pinus sylvestris) which represents the 18.4% of the area occupied by forests. The aim of this work is to model actual evapotranspiration in Pinus sylvestris forest stands, in a Mediterranean mountain region, using remote sensing data, and compare it with stand-scale sap flow measurements measured in the Vallcebre research area (42° 12' N, 1° 49' E), in the Eastern Pyrenees. To perform this study a set of 30 cloud-free TERRA-MODIS images and 10 Landsat-5 TM images of path 198 and rows 31 and 32 from June 2003 to January 2005 have been selected to perform evapotranspiration modelling in Pinus sylvestris forest stands. TERRA/AQUA MODIS images have been downloaded by means of the EOS Gateway. We have selected two different types of products which contain the remote sensing data we have used to model daily evapotranspiration, daily LST product and daily calibrated reflectances product. Landsat-5 TM images have been corrected by means of conventional techniques based on first order polynomials taking into account the effect of land surface relief using a Digital

  14. Microclimate and actual evapotranspiration in a humid coastal-plain environment

    NASA Astrophysics Data System (ADS)

    Dennehy, Kevin F.; McMahon, Peter B.

    1987-09-01

    Continuous hourly measurements of twelve meteorologic variables recorded during 1983 and 1984 were used to examine the microclimate and actual evapotranspiration at a low-level radioactive-waste burial site near Barnwell, South Carolina. The study area is in the Atlantic Coastal Plain of southwestern South Carolina. Monthly, daily, and hourly trends in net radiation, incoming and reflected short-wave radiation, incoming and emitted long-wave radiation, soil-heat flux, dry- and wet-bulb temperatures, soil temperatures, wind direction and speed, and precipitation were used to characterize the microclimate. Average daily air temperatures ranged from -9 to 32° Celsius during the period of study. Net radiation varied from about -27 to 251 watts m -2 and was dominated by incoming short-wave radiation throughout the year. The peak net radiation during a summer day generally occurred 2-3h before the peak vapor pressure deficit. In the winter, these peaks occurred at about the same time of day. Monthly precipitation varied from 15 to 241 mm. The Bowen ratio method was used to estimate hourly evapotranspiration, which was summed to also give daily and monthly evapotranspiration. Actual evapotranspiration varied from 0.0 to 0.7 mm h -1, 0.8-5 mm d -1, and 20-140 mm month -1 during 1983 and 1984. The maximum rate of evapotranspiration generally occurred at the same time of day as maximum net radiation, suggesting net radiation was the main driving force for evapotranspiration. Precipitation exceeded evapotranspiration during 14 months of the 2yr study period. Late fall, winter, and early spring contained the majority of these months. The maximum excess precipitation was 115 mm in February 1983.

  15. Microclimate and actual evapotranspiration in a humid coastal-plain environment

    USGS Publications Warehouse

    Dennehy, K.F.; McMahon, P.B.

    1987-01-01

    Continuous hourly measurements of twelve meteorologic variables recorded during 1983 and 1984 were used to examine the microclimate and actual evapotranspiration at a low-level radioactive-waste burial site near Barnwell, South Carolina. The study area is in the Atlantic Coastal Plain of southwestern South Carolina. Monthly, daily, and hourly trends in net radiation, incoming and reflected short-wave radiation, incoming and emitted long-wave radiation, soil-heat flux, dry- and wet-bulb temperatures, soil temperatures, wind direction and speed, and precipitation were used to characterize the microclimate. Average daily air temperatures ranged from -9 to 32?? Celsius during the period of study. Net radiation varied from about -27 to 251 watts m-2 and was dominated by incoming short-wave radiation throughout the year. The peak net radiation during a summer day generally occurred 2-3h before the peak vapor pressure deficit. In the winter, these peaks occurred at about the same time of day. Monthly precipitation varied from 15 to 241 mm. The Bowen ratio method was used to estimate hourly evapotranspiration, which was summed to also give daily and monthly evapotranspiration. Actual evapotranspiration varied from 0.0 to 0.7 mm h-1, 0.8-5 mm d-1, and 20-140 mm month-1 during 1983 and 1984. The maximum rate of evapotranspiration generally occurred at the same time of day as maximum net radiation, suggesting net radiation was the main driving force for evapotranspiration. Precipitation exceeded evapotranspiration during 14 months of the 2yr study period. Late fall, winter, and early spring contained the majority of these months. The maximum excess precipitation was 115 mm in February 1983. ?? 1987.

  16. Evapotranspiration estimation in heterogeneous urban vegetation

    NASA Astrophysics Data System (ADS)

    Nagler, P. L.; Nouri, H.; Beecham, S.; Anderson, S.; Sutton, P.; Chavoshi, S.

    2015-12-01

    Finding a valid approach to measure the water requirements of mixed urban vegetation is a challenge. Evapotranspiration (ET) is the main component of a plant's water requirement. A better understanding of the ET of urban vegetation is essential for sustainable urbanisation. Increased implementation of green infrastructure will be informed by this work. Despite promising technologies and sophisticated facilities, ET estimation of urban vegetation remains insufficiently characterized. We reviewed the common field, laboratory and modelling techniques for ET estimation, mostly agriculture and forestry applications. We opted for 3 approaches of ET estimation: 1) an observational-based method using adjustment factors applied to reference ET, 2) a field-based method of Soil Water Balance (SWB) and 3) a Remote Sensing (RS)-based method. These approaches were applied to an experimental site to evaluate the most suitable ET estimation approach for an urban parkland. To determine in-situ ET, 2 lysimeters and 4 Neutron Moisture Meter probes were installed. Based on SWB principles, all input water (irrigation, precipitation and upward groundwater movements) and output water (ET, drainage, soil moisture and runoff) were measured monthly for 14 months. The observation based approach and the ground-based approach (SWB) were compared. Our predictions were compared to the actual irrigation rates (data provided by the City Council). Results suggest the observational-based method is the most appropriate urban ET estimation. We examined the capability of RS to estimate ET for urban vegetation. Image processing of 5 WorldView2 satellite images enabled modelling of the relationship between urban vegetation and vegetation indices derived from high resolution images. Our results indicate that an ETobservational-based -NDVI modelling approach is a reliable method of ET estimation for mixed urban vegetation. It also has the advantage of not depending on extensive field data collection.

  17. Feedback Loop of Data Infilling Using Model Result of Actual Evapotranspiration from Satellites and Hydrological Model

    NASA Astrophysics Data System (ADS)

    Murdi Hartanto, Isnaeni; Alexandridis, Thomas K.; van Andel, Schalk Jan; Solomatine, Dimitri

    2014-05-01

    Using satellite data in a hydrological model has long been occurring in modelling of hydrological processes, as a source of low cost regular data. The methods range from using satellite products as direct input, model validation, and data assimilation. However, the satellite data frequently face the missing value problem, whether due to the cloud cover or the limited temporal coverage. The problem could seriously affect its usefulness in hydrological model, especially if the model uses it as direct input, so data infilling becomes one of the important parts in the whole modelling exercise. In this research, actual evapotranspiration product from satellite is directly used as input into a spatially distributed hydrological model, and validated by comparing the catchment's end discharge with measured data. The instantaneous actual evapotranspiration is estimated from MODIS satellite images using a variation of the energy balance model for land (SEBAL). The eight-day cumulative actual evapotranspiration is then obtained by a temporal integration that uses the reference evapotranspiration calculated from meteorological data [1]. However, the above method cannot fill in a cell if the cell is constantly having no-data value during the eight-day periods. The hydrological model requires full set of data without no-data cells, hence, the no-data cells in the satellite's evapotranspiration map need to be filled in. In order to fills the no-data cells, an output of hydrological model is used. The hydrological model is firstly run with reference evapotranspiration as input to calculate discharge and actual evapotranspiration. The no-data cells in the eight-day cumulative map from the satellite are then filled in with the output of the first run of hydrological model. The final data is then used as input in a hydrological model to calculate discharge, thus creating a loop. The method is applied in the case study of Rijnland, the Netherlands where in the winter, cloud cover is

  18. Estimating seasonal evapotranspiration from temporal satellite images

    USGS Publications Warehouse

    Singh, Ramesh K.; Liu, Shu-Guang; Tieszen, Larry L.; Suyker, Andrew E.; Verma, Shashi B.

    2012-01-01

    Estimating seasonal evapotranspiration (ET) has many applications in water resources planning and management, including hydrological and ecological modeling. Availability of satellite remote sensing images is limited due to repeat cycle of satellite or cloud cover. This study was conducted to determine the suitability of different methods namely cubic spline, fixed, and linear for estimating seasonal ET from temporal remotely sensed images. Mapping Evapotranspiration at high Resolution with Internalized Calibration (METRIC) model in conjunction with the wet METRIC (wMETRIC), a modified version of the METRIC model, was used to estimate ET on the days of satellite overpass using eight Landsat images during the 2001 crop growing season in Midwest USA. The model-estimated daily ET was in good agreement (R2 = 0.91) with the eddy covariance tower-measured daily ET. The standard error of daily ET was 0.6 mm (20%) at three validation sites in Nebraska, USA. There was no statistically significant difference (P > 0.05) among the cubic spline, fixed, and linear methods for computing seasonal (July–December) ET from temporal ET estimates. Overall, the cubic spline resulted in the lowest standard error of 6 mm (1.67%) for seasonal ET. However, further testing of this method for multiple years is necessary to determine its suitability.

  19. SEBAL-based Daily Actual Evapotranspiration Forecasting using Wavelets Decomposition Analysis and Multivariate Relevance Vector Machines

    NASA Astrophysics Data System (ADS)

    Torres, A. F.

    2011-12-01

    Agricultural lands are sources of food and energy for population around the globe. These lands are vulnerable to the impacts of climate change including variations in rainfall regimes, weather patterns, and decreased availability of water for irrigation. In addition, it is not unusual that irrigated agriculture is forced to divert less water in order to make it available for other uses, e.g. human consumption and others. As part of implementation of better policies for water control and management, irrigation companies and water user associations have been implemented water conveyance and distribution monitoring systems along with soil moisture sensors networks in the last decades. These systems allow them to manage and distribute water among the users based on their requirements and water availability while collecting information about actual soil moisture conditions in representative crop fields. In spite of this, requested water deliveries by farmers/water users is based typically on total water share, traditions and past experience on irrigation, which in most cases do not correspond to the actual crop evapotranspiration, already affected by climate change. Therefore it is necessary to provide actual information about the crop water requirements to water users/managers, so they can better quantify the required vs. available water for the irrigation events along the irrigation season. To estimate the actual evapotranspiration in a spatial extent the Sensitivity Analysis of the Surface Energy Balance Algorithm for Land (SEBAL) algorithm has demonstrated its effectiveness using satellite or airborne data. Nonetheless the estimation is restricted to the day when the geospatial information was obtained. Without information of precise future daily water crop demand there is a continuous challenge for the implementation of better water distribution and management policies in the irrigation system. The purpose of this study is to investigate the plausibility of using

  20. Assessing daily actual evapotranspiration through energy balance: an experiment to evaluate the selfpreservation hypothesis with acquisition time

    NASA Astrophysics Data System (ADS)

    Maltese, A.; Capodici, F.; Ciraolo, G.; La Loggia, G.; Rallo, G.

    2013-10-01

    An operational use of the actual evapotranspiration estimates requires the integration from instantaneous to daily values. This can commonly be achieved under the hypothesis of daytime self-preservation of the evaporative fraction. In this study, it has been evaluated the effect of this assumption on the assessment of daily evapotranspiration from proximity sensing images acquired at hourly intervals over a homogeneous olive groove. Results have been validated by comparison with observations made by a micrometeorological (EC-flux tower) and an eco-physiological (sap flux) sensor. SEBAL model has been applied to thermal and multispectral images acquired during a clear day on August 2009 trough a FLIR A320G thermal camera and a Tetracam MCA II multispectral camera, installed on a tethered helium balloon. Thermal and multispectral images were characterized by very high spatial resolution. This experiment aims to analyze two effects: 1) the consistency of the self-preservation hypothesis for daily estimates of the actual evapotranspiration from hourly assessments at different times of the day; 2) the effects of the spatial resolution on the performances of the energy balance model. To evaluate the effects of the spatial resolution, semi-hourly observations made by a flux tower and sap-flow measures were compared to the evapotranspiration estimates performed using downscaled images at resolutions close to canopy sizes (2, 5 and 10 m). Results show that the best estimates are obtained with a spatial resolution comparable to the average size of the canopy with images taken approximately at 10 UTC.

  1. Using lysimeters to test the Penman Monteith actual evapotranspiration.

    NASA Astrophysics Data System (ADS)

    Ben Asher, Jiftah; Volinski, Roman; Zilberman, Arkadi; Bar Yosef, Beni; Silber, Avner

    2015-04-01

    Differences in actual transpiration (ETa) of banana plants were quantified in a lysimeter experiment. ETA was computed using instantaneous data from two weighing lysimeters and compared to PM (Penman-Monteith) model for ETa. Two critical problems were faced in this test. A) Estimating canopy and aerodynamic resistances ("rc" and "ra" respectively ) and B) converting the lysimeter changes in water volume ( LYv cm3 ) to ETa length units ( cm ). The two unknowns " rc" and "ra" were obtained from continuous measurements of the differences between canopy and air temperature (Tc - Ta). This difference was established by means of the infrared thermometry which was followed by numerical and analytical calculation of ETa using the modification suggested by R. Jackson to the PM model. The conversion of lysimeter volumetric units (LYv) to ETa length units was derived from the slope of cumulative LYv/ETa. This relationship was significantly linear (r2=0.97and 0.98.). Its slope was interpreted as "evaporating leaf area" which accounted for 1.8E4 cm2 in lysimeter 1 and 2.3E4 cm2.in lysimeter 2 . The comparison between LYv and PM model was acceptable even under very low ETa. The average of two lysimeters was 1.1mm/day (1.4 mm/day , LYv 1 and 0.8 LYv 2) while ETa calculated on the basis of PM model was 1.2 mm/day. It was concluded that although lysimeters are most accurate systems to measure ETa one of its disadvantages ( beside the high cost) is the volumetric output that in many cases should be supported by a one dimensional energy balance system. The PM model was found to be a reliable complementary tool to convert lysimeters volumetric output into conventional length units of ETa.

  2. Estimating evapotranspiration in natural and constructed wetlands

    USGS Publications Warehouse

    Lott, R. Brandon; Hunt, Randall J.

    2001-01-01

    Difficulties in accurately calculating evapotranspiration (ET) in wetlands can lead to inaccurate water balances—information important for many compensatory mitigation projects. Simple meteorological methods or off-site ET data often are used to estimate ET, but these approaches do not include potentially important site-specific factors such as plant community, root-zone water levels, and soil properties. The objective of this study was to compare a commonly used meterological estimate of potential evapotranspiration (PET) with direct measurements of ET (lysimeters and water-table fluctuations) and small-scale root-zone geochemistry in a natural and constructed wetland system. Unlike what has been commonly noted, the results of the study demonstrated that the commonly used Penman combination method of estimating PET underestimated the ET that was measured directly in the natural wetland over most of the growing season. This result is likely due to surface heterogeneity and related roughness efffects not included in the simple PET estimate. The meterological method more closely approximated season-long measured ET rates in the constructed wetland but may overestimate the ET rate late in the growing season. ET rates also were temporally variable in wetlands over a range of time scales because they can be influenced by the relation of the water table to the root zone and the timing of plant senescence. Small-scale geochemical sampling of the shallow root zone was able to provide an independent evaluation of ET rates, supporting the identification of higher ET rates in the natural wetlands and differences in temporal ET rates due to the timing of senescence. These discrepancies illustrate potential problems with extrapolating off-site estimates of ET or single measurements of ET from a site over space or time.

  3. Geospatial approach for estimating land surface evapotranspiration

    NASA Astrophysics Data System (ADS)

    Singh, Ramesh K.

    Reliably and accurately quantifying evapotranspiration (ET) in a spatial and temporal domain is important in water management at the local, regional, and global scales. With advances in image processing and hardware computational ability, energy balance models which utilize remote sensing images are being increasingly utilized for quantifying ET and used as inputs in hydrologic modeling. The objectives of this research were to evaluate and improve some of the energy balance models for estimating land surface ET, and develop a framework for estimating seasonal ET from temporal satellite images. Surface Energy Balance Algorithm for Land (SEBAL) model was used to estimate energy fluxes for south-central Nebraska using Landsat images. Results were compared with Bowen Ratio Energy Balance System (BREBS) field measurements. SEBAL estimated ET images were also used for computing crop coefficients (K c) for maize, soybean, sorghum, and alfalfa under irrigated and dryland conditions. Performances of four remote sensing based models for estimating soil heat flux (G) were analyzed. A new model was developed for remotely estimating G. The Mapping Evapotranspiration at high Resolution with Internalized Calibration (METRIC) model was also used for estimating energy fluxes using Landsat images. The METRIC model was modified by incorporating the Priestley-Taylor (PT) approach. The SEBAL model estimated net radiation (Rn) with a root mean square error (RMSE) of 65 W m-2 (r2 = 0.76). Calibrating G locally reduced RMSE from 80 W m-2 to 20 W m-2. The SEBAL model yielded sensible heat flux (H) with RMSE of 108 W m -2 (r2=0.23), and ET with an RMSE of 1.04 mm day -1(r2 = 0.73). Validation of Kc regression for irrigated maize resulted in RMSE of 0.21 (r2=0.74). The METRIC model estimated Rn, G, and H with RMSE values of 45 W m -2 (r2=0.85), 19 W m-2 (r2=0.85), and 113 W m-2 (r2=0.50), respectively. The modified METRIC model reduced the RMSE of H from 113 W m-2 to 91 W m -2 and that for

  4. Estimating Evapotranspiration with Land Data Assimilation Systems

    NASA Technical Reports Server (NTRS)

    Peters-Lidard, C. D.; Kumar, S. V.; Mocko, D. M.; Tian, Y.

    2011-01-01

    Advancements in both land surface models (LSM) and land surface data assimilation, especially over the last decade, have substantially advanced the ability of land data assimilation systems (LDAS) to estimate evapotranspiration (ET). This article provides a historical perspective on international LSM intercomparison efforts and the development of LDAS systems, both of which have improved LSM ET skill. In addition, an assessment of ET estimates for current LDAS systems is provided along with current research that demonstrates improvement in LSM ET estimates due to assimilating satellite-based soil moisture products. Using the Ensemble Kalman Filter in the Land Information System, we assimilate both NASA and Land Parameter Retrieval Model (LPRM) soil moisture products into the Noah LSM Version 3.2 with the North American LDAS phase 2 (NLDAS-2) forcing to mimic the NLDAS-2 configuration. Through comparisons with two global reference ET products, one based on interpolated flux tower data and one from a new satellite ET algorithm, over the NLDAS2 domain, we demonstrate improvement in ET estimates only when assimilating the LPRM soil moisture product.

  5. Actual evapotranspiration and precipitation measured by lysimeters: a comparison with eddy covariance and tipping bucket

    NASA Astrophysics Data System (ADS)

    Gebler, S.; Hendricks Franssen, H.-J.; Pütz, T.; Post, H.; Schmidt, M.; Vereecken, H.

    2015-05-01

    This study compares actual evapotranspiration (ETa) measurements by a set of six weighable lysimeters, ETa estimates obtained with the eddy covariance (EC) method, and evapotranspiration calculated with the full-form Penman-Monteith equation (ETPM) for the Rollesbroich site in the Eifel (western Germany). The comparison of ETa measured by EC (including correction of the energy balance deficit) and by lysimeters is rarely reported in the literature and allows more insight into the performance of both methods. An evaluation of ETa for the two methods for the year 2012 shows a good agreement with a total difference of 3.8% (19 mm) between the ETa estimates. The highest agreement and smallest relative differences (< 8%) on a monthly basis between both methods are found in summer. ETa was close to ETPM, indicating that ET was energy limited and not limited by water availability. ETa differences between lysimeter and EC were mainly related to differences in grass height caused by harvest and the EC footprint. The lysimeter data were also used to estimate precipitation amounts in combination with a filter algorithm for the high-precision lysimeters recently introduced by Peters et al. (2014). The estimated precipitation amounts from the lysimeter data differ significantly from precipitation amounts recorded with a standard rain gauge at the Rollesbroich test site. For the complete year 2012 the lysimeter records show a 16 % higher precipitation amount than the tipping bucket. After a correction of the tipping bucket measurements by the method of Richter (1995) this amount was reduced to 3%. With the help of an on-site camera the precipitation measurements of the lysimeters were analyzed in more detail. It was found that the lysimeters record more precipitation than the tipping bucket, in part related to the detection of rime and dew, which contribute 17% to the yearly difference between both methods. In addition, fog and drizzle explain an additional 5.5% of the total

  6. Actual evapotranspiration and precipitation measured by lysimeters: a comparison with eddy covariance and tipping bucket

    NASA Astrophysics Data System (ADS)

    Gebler, S.; Hendricks Franssen, H.-J.; Pütz, T.; Post, H.; Schmidt, M.; Vereecken, H.

    2014-12-01

    This study compares actual evapotranspiration (ETa) measurements by a set of six weighable lysimeters, ETa estimates obtained with the eddy covariance (EC) method, and potential crop evapotranspiration according to FAO (ETc-FAO) for the Rollesbroich site in the Eifel (Western Germany). The comparison of ETa measured by EC (including correction of the energy balance deficit) and by lysimeters is rarely reported in literature and allows more insight into the performance of both methods. An evaluation of ETa for the two methods for the year 2012 shows a good agreement with a total difference of 3.8% (19 mm) between the ETa estimates. The highest agreement and smallest relative differences (<8%) on monthly basis between both methods are found in summer. ETa was close to ETc-FAO, indicating that ET was energy limited and not limited by water availability. ETa differences between lysimeter, ETc-FAO, and EC were mainly related to differences in grass height caused by harvesting management and the EC footprint. The lysimeter data were also used to estimate precipitation amounts in combination with a filter algorithm for high precision lysimeters recently introduced by Peters et al. (2014). The estimated precipitation amounts from the lysimeter data show significant differences compared to the precipitation amounts recorded with a standard rain gauge at the Rollesbroich test site. For the complete year 2012 the lysimeter records show a 16% higher precipitation amount than the tipping bucket. With the help of an on-site camera the precipitation measurements of the lysimeters were analyzed in more detail. It was found that the lysimeters record more precipitation than the tipping bucket in part related to the detection of rime and dew, which contributes 17% to the yearly difference between both methods. In addition, fog and drizzle explain an additional 5.5% of the total difference. Larger differences are also recorded for snow and sleet situations. During snowfall, the

  7. Basin scale estimates of evapotranspiration using GRACE and other observations

    NASA Astrophysics Data System (ADS)

    Rodell, M.; Famiglietti, J. S.; Chen, J.; Seneviratne, S. I.; Viterbo, P.; Holl, S.; Wilson, C. R.

    2004-10-01

    Evapotranspiration is integral to studies of the Earth system, yet it is difficult to measure on regional scales. One estimation technique is a terrestrial water budget, i.e., total precipitation minus the sum of evapotranspiration and net runoff equals the change in water storage. Gravity Recovery and Climate Experiment (GRACE) satellite gravity observations are now enabling closure of this equation by providing the terrestrial water storage change. Equations are presented here for estimating evapotranspiration using observation based information, taking into account the unique nature of GRACE observations. GRACE water storage changes are first substantiated by comparing with results from a land surface model and a combined atmospheric-terrestrial water budget approach. Evapotranspiration is then estimated for 14 time periods over the Mississippi River basin and compared with output from three modeling systems. The GRACE estimates generally lay in the middle of the models and may provide skill in evaluating modeled evapotranspiration.

  8. Influence of Micrometeorological factors for Actual Evapotranspiration in the Coastal Urban Area

    NASA Astrophysics Data System (ADS)

    Kim, S. J.; Kang, D. H.; Yu, H.; Kwon, B. H.

    2015-12-01

    Actual evapotranspiration(AET) in the coastal urban area was estimated and correlations between AET and meteorological factors were analyzed. The study was conducted in Suyeong-Gu lay at the east longitude 129°05'40″ ~ 129°08'08″ and north latitude 35°07'59 ″~35 °11'01″ from December 2001 to November 2011. Four equations on land use were used to estimate AET. Land use types were classified by impermeable, forest, water and grass. AET was estimated by weighting of land use. AET increased from January to the middle of July and decreased from the middle of July to December. Correlation analysis was conducted between AET and micrometeorological factors. Correlation coefficient of AET and dew point temperature was 0.63 and temperature, air pressure, duration of sunshine, net radiation were above 0.5. Regression analysis was conducted between AET and micrometeorological factors. AET variation is divided by existence of precipitation. The regression functions of AET as air temperature were increased lineary at precipitation and exponential at non-precipitation. The regression functions of AET as dew point temperature were increased lineary at precipitation and exponential at non-precipitation. The regression function of AET as net radiation was increased exponential at precipitation and lineary at non-precipitation. The regression function of AET as air pressure was decreased lineary at precipitation and exponential at non-precipitation. The regression function of AET as precipitation was increased logarithmically.

  9. Technical Note: Development of an automated lysimeter for the calculation of peat soil actual evapotranspiration

    NASA Astrophysics Data System (ADS)

    Proulx-McInnis, S.; St-Hilaire, A.; Rousseau, A. N.; Jutras, S.; Carrer, G.; Levrel, G.

    2011-05-01

    A limited number of publications in the literature deal with the measurement of actual evapotranspiration (AET) from a peat soil. AET is an important parameter in the description of water pathways of an ecosystem. In peatlands, where the water table is near the surface and the vegetation is composed of nonvascular plants without stomatal resistance, the AET measurement represents a challenge. This paper discusses the development of an automated lysimeter installed between 12 and 27 July 2010, at a 11-ha bog site, Pont-Rouge (42 km west of Quebec City, Canada). This system was made of an isolated block of peat, maintained at the same water level as the surrounding water table by a system of submersible pressure transmitters and pumps. The change in water level in millimetres in the isolated block of peat was used to calculate the water lost through evapotranspiration (ET) while accounting the precipitation. The rates of AET were calculated for each day of the study period. Temperature fluctuated between 17.2 and 23.3 °C and total rainfall was 43.76 mm. AET rates from 0.6 to 6.9 mm day-1 were recorded, with a ΣAET/ΣP ratio of 1.38. The estimated potential ET (PET) resulting from Thornthwaite's semi-empirical formula suggested values between 2.8 and 3.9 mm day-1. The average AET/PET ratio was 1.13. According to the literature, the results obtained are plausible. This system, relatively inexpensive and simple to install, may eventually be used to calculate AET on peaty soils in the years to come.

  10. Estimation of evapotranspiration using satellite TOA radiances

    NASA Astrophysics Data System (ADS)

    Peng, J.; Loew, A.

    2013-12-01

    ET (Evapotranspiration) is an important variable in the water and energy balance on the Earth's surface. Accurate estimation of the temporal and spatial pattern of ET is of great significance for hydrological, agricultural and meteorological studies. A simplified single-source energy balance parameterization scheme, known as the LST/NDVI (Land Surface Temperature/Normalized Difference Vegetation Index) feature space method, has been applied successfully to estimate clear sky ET in many studies. Based on the LST/NDVI feature space method, a new method is proposed in this study to estimate ET directly using the TOA (Top of Atmosphere) radiances without performing atmospheric correction and associated complex processes. Firstly, the feasibility and uncertainties in estimating NDTI (Normalized Difference Temperature Index, a key parameter in EF (evaporative fraction) estimation) from TOA radiances are investigated. Through a physical understanding of the Planck radiation law and radiative transfer equation, together with a detailed sensitivity analysis of NDTI on surface and atmosphere variability, it is found that the NDTI can be estimated from TOA radiances with an accuracy of 90% if the spatial variabilities of atmospheric parameters (water vapor, effective atmospheric temperature) and surface emissivity are below 10%, 4 K, and 0.05, respectively. Then the applicability and robustness of the MODIS TOA radiances based EF estimation scheme are investigated using FLUXNET (a global network of eddy covariance stations) observations. From direct comparison with measured EF at different FLUXNET sites, the estimated EF from TOA radiances perform mostly well across a wide variety of climate and biome types. The accuracy level is also comparable with published results in the literature. Furthermore, the FLUXNET measurements are used to examine the assumption of EF self preservation, and the conditions under which it can hold. It is found that the instantaneous EF can

  11. Evaluation of Pan Coefficients for Estimating Reference Evapotranspiration in Southern Taiwan

    NASA Astrophysics Data System (ADS)

    Yeh, H.

    2006-12-01

    Evapotranspiration is an important process of water transfer in the hydrosphere and atmosphere, which plays an active role in the hydrological cycle. Evaporation pan (Epan) data are often used to estimate reference evapotranspiration (ETref) for use in water resource planning. Generally, ETref is estimated as the product of the Epan data and a pan coefficient (Kpan). However, reliable estimation of ETref using Epan depends on the accurate determination of pan coefficients Kpan. Many different methods for estimating ETref have been developed, among which the Penman-Monteith method is demonstrated to be especially excellent by the Food and Agriculture Organization (FAO). In this study, the Penman-Monteith reference evapotranspiration, pan evaporation, and pan coefficient are calculated, compared and regionally mapped at nine meteorological stations during 1990-2004 in Southern Taiwan. The results show the reference evapotranspiration and pan evaporation have similar regional distribution patterns in the southern Taiwan both with the highest values being in the lower region and the lowest values being in the upper region. In addition, the pan coefficient, Kpan, varies both regionally and seasonally. Smallest Kpan values are found in the upper reach of the southern Taiwan, meaning that the relative difference between the reference evapotranspiration and pan evaporation is the biggest in the region, the largest Kpan values are obtained in the western area of southern Taiwan. This distribution pattern provides valuable information for regional hydrological studies since it is one of the most important factors determining regional actual evapotranspiration.

  12. A comparison of operational remote sensing-based models for estimating crop evapotranspiration

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The integration of remotely sensed data into models of actual evapotranspiration has allowed for the estimation of water consumption across agricultural regions. Two modeling approaches have been successfully applied. The first approach computes a surface energy balance using the radiometric surface...

  13. Progress in operational estimation of regional evapotranspiration using satellite imagery

    NASA Astrophysics Data System (ADS)

    Tasumi, Masahiro

    This dissertation presents a developed remote sensing model named SEBAL-ID, which estimates evapotranspiration (ET) from satellite images. The operationally usable remote sensing model was developed for Idaho and western United States conditions by refining the SEBAL (Surface Energy Balance Algorithm for Land) algorithm developed by Bastiaanssen in 1995. The original algorithm has been successfully applied in the world especially in developing countries. In the SEBAL Algorithm, ET from land surfaces is estimated by solving the land surface energy balance for each pixel of a satellite image. The instantaneous (satellite image time) ET is estimated as a residual of the energy balance at the land surface, and the estimated instantaneous value is extrapolated to 24-hour and seasonal ET, which are the final products of SEBAL. The refinements in SEBAL-ID include the application to mountainous regions, an increase in the reliability of estimates by adopting an internal calibration procedure using public weather data, and modifying empirical equations. The proposed model was applied in southern Idaho, and agreed well with lysimeter measured ET data. This dissertation presents results of many analyses with SEBAL-ID, which are valuable not only to SEBAL-ID users but also to SEBAL users around the world. The analyses cover the following topics: surface albedo estimation, estimated LAI by satellite image analyses, effect of atmospheric correction in surface temperature estimation, effect of elevation on surface temperature, ground heat flux estimation method and accuracy, impact of surface roughness for momentum transport, the sensible heat estimation method, windspeed and surface temperature relation, use of a soil water balance model in SEBAL-ID and the behavior of the ETr fraction. The developed model, SEBAL-ID, has already been applied for actual water resources management in Idaho State by the state agency Idaho Department of Water Resources.

  14. Actual evapotranspiration modeling using the operational Simplified Surface Energy Balance (SSEBop) approach

    USGS Publications Warehouse

    Savoca, Mark E.; Senay, Gabriel B.; Maupin, Molly A.; Kenny, Joan F.; Perry, Charles A.

    2013-01-01

    Remote-sensing technology and surface-energy-balance methods can provide accurate and repeatable estimates of actual evapotranspiration (ETa) when used in combination with local weather datasets over irrigated lands. Estimates of ETa may be used to provide a consistent, accurate, and efficient approach for estimating regional water withdrawals for irrigation and associated consumptive use (CU), especially in arid cropland areas that require supplemental water due to insufficient natural supplies from rainfall, soil moisture, or groundwater. ETa in these areas is considered equivalent to CU, and represents the part of applied irrigation water that is evaporated and/or transpired, and is not available for immediate reuse. A recent U.S. Geological Survey study demonstrated the application of the remote-sensing-based Simplified Surface Energy Balance (SSEB) model to estimate 10-year average ETa at 1-kilometer resolution on national and regional scales, and compared those ETa values to the U.S. Geological Survey’s National Water-Use Information Program’s 1995 county estimates of CU. The operational version of the operational SSEB (SSEBop) method is now used to construct monthly, county-level ETa maps of the conterminous United States for the years 2000, 2005, and 2010. The performance of the SSEBop was evaluated using eddy covariance flux tower datasets compiled from 2005 datasets, and the results showed a strong linear relationship in different land cover types across diverse ecosystems in the conterminous United States (correlation coefficient [r] ranging from 0.75 to 0.95). For example, r for woody savannas (0.75), grassland (0.75), forest (0.82), cropland (0.84), shrub land (0.89), and urban (0.95). A comparison of the remote-sensing SSEBop method for estimating ETa and the Hamon temperature method for estimating potential ET (ETp) also was conducted, using regressions of all available county averages of ETa for 2005 and 2010, and yielded correlations of r = 0

  15. Divergence of actual and reference evapotranspiration observations for irrigated sugarcane with windy tropical conditions

    NASA Astrophysics Data System (ADS)

    Anderson, R. G.; Wang, D.; Tirado-Corbalá, R.; Zhang, H.; Ayars, J. E.

    2015-01-01

    Standardized reference evapotranspiration (ET) and ecosystem-specific vegetation coefficients are frequently used to estimate actual ET. However, equations for calculating reference ET have not been well validated in tropical environments. We measured ET (ETEC) using eddy covariance (EC) towers at two irrigated sugarcane fields on the leeward (dry) side of Maui, Hawaii, USA in contrasting climates. We calculated reference ET at the fields using the short (ET0) and tall (ETr) vegetation versions of the American Society for Civil Engineers (ASCE) equation. The ASCE equations were compared to the Priestley-Taylor ET (ETPT) and ETEC. Reference ET from the ASCE approaches exceeded ETEC during the mid-period (when vegetation coefficients suggest ETEC should exceed reference ET). At the windier tower site, cumulative ETr exceeded ETEC by 854 mm over the course of the mid-period (267 days). At the less windy site, mid-period ETr still exceeded ETEC, but the difference was smaller (443 mm). At both sites, ETPT approximated mid-period ETEC more closely than the ASCE equations ((ETPT-ETEC) < 170 mm). Analysis of applied water and precipitation, soil moisture, leaf stomatal resistance, and canopy cover suggest that the lower observed ETEC was not the result of water stress or reduced vegetation cover. Use of a custom-calibrated bulk canopy resistance improved the reference ET estimate and reduced seasonal ET discrepancy relative to ETPT and ETEC in the less windy field and had mixed performance in the windier field. These divergences suggest that modifications to reference ET equations may be warranted in some tropical regions.

  16. Improving Evapotranspiration Estimates Using Multi-Platform Remote Sensing

    NASA Astrophysics Data System (ADS)

    Knipper, Kyle; Hogue, Terri; Franz, Kristie; Scott, Russell

    2016-04-01

    Understanding the linkages between energy and water cycles through evapotranspiration (ET) is uniquely challenging given its dependence on a range of climatological parameters and surface/atmospheric heterogeneity. A number of methods have been developed to estimate ET either from primarily remote-sensing observations, in-situ measurements, or a combination of the two. However, the scale of many of these methods may be too large to provide needed information about the spatial and temporal variability of ET that can occur over regions with acute or chronic land cover change and precipitation driven fluxes. The current study aims to improve the spatial and temporal variability of ET utilizing only satellite-based observations by incorporating a potential evapotranspiration (PET) methodology with satellite-based down-scaled soil moisture estimates in southern Arizona, USA. Initially, soil moisture estimates from AMSR2 and SMOS are downscaled to 1km through a triangular relationship between MODIS land surface temperature (MYD11A1), vegetation indices (MOD13Q1/MYD13Q1), and brightness temperature. Downscaled soil moisture values are then used to scale PET to actual ET (AET) at a daily, 1km resolution. Derived AET estimates are compared to observed flux tower estimates, the North American Land Data Assimilation System (NLDAS) model output (i.e. Variable Infiltration Capacity (VIC) Macroscale Hydrologic Model, Mosiac Model, and Noah Model simulations), the Operational Simplified Surface Energy Balance Model (SSEBop), and a calibrated empirical ET model created specifically for the region. Preliminary results indicate a strong increase in correlation when incorporating the downscaling technique to original AMSR2 and SMOS soil moisture values, with the added benefit of being able to decipher small scale heterogeneity in soil moisture (riparian versus desert grassland). AET results show strong correlations with relatively low error and bias when compared to flux tower

  17. Estimating riparian and agricultural evapotranspiration by reference crop evapotranspiration and MODIS Enhanced Vegetation Index

    USGS Publications Warehouse

    Nagler, Pamela L.; Glenn, Edward P.; Nguyen, Uyen; Scott, Russell; Doody, Tania

    2013-01-01

    Dryland river basins frequently support both irrigated agriculture and riparian vegetation and remote sensing methods are needed to monitor water use by both crops and natural vegetation in irrigation districts. We developed an algorithm for estimating actual evapotranspiration (ETa) based on the Enhanced Vegetation Index (EVI) from the Moderate Resolution Imaging Spectrometer (MODIS) sensor on the EOS-1 Terra satellite and locally-derived measurements of reference crop ET (ETo). The algorithm was calibrated with five years of ETa data from three eddy covariance flux towers set in riparian plant associations on the upper San Pedro River, Arizona, supplemented with ETa data for alfalfa and cotton from the literature. The algorithm was based on an equation of the form ETa = ETo [a(1 − e−bEVI) − c], where the term (1 − e−bEVI) is derived from the Beer-Lambert Law to express light absorption by a canopy, with EVI replacing leaf area index as an estimate of the density of light-absorbing units. The resulting algorithm capably predicted ETa across riparian plants and crops (r2 = 0.73). It was then tested against water balance data for five irrigation districts and flux tower data for two riparian zones for which season-long or multi-year ETa data were available. Predictions were within 10% of measured results in each case, with a non-significant (P = 0.89) difference between mean measured and modeled ETa of 5.4% over all validation sites. Validation and calibration data sets were combined to present a final predictive equation for application across crops and riparian plant associations for monitoring individual irrigation districts or for conducting global water use assessments of mixed agricultural and riparian biomes.

  18. Drought impacts and resilience on crops via evapotranspiration estimations

    NASA Astrophysics Data System (ADS)

    Timmermans, Joris; Asadollahi Dolatabad, Saeid

    2015-04-01

    Currently, the global needs for food and water is at a critical level. It has been estimated that 12.5 % of the global population suffers from malnutrition and 768 million people still do not have access to clean drinking water. This need is increasing because of population growth but also by climate change. Changes in precipitation patterns will result either in flooding or droughts. Consequently availability, usability and affordability of water is becoming challenge and efficient use of water and water management is becoming more important, particularly during severe drought events. Drought monitoring for agricultural purposes is very hard. While meteorological drought can accurately be monitored using precipitation only, estimating agricultural drought is more difficult. This is because agricultural drought is dependent on the meteorological drought, the impacts on the vegetation, and the resilience of the crops. As such not only precipitation estimates are required but also evapotranspiration at plant/plot scale. Evapotranspiration (ET) describes the amount of water evaporated from soil and vegetation. As 65% of precipitation is lost by ET, drought severity is highly linked with this variable. In drought research, the precise quantification of ET and its spatio-temporal variability is therefore essential. In this view, remote sensing based models to estimate ET, such as SEBAL and SEBS, are of high value. However the resolution of current evapotranspiration products are not good enough for monitoring the impact of the droughts on the specific crops. This limitation originates because plot scales are in general smaller than the resolution of the available satellite ET products. As such remote sensing estimates of evapotranspiration are always a combination of different land surface types and cannot be used for plant health and drought resilience studies. The goal of this research is therefore to enable adequate resolutions of daily evapotranspiration estimates

  19. Estimation of Evapotranspiration of Almond orchards using Remote Sensing based SEBAL model in Central Valley, California

    NASA Astrophysics Data System (ADS)

    Roy, S.; Ustin, S.; Kefauver, S. C.

    2009-12-01

    Evapotranspiration is one of the main components of the hydrologic cycle and its impact to hydrology, agriculture,forestry and environmental studies is very crucial. SEBAL (Surface Energy Balance Algorithm for Land) is an image-processing model comprised of twenty-five computational sub-models that computes actual evapotranspiration (ETa) and other energy exchanges as a component of energy balance which is used to derive the surface radiation balance equation for the net surface radiation flux (Rn) on a pixel-by-pixel basis. For this study, SEBAL method is applied to Level 1B dataset of visible, near-infrared and thermal infrared radiation channels of MASTER instrument on-board NASA-DC 8 flight. This paper uses the SEBAL method to (1) investigate the spatial distribution property of land surface temperature (Ls), NDVI, and ETa over the San Joaquin valley. (2) Estimate actual evapotranspiration of almond class on pixel-by-pixel basis in the Central valley, California. (3) Comparison of actual Evapotranspiration obtained from SEBAL model with reference evapotranspiration (Eto) using Penman Monteiths method based on the procedures and available data from California Irrigation Management Information System (CIMIS) stations. The results of the regression between extracted land surface temperature, NDVI and, evapotranspiration show negative (-) correlation. On the other hand Ls possessed a slightly stronger negative correlation with the ETa than with NDVI for Almond class. The correlation coefficient of actual ETa estimates from remote sensing with Reference ETo from Penmann Monteith are 0.8571. ETa estimated for almond crop from SEBAL were found to be almost same with the CIMIS_Penman Monteith method with bias of 0.77 mm and mean percentage difference is 0.10%. These results indicate that combination of MASTER data with surface meteorological data could provide an efficient tool for the estimation of regional actual ET used for water resources and irrigation scheduling

  20. Estimation of Evapotranspiration as a function of Photosynthetic Active Radiation

    NASA Astrophysics Data System (ADS)

    Wesley, E.; Migliaccio, K.; Judge, J.

    2012-12-01

    The purpose of this research project is to more accurately measure the water balance and energy movements to properly allocate water resources at the Snapper Creek Site in Miami-Dade County, FL, by quantifying and estimating evapotranspiration (ET). ET is generally estimated using weather based equations, this project focused on estimating ET as a function of Photosynthetic Active Radiation (PAR). The project objectives were first to compose a function of PAR and calculated coefficients that can accurately estimate daily ET values with the least amount of variables used in its estimation equation, and second, to compare the newly identified ET estimation PAR function to TURC estimations, in comparison to our actual Eddy Covariance (EC) ET data and determine the differences in ET values. PAR, volumetric water content (VWC), and temperature (T) data were quality checked and used in developing singular and multiple variable regression models fit with SigmaPlot software. Fifteen different ET estimation equations were evaluated against EC ET and TURC estimated ET using R2 and slope factors. The selected equation that best estimated EC ET was cross validated using a 5 month data set; its daily and monthly ET values and sums were compared against the commonly used TURC equation. Using a multiple variable regression model, an equation with three variables (i.e., VWC, T, and PAR) was identified that best fit EC ET daily data. However, a regression was also found that used only PAR and provided ET predictions of similar accuracy. The PAR based regression model predicted daily EC ET more accurately than the traditional TURC method. Using only PAR to estimate ET reduces the input variables as compared to using the TURC model which requires T and solar radiation. Thus, not only is the PAR approach more accurate but also more cost effective. The PAR-based ET estimation equation derived in this study may be over fit considering only 5 months of data were used to produce the PAR

  1. A Model for Estimating Evapotranspiration on a Watershed Scale

    NASA Astrophysics Data System (ADS)

    Tuttle, S. E.; Salvucci, G.

    2010-12-01

    Large-scale understanding of evapotranspiration (ET) is important for climate modeling and water resources management. However, ET is related to a large number of physical and biological processes that vary across a wide range of spatial scales, thus complicating our ability to predict actual ET at the watershed scale. A statistical methodology based on the stationarity of soil water storage was created to evaluate ET models on a watershed scale. The method uses widely available streamflow (Q), precipitation (P) and meteorological data, which are assumed to be representative of the conditions within a given watershed. The method is tested at Ameriflux sites. For each site, we identify the nearest downstream USGS stream gage, which in turn defines a watershed (~50-5,000 km2) to which the method is applied. Free parameters in the ET model allow for variation in how the ET depends on factors such as plant physiology, air temperature, and the water content of the watershed (V). The water balance is then integrated over a period of time for each combination of free parameters to obtain a predicted time series of watershed-scale water storage and ET. Empirically, there is a large amount of information in P and Q about ET dynamics, but it is obscured by the changes in moisture storage over time (dV/dt). However, this storage tendency term can be filtered out using conditional averaging and employing the concept of statistical stationarity of moisture storage (Salvucci, 2001). This yields an approximation of the model error based on the degree to which the time series of simulated storage is stationary. The approximated error that results from the stationarity measure can be used to determine the combination of free parameters in the ET model that best approximates the true basin wide ET. Preliminary results indicate that simpler estimates using Priestley-Taylor potential evapotranspiration coupled with an exponential decay term dependent on moisture storage may be

  2. [Spatiotemporal variation characteristics and related affecting factors of actual evapotranspiration in the Hun-Taizi River Basin, Northeast China].

    PubMed

    Feng, Xue; Cai, Yan-Cong; Guan, De-Xin; Jin, Chang-Jie; Wang, An-Zhi; Wu, Jia-Bing; Yuan, Feng-Hui

    2014-10-01

    Based on the meteorological and hydrological data from 1970 to 2006, the advection-aridity (AA) model with calibrated parameters was used to calculate evapotranspiration in the Hun-Taizi River Basin in Northeast China. The original parameter of the AA model was tuned according to the water balance method and then four subbasins were selected to validate. Spatiotemporal variation characteristics of evapotranspiration and related affecting factors were analyzed using the methods of linear trend analysis, moving average, kriging interpolation and sensitivity analysis. The results showed that the empirical parameter value of 0.75 of AA model was suitable for the Hun-Taizi River Basin with an error of 11.4%. In the Hun-Taizi River Basin, the average annual actual evapotranspiration was 347.4 mm, which had a slightly upward trend with a rate of 1.58 mm · (10 a(-1)), but did not change significantly. It also indicated that the annual actual evapotranspiration presented a single-peaked pattern and its peak value occurred in July; the evapotranspiration in summer was higher than in spring and autumn, and it was the smallest in winter. The annual average evapotranspiration showed a decreasing trend from the northwest to the southeast in the Hun-Taizi River Basin from 1970 to 2006 with minor differences. Net radiation was largely responsible for the change of actual evapotranspiration in the Hun-Taizi River Basin. PMID:25796880

  3. Vegetation index methods for estimating evapotranspiration by remote sensing

    USGS Publications Warehouse

    Glenn, Edward P.; Nagler, Pamela L.; Huete, Alfredo R.

    2010-01-01

    Evapotranspiration (ET) is the largest term after precipitation in terrestrial water budgets. Accurate estimates of ET are needed for numerous agricultural and natural resource management tasks and to project changes in hydrological cycles due to potential climate change. We explore recent methods that combine vegetation indices (VI) from satellites with ground measurements of actual ET (ETa) and meteorological data to project ETa over a wide range of biome types and scales of measurement, from local to global estimates. The majority of these use time-series imagery from the Moderate Resolution Imaging Spectrometer on the Terra satellite to project ET over seasons and years. The review explores the theoretical basis for the methods, the types of ancillary data needed, and their accuracy and limitations. Coefficients of determination between modeled ETa and measured ETa are in the range of 0.45–0.95, and root mean square errors are in the range of 10–30% of mean ETa values across biomes, similar to methods that use thermal infrared bands to estimate ETa and within the range of accuracy of the ground measurements by which they are calibrated or validated. The advent of frequent-return satellites such as Terra and planed replacement platforms, and the increasing number of moisture and carbon flux tower sites over the globe, have made these methods feasible. Examples of operational algorithms for ET in agricultural and natural ecosystems are presented. The goal of the review is to enable potential end-users from different disciplines to adapt these methods to new applications that require spatially-distributed ET estimates.

  4. Evapotranspiration: Mass balance measurements compared with flux estimation methods

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Evapotranspiration (ET) may be measured by mass balance methods and estimated by flux sensing methods. The mass balance methods are typically restricted in terms of the area that can be represented (e.g., surface area of weighing lysimeter (LYS) or equivalent representative area of neutron probe (NP...

  5. Estimation of evapotranspiration rate in irrigated lands using stable isotopes

    NASA Astrophysics Data System (ADS)

    Umirzakov, Gulomjon; Windhorst, David; Forkutsa, Irina; Brauer, Lutz; Frede, Hans-Georg

    2013-04-01

    Agriculture in the Aral Sea basin is the main consumer of water resources and due to the current agricultural management practices inefficient water usage causes huge losses of freshwater resources. There is huge potential to save water resources in order to reach a more efficient water use in irrigated areas. Therefore, research is required to reveal the mechanisms of hydrological fluxes in irrigated areas. This paper focuses on estimation of evapotranspiration which is one of the crucial components in the water balance of irrigated lands. Our main objective is to estimate the rate of evapotranspiration on irrigated lands and partitioning of evaporation into transpiration using stable isotopes measurements. Experiments has done in 2 different soil types (sandy and sandy loam) irrigated areas in Ferghana Valley (Uzbekistan). Soil samples were collected during the vegetation period. The soil water from these samples was extracted via a cryogenic extraction method and analyzed for the isotopic ratio of the water isotopes (2H and 18O) based on a laser spectroscopy method (DLT 100, Los Gatos USA). Evapotranspiration rates were estimated with Isotope Mass Balance method. The results of evapotranspiration obtained using isotope mass balance method is compared with the results of Catchment Modeling Framework -1D model results which has done in the same area and the same time.

  6. Comparison of Crop Evapotranspiration Estimates from Reference Evapotranspiration Equations and a Variational Data Assimilation Approach

    NASA Astrophysics Data System (ADS)

    Bateni, S. M.; Michalik, T.; Multsch, S.; Breuer, L.

    2015-12-01

    Crop evapotranspiration (ETc) is a key component of water resources management in irrigation of farmlands as it determines the crop water consumption. Numerous methods have been used to estimate ETc for scheduling irrigation and evaluating the soil water balance. However, there is a significant difference in ETc estimates from various models, which leads to a large uncertainty in the soil water balance, crop water consumption, and irrigation scheduling. In this study, several commonly-used ETc equations (Turc, Priestley-Taylor, Hargreaves-Samani, Penman-Monteith) are compared with the variational data assimilation approach (VDA) of Bateni et al. (2013). The ETc equations initially estimate the reference evapotranspiration (ETo), which is the evapotranspiration from a healthy and actively-transpiring grass field with ample water in the soil. Thereafter, ETc is calculated by multiplying ETo by the crop coefficient (Kc), which accounts for the crop type and soil water stress. To properly apply the Kc to non-standard conditions, a daily water balance estimation for the root zone is required, which is done by two soil water budget models (Cropwat, Hydrus-1D) that compute incoming and outgoing water flows in the soil profile. In contrast to these methods that estimate ETc in two steps, the VDA approach directly predicts ETc by assimilating sequences of land surface temperature into the heat diffusion equation and thus it is expected to provide more accurate ETc estimates. All approaches are applied over three cropland sites namely, Bondville, Fermi, and Mead in the summer of 2006 and 2007. These sites are part of the AmeriFlux network and provide a wide variety of hydrological conditions. The results show that the variational data assimilation approach performs better compared to other equations.

  7. Controls over spatial and temporal variations in annual actual evapotranspiration in snow-free California watersheds

    NASA Astrophysics Data System (ADS)

    Clark, Allison Marie

    Actual evapotranspiration (Eta) is one of the largest components of the hydrologic budget and accounts for a majority of water lost from a watershed. It is primarily controlled by soil water availability, which is largely controlled by rainfall, and atmospheric demand (potential evapotranspiration). Consequently, Eta is sensitive to changes in meteorologic conditions. Understanding the relationship between Et a and controlling meteorologic variables across time and space is important for future predictions of Eta under a changing climate, especially in California where demand for surface and groundwater is high. A regression modeling approach was used to (1) determine the relative control of rainfall, rainfall intensity, and potential evapotranspiration (Etp) over annual and long-term mean annual Eta across watersheds in western California, and (2) quantify the sensitivity of watershed annual Eta to changes in these variables. Annual Eta data for 20 snow-free California watersheds was derived using the water balance method for hydrologic years 1982-2011. Independent variables examined in this study were annual rainfall, rainfall intensity, and potential evapotranspiration. These quantities were obtained or calculated from daily PRISM rainfall and temperature datasets. Results indicated that rainfall was the dominant control over variations in mean annual Eta across the study region (Adj. R2 0.935) and was the primary control over interannual variations in Et a for 15 out of 17 study watersheds. Rainfall intensity was a significant but weaker predictor of mean annual Eta (adj. R2 0.833) and was a significant predictor of annual variations in Eta for 12 out of 17 watersheds. A weak relationship between Etp and Eta was observed across the study region (adj. R2 = 0.660) and the relationship was found to be negative. Etp was a significant, though weak, predictor of annual Eta for 8 out of 17 watersheds. The amount of variance in annual Eta explained by rainfall

  8. Utility of Penman-Monteith, Priestley-Taylor, reference evapotranspiration, and pan evaporation methods to estimate pasture evapotranspiration

    USGS Publications Warehouse

    Sumner, D.M.; Jacobs, J.M.

    2005-01-01

    Actual evapotranspiration (ETa) was measured at 30-min resolution over a 19-month period (September 28, 2000-April 23, 2002) from a nonirrigated pasture site in Florida, USA, using eddy correlation methods. The relative magnitude of measured ETa (about 66% of long-term annual precipitation at the study site) indicates the importance of accurate ET a estimates for water resources planning. The time and cost associated with direct measurements of ETa and the rarity of historical measurements of ETa make the use of methods relying on more easily obtainable data desirable. Several such methods (Penman-Monteith (PM), modified Priestley-Taylor (PT), reference evapotranspiration (ET 0), and pan evaporation (Ep)) were related to measured ETa using regression methods to estimate PM bulk surface conductance, PT ??, ET0 vegetation coefficient, and Ep pan coefficient. The PT method, where the PT ?? is a function of green-leaf area index (LAI) and solar radiation, provided the best relation with ET a (standard error (SE) for daily ETa of 0.11 mm). The PM method, in which the bulk surface conductance was a function of net radiation and vapor-pressure deficit, was slightly less effective (SE=0.15 mm) than the PT method. Vegetation coefficients for the ET0 method (SE=0.29 mm) were found to be a simple function of LAI. Pan coefficients for the Ep method (SE=0.40 mm) were found to be a function of LAI and Ep. Historical or future meteorological, LAI, and pan evaporation data from the study site could be used, along with the relations developed within this study, to provide estimates of ETa in the absence of direct measurements of ETa. Additionally, relations among PM, PT, and ET0 methods and ETa can provide estimates of ETa in other, environmentally similar, pasture settings for which meteorological and LAI data can be obtained or estimated. ?? 2004 Elsevier B.V. All rights reserved.

  9. A rational function approach for estimating land surface evapotranspiration based on the complementary hypothesis

    NASA Astrophysics Data System (ADS)

    Han, S.; Hu, H.; Tian, F.

    2007-12-01

    Evapotranspiration, which occurs in the boundary layer between the land surface and the bottom atmospheric layer, plays an important role in both water balance and energy balance. Models based on the Penman hypothesis (1948) and the Budyko hypothesis (1974) estimate actual evapotranspiration from a land surface process prospective, while models based on the complementary hypothesis (Bouchet, 1963) do this from the atmospheric perspective. Penman-based models require detailed data on soil moisture or stomatal resistance (Crago and Crowley, 2006); Budyko models, e.g. Fu's equation (1981), estimate the mean annual evapotranspiration only; while models based on the complementary hypothesis, including advection aridity model (AA for short) (Brutsaert and Stricker, 1979) and the Granger model (1989, 1991, 1996) estimate actual evapotranspiration at various time scales using climate data only. The AA and Granger models use different definitions for wet environment evaporation and potential evaporation and their comparative study are conducted by several researchers (Xu and Singh, 2005; Liu et al., 2006; Crago and Crowley, 2006). In this paper we explore the uniformity of the two complementary models by dimensional analysis. A new index (the proportion of the radiation term in Penman equation, termed the air humidity index) is proposed as a measure of the wetness of the evaporating surface via the wetness of over-passing air, and a general functional form for actual evaporation is developed in which the evaporation ratio is expressed as a function of the air humidity index. The similarity and differences between the AA and Granger models are interpreted via this rational function approach, and a new power function method is proposed. The theoretical analysis is confirmed by observational data under various climate conditions.

  10. Integration of Remote Sensing derived Actual Evapotranspiration with Meteorological Data for Real Time Demand Forecasting in Semi-arid Regions

    NASA Astrophysics Data System (ADS)

    Ullah, M. K.; Hafeez, M. M.; Chemin, Y.; Faux, R.; Sixsmith, J.

    2010-12-01

    Irrigated agriculture is major consumer of fresh water, but a large part of the water devour for irrigation is wasted due to poor management of irrigation systems. Improving water management in irrigated areas require the analysis of real time water demand in order to determine the possibilities in which it may be modified and rationalised. Real time water demand information in irrigated areas is a key for planning about sustainable use of irrigation water. These activities are needed not only to improve water productivity, but also to increase the sustainability of irrigated agriculture by saving irrigation water. Demand forecasting entail the complete understanding of spatial and expected temporal variability of metrological parameters and evapotranspiration (ET). ET is the overriding aspect for irrigation demand forecasting at farm to catchment scale. Many models have been used to measure the ET rate, either empirical or functional. The major disadvantage of this approach is that most methods generate only point values, resulting in estimates that are not representative of large areas. These methods are based on crop factors under ideal conditions and cannot therefore represent actual crop ET. Satellite remote sensing is a powerful mean to estimate ET over various spatial and temporal scales. For improved irrigation system management and operation, a holistic approach of integrating remote sensing derived ET from SAM-ET (spatial algorithm for mapping ET) algorithm, for Australian agro-ecosystem, with forecasted meteorological data and field application loss functions for major crops were used to forecast actual water demand in Coleambally Irrigation Area (CIA), New South Wales, Australia. It covers approximately 79,000 ha of intensive irrigation and comprise of number of secondary and tertiary canals. In order to capture the spatial variability, CIA has been divided into 22 nodes based on direction of flow and connectivity. All hydrological data of inflow (i

  11. A spatial downscaling procedure of MODIS derived actual evapotranspiration using Landsat images at central Greece

    NASA Astrophysics Data System (ADS)

    Spiliotopoulos, M.; Adaktylou, N.; Loukas, A.; Michalopoulou, H.; Mylopoulos, N.; Toulios, L.

    2013-08-01

    In this study, the Surface Energy Balance Algorithm for Land (SEBAL) was used to derive daily actual evapotranspiration (ETa) distributions from Landsat and MODIS images separately. The study area is the Lake Karla basin in Thessaly, Central Greece. Meteorological data from the archive of Center for Research and Technology, Thessaly (CERETETH) have also been used. The methodology was developed using satellite and ground data for the period of summer 2007. Landsat and MODIS imagery were combined in order to have data with high temporal and spatial resolution (downscaling). The downscaling technique applied is the output downscaling with regression between images. This technique disaggregates imagery by applying linear regression between two MODIS products to the previous or subsequent Landsat product. After the calculation of a first order linear regression between two MODIS-derived ETa maps the next step is the regression to the ETa map derived from the prior Landsat image to predict the disaggregated subsequent Landsat ETa map. The results are satisfactory, giving the general trend of ETa derived from the original SEBAL procedure.

  12. Actual evapotranspiration for a reference crop within measured and future changing climate periods in the Mediterranean region

    NASA Astrophysics Data System (ADS)

    Katerji, Nader; Rana, Gianfranco; Ferrara, Rossana Monica

    2016-05-01

    The study compares two formulas for calculating the daily evapotranspiration ET0 for a reference crop. The first formula was proposed by Allen et al. (AL), while the second one was proposed by Katerji and Perrier with the addition of the carbon dioxide (CO2) effect on evapotranspiration (KP). The study analyses the impact of the calculation by the two formulas on the irrigation requirement (IR). Both formulas are based on the Penman-Monteith equation but adopt different approaches for parameterising the canopy resistance r c . In the AL formula, r c is assumed constant and not sensitive to climate change, whereas in the KP formula, r c is first parameterised as a function of climatic variables, then ET0 is corrected for the air CO2 concentration. The two formulas were compared in two periods. The first period involves data from two sites in the Mediterranean region within a measured climate change period (1981-2006) when all the input climatic variables were measured. The second period (2070-2100) involves data from a future climate change period at one site when the input climatic variables were forecasted for two future climate scenarios (A2 and B2). The annual cumulated values of ET0 calculated by the AL formula are systematically lower than those determined by the KP formula. The differences between the ET0 estimation with the AL and KP formulas have a strong impact on the determination of the IR for the reference crop. In fact, for the two periods, the annual values of IR when ET0 is calculated by the AL formula are systematically lower than those calculated by the KP formula. For the actual measured climate change period, this reduction varied from 26 to 28 %, while for the future climate change period, it varied based on the scenario from 16 % (A2) to 20 % (B2).

  13. Soil water availability as controlling factor for actual evapotranspiration in urban soil-vegetation-systems

    NASA Astrophysics Data System (ADS)

    Thomsen, Simon; Reisdorff, Christoph; Gröngröft, Alexander; Jensen, Kai; Eschenbach, Annette

    2015-04-01

    The City of Hamburg is characterized by a large number of greens, parks and roadside trees: 600.000 trees cover about 14% of the city area, and moreover, 245.000 roadside trees can be found here. Urban vegetation is generally known to positively contribute to the urban micro-climate via cooling by evapotranspiration (ET). The water for ET is predominantly stored in the urban soils. Hence, the actual evapotranspiration (ETa) is - beside atmospheric drivers - determined by soil water availability at the soil surface and in the rooting zones of the respective vegetation. The overall aim of this study is to characterize soil water availability as a regulative factor for ETa in urban soil-vegetation systems. The specific questions addressed are: i) What is the spatio-temporal variation in soil water availability at the study sites? ii) Which soil depths are predominantly used for water uptake by the vegetation forms investigated? and iii) Which are the threshold values of soil water tension and soil water content (Θ), respectively, that limit ETa under dry conditions on both grass-dominated and tree-dominated sites? Three study areas were established in the urban region of Hamburg, Germany. We selected areas featuring both single tree stands and grass-dominated sites, both representing typical vegetation forms in Hamburg. The areas are characterized by relatively dry soil conditions. However, they differ in regard to soil water availability. At each area we selected one site dominated by Common Oak (Quercus ruber L.) with ages from 40 to 120 years, and paired each oak tree site with a neighboring grass-dominated site. All field measurements were performed during the years 2013 and 2014. At each site, we continuously measured soil water tension and Θ up to 160 cm depth, and xylem sap flux of each of three oak trees per site in a 15 min-resolution. Furthermore, we measured soil hydraulic properties as pF-curve, saturated and unsaturated conductivity at all sites

  14. Evaluation of different methods to estimate daily reference evapotranspiration in ungauged basins in Southern Brazil

    NASA Astrophysics Data System (ADS)

    Ribeiro Fontoura, Jessica; Allasia, Daniel; Herbstrith Froemming, Gabriel; Freitas Ferreira, Pedro; Tassi, Rutineia

    2016-04-01

    Evapotranspiration is a key process of hydrological cycle and a sole term that links land surface water balance and land surface energy balance. Due to the higher information requirements of the Penman-Monteith method and the existing data uncertainty, simplified empirical methods for calculating potential and actual evapotranspiration are widely used in hydrological models. This is especially important in Brazil, where the monitoring of meteorological data is precarious. In this study were compared different methods for estimating evapotranspiration for Rio Grande do Sul, the Southernmost State of Brazil, aiming to suggest alternatives to the recommended method (Penman-Monteith-FAO 56) for estimate daily reference evapotranspiration (ETo) when meteorological data is missing or not available. The input dataset included daily and hourly-observed data from conventional and automatic weather stations respectively maintained by the National Weather Institute of Brazil (INMET) from the period of 1 January 2007 to 31 January 2010. Dataset included maximum temperature (Tmax, °C), minimum temperature (Tmin, °C), mean relative humidity (%), wind speed at 2 m height (u2, m s-1), daily solar radiation (Rs, MJ m- 2) and atmospheric pressure (kPa) that were grouped at daily time-step. Was tested the Food and Agriculture Organization of the United Nations (FAO) Penman-Monteith method (PM) at its full form, against PM assuming missing several variables not normally available in Brazil in order to calculate daily reference ETo. Missing variables were estimated as suggested in FAO56 publication or from climatological means. Furthermore, PM was also compared against the following simplified empirical methods: Hargreaves-Samani, Priestley-Taylor, Mccloud, McGuiness-Bordne, Romanenko, Radiation-Temperature, Tanner-Pelton. The statistical analysis indicates that even if just Tmin and Tmax are available, it is better to use PM estimating missing variables from syntetic data than

  15. Hydrological model uncertainty due to spatial evapotranspiration estimation methods

    NASA Astrophysics Data System (ADS)

    Yu, Xuan; Lamačová, Anna; Duffy, Christopher; Krám, Pavel; Hruška, Jakub

    2016-05-01

    Evapotranspiration (ET) continues to be a difficult process to estimate in seasonal and long-term water balances in catchment models. Approaches to estimate ET typically use vegetation parameters (e.g., leaf area index [LAI], interception capacity) obtained from field observation, remote sensing data, national or global land cover products, and/or simulated by ecosystem models. In this study we attempt to quantify the uncertainty that spatial evapotranspiration estimation introduces into hydrological simulations when the age of the forest is not precisely known. The Penn State Integrated Hydrologic Model (PIHM) was implemented for the Lysina headwater catchment, located 50°03‧N, 12°40‧E in the western part of the Czech Republic. The spatial forest patterns were digitized from forest age maps made available by the Czech Forest Administration. Two ET methods were implemented in the catchment model: the Biome-BGC forest growth sub-model (1-way coupled to PIHM) and with the fixed-seasonal LAI method. From these two approaches simulation scenarios were developed. We combined the estimated spatial forest age maps and two ET estimation methods to drive PIHM. A set of spatial hydrologic regime and streamflow regime indices were calculated from the modeling results for each method. Intercomparison of the hydrological responses to the spatial vegetation patterns suggested considerable variation in soil moisture and recharge and a small uncertainty in the groundwater table elevation and streamflow. The hydrologic modeling with ET estimated by Biome-BGC generated less uncertainty due to the plant physiology-based method. The implication of this research is that overall hydrologic variability induced by uncertain management practices was reduced by implementing vegetation models in the catchment models.

  16. Actual evapotranspiration and deficit: Biologically meaningful correlates of vegetation distribution across spatial scales

    USGS Publications Warehouse

    Stephenson, N.L.

    1998-01-01

    Correlative approaches to understanding the climatic controls of vegetation distribution have exhibited at least two important weaknesses: they have been conceptually divorced across spatial scales, and their climatic parameters have not necessarily represented aspects of climate of broad physiological importance to plants. Using examples from the literature and from the Sierra Nevada of California, I argue that two water balance parameters-actual evapotranspiration (AET) and deficit (D)-are biologically meaningful, are well correlated with the distribution of vegetation types, and exhibit these qualities over several orders of magnitude of spatial scale (continental to local). I reach four additional conclusions. (1) Some pairs of climatic parameters presently in use are functionally similar to AET and D; however, AET and D may be easier to interpret biologically. (2) Several well-known climatic parameters are biologically less meaningful or less important than AET and D, and consequently are poorer correlates of the distribution of vegetation types. Of particular interest, AET is a much better correlate of the distributions of coniferous and deciduous forests than minimum temperature. (3) The effects of evaporative demand and water availability on a site's water balance are intrinsically different. For example, the 'dry' experienced by plants on sunward slopes (high evaporative demand) is not comparable to the 'dry' experienced by plants on soils with low water-holding capacities (low water availability), and these differences are reflected in vegetation patterns. (4) Many traditional topographic moisture scalars-those that additively combine measures related to evaporative demand and water availability are not necessarily meaningful for describing site conditions as sensed by plants; the same holds for measured soil moisture. However, using AET and D in place of moisture scalars and measured soil moisture can solve these problems.

  17. Using the TIMS to estimate evapotranspiration from a forest

    NASA Technical Reports Server (NTRS)

    Teskey, Robert

    1991-01-01

    The main goals were: (1) to characterize the evapotranspiration (Et) of two forested watersheds using direct measurement techniques, and (2) to evaluate if remotely sensed surface temperatures could be used to estimate Et from the same watersheds. Two independent approaches for estimating the Et from watersheds were used. The first was derived using the Penman-Monteith Equation. This model requires the direct measurement of the microclimate of the site as well as biological measurements, i.e., stomatal conductance to water vapor and the leaf area of the stand. The primary limitation of this approach is that the measurement of stomatal conductance is time consuming, and in large trees, access to the foliage is difficult so the sample must be limited to the small number of trees. In the study, the sample was limited to the trees which could be measured from a single tower in each stand.

  18. A critical analysis of three remote sensing-based actual evapotranspiration assessment methods over sparse crops agricultural areas

    NASA Astrophysics Data System (ADS)

    Cammalleri, Carmelo; Ciraolo, Giuseppe; La Loggia, Goffredo; Minacapilli, Mario

    2010-10-01

    During last two decades the increasing availability of remotely sensed acquisitions in the thermal infrared part of the spectrum has encouraged hydrologist community to develop models and methodologies based on these kind of data. The aim of this paper is to compare three methods developed to assess the actual evapotranspiration spatial distribution by means of remote sensing data. The comparison was focused on the differences between the "single" (SEBAL) and "two" source (TSEB) surface energy balance approaches and the S-SEBI semi-empirical method. The first assumes a semiempirical internal calibration for the sensible heat flux assessment; the second uses a physically based approach in order to assess separately the soil and vegetation fluxes. Finally, the last one is based on the correlation between albedo and surface temperature for evaporative fraction estimations. The models were applied using 7 high resolution images, collected by an airborne platform between June and October 2008, approximately every 3 weeks. The acquired data include multi-spectral images (red, green and near infrared) and thermal infrared images for surface temperature estimation. The study area, located in the south-west cost of Sicily, Italy), is characterised by the presence of typical Mediterranean cultivations: olive, vineyard and citrus. Due to irrigation supplies and rainfall events, the water availability for the crops varies in time and this allowed to perform the comparison in a wide range of the modelled variables. Additionally, the availability of high spatial resolution images allowed the testing of the models performances at field scale despite the high vegetation fragmentation of the study area. The comparison of models performance highlights a good agreements of model estimations, analyzed by means of MAD (Mean Absolute Differences) and MAPD (Mean Absolute Percent Differences) indices, especially in terms of study area averaged fluxes. The analysis in correspondence of

  19. Spatiotemporal variations of actual evapotranspiration over the Lake Selin Co Basin (Tibetan Plateau) during 2003-2012

    NASA Astrophysics Data System (ADS)

    Zhou, Jing; Wang, Lei

    2016-04-01

    Actual evapotranspiration (ETa) over the Tibetan Plateau (TP) is an important component of the water cycle, and greatly influences the water budgets of the TP lake basins. Quantitative estimation of ETa within lake basins is fundamental to physically understanding ETa changes, and thus will improve the understanding of the hydrological processes and energy balance throughout the lake basins. In this study, the spatiotemporal dynamic changes of ETa within the Lake Selin Co Basin (the TP's largest lake basin) during 2003-2012 are examined at the basin scale. This was carried out using the previously calibrated and validated Water and Energy Budget-based Distributed Hydrological Model (WEB-DHM) for the land area, the Penman-Monteith method for the water area when unfrozen, and a simple sublimation estimation approach for the water area when frozen. The relationship between ETa changes and controlling factors is also discussed. Results indicate that the simulated land ETa from the WEB-DHM reasonably agrees with the estimated ETa values from the nonlinear complementary relationship model using appropriately calibrated parameter values at a point scale. Land ETa displayed an insignificant increase of 7.03 mm/y, and largely depends on precipitation. For the water area, the combined effects of reduced wind speed and net radiation offset the effect of rising temperature and vapor pressure deficit, and contributed to an insignificant decrease in evaporation of 4.17 mm/y. Sensitivity analysis shows that vapor pressure deficit and wind speed are the most sensitive variables to the changes of evaporation from the water area.

  20. Comparisons of Four Methods for Evapotranspiration Estimates in Jordan

    NASA Astrophysics Data System (ADS)

    Zhang, H.; Gorelick, S.; Yoon, J.

    2014-12-01

    We compared evapotranspiration (ET) estimates in Jordan calculated by four theoretically-different methods. The first method was the FAO Single Crop Coefficient method. Our calculation took into account 20 dominant crop species in Jordan, utilized the global Climate Forecast System Reanalysis (CFSR) data set, and generated spatially heterogeneous crop coefficients. The second approach was the Surface Energy Balance Algorithms for Land (SEBAL) method. It was used with Landsat TM/ETM+ images to calculate instantaneous ET at the moment of satellite overpass, and the results of multiple images were combined to derive seasonal and annual ET estimates. The third method was based on the 1-km land surface ET product from MODIS, which was calculated using MODIS-observed land cover and photosynthetically active radiation. The fourth method was based on the SWAT model, which combines the Penman-Monteith equation and vegetation growth to estimate daily ET rates at the watershed scale. The results show substantial differences in both magnitude and spatiotemporal patterns of ET estimates across different regions from the four methods. Such differences were particularly evident in the Highlands region, where irrigation plays a critical role in local water balance. Results also suggest that land cover data is a major source of uncertainty in estimating regional ET rates. Although it is difficult to conclude which method was more reliable due to the limited availability of validation data, the results suggest caution in developing and interpreting ET estimates in this arid environment.

  1. Spatio-temporal Characteristics of Actual Evapotranspiration Trends in sub-Saharan Africa

    NASA Astrophysics Data System (ADS)

    Marshall, M. T.; Funk, C. C.; Michaelsen, J.

    2010-12-01

    Actual evapotranspiration (AET) is an important moisture flux linking the Earth’s surface to the atmospheric hydrologic cycle. Global warming is expected to intensify this cycle, leading to moisture deficits over the sub-tropics, which will influence climate at higher latitudes. The spatio-temporal characterization of tropical AET is critical to understanding regional and global climate. To date, many studies on the temporal characteristics of AET across sub-Saharan Africa have employed vegetation-based indices derived from satellite imagery. Although these studies implicitly reflect trends in AET, they quantify the magnitude of change. In this study, we used the latest developments in remote sensing and land-surface modeling to characterize the magnitude and timing of AET in sub-Saharan Africa. We considered several models were evaluated from 1981-2000 using monthly discharge and precipitation from ten sub-basins representative of hydrology in sub-Saharan Africa. Discharge data was provided by the Global Runoff Data Centre, while precipitation data was comprised of ECMWF, NCAR, NOAA/GDAS, and CMAP reanalysis fields synthesized in the Global Land Data Assimilation System (GLDAS). The AET models included the Community Land Model, Variable Infiltration Capacity (VIC) model, Noah, and two hybrids that we developed driven by a dynamic vegetation component defined in Fisher et al. 2008. The dynamic canopy components in our hybrid models were driven by the LTDR AVHRR daily corrected reflectance data over the evaluation period. The evaluation revealed that VIC was superior to the other models in capturing the magnitude and variability of runoff in the sub-basins. A trend analysis was then performed on VIC AET from 1979-2009 using standard parametric and non-parametric techniques. Linear and median trend analysis was performed on seasonal and annual AET totals to measure the magnitude of change. The analysis revealed several alarming patterns, including large and

  2. Using Satellite-based Evapotranspiration Estimation to Characterize Agricultural Irrigation Water Use

    NASA Astrophysics Data System (ADS)

    Zheng, B.; Myint, S. W.; Hendrickx, J. M. H.

    2014-12-01

    The satellite-based evapotranspiration (ET) model permits estimation of water consumption across space and time in a systematic way. Developing tools to monitor water availability and water use is critical to meet future water shortage challenges in the American West. This study applied METRIC (Mapping Evapotranspiration at high Resolution and with Internalized Calibration) to 2001 Landsat imagery to estimate ET of various crop types in Phoenix. The total annual ET estimates are correlated well with the actual water use at the irrigation district level (r=0.99). We further incorporated a crop type map to estimate annual ET for the major crop types in the region, and to examine variability in crop water use among different irrigation districts. Our results show that alfalfa and double crops consume more water than other crop types with mean annual ET estimations of 1300 to 1580 mm/year, and that cotton uses more water (1162 mm/year) than corn (838 mm/year) and sorghum (829 mm/year) as expected. Crop water use varies from one irrigation district to another due to differences in soil quality, water quality, and farming practices. Results from our study suggest that the ET maps derived from METRIC can be used to quantify the spatial distribution of ET and to characterize agricultural water use by crop types at different spatial scales.

  3. Diurnal evapotranspiration estimates in the Walnut River Watershed.

    SciTech Connect

    Song, J.

    1998-10-05

    Evapotranspiration is an essential component of the surface hydrological balance, but obtaining accurate estimates of the water vapor flux over large terrestrial areas can be difficult because of the substantial temporal and spatial variability in surface moisture conditions that can occur. This variability is often very large in the Great Plains and other portions of the Mississippi River Basin. Nevertheless, variations in soil moisture content, groundwater levels, and runoff in streams and rivers cannot be fully assessed without some knowledge of evapotranspiration rates. Here, observations made at the Walnut River Watershed (WRW), which is near Wichita, Kansas, and has an area of approximately 5000 km{sup 2}, are used to improve and test a modeling system that estimates long-term evapotranspiration with use of satellite remote sensing data with limited surface measurements. The techniques may be applied to much larger areas. As is shown in Fig. 1, the WRW is located in the Red River Basin and is enclosed by the southern Great Plains Clouds and Radiation Testbed (CART) of the US Department of Energy's Atmospheric Radiation Measurement (ARM) program. The functional relationships involving the satellite data, surface parameters, and associated subgrid-scale fluxes are modeled in this study by the parameterization of subgrid-scale surface (PASS) fluxes scheme (Gao, 1995; Gao et al., 1998), which is used in a modified and improved form (PASS2). The advantage of this modeling system is that it can make effective use of satellite remote sensing data and can be run for large areas for which flux data do not exist and surface meteorological data are available from only a limited number of ground stations. In this study, the normalized difference vegetation index (NDVI) or simple ratio (SR) and surface brightness temperature at each pixel for the WRW were derived from advanced very high resolution radiometers data collected by a ground station at Argonne National

  4. Estimating plant available water content from remotely sensed evapotranspiration

    NASA Astrophysics Data System (ADS)

    van Dijk, A. I. J. M.; Warren, G.; Doody, T.

    2012-04-01

    Plant available water content (PAWC) is an emergent soil property that is a critical variable in hydrological modelling. PAWC determines the active soil water storage and, in water-limited environments, is the main cause of different ecohydrological behaviour between (deep-rooted) perennial vegetation and (shallow-rooted) seasonal vegetation. Conventionally, PAWC is estimated for a combination of soil and vegetation from three variables: maximum rooting depth and the volumetric water content at field capacity and permanent wilting point, respectively. Without elaborate local field observation, large uncertainties in PAWC occur due to the assumptions associated with each of the three variables. We developed an alternative, observation-based method to estimate PAWC from precipitation observations and CSIRO MODIS Reflectance-based Evapotranspiration (CMRSET) estimates. Processing steps include (1) removing residual systematic bias in the CMRSET estimates, (2) making spatially appropriate assumptions about local water inputs and surface runoff losses, (3) using mean seasonal patterns in precipitation and CMRSET to estimate the seasonal pattern in soil water storage changes, (4) from these, calculating the mean seasonal storage range, which can be treated as an estimate of PAWC. We evaluate the resulting PAWC estimates against those determined in field experiments for 180 sites across Australia. We show that the method produces better estimates of PAWC than conventional techniques. In addition, the method provides detailed information with full continental coverage at moderate resolution (250 m) scale. The resulting maps can be used to identify likely groundwater dependent ecosystems and to derive PAWC distributions for each combination of soil and vegetation type.

  5. Understanding the relationship between actual and potential evapotranspirations from long- term water balance analysis and flux observation

    NASA Astrophysics Data System (ADS)

    Yang, D.; Yang, H.; Sun, F.

    2007-12-01

    Increase in air temperature and decrease in pan evaporation was found to be common worldwide during the past half century. This results in controversy in view of the changes to the hydrological cycle. Increases in precipitation have been expected due to the Clausius¡§CClapyeron relation in that the specific humidity increases exponentially with the greenhouse-gas induced temperature increasing and confirmed by measurements over northern extratropical land areas. The hydrologic cycle is expected to be intensified (or accelerated). However, the decreased pan evaporation is found to be well related to the global dimming, i.e., the decreased solar radiation induced by the pollution increasing, thus evaporation (i.e., the latent heat flux) should be steadily decreasing from the energy balance perspective. Many researchers explained that the potential evaporation (usually measured by pan) is decreased with increasing of precipitation; however, the increased soil moisture (due to precipitation increasing) can be evaporated because of extra energy available. Therefore, the actual and potential evaporation are in complementary relationship, which is expected to unify the controversy between global warming and dimming. This means that pan evaporation decrease implicates acceleration of the global hydrologic cycle, i.e., increase in the terrestrial evaporation. Based on the complementary theory, many operational formulae have been introduced to estimated actual evaporation from the potential evaporation. Our recent water balance analysis of 108 catchments in non-humid regions of China has shown that there are no general opposite trends between potential and actual evaporation in the same period. A novel phenomenon has been found that the complementary relationships in evaporation are distinctly confirmed when the annual actual and potential evaporation are plotted against annual precipitation; However, complementary relationships disappear in many catchments when actual and

  6. A parabolic function to modify Thornthwaite estimates of potential evapotranspiration for the eastern United States

    USGS Publications Warehouse

    McCabe, G.J., Jr.

    1989-01-01

    Errors of the Thornthwaite model can be analyzed using adjusted pan evaporation as an index of potential evapotranspiration. An examination of ratios of adjusted pan evaporation to Thornthwaite potential evapotranspiration indicates that the ratios are highest in the winter and lowest during summer months. This trend suggests a parabolic pattern. In this study a parabolic function is used to adjust Thornthwaite estimates of potential evapotranspiration. Forty locations east of the Rocky Mountains are analyzed. -from Author

  7. Estimation of Regional Evapotranspiration Using Remotely Sensed Land Surface Temperature. Part 2: Application of Equilibrium Evaporation Model to Estimate Evapotranspiration by Remote Sensing Technique. [Japan

    NASA Technical Reports Server (NTRS)

    Kotoda, K.; Nakagawa, S.; Kai, K.; Yoshino, M. M.; Takeda, K.; Seki, K.

    1985-01-01

    In a humid region like Japan, it seems that the radiation term in the energy balance equation plays a more important role for evapotranspiration then does the vapor pressure difference between the surface and lower atmospheric boundary layer. A Priestley-Taylor type equation (equilibrium evaporation model) is used to estimate evapotranspiration. Net radiation, soil heat flux, and surface temperature data are obtained. Only temperature data obtained by remotely sensed techniques are used.

  8. 10-year evapotranspiration estimates in a Bornean tropical rainforest

    NASA Astrophysics Data System (ADS)

    Kume, T.; Tanaka, N.; Komatsu, H.; Yoshifuji, N.; Saitoh, T. M.; Suzuki, M.; Kumagai, T.

    2010-12-01

    This study was undertaken to quantify 10-year evapotranspiration (ET) in a tropical rainforest, Sarawak, Malaysia. To this aim, a simplified big-leaf model was formulated, which can consider transpiration (Et) and rainfall interception (Ei). The model was independently validated using eddy covariance fluxes, rainfall interception based on throughfall and stemflow measurements, and sap flow measurements conducted for more than two years. Consequently, our big-leaf model could successfully reproduce Et and Ei. By using the model and a 10-year meteorological data set, Et, Ei, and ET was estimated in the period between 2000 and 2009. The annual Et , Ei, and ET averaged over 10 years were estimated as 1114, 209, and 1323 mm, respectively, with the small seasonal fluctuations. The derived estimations for 10 years showed conservative year-to-year variations in Et, Ei, and ET (CV = 5-7%) against considerable year-to-year variations in annual rainfall (CV = 11%). Specific rainfall characteristics in this site could be a reason for conservative year-to-year variations in Ei. Small interannual variations in meteorological conditions and no occurrence of unusually severe drought in this study period could be a reason for the small year-to-year variations in Et. As well, we compared ET, Ei at this site with those of other tropical forests. Our forest ET was smaller than global maximum value of ET estimated in other tropical forests because of the smaller Ei, relative to annual rainfall at this site. Based on the derived characteristics of ET, we also discussed possible changes in ET, Et, and Ei in response to changes in rainfall regime at this site.

  9. Evaluation of Physically and Empirically Based Models for the Estimation of Green Roof Evapotranspiration

    NASA Astrophysics Data System (ADS)

    Digiovanni, K. A.; Montalto, F. A.; Gaffin, S.; Rosenzweig, C.

    2010-12-01

    Green roofs and other urban green spaces can provide a variety of valuable benefits including reduction of the urban heat island effect, reduction of stormwater runoff, carbon sequestration, oxygen generation, air pollution mitigation etc. As many of these benefits are directly linked to the processes of evaporation and transpiration, accurate and representative estimation of urban evapotranspiration (ET) is a necessary tool for predicting and quantifying such benefits. However, many common ET estimation procedures were developed for agricultural applications, and thus carry inherent assumptions that may only be rarely applicable to urban green spaces. Various researchers have identified the estimation of expected urban ET rates as critical, yet poorly studied components of urban green space performance prediction and cite that further evaluation is needed to reconcile differences in predictions from varying ET modeling approaches. A small scale green roof lysimeter setup situated on the green roof of the Ethical Culture Fieldston School in the Bronx, NY has been the focus of ongoing monitoring initiated in June 2009. The experimental setup includes a 0.6 m by 1.2 m Lysimeter replicating the anatomy of the 500 m2 green roof of the building, with a roof membrane, drainage layer, 10 cm media depth, and planted with a variety of Sedum species. Soil moisture sensors and qualitative runoff measurements are also recorded in the Lysimeter, while a weather station situated on the rooftop records climatologic data. Direct quantification of actual evapotranspiration (AET) from the green roof weighing lysimeter was achieved through a mass balance approaches during periods absent of precipitation and drainage. A comparison of AET to estimates of potential evapotranspiration (PET) calculated from empirically and physically based ET models was performed in order to evaluate the applicability of conventional ET equations for the estimation of ET from green roofs. Results have

  10. Estimating Evapotranspiration Using an Observation Based Terrestrial Water Budget

    NASA Technical Reports Server (NTRS)

    Rodell, Matthew; McWilliams, Eric B.; Famiglietti, James S.; Beaudoing, Hiroko K.; Nigro, Joseph

    2011-01-01

    Evapotranspiration (ET) is difficult to measure at the scales of climate models and climate variability. While satellite retrieval algorithms do exist, their accuracy is limited by the sparseness of in situ observations available for calibration and validation, which themselves may be unrepresentative of 500m and larger scale satellite footprints and grid pixels. Here, we use a combination of satellite and ground-based observations to close the water budgets of seven continental scale river basins (Mackenzie, Fraser, Nelson, Mississippi, Tocantins, Danube, and Ubangi), estimating mean ET as a residual. For any river basin, ET must equal total precipitation minus net runoff minus the change in total terrestrial water storage (TWS), in order for mass to be conserved. We make use of precipitation from two global observation-based products, archived runoff data, and TWS changes from the Gravity Recovery and Climate Experiment satellite mission. We demonstrate that while uncertainty in the water budget-based estimates of monthly ET is often too large for those estimates to be useful, the uncertainty in the mean annual cycle is small enough that it is practical for evaluating other ET products. Here, we evaluate five land surface model simulations, two operational atmospheric analyses, and a recent global reanalysis product based on our results. An important outcome is that the water budget-based ET time series in two tropical river basins, one in Brazil and the other in central Africa, exhibit a weak annual cycle, which may help to resolve debate about the strength of the annual cycle of ET in such regions and how ET is constrained throughout the year. The methods described will be useful for water and energy budget studies, weather and climate model assessments, and satellite-based ET retrieval optimization.

  11. Estimating basin scale evapotranspiration (ET) by water balance and remote sensing methods

    USGS Publications Warehouse

    Senay, G.B.; Leake, S.; Nagler, P.L.; Artan, G.; Dickinson, J.; Cordova, J.T.; Glenn, E.P.

    2011-01-01

    Evapotranspiration (ET) is an important hydrological process that can be studied and estimated at multiple spatial scales ranging from a leaf to a river basin. We present a review of methods in estimating basin scale ET and its applications in understanding basin water balance dynamics. The review focuses on two aspects of ET: (i) how the basin scale water balance approach is used to estimate ET; and (ii) how ‘direct’ measurement and modelling approaches are used to estimate basin scale ET. Obviously, the basin water balance-based ET requires the availability of good precipitation and discharge data to calculate ET as a residual on longer time scales (annual) where net storage changes are assumed to be negligible. ET estimated from such a basin water balance principle is generally used for validating the performance of ET models. On the other hand, many of the direct estimation methods involve the use of remotely sensed data to estimate spatially explicit ET and use basin-wide averaging to estimate basin scale ET. The direct methods can be grouped into soil moisture balance modelling, satellite-based vegetation index methods, and methods based on satellite land surface temperature measurements that convert potential ET into actual ET using a proportionality relationship. The review also includes the use of complementary ET estimation principles for large area applications. The review identifies the need to compare and evaluate the different ET approaches using standard data sets in basins covering different hydro-climatic regions of the world.

  12. Riparian Zone Evapotranspiration Estimates using Streamflow Diel Signals

    NASA Astrophysics Data System (ADS)

    Geisler, E.; McNamara, J. P.; Benner, S. G.; Flores, A. N.

    2015-12-01

    Diel climate variations impact vegetation and hydrologic systems in semi-arid mountainous watersheds primarily through transpiration. The impact diel variations have are particularly evident in streamflow during low flows. Understanding the controls on streamflow diel signals and the interaction they have within the riparian zone has been a focus of multiple studies to better understand the riparian zones as a system. The focus of the study was to monitor streamflow diel signals at five gauging stations within the same watershed to calculate riparian zone evapotranspiration (ET) and to understand diel signal variability throughout the watershed. Amplitude and timing of diel signals were analyzed at each site and used in determining controls on the diel signal. Meteorological and sap flux measurements were also monitored on both hillslope and riparian areas for comparison of fluxes. A spatially distributed hypsometric method was used to calculate ET for each gauging station sub-watershed for comparison with riparian ET estimates. The study found that, with the use of diel signals and a fixed riparian area, the estimated riparian zone ET ranged from a fraction to several times the calculated meteorological ET depending on the season. Although the riparian zone ET calculation was highly variable, it was constrained using diel signal timing and amplitude. Observations of differences in hillslope and riparian zone meteorological and sap flux variables also supported diel signal calculations. The study concludes that riparian zone ET is a substantial contributor to watershed scale ET during the summer months and that streamflow diel signal plays a large role in understanding watershed scale interactions and the riparian zone's influence on a semi-arid watershed.

  13. Determination of actual crop evapotranspiration (ETc) and dual crop coefficients (Kc) for cotton, wheat and maize in Fergana Valley: integration of the FAO-56 approach and BUDGET

    NASA Astrophysics Data System (ADS)

    Kenjabaev, Shavkat; Dernedde, Yvonne; Frede, Hans-Georg; Stulina, Galina

    2014-05-01

    Determination of the actual crop evapotranspiration (ETc) during the growing period is important for accurate irrigation scheduling in arid and semi-arid regions. Development of a crop coefficient (Kc) can enhance ETc estimations in relation to specific crop phenological development. This research was conducted to determine daily and growth-stage-specific Kc and ETc values for cotton (Gossypium hirsutum L.), winter wheat (Triticum aestivum L.) and maize (Zea mays L.) for silage at fields in Fergana Valley (Uzbekistan). The soil water balance model - Budget with integration of the dual crop procedure of the FAO-56 was used to estimate the ETc and separate it into evaporation (Ec) and transpiration (Tc) components. An empirical equation was developed to determine the daily Kc values based on the estimated Ec and Tc. The ETc, Kc determination and comparison to existing FAO Kc values were performed based on 10, 5 and 6 study cases for cotton, wheat and maize, respectively. Mean seasonal amounts of crop water consumption in terms of ETc were 560±50, 509±27 and 243±39 mm for cotton, wheat and maize, respectively. The growth-stage-specific Kc for cotton, wheat and maize was 0.15, 0.27 and 0.11 at initial; 1.15, 1.03 and 0.56 at mid; and 0.45, 0.89 and 0.53 at late season stages. These values correspond to those reported by the FAO-56. Development of site specific Kc helps tremendously in irrigation management and furthermore provides precise water applications in the region. The developed simple approach to estimate daily Kc for the three main crops grown in the Fergana region was a first attempt to meet this issue. Keywords: Actual crop evapotranspiration, evaporation and transpiration, crop coefficient, model BUDGET, Fergana Valley.

  14. Divergence of reference evapotranspiration estimates under advective tropical conditions

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Standardized reference evapotranspiration (ET) and crop specific coefficients are frequently used to assess crop water use in irrigated agriculture. However, equations for calculating reference ET have not been well validated in more humid environments where optimal crop yields can depend on supplem...

  15. Ecosystem evapotranspiration: Challenges in measurements, estimates, and modeling

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Evapotranspiration (ET) processes at the leaf-to-landscape scales in multiple land uses have important controls and feedbacks for the local, regional and global climate and water resource systems. Innovative methods, tools, and technologies for improved understanding and quantification of ET and cro...

  16. Remote sensing estimation of evapotranspiration for SWAT Model Calibration

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Hydrological models are used to assess many water resource problems from water quantity to water quality issues. The accurate assessment of the water budget, primarily the influence of precipitation and evapotranspiration (ET), is a critical first-step evaluation, which is often overlooked in hydro...

  17. An investigation of spectral change as influenced by irrigation and evapotranspiration volume estimation in western Nebraska

    USGS Publications Warehouse

    Seevers, P.M.; Sadowski, F.C.; Lauer, D.T.

    1990-01-01

    Retrospective satellite image data were evaluated for their ability to demonstrate the influence of center-pivot irrigation development in western Nebraska on spectral change and climate-related factors for the region. Periodic images of an albedo index and a normalized difference vegetation index (NDVI) were generated from calibrated Landsat multispectral scanner (MSS) data and used to monitor spectral changes associated with irrigation development from 1972 through 1986. The albedo index was not useful for monitoring irrigation development. For the NDVI, it was found that proportions of counties in irrigated agriculture, as discriminated by a threshold, were more highly correlated with reported ground estimates of irrigated agriculture than were county mean greenness values. A similar result was achieved when using coarse resolution Advanced Very High Resolution Radiometer (AVHRR) image data for estimating irrigated agriculture. The NDVI images were used to evaluate a procedure for making areal estimates of actual evapotranspiration (ET) volumes. Estimates of ET volumes for test counties, using reported ground acreages and corresponding standard crop coefficients, were correlated with the estimates of ET volume using crop coefficients scaled to NDVI values and pixel counts of crop areas. These county estimates were made under the assumption that soil water availability was unlimited. For nonirrigated vegetation, this may result in over-estimation of ET volumes. Ground information regarding crop types and acreages are required to derive the NDVI scaling factor. Potential ET, estimated with the Jensen-Haise model, is common to both methods. These results, achieved with both MSS and AVHRR data, show promise for providing climatologically important land surface information for regional and global climate models. ?? 1990 Kluwer Academic Publishers.

  18. Spatially distributed evapotranspiration and recharge estimation for sand regions of Hungary in the context of climate change

    NASA Astrophysics Data System (ADS)

    Csáki, Péter; Kalicz, Péter; Gribovszki, Zoltán

    2016-04-01

    Water balance of sand regions of Hungary was analysed using remote-sensing based evapotranspiration (ET) maps (1*1 km spatial resolution) by CREMAP model over the 2000-2008 period. The mean annual (2000-2008) net groundwater recharge (R) estimated as the difference in mean annual precipitation (P) and ET, taking advantage that for sand regions the surface runoff is commonly negligible. For the examined nine-year period (2000-2008) the ET and R were about 90 percent and 10 percent of the P. The mean annual ET and R were analysed in the context of land cover types. A Budyko-model was used in spatially-distributed mode for the climate change impact analysis. The parameters of the Budyko-model (α) was calculated for pixels without surplus water. For the extra-water affected pixels a linear model with β-parameters (actual evapotranspiration / pan-evapotranspiration) was used. These parameter maps can be used for evaluating future ET and R in spatially-distributed mode (1*1 km resolution). By using the two parameter maps (α and β) and data of regional climate models (mean annual temperature and precipitation) evapotranspiration and net groundwater recharge projections have been done for three future periods (2011-2040, 2041-2070, 2071-2100). The expected ET and R changes have been determined relative to a reference period (1981-2010). According to the projections, by the end of the 21th century, ET may increase while in case of R a heavy decrease can be detected for the sand regions of Hungary. This research has been supported by Agroclimate.2 VKSZ_12-1-2013-0034 project. Keywords: evapotranspiration, net groundwater recharge, climate change, Budyko-model

  19. Processes driving nocturnal transpiration and implications for estimating land evapotranspiration

    NASA Astrophysics Data System (ADS)

    de Dios, Víctor Resco; Roy, Jacques; Ferrio, Juan Pedro; Alday, Josu G.; Landais, Damien; Milcu, Alexandru; Gessler, Arthur

    2015-06-01

    Evapotranspiration is a major component of the water cycle, yet only daytime transpiration is currently considered in Earth system and agricultural sciences. This contrasts with physiological studies where 25% or more of water losses have been reported to occur occurring overnight at leaf and plant scales. This gap probably arose from limitations in techniques to measure nocturnal water fluxes at ecosystem scales, a gap we bridge here by using lysimeters under controlled environmental conditions. The magnitude of the nocturnal water losses (12-23% of daytime water losses) in row-crop monocultures of bean (annual herb) and cotton (woody shrub) would be globally an order of magnitude higher than documented responses of global evapotranspiration to climate change (51-98 vs. 7-8 mm yr-1). Contrary to daytime responses and to conventional wisdom, nocturnal transpiration was not affected by previous radiation loads or carbon uptake, and showed a temporal pattern independent of vapour pressure deficit or temperature, because of endogenous controls on stomatal conductance via circadian regulation. Our results have important implications from large-scale ecosystem modelling to crop production: homeostatic water losses justify simple empirical predictive functions, and circadian controls show a fine-tune control that minimizes water loss while potentially increasing posterior carbon uptake.

  20. Processes driving nocturnal transpiration and implications for estimating land evapotranspiration

    PubMed Central

    de Dios, Víctor Resco; Roy, Jacques; Ferrio, Juan Pedro; Alday, Josu G.; Landais, Damien; Milcu, Alexandru; Gessler, Arthur

    2015-01-01

    Evapotranspiration is a major component of the water cycle, yet only daytime transpiration is currently considered in Earth system and agricultural sciences. This contrasts with physiological studies where 25% or more of water losses have been reported to occur occurring overnight at leaf and plant scales. This gap probably arose from limitations in techniques to measure nocturnal water fluxes at ecosystem scales, a gap we bridge here by using lysimeters under controlled environmental conditions. The magnitude of the nocturnal water losses (12–23% of daytime water losses) in row-crop monocultures of bean (annual herb) and cotton (woody shrub) would be globally an order of magnitude higher than documented responses of global evapotranspiration to climate change (51–98 vs. 7–8 mm yr−1). Contrary to daytime responses and to conventional wisdom, nocturnal transpiration was not affected by previous radiation loads or carbon uptake, and showed a temporal pattern independent of vapour pressure deficit or temperature, because of endogenous controls on stomatal conductance via circadian regulation. Our results have important implications from large-scale ecosystem modelling to crop production: homeostatic water losses justify simple empirical predictive functions, and circadian controls show a fine-tune control that minimizes water loss while potentially increasing posterior carbon uptake. PMID:26074373

  1. Processes driving nocturnal transpiration and implications for estimating land evapotranspiration.

    PubMed

    de Dios, Víctor Resco; Roy, Jacques; Ferrio, Juan Pedro; Alday, Josu G; Landais, Damien; Milcu, Alexandru; Gessler, Arthur

    2015-06-15

    Evapotranspiration is a major component of the water cycle, yet only daytime transpiration is currently considered in Earth system and agricultural sciences. This contrasts with physiological studies where 25% or more of water losses have been reported to occur occurring overnight at leaf and plant scales. This gap probably arose from limitations in techniques to measure nocturnal water fluxes at ecosystem scales, a gap we bridge here by using lysimeters under controlled environmental conditions. The magnitude of the nocturnal water losses (12-23% of daytime water losses) in row-crop monocultures of bean (annual herb) and cotton (woody shrub) would be globally an order of magnitude higher than documented responses of global evapotranspiration to climate change (51-98 vs. 7-8 mm yr(-1)). Contrary to daytime responses and to conventional wisdom, nocturnal transpiration was not affected by previous radiation loads or carbon uptake, and showed a temporal pattern independent of vapour pressure deficit or temperature, because of endogenous controls on stomatal conductance via circadian regulation. Our results have important implications from large-scale ecosystem modelling to crop production: homeostatic water losses justify simple empirical predictive functions, and circadian controls show a fine-tune control that minimizes water loss while potentially increasing posterior carbon uptake.

  2. Processes driving nocturnal transpiration and implications for estimating land evapotranspiration.

    PubMed

    de Dios, Víctor Resco; Roy, Jacques; Ferrio, Juan Pedro; Alday, Josu G; Landais, Damien; Milcu, Alexandru; Gessler, Arthur

    2015-01-01

    Evapotranspiration is a major component of the water cycle, yet only daytime transpiration is currently considered in Earth system and agricultural sciences. This contrasts with physiological studies where 25% or more of water losses have been reported to occur occurring overnight at leaf and plant scales. This gap probably arose from limitations in techniques to measure nocturnal water fluxes at ecosystem scales, a gap we bridge here by using lysimeters under controlled environmental conditions. The magnitude of the nocturnal water losses (12-23% of daytime water losses) in row-crop monocultures of bean (annual herb) and cotton (woody shrub) would be globally an order of magnitude higher than documented responses of global evapotranspiration to climate change (51-98 vs. 7-8 mm yr(-1)). Contrary to daytime responses and to conventional wisdom, nocturnal transpiration was not affected by previous radiation loads or carbon uptake, and showed a temporal pattern independent of vapour pressure deficit or temperature, because of endogenous controls on stomatal conductance via circadian regulation. Our results have important implications from large-scale ecosystem modelling to crop production: homeostatic water losses justify simple empirical predictive functions, and circadian controls show a fine-tune control that minimizes water loss while potentially increasing posterior carbon uptake. PMID:26074373

  3. Daily evapotranspiration estimates from extrapolating instantaneous airborne remote sensing ET values

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In this study, six extrapolation methods have been compared for their ability to estimate daily crop evapotranspiration (ETd) from instantaneous latent heat flux estimates derived from digital airborne multispectral remote sensing imagery. Data used in this study were collected during an experiment...

  4. Integration of vegetation indices into a water balance model to estimate evapotranspiration of wheat and corn

    NASA Astrophysics Data System (ADS)

    Padilla, F. L. M.; González-Dugo, M. P.; Gavilán, P.; Domínguez, J.

    2010-10-01

    Vegetation indices (VIs) have been traditionally used for quantitative monitoring of vegetation. Remotely sensed radiometric measurements of visible and infrared solar energy, which is reflected or emitted by plant canopies, can be used to obtain rapid, non-destructive estimates of certain canopy attributes and parameters. One parameter of special interest for water management applications, is the crop coefficient employed by the FAO-56 model to derive actual crop evapotranspiration (ET). The aim of this study was to evaluate a methodology that combines the basal crop coefficient derived from VIs with a daily soil water balance in the root zone to estimate daily evapotranspiration rates for corn and wheat crops at field scale. The ability of the model to trace water stress in these crops was also assessed. Vegetation indices were first retrieved from field hand-held radiometer measurements and then from Landsat 5 and 7 satellite images. The results of the model were validated using two independent measurement systems for ET and regular soil moisture monitoring, in order to evaluate the behavior of the soil and atmosphere components of the model. ET estimates were compared with latent heat flux measured by an eddy covariance system and with weighing lysimeter measurements. Average overestimates of daily ET of 8 and 11% were obtained for corn and wheat, respectively, with good agreement between the estimated and measured root-zone water deficit for both crops when field radiometry was employed. Satellite remote-sensing inputs overestimated ET by 4 to 9%, showing a non-significant lost of accuracy when the satellite sensor data replaced the field radiometry data. The model was also used to monitor the water stress during the 2009 growing season, detecting several periods of water stress in both crops. Some of these stresses occurred during stages like grain filling, when the water stress is know to have a negative effect on yield. This fact could explain the lower

  5. Integration of vegetation indices into a water balance model to estimate evapotranspiration of wheat and corn

    NASA Astrophysics Data System (ADS)

    Padilla, F. L. M.; González-Dugo, M. P.; Gavilán, P.; Domínguez, J.

    2011-04-01

    Vegetation indices (VIs) have been traditionally used for quantitative monitoring of vegetation. Remotely sensed radiometric measurements of visible and infrared solar energy, which is reflected or emitted by plant canopies, can be used to obtain rapid, non-destructive estimates of certain canopy attributes and parameters. One parameter of special interest for water management applications, is the crop coefficient employed by the FAO-56 model to derive actual crop evapotranspiration (ET). The aim of this study was to evaluate a methodology that combines the basal crop coefficient derived from VIs with a daily soil water balance in the root zone to estimate daily evapotranspiration rates for corn and wheat crops at field scale. The ability of the model to trace water stress in these crops was also assessed. Vegetation indices were first retrieved from field hand-held radiometer measurements and then from Landsat 5 and 7 satellite images. The results of the model were validated using two independent measurement systems for ET and regular soil moisture monitoring, in order to evaluate the behavior of the soil and atmosphere components of the model. ET estimates were compared with latent heat flux measured by an eddy covariance system and with weighing lysimeter measurements. Average overestimates of daily ET of 8 and 11% were obtained for corn and wheat, respectively, with good agreement between the estimated and measured root-zone water deficit for both crops when field radiometry was employed. When the satellite sensor data replaced the field radiometry data the overestimation figures slightly changed to 9 and 6% for the same two crops. The model was also used to monitor the water stress during the 2009 growing season, detecting several periods of water stress in both crops. Some of these stresses occurred during stages like grain filling, when the water stress is know to have a negative effect on yield. This fact could explain the lower yield reached compared to

  6. Evapotranspiration estimation in pastures at the municipality of Campo Grande, Brazil, using SEBAL and remote sensing data

    NASA Astrophysics Data System (ADS)

    Andrade, R. G.; Leivas, J. F.; Alvarez, I. A.; Vicente, L. E.; Nogueira, S. F.; Hott, M. C.; Takemura, C. M.; Gomes, D.

    2011-12-01

    The knowledge of the total water loss by evapotranspiration is essential for plant growth and development assessments. Studies show that the success of the Brazilian livestock is directly linked to the fact that bovine cattle is reared in pastures, which enables low cost beef production. However, many factors influence the productive capacity of pastures and, consequently, beef production. Among these, there are variations in precipitation, causing periods of water deficit even during rainy seasons, which makes evapotranspiration a major factor in the diagnosis of climatic and environmental conditions of pasture areas. Remote sensing information has been used by several models and algorithms for obtaining parameters of the Earth's surface. The Surface Energy Balance Algorithms for Land (SEBAL) is an algorithm for evapotranspiration estimation for large areas. It is processed by means of computational steps, which predict a full assessment of the solar radiation and energy on the Earth's surface. For that it uses data of sensors that collect wavelengths in the visible, reflective infrared and thermal bands. This study aimed at estimating actual daily evapotranspiration (ETdaily) in pasture areas at Embrapa Beef Cattle's Experimental Farm, located in the municipality of Campo Grande, Brazil, by means of the SEBAL algorithm and Landsat 5-TM images. For the scenes of May 9, June 28, July 7 and October 2, 2009, the ETdaily varied from 0.50 to 3.50 mm/day with an average of 1.85 mm/day for pasture areas. The application of the SEBAL algorithm proved itself adequate in extensive areas, and it is possible to use it for monitoring pasture conditions, thus contributing to making decisions that favor beef cattle production with environmental sustainability.

  7. Evapotranspiration estimation in pastures at the municipality of Campo Grande, Brazil, using SEBAL and remote sensing data

    NASA Astrophysics Data System (ADS)

    Andrade, R. G.; Leivas, J. F.; Hott, M. C.; Alvarez, I. A.; Vicente, L. E.; Nogueira, S. F.; Takemura, C. M.

    2011-12-01

    The knowledge of the total water loss by evapotranspiration is essential for plant growth and development assessments. Studies show that the success of the Brazilian livestock is directly linked to the fact that bovine cattle is reared in pastures, which enables low cost beef production. However, many factors influence the productive capacity of pastures and, consequently, beef production. Among these, there are variations in precipitation, causing periods of water deficit even during rainy seasons, which makes evapotranspiration a major factor in the diagnosis of climatic and environmental conditions of pasture areas. Remote sensing information has been used by several models and algorithms for obtaining parameters of the Earth's surface. The Surface Energy Balance Algorithms for Land (SEBAL) is an algorithm for evapotranspiration estimation for large areas. It is processed by means of computational steps, which predict a full assessment of the solar radiation and energy on the Earth's surface. For that it uses data of sensors that collect wavelengths in the visible, reflective infrared and thermal bands. This study aimed at estimating actual daily evapotranspiration (ETdaily) in pasture areas at Embrapa Beef Cattle's Experimental Farm, located in the municipality of Campo Grande, Brazil, by means of the SEBAL algorithm and Landsat 5-TM images. For the scenes of May 9, June 28, July 7 and October 2, 2009, the ETdaily varied from 0.50 to 3.50 mm d-1 with an average of 1.85 mm d-1 for pasture areas. The application of the SEBAL algorithm proved itself adequate in extensive areas, and it is possible to use it for monitoring pasture conditions, thus contributing to making decisions that favor beef cattle production with environmental sustainability.

  8. Estimation of land surface evapotranspiration with A satellite remote sensing procedure

    USGS Publications Warehouse

    Irmak, A.; Ratcliffe, I.; Ranade, P.; Hubbard, K.G.; Singh, R.K.; Kamble, B.; Kjaersgaard, J.

    2011-01-01

    There are various methods available for estimating magnitude and trends of evapotranspiration. Bowen ratio energy balance system and eddy correlation techniques offer powerful alternatives for measuring land surface evapotranspiration. In spite of the elegance, high accuracy, and theoretical attractions of these techniques for measuring evapotranspiration, their practical use over large areas can be limited due to the number of sites needed and the related expense. Application of evapotranspiration mapping from satellite measurements can overcome the limitations. The objective of this study was to utilize the METRIC??? (Mapping Evapotranspiration at High Resolution using Internalized Calibration) model in Great Plains environmental settings to understand water use in managed ecosystems on a regional scale. We investigated spatiotemporal distribution of a fraction of reference evapotranspiration (ETrF) using eight Landsat 5 images during the 2005 and 2006 growing season for path 29, row 32. The ETrF maps generated by METRIC??? allowed us to follow the magnitude and trend in ETrF for major land-use classes during the growing season. The ETrF was lower early in the growing season for agricultural crops and gradually increased as the normalized difference vegetation index of crops increased, thus presenting more surface area over which water could transpire toward the midseason. Comparison of predictions with Bowen ratio energy balance system measurements at Clay Center, NE, showed that METRIC??? performed well at the field scale for predicting evapotranspiration from a cornfield. If calibrated properly, the model could be a viable tool to estimate water use in managed ecosystems in subhumid climates at a large scale. ?? 2011 Copyright by the Center for Great Plains Studies, University of Nebraska-Lincoln.

  9. Estimated ground-water discharge by evapotranspiration, Ash Meadows Area, Nye County, Nevada, 1994

    SciTech Connect

    Nichols, W.D.; Laczniak, R.J.; DeMeo, G.A.; Rapp, T.R.

    1997-05-01

    Ground water discharges from the regional ground-water flow system that underlies the eastern part of the Nevada Test Site through numerous springs and seeps in the Ash Meadows National Wildlife Refuge in southern Nevada. The total spring discharge was estimated to be about 17,000 acre-feet per year by earlier studies. Previous studies estimated that about 10,500 acre-feet of this discharge was lost to evapotranspiration. The present study was undertaken to develop a more rigorous approach to estimating ground-water discharge in the Ash Meadows area. Part of the study involves detailed field investigation of evapotranspiration. Data collection began in early 1994. The results of the first year of study provide a basis for making preliminary estimates of ground-water discharge by evapotranspiration. An estimated 13,100 acre-feet of ground water was evapotranspired from about 6,800 acres of marsh and salt-grass. Additional 3,500 acre-feet may have been transpired from the open water and from about 1,460 acres of other areas of Ash Meadows in which field studies have not yet been made.

  10. Geohydrology and evapotranspiration at Franklin Lake playa, Inyo County, California; with a section on estimating evapotranspiration using the energy-budget eddy-correlation technique

    USGS Publications Warehouse

    Czarnecki, John B.; Stannard, David I.

    1997-01-01

    Franklin Lake playa is one of the principal discharge areas of the ground-water-flow system associated with Yucca Mountain, Nevada, the potential site of a high-level nuclear-waste repository. By using the energy-budget eddy-correlation technique, measurements made between June 1983 and April 1984 to estimate evapotranspiration were found to range from 0.1 centimeter per day during winter months to about 0.3 centimeter per day during summer months; the annual average was 0.16 centimeter per day. These estimates were compared with evapotranspiration estimates calculated from six other methods.

  11. Comparison of methods for estimating evapotranspiration in a small rangeland catchment

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Evapotranspiration (ET) was quantified for two rangeland vegetation types, aspen and sagebrush/grassland, over an eight year study period by comparing several approaches for estimating ET: eddy covariance systems (EC, available for only six years); soil water storage loss measured by time domain ref...

  12. Estimating Agricultural Water Use using the Operational Simplified Surface Energy Balance Evapotranspiration Estimation Method

    NASA Astrophysics Data System (ADS)

    Forbes, B. T.

    2015-12-01

    Due to the predominantly arid climate in Arizona, access to adequate water supply is vital to the economic development and livelihood of the State. Water supply has become increasingly important during periods of prolonged drought, which has strained reservoir water levels in the Desert Southwest over past years. Arizona's water use is dominated by agriculture, consuming about seventy-five percent of the total annual water demand. Tracking current agricultural water use is important for managers and policy makers so that current water demand can be assessed and current information can be used to forecast future demands. However, many croplands in Arizona are irrigated outside of areas where water use reporting is mandatory. To estimate irrigation withdrawals on these lands, we use a combination of field verification, evapotranspiration (ET) estimation, and irrigation system qualification. ET is typically estimated in Arizona using the Modified Blaney-Criddle method which uses meteorological data to estimate annual crop water requirements. The Modified Blaney-Criddle method assumes crops are irrigated to their full potential over the entire growing season, which may or may not be realistic. We now use the Operational Simplified Surface Energy Balance (SSEBop) ET data in a remote-sensing and energy-balance framework to estimate cropland ET. SSEBop data are of sufficient resolution (30m by 30m) for estimation of field-scale cropland water use. We evaluate our SSEBop-based estimates using ground-truth information and irrigation system qualification obtained in the field. Our approach gives the end user an estimate of crop consumptive use as well as inefficiencies in irrigation system performance—both of which are needed by water managers for tracking irrigated water use in Arizona.

  13. How do alternative root water uptake models affect the inverse estimation of soil hydraulic parameters and the prediction of evapotranspiration?

    NASA Astrophysics Data System (ADS)

    Gayler, Sebastian; Salima-Sultana, Daisy; Selle, Benny; Ingwersen, Joachim; Wizemann, Hans-Dieter; Högy, Petra; Streck, Thilo

    2016-04-01

    equation combined with the Mualem-van Genuchten approach to parametrize the soil hydraulic functions was coupled to three different root-water uptake modules according to Nimah & Hanks, Feddes, and van Genuchten. Potential evapotranspiration was estimated following Penman-Monteith, whereas leaf area index and rooting depth were predefined model inputs derived from observations. Simulation results were compared to 3-year time-series of time-domain reflectometry measurements of soil moisture in two to five different depths (depending on solum thickness) and eddy-covariance measurements of evapotranspiration. Data of two growing seasons (2010, 2011) were used for the inverse estimation of saturated water content, saturated hydraulic conductivity and the van Genuchten parameters α and n using the universal optimization tool UCODE. Data from the growing season 2012 were used for model validation. The model calibration results showed a similar and acceptable goodness of fit between simulated and observed soil water contents and actual evapotranspiration for all there models. There was no substantial difference in model performance between the alternative root water uptake models during the calibration phase 2010-2011. However, the values of the optimized soil hydraulic parameters substantially differed in some cases, resulting in an increased model uncertainty during the prediction phase 2012, especially during phases of strong drying out of the soil. Albeit single model combinations are superior over the others for single locations with respect to the different observables (soil moisture, evapotranspiration), none of the models outcompeted the others over all years, locations and observables. We conclude that model solutions cannot be considered unique when different process representations are selected and the respective soil hydraulic parameters fitted (equifinality problem).

  14. Estimating evapotranspiration in different rain-fed peatlands from groundwater level changes

    NASA Astrophysics Data System (ADS)

    Dettmann, Ullrich; Maurer, Eike; Bechtold, Michel; Brümmer, Christian; Tiemeyer, Bärbel

    2014-05-01

    groundwater level continuously declined during rain-free periods with different slopes during the night and the day, resulting in a step-like shape of the hydrograph. Other sites showed a continuous decline at daytime followed by weakly increasing or constant groundwater levels at night. Based on this analysis, we developed a modification of the White-method for estimating the evapotranspiration of rain-fed peatlands. The approach will be validated with eddy-covariance data from one site.

  15. Estimating evapotranspiration with thermal UAV data and two source energy balance models

    NASA Astrophysics Data System (ADS)

    Hoffmann, H.; Nieto, H.; Jensen, R.; Guzinski, R.; Zarco-Tejada, P. J.; Friborg, T.

    2015-08-01

    Estimating evapotranspiration is important when managing water resources and cultivating crops. Evapotranspiration can be estimated using land surface heat flux models and remotely sensed land surface temperatures (LST) which recently have become obtainable in very high resolution using Unmanned Aerial Vehicles (UAVs). Very high resolution LST can give insight into e.g. distributed crop conditions within cultivated fields. In this study evapotranspiration is estimated using LST retrieved with a UAV and the physically-based, two source energy balance models: the Priestley-Taylor TSEB (TSEB-PT) and the Dual-Temperature-Difference (DTD). A fixed-wing UAV was flown over a barley field in western Denmark during the spring and summer in 2014 and retrieved images of LST is successfully processed into thermal mosaics which serve as model input for both TSEB-PT and DTD. The aim is to assess whether a lightweight thermal camera mounted on a UAV is able to provide data of sufficient quality to obtain high spatial and temporal resolution surface energy heat fluxes. Furthermore, this study evaluates the performance of the two source energy balance (TSEB) model scheme during cloudy and overcast weather conditions. This is feasible due to the low data retrieval altitude compared to satellite thermal data that are only available during clear skies and sunny conditions. Flux estimates from TSEB-PT and DTD are compared and validated against field data collected using an eddy covariance system located at same site at which the UAV flights were conducted. Furthermore, spatially distributed evapotranspiration patterns are evaluated using known irrigation patterns. Evapotranspiration is well estimated by both TSEB-PT and DTD with DTD as the best predictor. The DTD model provides results comparable to studies estimating evapotranspiration with satellite retrieved LST and physical land-surface models. This study shows that the UAV platform and the lightweight thermal camera provide high

  16. Barren area evapotranspiration estimates generated from energy budget measurements in the Gila River valley of Arizona

    USGS Publications Warehouse

    Leppanen, O.E.

    1980-01-01

    Estimates of evapotranspiration for 479 successive days were created by using energy budget measurements. The measurement point was on the 2-kilometer wide flood plain of the Gila River in east-central Arizona, about 18 kilometers above Coolidge Dam. The flood plain had been cleared of all tall vegetation for distances of about 20 kilometers upstream and 5 kilometers downstream from the measurement site. Chaining, raking, and burning had been used to clear the area immediately surrounding the measurement site about 6 months before measurements began. Ground cover was sparse volunteer Bermudagrass and scattered seepwillow for a distance of at least 1 kilometer in all directions from the measurement point . The water table was deep , so most of the evaporated water came from rainfall, but some came from soil moisture deeper than 2 meters. The March to March water loss (evapotranspiration less rain) was about 47 millimeters, evapotranspiration demand was 377 millimeters. Daily rates varied from very small amounts of condensation to almost 5 millimeters of evapotranspiration. (USGS)

  17. Actual evapotranspiration (water use) assessment of the Colorado River Basin at the Landsat resolution using the operational simplified surface energy balance model

    USGS Publications Warehouse

    Singh, Ramesh K.; Senay, Gabriel B.; Velpuri, Naga Manohar; Bohms, Stefanie; Russell L, Scott; Verdin, James P.

    2014-01-01

    Accurately estimating consumptive water use in the Colorado River Basin (CRB) is important for assessing and managing limited water resources in the basin. Increasing water demand from various sectors may threaten long-term sustainability of the water supply in the arid southwestern United States. We have developed a first-ever basin-wide actual evapotranspiration (ETa) map of the CRB at the Landsat scale for water use assessment at the field level. We used the operational Simplified Surface Energy Balance (SSEBop) model for estimating ETa using 328 cloud-free Landsat images acquired during 2010. Our results show that cropland had the highest ETa among all land cover classes except for water. Validation using eddy covariance measured ETa showed that the SSEBop model nicely captured the variability in annual ETa with an overall R2 of 0.78 and a mean bias error of about 10%. Comparison with water balance-based ETa showed good agreement (R2 = 0.85) at the sub-basin level. Though there was good correlation (R2 = 0.79) between Moderate Resolution Imaging Spectroradiometer (MODIS)-based ETa (1 km spatial resolution) and Landsat-based ETa (30 m spatial resolution), the spatial distribution of MODIS-based ETa was not suitable for water use assessment at the field level. In contrast, Landsat-based ETa has good potential to be used at the field level for water management. With further validation using multiple years and sites, our methodology can be applied for regular production of ETa maps of larger areas such as the conterminous United States.

  18. Combining land surface models and remote sensing data to estimate evapotranspiration for drought monitoring in Europe

    NASA Astrophysics Data System (ADS)

    Cammalleri, C.; Sepulcre-Cantó, G.; Vogt, J.

    2014-10-01

    The main hydrologic feedback from the land-surface to the atmosphere is the evapotranspiration, ET, which embraces the response of both the soil and vegetated surface to the atmospheric forcing (e.g., precipitation and temperature), as well as influences locally atmospheric humidity, cloud formation and precipitation, the main driver for drought. Actual ET is regulated by several factors, including biological quantities (e.g., rooting depth, leaf area, fraction of absorbed photosynthetically active radiation) and soil water status. The ET temporal dynamic is strongly affected by rainfall deficits, and in turn it represents a robust proxy of the effects of water shortage on plants. These characteristics make ET a promising quantity for monitoring environmental drought, defined as a shortage of water availability that reduces the ecosystem productivity. In the last few decades, the capability to accurately model ET over large areas in a spatial-distributed fashion has increased notably. Most of the improvements in this field are related to the increasing availability of remote sensing data, and the achievements in modelling of ET-related quantities. Several land-surface models exploit the richness of newly available datasets, including the Community Land Model (CLM) and the Meteosat Second Generation (MSG) ET outputs. Here, the potentiality of ET maps obtained by combining land-surface models and remote sensing data through these two schemes is explored, with a special focus on the reliability of ET (and derived standardized variables) as drought indicator. Tests were performed over Europe at moderate spatial resolution (3-5 km), with the final goal to improve the estimation of soil water status as a contribution to the European Drought Observatory (EDO, http://edo.jrc.ec.europa.eu).

  19. A comparison of estimates of basin-scale soil-moisture evapotranspiration and estimates of riparian groundwater evapotranspiration with implications for water budgets in the Verde Valley, Central Arizona, USA

    USGS Publications Warehouse

    Tillman, Fred; Wiele, Stephen M.; Pool, Donald R.

    2015-01-01

    Population growth in the Verde Valley in Arizona has led to efforts to better understand water availability in the watershed. Evapotranspiration (ET) is a substantial component of the water budget and a critical factor in estimating groundwater recharge in the area. In this study, four estimates of ET are compared and discussed with applications to the Verde Valley. Higher potential ET (PET) rates from the soil-water balance (SWB) recharge model resulted in an average annual ET volume about 17% greater than for ET from the basin characteristics (BCM) recharge model. Annual BCM PET volume, however, was greater by about a factor of 2 or more than SWB actual ET (AET) estimates, which are used in the SWB model to estimate groundwater recharge. ET also was estimated using a method that combines MODIS-EVI remote sensing data and geospatial information and by the MODFLOW-EVT ET package as part of a regional groundwater-flow model that includes the study area. Annual ET volumes were about same for upper-bound MODIS-EVI ET for perennial streams as for the MODFLOW ET estimates, with the small differences between the two methods having minimal impact on annual or longer groundwater budgets for the study area.

  20. Estimation of reference evapotranspiration using multivariate fractional polynomial, Bayesian regression, and robust regression models in three arid environments

    NASA Astrophysics Data System (ADS)

    Khoshravesh, Mojtaba; Sefidkouhi, Mohammad Ali Gholami; Valipour, Mohammad

    2015-12-01

    The proper evaluation of evapotranspiration is essential in food security investigation, farm management, pollution detection, irrigation scheduling, nutrient flows, carbon balance as well as hydrologic modeling, especially in arid environments. To achieve sustainable development and to ensure water supply, especially in arid environments, irrigation experts need tools to estimate reference evapotranspiration on a large scale. In this study, the monthly reference evapotranspiration was estimated by three different regression models including the multivariate fractional polynomial (MFP), robust regression, and Bayesian regression in Ardestan, Esfahan, and Kashan. The results were compared with Food and Agriculture Organization (FAO)-Penman-Monteith (FAO-PM) to select the best model. The results show that at a monthly scale, all models provided a closer agreement with the calculated values for FAO-PM (R 2 > 0.95 and RMSE < 12.07 mm month-1). However, the MFP model gives better estimates than the other two models for estimating reference evapotranspiration at all stations.

  1. Estimating evapotranspiration and drought stress with ground-based thermal remote sensing in agriculture: a review.

    PubMed

    Maes, W H; Steppe, K

    2012-08-01

    As evaporation of water is an energy-demanding process, increasing evapotranspiration rates decrease the surface temperature (Ts) of leaves and plants. Based on this principle, ground-based thermal remote sensing has become one of the most important methods for estimating evapotranspiration and drought stress and for irrigation. This paper reviews its application in agriculture. The review consists of four parts. First, the basics of thermal remote sensing are briefly reviewed. Second, the theoretical relation between Ts and the sensible and latent heat flux is elaborated. A modelling approach was used to evaluate the effect of weather conditions and leaf or vegetation properties on leaf and canopy temperature. Ts increases with increasing air temperature and incoming radiation and with decreasing wind speed and relative humidity. At the leaf level, the leaf angle and leaf dimension have a large influence on Ts; at the vegetation level, Ts is strongly impacted by the roughness length; hence, by canopy height and structure. In the third part, an overview of the different ground-based thermal remote sensing techniques and approaches used to estimate drought stress or evapotranspiration in agriculture is provided. Among other methods, stress time, stress degree day, crop water stress index (CWSI), and stomatal conductance index are discussed. The theoretical models are used to evaluate the performance and sensitivity of the most important methods, corroborating the literature data. In the fourth and final part, a critical view on the future and remaining challenges of ground-based thermal remote sensing is presented. PMID:22922637

  2. A Hybrid Surface Energy Balance Approach for Large Scale Evapotranspiration Estimation and Prediction in Agricultural Areas

    NASA Astrophysics Data System (ADS)

    Neale, C. M.; Vinukollu, R. K.; Chavez, J. L.

    2005-05-01

    Over the last few years, several surface energy balance methods for the estimation of latent heat fluxes from remotely sensed satellite imagery have been introduced and/or refined. These models have shown the ability of obtaining seasonal spatially distributed evapotranspiration fluxes at various scales and over large areas. In the arid western United States, water managers are challenged in balancing the high consumptive use of irrigated agriculture with competing urban and ecological uses of fresh water. Water managers from Irrigation Districts and Federal Agencies such as the US Bureau of Reclamation have a need for improved operational tools for the prediction of evapotranspiration and irrigation water demand on a five to ten day timeframe. The paper will present a hybrid model that couples the surface energy balance approach with a simple empirical reflectance-based crop coefficient model, for estimation and prediction of evapotranspiration over large agricultural areas. The model is applied to a rain-fed intensively cultivated agricultural area, close to Ames, Iowa during the summer of 2002. The satellite, airborne and ground fluxes were collected during the SMACEX 02 experiment. The model is run in both simulation and prediction mode and the derived latent heat fluxes are compared spatially and temporally to aircraft derived fluxes from the USU airborne system and ground measured fluxes at thirteen eddy covariance stations, using appropriate upwind footprint source area functions.

  3. Estimating evapotranspiration and drought stress with ground-based thermal remote sensing in agriculture: a review.

    PubMed

    Maes, W H; Steppe, K

    2012-08-01

    As evaporation of water is an energy-demanding process, increasing evapotranspiration rates decrease the surface temperature (Ts) of leaves and plants. Based on this principle, ground-based thermal remote sensing has become one of the most important methods for estimating evapotranspiration and drought stress and for irrigation. This paper reviews its application in agriculture. The review consists of four parts. First, the basics of thermal remote sensing are briefly reviewed. Second, the theoretical relation between Ts and the sensible and latent heat flux is elaborated. A modelling approach was used to evaluate the effect of weather conditions and leaf or vegetation properties on leaf and canopy temperature. Ts increases with increasing air temperature and incoming radiation and with decreasing wind speed and relative humidity. At the leaf level, the leaf angle and leaf dimension have a large influence on Ts; at the vegetation level, Ts is strongly impacted by the roughness length; hence, by canopy height and structure. In the third part, an overview of the different ground-based thermal remote sensing techniques and approaches used to estimate drought stress or evapotranspiration in agriculture is provided. Among other methods, stress time, stress degree day, crop water stress index (CWSI), and stomatal conductance index are discussed. The theoretical models are used to evaluate the performance and sensitivity of the most important methods, corroborating the literature data. In the fourth and final part, a critical view on the future and remaining challenges of ground-based thermal remote sensing is presented.

  4. Estimation of evapotranspiration across the conterminous United States using a regression with climate and land-cover data

    USGS Publications Warehouse

    Sanford, Ward E.; Selnick, David L.

    2013-01-01

    Evapotranspiration (ET) is an important quantity for water resource managers to know because it often represents the largest sink for precipitation (P) arriving at the land surface. In order to estimate actual ET across the conterminous United States (U.S.) in this study, a water-balance method was combined with a climate and land-cover regression equation. Precipitation and streamflow records were compiled for 838 watersheds for 1971-2000 across the U.S. to obtain long-term estimates of actual ET. A regression equation was developed that related the ratio ET/P to climate and land-cover variables within those watersheds. Precipitation and temperatures were used from the PRISM climate dataset, and land-cover data were used from the USGS National Land Cover Dataset. Results indicate that ET can be predicted relatively well at a watershed or county scale with readily available climate variables alone, and that land-cover data can also improve those predictions. Using the climate and land-cover data at an 800-m scale and then averaging to the county scale, maps were produced showing estimates of ET and ET/P for the entire conterminous U.S. Using the regression equation, such maps could also be made for more detailed state coverages, or for other areas of the world where climate and land-cover data are plentiful.

  5. Investigating the Use of LIS and Satellite Products to Improve Evapotranspiration Estimates

    NASA Astrophysics Data System (ADS)

    Stodt, R.; Arsenault, K.; Pinheiro, A.; Nigro, J.; Houser, P.

    2005-12-01

    Prolonged droughts in different semi-arid regions have increased awareness and research efforts to better understand and predict their impact and effects on water demand. One such effort includes the Land Information System (LIS) project which employs land surface models (LSMs) to incorporate improved land surface parameters and assimilate appropriate, quality-controlled remote sensing and in-situ fields. These enhanced models produce a wide range of water and energy budget variables that can be used in modeling and predicting drought conditions. One region that LIS is being customized for involves the Middle Rio Grande River in New Mexico. The LIS software is being set-up to conduct studies on water consumption and land cover /land use impacts on estimating evapotranspiration. The satellite datasets used in this work include the TERRA and AQUA MODIS datasets, Landsat, and ASTER. The MODIS land cover type product has been merged with a local, high-resolution land use dataset employed by the decision support system, theAgricultural WAter Resources Decision Support system (AWARDS) - ET Toolbox. This merged dataset has been setup for use in LIS to produce more high-resolution, heterogeneous moisture and energy flux fields, so more of the land use characterization can be captured in monitoring evapotranspiration and other drought-relevant variables. Certain LIS LSM experiment simulations will be evaluated and shown in relation to other observation datasets. Also, initial comparisons of the LSMs ET results with the AWARDS ET Toolbox evapotranspiration output will be presented.

  6. Comparative analysis of the actual evapotranspiration of Flemish forest and cropland, using the soil water balance model WAVE

    NASA Astrophysics Data System (ADS)

    Verstraeten, W. W.; Muys, B.; Feyen, J.; Veroustraete, F.; Minnaert, M.; Meiresonne, L.; de Schrijver, A.

    2005-05-01

    This paper focuses on the quantification of the green - vegetation related - water flux of a forest stand in the temperate lowland of Flanders. The underlying reason of the research was to develop a methodology for assessing the impact of forests on the hydrologic cycle in comparison to agriculture. The approach tested for calculating the water consumption by forests was based on the application of the soil water balance model WAVE. The study involved the collection of data from 14 forest stands, the calibration and validation of the WAVE model, and the comparison of the water use (WU) components - transpiration, soil and interception evaporation - between forest and cropland. For model calibration purposes simulated and measured time series of soil water content at different soil depths, period March 2000-August 2001, were compared. A multiple-site validation was conducted as well. Actual tree transpiration calculated with sap flow measurements in three forest stands gave similar results for two of the three stands of pine (Pinus sylvestris L.), but WAVE overestimated the actual measured transpiration for a stand of poplar (Populus sp.). A useful approach to compare the WU components of forest versus cropland is scenario analysis based on the validated WAVE model. The statistical Profile Analysis method was implemented to explore and analyse the simulated WU time-series. With an average annual rainfall of 819 mm, the results show that forests in Flanders consume more water than agricultural crops. A 30 years average of 491 mm for 10 forests stands versus 398 mm for 10 cropped agricultural fields was derived. The WU components, on yearly basis, also differ between the two land use types (transpiration: 315 mm for forest and 261 mm for agricultural land use; soil evaporation: 47 mm and 131 mm, for forest and cropland, respectively). Forest canopy interception evaporation was estimated at 126 mm, while it was negligible for cropland.

  7. Comparative analysis of the actual evapotranspiration of Flemish forest and cropland, using the soil water balance model WAVE

    NASA Astrophysics Data System (ADS)

    Verstraeten, W. W.; Muys, B.; Feyen, J.; Veroustraete, F.; Minnaert, M.; Meiresonne, L.; de Schrijver, A.

    2005-09-01

    This paper focuses on the quantification of the green - vegetation related - water flux of forest stands in the temperate lowland of Flanders. The underlying reason of the research was to develop a methodology for assessing the impact of forests on the hydrologic cycle in comparison to agriculture. The tested approach for calculating the water use by forests was based on the application of the soil water balance model WAVE. The study involved the collection of data from 14 forest stands, the calibration and validation of the WAVE model, and the comparison of the water use (WU) components - transpiration, soil and interception evaporation - between forest and cropland. For model calibration purposes simulated and measured time series of soil water content at different soil depths, period March 2000-August 2001, were compared. A multiple-site validation was conducted as well. Actual tree transpiration calculated with sap flow measurements in three forest stands gave similar results for two of the three stands of pine (Pinus sylvestris L.), but WAVE overestimated the actual measured transpiration for a stand of poplar (Populus sp.). A useful approach to compare the WU components of forest versus cropland is scenario analysis based on the validated WAVE model. The statistical Profile Analysis method was implemented to explore and analyse the simulated WU time series. With an average annual rainfall of 819 mm, the results reveal that forests in Flanders consume more water than agricultural crops. A 30 years average of 491 mm for 10 forests stands versus 398 mm for 10 cropped agricultural fields was derived. The WU components, on yearly basis, also differ between the two land use types (transpiration: 315 mm for forest and 261 mm for agricultural land use; soil evaporation: 47 mm and 131 mm, for forest and cropland, respectively). Forest canopy interception evaporation was estimated at 126 mm, while it was negligible for cropland.

  8. Estimating wide-area evapotranspiration at multiple scales using optical vegetation index methods

    NASA Astrophysics Data System (ADS)

    Nagler, P. L.; Glenn, E.; Jarchow, C.; Barreto-munoz, A.; Didan, K.; Nouri, H.; Anderson, S.; Doody, T.

    2015-12-01

    We provide three examples of remotely sensed evapotranspiration (ET) from our research using optical methods at different spatial scales and applied to (i) urban landscapes, (ii) riparian vegetation in Mexico in response to river flows, and (iii) riparian vegetation in Australia in response to different flood frequencies. In the first example, we will compare ground methods for estimating ET by horticultural plants with scaled estimates of ET using both WV2 NDVI imagery and MODIS EVI which were used to determine water requirements of urban gardens in Adelaide, South Australia. In the second example, we will present the impacts of a 2014 environmental flow, released to the Colorado River delta in Mexico, on vegetation greenness and estimated ET using Landsat and MODIS data. Lastly, we will show the results for scaling sap flow transpiration of Red Gum (Eucalyptus camaldulensis) and associated vegetation along the Murrumbidgee River (a tributary of the River Murray) to MODIS-based estimates of evapotranspiration in the wider riparian reaches along the river. These three applications range in spatial scales from a few hectares for urban gardens, to several thousand hectares for the riparian ecosystem in Mexico, to a regional scale of a hundred thousand hectares for the Red Gum forest in Australia. Remote sensing methods can produce accurate estimates of ET across wide temporal and spatial scales, limited mainly by the accuracy of the ground methods by which they are calibrated and validated.

  9. Application of remote sensing in estimating evapotranspiration in the Platte river basin

    NASA Technical Reports Server (NTRS)

    Blad, B. L.; Rosenberg, N. J.

    1976-01-01

    A 'resistance model' and a mass transport model for estimating evapotranspiration (ET) were tested on large fields of naturally subirrigated alfalfa. Both models make use of crop canopy temperature data. Temperature data were obtained with an IR thermometer and with leaf thermocouples. A Bowen ratio-energy balance (BREB) model, adjusted to account for underestimation of ET during periods of strong sensible heat advection, was used as the standard against which the resistance and mass transport models were compared. Daily estimates by the resistance model were within 10% of estimates made by the BREB model. Daily estimates by the mass transport model did not agree quite as well. Performance was good on clear and cloudy days and also during periods of non-advection and strong advection of sensible heat. The performance of the mass transport and resistance models was less satisfactory for estimation of fluxes of latent heat for short term periods. Both models tended to overestimate at low LE fluxes.

  10. Spatial distribution of water stress and evapotranspiration estimates using an unmanned aerial vehicle (UAV)

    NASA Astrophysics Data System (ADS)

    Rauneker, P.; Lischeid, G.

    2012-04-01

    The estimation of spatial distribution of evapotranspiration poses a particular challenge in quantitative hydrology. Conventional methods provide punctual measurements of evapotranspiration rates which may be transformed into aggregated mean values by extrapolation or the application of empirical models. The influence of spatial structures (heterogeneity of the landscape) in relevant small spatial scales is captured insufficiently by these methods. Modern optical remote sensors aboard an unmanned aerial vehicle (UAV) provide the basis for the generation of high spatial resolution data. Spectral data in the optical, near infrared and thermal infrared domain will be used as input into a surface energy balance (SEB) model to produce evapotranspiration maps. The spectral properties of vegetation are of particular importance for the calculation, since plants are the link between soil and atmosphere and thus have major impact on evapotranspiration rates of land surfaces. First estimates of plant status and indicators of transpiration behavior will be obtained by applying and combining water stress parameters of different wavelengths. As opposed to satellite data, time-series of self-determined spatial and temporal resolution may be created by varying flight altitude and turnaround times. Thus it is possible to analyze the influence of landscape structures, as well as the chronological development of the observed parameters. Located at the interface between hydrology and remote sensing this work utilizes an innovative remote sensing platform to gain distributed spectral information. This information will be used to visualize evapotranspiration patterns in hydrological heterogeneous areas. Particular attention will be paid to the analysis of transition zones of varying water supply and under the influence of selected environmental parameters (e.g. soil moisture, depth of GW-table). To reach that goal it is essential to generate a robust processing chain, involving all

  11. Evapotranspiration Estimates in the Mountain West Utilizing Multi-platform Remote Sensing

    NASA Astrophysics Data System (ADS)

    Knipper, K. R.; Hogue, T. S.; Franz, K.

    2015-12-01

    Understanding the linkages between energy and water cycles through evapotranspiration (ET) in the western U.S. is uniquely challenging given the climatic and ecological heterogeneity coupled with the added complexities of population growth, land use change and ongoing disturbance (beetle infestation, wildfire, etc.). A number of models have been developed to estimate ET based primarily on remote-sensing observations [MODIS global ET (MOD16) and Operational Simplified Surface Energy Balance (SSEBop)]. However, the scale of MOD16 and SSEBop (1km/monthly) may be too large to provide information on the spatial and temporal variability of ET that occurs over regions with acute or chronic land cover change and precipitation driven fluxes. The current study aims to improve the spatial and temporal resolution of ET utilizing only satellite-based observations by incorporating a previously developed potential evapotranspiration (PET) methodology with satellite-based soil moisture estimates. Initially, remotely-sensed soil moisture observations (AMSR2) are compared to ground-based estimates (AmeriFlux) and land-surface model (NLDAS) outputs at four sites within the Colorado River Basin. Soil moisture estimates are then downscaled to a final 250m resolution to estimate ET. Final values are compared to ground-based estimates, satellite-based estimates (SSEBop, MOD16), as well as land-surface model estimates (NLDAS). Results indicate poor AMSR2 performance, with slightly improved estimates reported by the downscaling approach (average RMSE of 0.076 m3/m3 and 0.065 m3/m3, respectively). However, the approach provides an improved spatial resolution, capable of deciphering small scale changes in soil moisture following a precipitation event. Subsequently calculated ET estimates display patterns representative of the basin's elevation and vegetative characteristics, with improved spatial resolution and temporal heterogeneity when compared to MOD16 and SSEBop.

  12. Comparison of four different energy balance models for estimating evapotranspiration in the Midwestern United States

    USGS Publications Warehouse

    Singh, Ramesh K.; Senay, Gabriel B.

    2016-01-01

    The development of different energy balance models has allowed users to choose a model based on its suitability in a region. We compared four commonly used models—Mapping EvapoTranspiration at high Resolution with Internalized Calibration (METRIC) model, Surface Energy Balance Algorithm for Land (SEBAL) model, Surface Energy Balance System (SEBS) model, and the Operational Simplified Surface Energy Balance (SSEBop) model—using Landsat images to estimate evapotranspiration (ET) in the Midwestern United States. Our models validation using three AmeriFlux cropland sites at Mead, Nebraska, showed that all four models captured the spatial and temporal variation of ET reasonably well with an R2 of more than 0.81. Both the METRIC and SSEBop models showed a low root mean square error (<0.93 mm·day−1) and a high Nash–Sutcliffe coefficient of efficiency (>0.80), whereas the SEBAL and SEBS models resulted in relatively higher bias for estimating daily ET. The empirical equation of daily average net radiation used in the SEBAL and SEBS models for upscaling instantaneous ET to daily ET resulted in underestimation of daily ET, particularly when the daily average net radiation was more than 100 W·m−2. Estimated daily ET for both cropland and grassland had some degree of linearity with METRIC, SEBAL, and SEBS, but linearity was stronger for evaporative fraction. Thus, these ET models have strengths and limitations for applications in water resource management.

  13. Improving the complementary methods to estimate evapotranspiration under diverse climatic and physical conditions

    NASA Astrophysics Data System (ADS)

    Anayah, F. M.; Kaluarachchi, J. J.

    2014-06-01

    Reliable estimation of evapotranspiration (ET) is important for the purpose of water resources planning and management. Complementary methods, including complementary relationship areal evapotranspiration (CRAE), advection aridity (AA) and Granger and Gray (GG), have been used to estimate ET because these methods are simple and practical in estimating regional ET using meteorological data only. However, prior studies have found limitations in these methods especially in contrasting climates. This study aims to develop a calibration-free universal method using the complementary relationships to compute regional ET in contrasting climatic and physical conditions with meteorological data only. The proposed methodology consists of a systematic sensitivity analysis using the existing complementary methods. This work used 34 global FLUXNET sites where eddy covariance (EC) fluxes of ET are available for validation. A total of 33 alternative model variations from the original complementary methods were proposed. Further analysis using statistical methods and simplified climatic class definitions produced one distinctly improved GG-model-based alternative. The proposed model produced a single-step ET formulation with results equal to or better than the recent studies using data-intensive, classical methods. Average root mean square error (RMSE), mean absolute bias (BIAS) and R2 (coefficient of determination) across 34 global sites were 20.57 mm month-1, 10.55 mm month-1 and 0.64, respectively. The proposed model showed a step forward toward predicting ET in large river basins with limited data and requiring no calibration.

  14. Improving the complementary methods to estimate evapotranspiration under diverse climatic and physical conditions

    NASA Astrophysics Data System (ADS)

    Anayah, F. M.; Kaluarachchi, J. J.

    2013-11-01

    Reliable estimation of evapotranspiration (ET) is important for the purpose of water resources planning and management. Complementary methods, including Complementary Relationship Areal Evapotranspiration (CRAE), Advection-Aridity (AA) and Granger and Gray (GG), have been used to estimate ET because these methods are simple and practical in estimating regional ET using meteorological data only. However, prior studies have found limitations in these methods especially in contrasting climates. This study aims to develop a calibration-free universal model using the complementary relationships to compute regional ET in contrasting climatic and physical conditions with meteorological data only. The proposed methodology consists of a systematic sensitivity analysis using the existing complementary methods. This work used 34 global FLUXNET sites where eddy covariance (EC) fluxes of ET are available for validation. A total of 33 alternative model variations from the original complementary methods were proposed. Further analysis using statistical methods and simplified climatic class definitions produced one distinctly improved GG-model based alternative. The proposed model produced a single-step ET formulation with results equal or better than the recent studies using data-intensive, classical methods. Average root mean square error (RMSE), mean absolute bias (BIAS) and R2 values across 34 global sites were 20.57 mm month-1, 10.55 mm month-1 and 0.64, respectively. The proposed model showed a step forward toward predicting ET in large river basins with limited data and requiring no calibration.

  15. Estimating evapotranspiration and groundwater flow from water-table fluctuations for a general wetland scenario

    USGS Publications Warehouse

    Carlson Mazur, Martha L.; Michael J. Wiley,; Douglas A. Wilcox,

    2015-01-01

    The use of diurnal water-table fluctuation methods to calculate evapotranspiration (ET) and groundwater flow is of increasing interest in ecohydrological studies. Most studies of this type, however, have been located in riparian wetlands of semi-arid regions where groundwater levels are consistently below topographic surface elevations and precipitation events are infrequent. Current methodologies preclude application to a wider variety of wetland systems. In this study, we extended a method for estimating sub-daily ET and groundwater flow rates from water-level fluctuations to fit highly dynamic, non-riparian wetland scenarios. Modifications included (1) varying the specific yield to account for periodic flooded conditions and (2) relating empirically derived ET to estimated potential ET for days when precipitation events masked the diurnal signal. To demonstrate the utility of this method, we estimated ET and groundwater fluxes over two growing seasons (2006–2007) in 15 wetlands within a ridge-and-swale wetland complex of the Laurentian Great Lakes under flooded and non-flooded conditions. Mean daily ET rates for the sites ranged from 4.0 mm d−1 to 6.6 mm d−1. Shallow groundwater discharge rates resulting from evaporative demand ranged from 2.5 mm d−1 to 4.3 mm d−1. This study helps to expand our understanding of the evapotranspirative demand of plants under various hydrologic and climate conditions.

  16. Evapotranspiration estimates using remote-sensing data, Parker and Palo Verde valleys, Arizona and California

    USGS Publications Warehouse

    Raymond, L.H.; Rezin, K.V.

    1986-01-01

    In 1981 the U.S. Geological Survey established an experimental project to assess the possible and practical use of remote sensing data to estimate evapotranspiration as an approximation of consumptive use in the lower Colorado River flood plain. The project area was in Parker Valley, Arizona. The approach selected was to measure the areas covered by each type of vegetation using remote sensing data in various types of analyses and to multiply each area by a predetermined water use rate. Two calibration and six remote sensing methods of classifying crop types were compared for cost, accuracy, consistency, and labor requirements. Included were one method each for field reconnaissance using 1982 data, low altitude (< than 5,000 ft) aerial photography using 1982 data, and visual photointerpretation of Landsat satellite images using 1981 and 1982 data; two methods for medium-altitude (15,000-18,000 ft) aerial photography using 1982 data; and three methods for digital Landsat satellite images using 1981 data. A test of the most promising digital processing method, which used three image dates, was made in part of Palo Verde Valley, California, where 1981 crop data were more complete than in Parker Valley. Of the eight methods studied, the three-date digital processing method was the most consistent and least labor-intensive; visual photointerpretation of Landsat images was the least expensive. Evapotranspiration estimates from crop classifications by all methods differed by a maximum of 6%. Total evapotranspiration calculated from crop data and phreatophyte maps in 1981 ranged from 12% lower in Palo Verde Valley to 17% lower in Parker Valley than consumptive use calculated by water budgets. The difference was greater in Parker Valley because the winter crop data were not included. (Author 's abstract)

  17. Evapotranspiration estimates using remote-sensing data, Parker and Palo Verde valleys, Arizona and California

    USGS Publications Warehouse

    Raymond, Lee H.; Rezin, Kelly V.

    1989-01-01

    In 1981 the U.S. Geological Survey established an experimental project to assess the possible and practical use of remote-sensing data to estimate evapotranspiration as an approximation of consumptive use of water in the lower Colorado River flood plain. The project area was in Parker Valley, Arizona. The approach selected was to measure the areas covered by each type of vegetation, using remote-sensing data in various types of analyses, and to multiply each area by a predetermined water-use rate. Two calibration and six remote-sensing methods of classifying crop types were compared for cost, accuracy, consistency, and labor requirements. Included were one method each for field reconnaissance using 1982 data, low-altitude (less than 5,000 feet) aerial photography using 1982 data, and visual photointerpretation of Landsat satellite images using 1981 and 1982 data; two methods for medium-altitude (15,000-18,000 feet) aerial photography using 1982 data; and three methods for digital Landsat satellite images using 1981 data. A test of the most promising digital-processing method, which used three image dates, was made in part of Palo Verde Valley, California, where 1981 crop data were more complete than in Parker Valley. Of the eight methods studied, the two-date digital-processing method was the most consistent and least labor intensive for identifying two or three major crops; visual photointerpretation of Landsat images was the least expensive. Evapotranspiration estimates from crop classifications by all methods differed by a maximum of 6 percent. Total evapotranspiration calculated from crop data and phreatophyte maps in 1981 ranged from 11 percent lower in Palo Verde Valley to 17 percent lower in Parker Valley than consumptive use calculated by water budgets. The difference was greater in Parker Valley because the winter crop data were not included.

  18. Estimating evapotranspiration of riparian vegetation using high resolution multispectral, thermal infrared and lidar data

    NASA Astrophysics Data System (ADS)

    Neale, Christopher M. U.; Geli, Hatim; Taghvaeian, Saleh; Masih, Ashish; Pack, Robert T.; Simms, Ronald D.; Baker, Michael; Milliken, Jeff A.; O'Meara, Scott; Witherall, Amy J.

    2011-11-01

    High resolution airborne multispectral and thermal infrared imagery was acquired over the Mojave River, California with the Utah State University airborne remote sensing system integrated with the LASSI imaging Lidar also built and operated at USU. The data were acquired in pre-established mapping blocks over a 2 day period covering approximately 144 Km of the Mojave River floodplain and riparian zone, approximately 1500 meters in width. The multispectral imagery (green, red and near-infrared bands) was ortho-rectified using the Lidar point cloud data through a direct geo-referencing technique. Thermal Infrared imagery was rectified to the multispectral ortho-mosaics. The lidar point cloud data was classified to separate ground surface returns from vegetation returns as well as structures such as buildings, bridges etc. One-meter DEM's were produced from the surface returns along with vegetation canopy height also at 1-meter grids. Two surface energy balance models that use remote sensing inputs were applied to the high resolution imagery, namely the SEBAL and the Two Source Model. The model parameterizations were slightly modified to accept high resolution imagery (1-meter) as well as the lidar-based vegetation height product, which was used to estimate the aerodynamic roughness length. Both models produced very similar results in terms of latent heat fluxes (LE). Instantaneous LE values were extrapolated to daily evapotranspiration rates (ET) using the reference ET fraction, with data obtained from a local weather station. Seasonal rates were obtained by extrapolating the reference ET fraction according to the seasonal growth habits of the different species. Vegetation species distribution and area were obtained from classification of the multispectral imagery. Results indicate that cottonwood and salt cedar (tamarisk) had the highest evapotranspiration rates followed by mesophytes, arundo, mesquite and desert shrubs. This research showed that high

  19. A comparison of methods of estimating potential evapotranspiration from climatological data in arid and subhumid environments

    USGS Publications Warehouse

    Cruff, R.W.; Thompson, T.H.

    1967-01-01

    This study compared potential evapotranspiration, computed from climatological data by each of six empirical methods, with pan evaporation adjusted to equivalent lake evaporation by regional coefficients. The six methods tested were the Thornthwaite, U.S. Weather Bureau (a modification of the Permian method), Lowry-Johnson, Blaney-Criddle, Lane, and Hamon methods. The test was limited to 25 sites in the arid and subhumid parts of Arizona, California, and Nevada, where pan evaporation and concurrent climatological data were available. However, some of the sites lacked complete climatological data for the application of all six methods. Average values of adjusted pan evaporation and computed potential evapotransp4ration were compared for two periods---the calendar year and the 6-month period from May 1 through October 31. The 25 sites sampled a wide range of climatic conditions. Ten sites (group 1) were in a highly arid environment and four (group 2) were in an arid environment that was modified by extensive irrigation. The remaining 11 sites (group 3) were in a subhumid environment. Only the Weather Bureau method gave estimates of potential evapotranspiration that closely agreed with the adjusted pan evaporation at all sites where the method was used. However, lack of climatological data restricted the use of the Weather Bureau method to seven sites. Results obtained by use of the Thornthwaite, Lowry-Johnson, and Hamon methods were consistently low. Results obtained by use of the Lane method agreed with adjusted pan evaporation at the group 1 sites but were consistently high at the group 2 and 3 sites. During the analysis it became apparent that adjusted pan evaporation in an arid environment (group 1 sites) was a spurious standard for evaluating the reliability of .the methods that were tested. Group 1 data were accordingly not considered when making conclusions as ,to which of the six methods tested was best. The results of this study for group 2 and 3 data

  20. A Budyko framework for estimating how lateral redistribution affects large-scale evapotranspiration

    NASA Astrophysics Data System (ADS)

    Rouholahnejad, Elham; Kirchner, James W.

    2016-04-01

    Most earth system models are based on grid-averaged soil columns that do not communicate with one another, and that average over considerable sub-grid heterogeneity in land surface properties, precipitation (P), and potential evapotranspiration (PET). These models typically ignore topographically driven lateral redistribution of water (either as groundwater or surface flows), both within and between model grid cells. Lateral redistribution may alter not only local evapotranspiration (ET) fluxes, but also regional average ET as seen from the atmosphere over heterogeneous landscapes. For example, if water is laterally transferred from a source location with high precipitation (but low PET) to a recipient location with low precipitation (but high PET), the resulting ET increase in the recipient location may more than offset the ET reduction in the source location. In this example the regional average ET flux, as viewed from the atmosphere, would be increased by lateral redistribution. The earth system modeling community has recognized the need to account for lateral redistribution of water and its effects on evapotranspiration rates, and our work represents a first attempt to quantify these effects. Our approach uses simple Budyko curves to estimate ET as a function of atmospheric forcing by P and PET. From these curves, we derive a simple criterion for determining whether lateral redistribution will increase or decrease regional average ET, as seen from the atmosphere. Using only estimates of P and PET in the source and recipient locations, we derive expressions for the maximum possible effect of redistribution on regional ET, and the amount of lateral redistribution required to achieve this effect. We likewise derive a dimensionless ratio that quantifies the change in ET per unit of lateral redistribution, again as a function of P and PET in the source and recipient locations. This approach yields a simple conceptual framework for determining whether, and how much

  1. Particle swarm optimization-based radial basis function network for estimation of reference evapotranspiration

    NASA Astrophysics Data System (ADS)

    Petković, Dalibor; Gocic, Milan; Shamshirband, Shahaboddin; Qasem, Sultan Noman; Trajkovic, Slavisa

    2016-08-01

    Accurate estimation of the reference evapotranspiration (ET0) is important for the water resource planning and scheduling of irrigation systems. For this purpose, the radial basis function network with particle swarm optimization (RBFN-PSO) and radial basis function network with back propagation (RBFN-BP) were used in this investigation. The FAO-56 Penman-Monteith equation was used as reference equation to estimate ET0 for Serbia during the period of 1980-2010. The obtained simulation results confirmed the proposed models and were analyzed using the root mean-square error (RMSE), the mean absolute error (MAE), and the coefficient of determination ( R 2). The analysis showed that the RBFN-PSO had better statistical characteristics than RBFN-BP and can be helpful for the ET0 estimation.

  2. An Integrated Lysimeter and Satellite Imagery Approach for Estimating Crop Evapotranspiration

    NASA Astrophysics Data System (ADS)

    Goorahoo, D.; Cassel-Sharma, F.; Johnson, L.; Melton, F. S.

    2014-12-01

    Accurate estimation of crop water requirement (CWR) is essential for the implementation efficient irrigation schedules in an effort to optimize water use efficiency. This is particularly important in the central San Joaquin Valley (SJV), California, USA, where severe droughts have accentuated the need to conserve water and improve on-farm water management. In the current study, we adopt an integrated approach for estimation of crop evapotranspiration (ETc) involving the use of weighing lysimeters and satellite imagery. In the first phase of the study with the crop lysimeter, conducted on a clay loam soil with processing tomatoes grown under sub-surface drip irrigation, observations of crop ground cover were conducted weekly and evapotranspiration (ET) data were collected daily to derive relationships between crop coefficients and fractional cover. Data collected during the first year of the study, indicted that the crop coefficients (Kc) obtained at peak season were relatively higher than those generally reported for tomatoes commonly grown in the central SJV. Overall, there was a good correlation between fractional cover and crop coefficients (r2 = 0.91), with the average peak ET and Kc values ranging from 6 to 7 mm per day and from 0.8 to 0.9, respectively. Data obtained from satellite imagery, representing relatively larger spatial measurements than the lysimeters, are being compared with the surface observations from the lysimeters and will also be discussed in our presentation.

  3. Modeling soybean canopy resistance from micrometeorological and plant variables for estimating evapotranspiration using one-step Penman-Monteith approach

    NASA Astrophysics Data System (ADS)

    Irmak, Suat; Mutiibwa, Denis; Payero, Jose; Marek, Thomas; Porter, Dana

    2013-12-01

    Canopy resistance (rc) is one of the most important variables in evapotranspiration, agronomy, hydrology and climate change studies that link vegetation response to changing environmental and climatic variables. This study investigates the concept of generalized nonlinear/linear modeling approach of rc from micrometeorological and plant variables for soybean [Glycine max (L.) Merr.] canopy at different climatic zones in Nebraska, USA (Clay Center, Geneva, Holdrege and North Platte). Eight models estimating rc as a function of different combination of micrometeorological and plant variables are presented. The models integrated the linear and non-linear effects of regulating variables (net radiation, Rn; relative humidity, RH; wind speed, U3; air temperature, Ta; vapor pressure deficit, VPD; leaf area index, LAI; aerodynamic resistance, ra; and solar zenith angle, Za) to predict hourly rc. The most complex rc model has all regulating variables and the simplest model has only Rn, Ta and RH. The rc models were developed at Clay Center in the growing season of 2007 and applied to other independent sites and years. The predicted rc for the growing seasons at four locations were then used to estimate actual crop evapotranspiration (ETc) as a one-step process using the Penman-Monteith model and compared to the measured data at all locations. The models were able to account for 66-93% of the variability in measured hourly ETc across locations. Models without LAI generally underperformed and underestimated due to overestimation of rc, especially during full canopy cover stage. Using vapor pressure deficit or relative humidity in the models had similar effect on estimating rc. The root squared error (RSE) between measured and estimated ETc was about 0.07 mm h-1 for most of the models at Clay Center, Geneva and Holdrege. At North Platte, RSE was above 0.10 mm h-1. The results at different sites and different growing seasons demonstrate the robustness and consistency of the

  4. Kohonen self-organizing map estimator for the reference crop evapotranspiration

    NASA Astrophysics Data System (ADS)

    Adeloye, Adebayo J.; Rustum, Rabee; Kariyama, Ibrahim D.

    2011-08-01

    Reference crop evapotranspiration (ETo) estimation is of importance in irrigation water management for the calculation of crop water requirements and its scheduling, in rainfall-runoff modeling and in numerous other water resources studies. Due to its importance, several direct and indirect methods have been employed to determine the reference crop evapotranspiration but success has been limited because the direct measurement methods lack in precision and accuracy due to scale issues and other problems, while some of the more accurate indirect methods, e.g., the Penman-Monteith benchmark model, are time-consuming and require weather input data that are not routinely monitored. This paper has used the Kohonen self-organizing map (KSOM), unsupervised artificial neural networks, to predict the ETo. based on observed daily weather data at two climatically diverse basins: a small experimental catchment in temperate Edinburgh, UK and a semiarid lake basin in Udaipur, India. This was achieved by using the powerful clustering capability of the KSOM to analyze the multidimensional data array comprising the estimated ETo (based on the Food and Agricultural Organization (FAO) Penman-Monteith model) and different subsets of climatic variables known to affect it. The findings indicate that the KSOM-based ETo estimates even with fewer input variables were in good agreement with those obtained using the conventional FAO Penman-Monteith formulation employing the full complement of weather data at the two locations. More crucially, the KSOM-based estimates were also found to be significantly superior to those estimated using currently recommended empirical ETo methods for data scarce situations such as those in developing countries.

  5. Comparison of Four Different Energy Balance Models for Estimating Evapotranspiration in the Midwest United States

    NASA Astrophysics Data System (ADS)

    Singh, R. K.; Senay, G. B.; Verdin, J. P.

    2015-12-01

    Availability of no-cost satellite images helped in development and utilization of remotely sensed images for water use estimation. Remotely sensed images are increasingly used for estimating evapotranspiration (ET) at different temporal and spatial scales. However, selecting any particular model from a plethora of energy balance models for estimating ET is challenging as each different model has its strengths and limitations. We compared four commonly used ET models, namely, Mapping EvapoTranspiration at high Resolution with Internalized Calibration (METRIC) model, Surface Energy Balance Algorithm for Land (SEBAL) model, Surface Energy Balance System (SEBS) model, and Operational Simplified Surface Energy Balance (SSEBop) model using Landsat images for estimating ET in the Midwest United States. We validated our model results using three AmeriFlux cropland sites at Mead, Nebraska. Our results showed that the METRIC and the SSEBop model worked very well at these sites with a root mean square error (RMSE) of less than 1 mm/day and an R2 of 0.96 (N=24). The mean bias error (MBE) was less than 10% for both the METRIC and the SSEBop models. In contrast, the SEBAL and the SEBS models have relatively higher RMSE (> 1.7 mm/day) and MBE (> 27%). However, all four models captured the spatial and temporal variation of ET reasonably well (R2 > 0.80). We found that the model simplification of the SSEBop for operational capability was not at the expense of model accuracy. Since the SSEBop model is relatively less data intensive and independent of user/automatic selection of anchor (hot/dry and cold/wet) pixels, it is more user friendly and operationally efficient. The SSEBop model can be reliably used for estimating water use using Landsat and MODIS images at daily, weekly, monthly, or annual time scale even in data scarce regions for sustainable use of limited water resources.

  6. Historical estimates of spatial reference evapotranspiration for the Central Valley of California

    NASA Astrophysics Data System (ADS)

    Falk, M.; Snyder, R. L.; Orang, M.; Hayes, S.

    2009-12-01

    In this study we present spatial reference evapotranspiration (ETo) estimates for the Central Valley from 1921 to 2008 derived from NCDC/NOAA daily climate data and PRISM monthly climate data grids (PRISM group; Oregon State University, Corvallis, USA; http://www.prism.oregonstate.edu). Data from the California Irrigation Management Information System (CIMIS) weather station were also used. 2009 is currently the third year of drought in California and better tools for irrigation and water resource management are needed to provide a secure water supply in the future. Temperature and Precipitation are driving variables in the estimation of ET occurring on the landscape scale. Consequently, modeling evaluations of a growing number of hydrological issues are increasingly requiring reliable area coverage of meteorological datasets. The availability of these datasets with adequate spatial and temporal resolution is particularly critical for decision support models for better management of water resources, such as the SIMETAW-II project supported with this study. Daily maximum-minimum temperature and precipitation spatial datasets were calculated by combining daily NCDC climate station data and monthly PRISM climate data grids. This study relies on the input PRISM grids to reproduce spatial climate patterns as well as anchor the daily climate values to the monthly averages given in the PRISM dataset such as total monthly precipitation and average daily temperatures. The historic daily climate data available for the period from 1921 to present consists of data for minimum temperature, maximum temperature and precipitation. Due to this restricted historical data set we cannot directly compute Penman-Monteith Reference Evapotranspiration (ETo) as adopted by the Environmental Water Resources Institute - American Society of Civil Engineers (ASCE-EWRI, 2004). Instead this study uses the Hargreaves-Samani equation for estimating Reference Evapotranspiration (ETh). For the final

  7. Evaluation of evapotranspiration estimation methods for sweet cherry trees (Prunus avium) in sub-humid climate.

    PubMed

    Denmirtas, Cigdem; Buyukcangaz, Hakan; Yazgan, Senih; Candogan, Burak Nazmi

    2007-02-01

    This study was carried out in the summer of 2001 in a 3 year old and in the summer of 2002 in a 4 year old sweet cherry trees (Prunus avium, variety Z-900) on Mazzard rootstocks in Bayramic-Canakkale which is located in the west part of Turkey. Micro-sprinkler irrigation was selected as the irrigation method. The trees were subjected to four micro-sprinkler irrigation treatments (T-1, T-2, T-3 and T-4). The water applied in treatment T-3 was considered sufficient to satisfy fully needs of the crop (100% of ETc) and to allow good rooting and tree growth. The water balance relationship was used in estimating ETc. A total of 4 climatological methods were selected for estimating reference crop evapotranspiration on a daily basis. Some of these methods are based on combination theory and others are empirical methods based primarily on solar radiation, temperature ans relative humidity. An attempt was made in the current study to develop regional relationship between the evapotranspiration measured and that estimated by the climatological methods, such as FAO-Penman, Penman-Monteith, FAO-Radiation and FAO-Blaney-Criddle. Performance of the climatological methods in estimating the ETo values as compared to the measured values was evaluated on the basis of root mean square error (RMSE). In 2001, the Penman-Monteith equation gave the best results followed by FAO-Penman, FAO-Radiation and FAO-Blaney-Criddle. In 2002, the Penman-Monteith and FAO-Blaney-Criddle equations gave same results. PMID:19069518

  8. Estimation of evapotranspiration in an arid region by remote sensing—A case study in the middle reaches of the Heihe River Basin

    NASA Astrophysics Data System (ADS)

    Li, Xingmin; Lu, Ling; Yang, Wenfeng; Cheng, Guodong

    2012-07-01

    Estimating surface evapotranspiration is extremely important for the study of water resources in arid regions. Data from the National Oceanic and Atmospheric Administration's Advanced Very High Resolution Radiometer (NOAA/AVHRR), meteorological observations and data obtained from the Watershed Allied Telemetry Experimental Research (WATER) project in 2008 are applied to the evaporative fraction model to estimate evapotranspiration over the Heihe River Basin. The calculation method for the parameters used in the model and the evapotranspiration estimation results are analyzed and evaluated. The results observed within the oasis and the banks of the river suggest that more evapotranspiration occurs in the inland river basin in the arid region from May to September. Evapotranspiration values for the oasis, where the land surface types and vegetations are highly variable, are relatively small and heterogeneous. In the Gobi desert and other deserts with little vegetation, evapotranspiration remains at its lowest level during this period. These results reinforce the conclusion that rational utilization of water resources in the oasis is essential to manage the water resources in the inland river basin. In the remote sensing-based evapotranspiration model, the accuracy of the parameter estimate directly affects the accuracy of the evapotranspiration results; more accurate parameter values yield more precise values for evapotranspiration. However, when using the evaporative fraction to estimate regional evapotranspiration, better calculation results can be achieved only if evaporative fraction is constant in the daytime.

  9. Estimating root-zone moisture and evapotranspiration with AVHRR data[Advanced Very High Resolution Radiometer

    SciTech Connect

    Song, J.; Wesely, M. L.

    1999-10-08

    The parameterized subgrid-scale surface fluxes (PASS) model uses satellite data and limited surface observations to infer root-zone available moisture content and evapotranspiration rate with moderate spatial resolution over extended terrestrial areas. The ultimate goal of this work is to produce estimates of water loss by evapotranspiration, for application in hydrological models. The major advantage to the method is that it can be applied to areas having diverse surface characteristics where direct surface flux measurements either do not exist or are not feasible and where meteorological data are available from only a limited number of ground stations. The emphasis of this work with the PASS model is on improving (1) methods of using satellite remote sensing data to derive the essential parameters for individual types of surfaces over large areas, (2) algorithms for describing the interactions of near-surface atmospheric conditions with surface processes, and (3) algorithms for computing surface energy and water vapor flux at a scale close to the size of a satellite-derived image pixel. The PASS approach is being developed and tested further with observations from the 1997 Cooperative Atmosphere-Surface Exchange Study (CASES-97) at the Atmospheric Boundary Layer Experiments (ABLE) site in the Walnut River Watershed (WRW), an area of about 5,000 km{sup 2} in southern Kansas. Here the authors describe some of the progress made since the previous report.

  10. Comparison of artificial neural network and empirical equations for daily reference evapotranspiration estimation from pan evaporation

    NASA Astrophysics Data System (ADS)

    Mosaedi, Abolfazl; Ghabaei S., Mohammad

    2010-05-01

    Evaporation and Evapotranspiration Process are the major components of the hydrologic cycle which play an important role in agricultural studies such as design of irrigation and drainage systems, and irrigation scheduling. Evapotranspiration is a complex non-linear phenomenon which depends on several climatologic factors. It can be measured directly by high-cost micrometeorological techniques. Hence, many mathematical models and empirical equations were developed to estimate this phenomenon. One conventional method to estimate reference crop evapotranspiration (ET0) is converting the class A pan evaporation (EPan) into ETo by using a pan coefficient (KPan) according to following this equation. ETo = Kpan * Epan PIC Another alternative method to estimate ETo is the application of mathematical models like artificial neural networks (ANNs). ANNs are mathematical models whose architecture has been inspired by biological neural networks. ANNs are very appropriate for the modeling of nonlinear processes, i.e. the case of ETo.Kpan is the important factor for computation of ETo from Epan, There for several empirical equations purposed to determine KPan, using wind speed, relative humidity and fetch length conditions by many researchers. The main objective of this study was to comparison between ability of ANNs and empirical equations for estimation daily ET0 from Epan. For this object Daily measured weather data for a 16 year (from 1992 to 2007) period were obtained from the Shiraz synoptic station (latitude 29o 36' N, longitude 52o 32' E, elevation 1480 m) that located in Fars province of Iran. The climate in the study area is semi-arid with an average annual rainfall of 346 mm year-1. In This paper first, we use seven empirical equations: Cuenca (1989), Snyder (1992), Modified Snyder (1992), Doorenbos and Pruitt (1977), Pereira et al. (1995), Orang (1998) and Raghuwanshi and Wallender (1998) for estimation KPan values and second then we use ANNs for converting Epan to

  11. Evaluation of Water Stress Coefficient Methods to Estimate Actual Corn Evapotranspiration in Colorado

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Abstract for Kullberg Hydrology Days: Abstract. Increased competition for water resources is placing pressure on the agricultural sector to remain profitable while reducing water use. Remote sensing techniques have been developed to monitor crop water stress and produce information for evapotranspi...

  12. A Comparison of Methods for Estimating Evapotranspiration (ET) in a Semi-Arid Agricultural System

    NASA Astrophysics Data System (ADS)

    Gordon, B. L.; Claes, N.; Miller, S. N.; Paige, G. B.; Parsekian, A.; Beverly, D.

    2015-12-01

    In the intermountain West, much like the rest of the world, agriculture is the oldest and largest water consumer. Particularly in the arid headwaters states of the intermountain west changing water demands are highlighting the importance of water use efficiency in agriculture. In flood irrigation an area is irrigated until saturation is achieved although crops only consume a portion of the total water applied. The remaining water eventually returns to streams or aquifers. Accurately quantifying the portion of applied water that is consumptively used—and its corollary in the form of return flows—represents an important avenue for potential water use reduction in the face of increasing demands from sundry downstream users. Consumptive use has historically been understood as the difference between the irrigation water applied and irrigation water returned to adjacent surface waters via quick or delayed return flow as well as overland flow. Penman-derived models, which calculate evapotranspiration based on meteorological data, are another widely recognized method for estimating consumptive use. We determined consumptive use on an agricultural field in northeastern Wyoming using both of these two traditional methods as well as a quantitative scintillometer-based estimate, which couples meteorological data with the latent heat flux across a field to measure evapotranspiration for a given area. Since the wider application of the scintillometer is limited by the instrument's complexity and cost, a comparison of the resulting data with these two more customary methods provides critical insight in to where certain methods might under or overestimate consumptive use. The purpose of this comparison is twofold. First, the comparison of these three methods allows for the optimization of a reach-scale water budget that aims to better characterize and quantify return flow processes. Second, the addition of information that couples hydrology, meteorology, geophysics, and heat

  13. Estimating evapotranspiration and groundwater flow from water-table fluctuations for a general wetland scenario

    USGS Publications Warehouse

    Migration_USER, IPDS; Wiley, Michael J.; Wilcox, Douglas A.

    2016-01-01

    The use of diurnal water-table fluctuation methods to calculate evapotranspiration (ET) and groundwater flow is of increasing interest in ecohydrological studies. Most studies of this type, however, have been located in riparian wetlands of semi-arid regions where groundwater levels are consistently below topographic surface elevations and precipitation events are infrequent. Current methodologies preclude application to a wider variety of wetland systems. In this study, we extended a method for estimating sub-daily ET and groundwater flow rates from water-level fluctuations to fit highly dynamic, non-riparian wetland scenarios. Modifications included (1) varying the specific yield to account for periodic flooded conditions and (2) relating empirically derived ET to estimated potential ET for days when precipitation events masked the diurnal signal. To demonstrate the utility of this method, we estimated ET and groundwater fluxes over two growing seasons (2006–2007) in 15 wetlands within a ridge-and-swale wetland complex of the Laurentian Great Lakes under flooded and non-flooded conditions. Mean daily ET rates for the sites ranged from 4.0 mm d−1 to 6.6 mm d−1. Shallow groundwater discharge rates resulting from evaporative demand ranged from 2.5 mm d−1 to 4.3 mm d−1. This study helps to expand our understanding of the evapotranspirative demand of plants under various hydrologic and climate conditions. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

  14. Study on estimating the evapotranspiration cover coefficient for stream flow simulation through remote sensing techniques

    NASA Astrophysics Data System (ADS)

    Wu, Chihda; Cheng, Chichuan; Lo, Hannchung; Chen, Yeongkeung

    2010-08-01

    This study focuses on using remote sensing techniques to estimate the evapotranspiration cover coefficient (CV) which is an important parameter for stream flow. The objective is to derive more accurate stream flow from the estimated CV. The study area is located in the Dan-Shuei watershed in northern Taiwan. The processes include the land-use classification using hybrid classification and four Landsat-5 TM images; the CV estimations based on remote sensing and traditional approaches; comparison of stream flow simulation according to the above two CV values. The result indicated that the study area was classified into seven land-use types with 88.3% classification accuracy. The simulated stream flow using remote sensing approach could represent more accurate hydrological characteristics than a traditional approach. Obviously integrating remote sensing technique and the SEBAL model is a useful approach to estimate the CV. The CV parameter estimated by remote sensing technique did improve the accuracy of the stream flow simulation. Therefore, the results can be extended to further studies such as forest water management.

  15. A comparison of models for estimating potential evapotranspiration for Florida land cover types

    USGS Publications Warehouse

    Douglas, E.M.; Jacobs, J.M.; Sumner, D.M.; Ray, R.L.

    2009-01-01

    We analyzed observed daily evapotranspiration (DET) at 18 sites having measured DET and ancillary climate data and then used these data to compare the performance of three common methods for estimating potential evapotranspiration (PET): the Turc method (Tc), the Priestley-Taylor method (PT) and the Penman-Monteith method (PM). The sites were distributed throughout the State of Florida and represent a variety of land cover types: open water (3), marshland (4), grassland/pasture (4), citrus (2) and forest (5). Not surprisingly, the highest DET values occurred at the open water sites, ranging from an average of 3.3 mm d-1 in the winter to 5.3 mm d-1 in the spring. DET at the marsh sites was also high, ranging from 2.7 mm d-1 in winter to 4.4 mm d-1 in summer. The lowest DET occurred in the winter and fall seasons at the grass sites (1.3 mm d-1 and 2.0 mm d-1, respectively) and at the forested sites (1.8 mm d-1 and 2.3 mm d-1, respectively). The performance of the three methods when applied to conditions close to PET (Bowen ratio ??? 1) was used to judge relative merit. Under such PET conditions, annually aggregated Tc and PT methods perform comparably and outperform the PM method, possibly due to the sensitivity of the PM method to the limited transferability of previously determined model parameters. At a daily scale, the PT performance appears to be superior to the other two methods for estimating PET for a variety of land covers in Florida. ?? 2009 Elsevier B.V.

  16. A comparison of models for estimating potential evapotranspiration for Florida land cover types

    USGS Publications Warehouse

    Douglas, Ellen M.; Jacobs, Jennifer M.; Sumner, David M.; Ray, Ram L.

    2013-01-01

    We analyzed observed daily evapotranspiration (DET) at 18 sites having measured DET and ancillary climate data and then used these data to compare the performance of three common methods for estimating potential evapotranspiration (PET): the Turc method (Tc), the Priestley-Taylor method (PT) and the Penman-Monteith method (PM). The sites were distributed throughout the State of Florida and represent a variety of land cover types: open water (3), marshland (4), grassland/pasture (4), citrus (2) and forest (5). Not surprisingly, the highest DET values occurred at the open water sites, ranging from an average of 3.3 mm d-1 in the winter to 5.3 mm d-1 in the spring. DET at the marsh sites was also high, ranging from 2.7 mm d-1 in winter to 4.4 mm d-1 in summer. The lowest DET occurred in the winter and fall seasons at the grass sites (1.3 mm d-1 and 2.0 mm d-1, respectively) and at the forested sites (1.8 mm d-1 and 2.3 mm d-1, respectively). The performance of the three methods when applied to conditions close to PET (Bowen ratio ≤ 1) was used to judge relative merit. Under such PET conditions, annually aggregated Tc and PT methods perform comparably and outperform the PM method, possibly due to the sensitivity of the PM method to the limited transferability of previously determined model parameters. At a daily scale, the PT performance appears to be superior to the other two methods for estimating PET for a variety of land covers in Florida.

  17. Comparison of sap flux, moisture flux tower and MODIS enhanced vegetation index methods for estimating riparian evapotranspiration

    USGS Publications Warehouse

    Nagler, Pamela L.; Glenn, Edward P.; Morino, Kiyomi; Neale, Christopher M.U; Cosh, Michael H.

    2010-01-01

    Riparian evapotranspiration (ET) was measured on a salt cedar (Tamarix spp.) dominated river terrace on the Lower Colorado River from 2007 to 2009 using tissue-heat-balance sap flux sensors at six sites representing very dense, medium dense, and sparse stands of plants. Salt cedar ET varied markedly across sites, and sap flux sensors showed that plants were subject to various degrees of stress, detected as mid-day depression of transpiration and stomatal conductance. Sap flux results were scaled from the leaf level of measurement to the stand level by measuring plant-specific leaf area index and fractional ground cover at each site. Results were compared to Bowen ratio moisture tower data available for three of the sites. Sap flux sensors and flux tower results ranked the sites the same and had similar estimates of ET. A regression equation, relating measured ET of salt cedar and other riparian plants and crops on the Lower Colorado River to the Enhanced Vegetation Index from the MODIS sensor on the Terra satellite and reference crop ET measured at meteorological stations, was able to predict actual ET with an accuracy or uncertainty of about 20%, despite between-site differences for salt cedar. Peak summer salt cedar ET averaged about 6 mm d-1 across sites and methods of measurement.

  18. Remotely Sensed Estimates of Evapotranspiration in Agricultural Areas of Northwestern Nevada: Drought, Reliance, and Water Transfers

    NASA Astrophysics Data System (ADS)

    Bromley, Matthew

    The arid landscape of northwestern Nevada is punctuated by agricultural communities that rely on water primarily supplied by the diversion of surface waters and secondarily by groundwater resources. Annual precipitation in the form of winter snowfall largely determines the amount of surface water that is available for irrigation for the following agricultural growing season. During years of insufficient surface water supplies, particular basins can use groundwater in order to meet irrigation needs. The amount of water used to irrigate agricultural land is influenced by land use changes, such as fallowing, and water right transfers from irrigation to municipal use. To evaluate agricultural water consumption with respect to variations in weather, water supply, and land use changes, monthly estimates of evapotranspiration (ET) were derived from Landsat multispectral optical and thermal imagery over a eleven-year period (2001 to 2011) and compared to variations in weather, water supply, and land use across four hydrographic areas in northwestern Nevada. Monthly ET was estimated using a land surface energy balance model, Mapping EvapoTranspiration at high Resolution with Internalized Calibration (METRIC), using Landsat 5 and Landsat 7 imagery combined with local atmospheric water demand estimates. Estimates of net ET were created by subtracting monthly precipitation from METRIC-derived ET, and seasonal estimates were generated by combining monthly ET for April-October (the regional agricultural growing season). Results highlight that a range of geographic, climatic, hydrographic, and anthropogenic factors influence ET. Hydrographic areas such as Mason Valley have the ability to mitigate deficiencies in surface water supplies by pumping supplemental groundwater, thereby resulting in low annual variability in ET. Conversely, the community of Lovelock has access to limited upstream surface water storage and is restricted by groundwater that is saline and unsuitable for

  19. Parameterizing ecosystem light use efficiency and water use efficiency to estimate maize gross primary production and evapotranspiration using MODIS EVI

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Quantifying global carbon and water balances requires accurate estimation of gross primary production (GPP) and evapotranspiration (ET), respectively, across space and time. Models that are based on the theory of light use efficiency (LUE) and water use efficiency (WUE) have emerged as efficient met...

  20. Global estimation of evapotranspiration using a leaf area index-based surface energy and water balance model

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Studies of global hydrologic cycles, carbon cycles and climate change are greatly facilitated when global estimates of evapotranspiration (E) are available. We have developed an air-relative-humidity-based two-source (ARTS) E model that simulates the surface energy balance, soil water balance, and e...

  1. Development of a reservoir model to improve evapotranspiration estimates in a regional land atmospheric model

    NASA Astrophysics Data System (ADS)

    Voisin, N.; Li, H.; Huang, M.; Leung, L.; Wigmosta, M. S.

    2011-12-01

    The community land model (CLM) was designed for coupling with atmospheric model to simulate the water, energy, and carbon fluxes between the land surface and atmosphere. These fluxes are regulated in various degrees by its hydrologic processes, which have not been vigorously evaluated for applications at watershed or regional scales. In the framework of an integrated regional earth system model being developed, accurate hydrologic information in all of its components including socio-economy, atmosphere, land, and energy infrastructure is needed to represent the interactions between human and earth system processes. Incorporating CLM in this framework requires model evaluation and improvement so that CLM could be used to represent hydrology, soil, managed and unmanaged ecosystems, and biogeochemical processes across scales in a coherent modeling framework. As part of this effort, an irrigation-runoff routing-reservoir model is developed as a relatively simple and generic way to represent water management in CLM, which only deals with natural land surface and hydrologic processes. The objective is to improve evapotranspiration estimates in time and space resulting from human influence, i.e., from irrigation and large reservoir storage. Once fully coupled, it will also allow i) assessing the feedback of increased evapotranspiration in an atmospheric model, ii) investigations of water use and its influence on other human and earth system components. The concept of the preliminary reservoir model is presented over the Columbia River Basin. Challenges due to the differences in time and spatial scales between the physical processes versus reservoir operations and targets (irrigation, flood control, hydropower generation, navigation, environmental flow) are discussed.

  2. Use of Sharpened Land Surface Temperature for Daily Evapotranspiration Estimation over Irrigated Crops in Arid Lands

    NASA Astrophysics Data System (ADS)

    Rosas Aguilar, J.; McCabe, M. F.; Houborg, R.; Gao, F.

    2014-12-01

    Satellite remote sensing provides data on land surface characteristics, useful for mapping land surface energy fluxes and evapotranspiration (ET). Land-surface temperature (LST) derived from thermal infrared (TIR) satellite data has been reliably used as a remote indicator of ET and surface moisture status. However, TIR imagery usually operates at a coarser resolution than that of shortwave sensors on the same satellite platform, making it sometimes unsuitable for monitoring of field-scale crop conditions. This study applies the data mining sharpener (DMS; Gao et al., 2012) technique to data from the Moderate Resolution Imaging Spectroradiometer (MODIS), which sharpens the 1 km thermal data down to the resolution of the optical data (250-500 m) based on functional LST and reflectance relationships established using a flexible regression tree approach. The DMS approach adopted here has been enhanced/refined for application over irrigated farming areas located in harsh desert environments in Saudi Arabia. The sharpened LST data is input to an integrated modeling system that uses the Atmosphere-Land Exchange Inverse (ALEXI) model and associated flux disaggregation scheme (DisALEXI) in conjunction with model reanalysis data and remotely sensed data from polar orbiting (MODIS) and geostationary (MSG; Meteosat Second Generation) satellite platforms to facilitate daily estimates of evapotranspiration. Results are evaluated against available flux tower observations over irrigated maize near Riyadh in Saudi Arabia. Successful monitoring of field-scale changes in surface fluxes are of importance towards an efficient water use in areas where fresh water resources are scarce and poorly monitored. Gao, F.; Kustas, W.P.; Anderson, M.C. A Data Mining Approach for Sharpening Thermal Satellite Imagery over Land. Remote Sens. 2012, 4, 3287-3319.

  3. Estimation of evapotranspiration using satellite remote sensing data in Northeast Asia

    NASA Astrophysics Data System (ADS)

    Jang, K.; Kang, S.

    2013-12-01

    The land surface evapotranspiration (ET) that is the sum of evaporation and transpiration is one of key components for understanding the land surface water cycle and the energy interaction between land surface and atmosphere. The quantification of ET is important to improve our understandings such as the terrestrial water budget as well as water management. Although numerous studies for ET estimation have been performed, the regional studies on ET in Northeast Asia are still few. In this study, we present the method for the satellite data-based ET estimates under clear and cloudy sky conditions in Northeast Asia. The input variables for ET calculation were obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) atmosphere and land products. Frequent cloud cover results in a substantial loss of remote sensing information, limiting the capability of continuous ET monitoring for the monsoon region such as the Northeast Asia. For this reason, the gap-filling processes were conducted for the temperature variables using the Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) data and the radiation components using MODIS cloud properties product. The operational MODIS ET algorithm was applied to estimate the terrestrial ET in Northeast Asia. Flux tower measurements at eight sites over study domain were used to evaluate the satellite-derived inputs and ET estimates. The satellite-based input variables for estimating ET showed good agreements in comparison with flux tower observations. The resulting ET calculations showed generally favorable agreement (RMSE < 1.3 mm day-1) with respect to in situ measurements from eight regional flux tower sites. The estimated mean annual ET for three years from 2006 to 2008 was approximately 360 mm yr-1 over the Northeast Asia domain. The results generated by this study indicated that the integration of MODIS and AMSR-E products provides the potentials to estimate ET and radiation components for clear and

  4. Vegetation index-based crop coefficients to estimate evapotranspiration by remote sensing in agricultural and natural ecosystems

    USGS Publications Warehouse

    Glenn, E.P.; Neale, C. M. U.; Hunsaker, D.J.; Nagler, P.L.

    2011-01-01

    Crop coefficients were developed to determine crop water needs based on the evapotranspiration (ET) of a reference crop under a given set of meteorological conditions. Starting in the 1980s, crop coefficients developed through lysimeter studies or set by expert opinion began to be supplemented by remotely sensed vegetation indices (VI) that measured the actual status of the crop on a field-by-field basis. VIs measure the density of green foliage based on the reflectance of visible and near infrared (NIR) light from the canopy, and are highly correlated with plant physiological processes that depend on light absorption by a canopy such as ET and photosynthesis. Reflectance-based crop coefficients have now been developed for numerous individual crops, including corn, wheat, alfalfa, cotton, potato, sugar beet, vegetables, grapes and orchard crops. Other research has shown that VIs can be used to predict ET over fields of mixed crops, allowing them to be used to monitor ET over entire irrigation districts. VI-based crop coefficients can help reduce agricultural water use by matching irrigation rates to the actual water needs of a crop as it grows instead of to a modeled crop growing under optimal conditions. Recently, the concept has been applied to natural ecosystems at the local, regional and continental scales of measurement, using time-series satellite data from the MODIS sensors on the Terra satellite. VIs or other visible-NIR band algorithms are combined with meteorological data to predict ET in numerous biome types, from deserts, to arctic tundra, to tropical rainforests. These methods often closely match ET measured on the ground at the global FluxNet array of eddy covariance moisture and carbon flux towers. The primary advantage of VI methods for estimating ET is that transpiration is closely related to radiation absorbed by the plant canopy, which is closely related to VIs. The primary disadvantage is that they cannot capture stress effects or soil

  5. Evaluating the generalizability of GEP models for estimating reference evapotranspiration in distant humid and arid locations

    NASA Astrophysics Data System (ADS)

    Kiafar, Hamed; Babazadeh, Hosssien; Marti, Pau; Kisi, Ozgur; Landeras, Gorka; Karimi, Sepideh; Shiri, Jalal

    2016-08-01

    Evapotranspiration estimation is of crucial importance in arid and hyper-arid regions, which suffer from water shortage, increasing dryness and heat. A modeling study is reported here to cross-station assessment between hyper-arid and humid conditions. The derived equations estimate ET0 values based on temperature-, radiation-, and mass transfer-based configurations. Using data from two meteorological stations in a hyper-arid region of Iran and two meteorological stations in a humid region of Spain, different local and cross-station approaches are applied for developing and validating the derived equations. The comparison of the gene expression programming (GEP)-based-derived equations with corresponding empirical-semi empirical ET0 estimation equations reveals the superiority of new formulas in comparison with the corresponding empirical equations. Therefore, the derived models can be successfully applied in these hyper-arid and humid regions as well as similar climatic contexts especially in data-lack situations. The results also show that when relying on proper input configurations, cross-station might be a promising alternative for locally trained models for the stations with data scarcity.

  6. Testing data evaluation strategies for estimating precipitation and actual evaporation from precision lysimeter measurements

    NASA Astrophysics Data System (ADS)

    Schrader, Frederik; Durner, Wolfgang; Fank, Johann; Pütz, Thomas; Wollschläger, Ute

    2014-05-01

    Weighing lysimeters have long been recognized as valuable tools not only for monitoring of groundwater recharge and solute transport, but also for the determination of the soil water balance and quantification of water exchange processes at the soil-plant-atmosphere interface. If well embedded into an equally-vegetated environment, they reach a hitherto unprecedented accuracy in estimating precipitation (P) by rain, dew, fog, rime and snow, as well as actual evapotranspiration (ET). At the same time, they largely avoid errors made by traditional micrometeorological instruments, such as the wind error of Hellman rain samplers or the influence of subsurface heterogeneity on readings from in situ instrumentation of soil water state variables. Beginning in 2008, the Helmholtz Association established a network of terrestrial environmental observatories (TERENO) that aim at long-term monitoring of climate and land-use change consequences. A total of 126 identically designed large weighing lysimeters, operating at a sampling frequency of 1 min-1, were installed for this purpose, which raises the demand for standardized data processing methods. In theory, estimating P and ET from these measurements is straightforward: An increase in the combined mass of the soil monolith and the collected seepage water indicates P, while a decrease indicates ET. However, in practice, lysimeter data are prone to numerous sources of error, including, but not limited to, outliers, systematic errors due to plant growth and removal, data gaps, and stochastic fluctuations. The latter pose a particularly challenging problem - if we would directly calculate P and ET from a time-series that is affected by random noise, every positive fluctuation would be interpreted as P and every negative one as ET. Consequently, we would overestimate both quantities by far. The aim of this study was to evaluate algorithms that focus on eliminating the effect of these fluctuations and to estimate actual fluxes

  7. Estimates of evapotranspiration in alkaline scrub and meadow communities of Owens Valley, California, using the Bowen-ratio, eddy-correlation, and Penman-combination methods

    USGS Publications Warehouse

    Duell, L. F. W.

    1988-01-01

    In Owens Valley, evapotranspiration (ET) is one of the largest components of outflow in the hydrologic budget and the least understood. ET estimates for December 1983 through October 1985 were made for seven representative locations selected on the basis of geohydrology and the characteristics of phreatophytic alkaline scrub and meadow communities. The Bowen-ratio, eddy-correlation, and Penman-combination methods were used to estimate ET. The results of the analyses appear satisfactory when compared to other estimates of ET. Results by the eddy-correlation method are for a direct and a residual latent-heat flux that is based on sensible-heat flux and energy budget measurements. Penman-combination potential ET estimates were determined to be unusable because they overestimated actual ET. Modification in the psychrometer constant of this method to account for differences between heat-diffusion resistance and vapor-diffusion resistance permitted actual ET to be estimated. The methods may be used for studies in similar semiarid and arid rangeland areas in the Western United States. Meteorological data for three field sites are included in the appendix. Simple linear regression analysis indicates that ET estimates are correlated to air temperature, vapor-density deficit, and net radiation. Estimates of annual ET range from 300 mm at a low-density scrub site to 1,100 mm at a high-density meadow site. The monthly percentage of annual ET was determined to be similar for all sites studied. (Author 's abstract)

  8. The estimation of evapotranspiration from wetland sites - the impact of soil physical properties near saturation

    NASA Astrophysics Data System (ADS)

    Frahm, Enrico; Tiemeyer, Bärbel; Salzmann, Thomas; Miegel, Konrad

    2010-05-01

    The evapotranspiration (ET) is a significant process within the soil-plant-atmosphere continuum (SPAC). Especially on wetland sites ET is an important component of the water balance due to the high biomass and ET of wetland vegetation. Thus, comprehensive knowledge of all hydrological processes is the basis for a sustainable management of wetlands. Determining wetland ET still suffers from large uncertainties as it is notoriously difficult to measure directly due to its inherent complexities and small scale spatial and temporal variations. Consequently, there is a wide range of approaches to derive evapotranspiration losses indirectly from other parameters, but all have their significant assets and drawbacks. One of the commonly used methods is the interpretation of diurnal ground water fluctuations (DGF), which has been successfully applied to estimate the ET of phreatophytic vegetation (ETGW). The basic idea behind this method is the assumption of a directly coupled system of incoming solar radiation, vegetation ET, water transport within the plants and water uptake by the root system of the phreatophytic vegetation from both the vadose zone and the groundwater. Such a system is characterised by a strong diurnal cycle and significant DGFs. In the presented study, DGFs measured in a rewetted riverine fen in North-Eastern Germany were analysed to estimate ETGW. With maximum daily values of 5.9 mm for reed (Phragmites australis) and 7.9 mm for willow (Salix spp.), the method yields generally plausible results. However, a comparison of the time series of ETGW and ET according to the Penman-Monteith method (ETPM) shows considerable discrepancies. Despite continuous sufficient water supply the ETGW results fall up to 90 % below the results of ETPM. The aim of the presented study was to identify processes explaining these differences. As a first step, we could identify a clear connection between these errors and the hydrological conditions: The difference between ETGW

  9. Temperature-based approaches for estimating monthly reference evapotranspiration based on MODIS data over North China

    NASA Astrophysics Data System (ADS)

    Zheng, X.; Zhu, Jiaojun

    2015-08-01

    Reference evapotranspiration (ETo) maps play an important role in distributed hydrological modeling and are particularly useful for regional agricultural and water resource management. In the Three-North Shelter Forest Program, water requirements (i.e., ETo) of different land use types are important preconditions for afforestation program management. The Food and Agriculture Organization Penman-Monteith (FAO-PM) method is the most common method for estimating ETo, but it requires many different types of meteorological data, and few stations with adequate meteorological resources exist in the Three-North regions. In addition, the spatial distribution of ordinary meteorological stations is limited. This study employed two temperature-based ETo methods, Hargreaves and Thornthwaite. The monthly mean, maximum, and minimum air temperatures were estimated using moderate resolution imaging spectroradiometer (MODIS) data. The original coefficients of Hargreaves and mean temperatures of Thornthwaite were modified for regional calibration (with the FAO-PM method as the standard). In the comparison between the original/adjusted Hargreaves and the original/adjusted Thornthwaite methods, the adjusted Hargreaves method was appropriate for estimating ETo in the Three-North regions. The average mean bias error (MBE) was -0.21 mm, the relatively root mean square error (RRMSE) was 13.44 %, the correlation coefficient ( R 2) was 0.85, and the slope ( b) was 1.00 for the monthly ETo. While the MBE was 2.32 mm, the RRMSE was 7.07 %, the R 2 was 0.90, and the b was 1.00 for the annual ETo. Therefore, it is possible to estimate monthly and annual ETo values for other parts of the country or the world using adjusted Hargreaves with the estimated air temperature data instead of using the FAO-PM with observed data.

  10. A Review of Current Methodologies for Regional Evapotranspiration Estimation from Remotely Sensed Data

    PubMed Central

    Li, Zhao-Liang; Tang, Ronglin; Wan, Zhengming; Bi, Yuyun; Zhou, Chenghu; Tang, Bohui; Yan, Guangjian; Zhang, Xiaoyu

    2009-01-01

    An overview of the commonly applied evapotranspiration (ET) models using remotely sensed data is given to provide insight into the estimation of ET on a regional scale from satellite data. Generally, these models vary greatly in inputs, main assumptions and accuracy of results, etc. Besides the generally used remotely sensed multi-spectral data from visible to thermal infrared bands, most remotely sensed ET models, from simplified equations models to the more complex physically based two-source energy balance models, must rely to a certain degree on ground-based auxiliary measurements in order to derive the turbulent heat fluxes on a regional scale. We discuss the main inputs, assumptions, theories, advantages and drawbacks of each model. Moreover, approaches to the extrapolation of instantaneous ET to the daily values are also briefly presented. In the final part, both associated problems and future trends regarding these remotely sensed ET models were analyzed to objectively show the limitations and promising aspects of the estimation of regional ET based on remotely sensed data and ground-based measurements. PMID:22412339

  11. A methodology for evaluating evapotranspiration estimates at the watershed-scale using GRACE

    NASA Astrophysics Data System (ADS)

    Billah, Mirza M.; Goodall, Jonathan L.; Narayan, Ujjwal; Reager, J. T.; Lakshmi, Venkat; Famiglietti, James S.

    2015-04-01

    Accurate quantification of evapotranspiration (ET) at the watershed-scale remains an important research challenge. ET products from model simulations and remote sensing, even after incorporating in situ ET observations from flux towers in calibration or assimilation procedures, often produce different watershed areal-averaged ET estimates. These differences in ET estimates are magnified when they are integrated over time as part of water balance calculations. To address this challenge, we present a methodology for comparing watershed-average ET within a water balance framework that makes use of Gravity Recovery and Climate Experiment (GRACE)-observed terrestrial water storage change (TWSC). The methodology is demonstrated for South Carolina for a five-year period (2003-2007) using four different ET products: ET generated using a locally calibrated VIC model, a MODIS-derived ET product, and ET generated from two models (NOAH and VIC) as part of the North American Land Data Assimilation Systems 2 (NLDAS-2) project. The results of the example application suggest that the NLDAS-NOAH ET product is most consistent with GRACE-observed TWSC for the overall study region and time period. However, for periods of decreasing TWS, when ET becomes a more significant term in the water balance, the locally calibrated VIC model showed the most agreement with GRACE-observed TWSC. Application of the methodology for other regions and time periods can provide insight into different ET products when used for watershed-scale water resources management.

  12. Evapotranspiration estimates using remote sensing in a tropical forest in Brazil

    NASA Astrophysics Data System (ADS)

    Biudes, M. S.; Machado, N. G.; Vourlitis, G. L.; Geli, H. M. E.; Neale, C. M. U.; Nogueira, J. D. S.

    2014-12-01

    Tropical forests exchange large amounts of water with the atmosphere and play a key role in global hydrological cycles. The Amazon-Cerrado Transitional Forest exhibits little seasonal variation in evapotranspiration (ET) due to its ability to extract water from deep soil profiles and water tables. Seasonal variability of ET over the transitional forest was monitored using an eddy covariance (EC) tower that acquired energy balance flux measurements from about 45 m above the ground surface near Sinop, Mato Grosso, Brazil. The remote sensing based surface Energy Balance Algorithm for Land (SEBAL) model was applied to test its ability to provide estimates of ET that can be used to account for the spatial and temporal variability over such regions. SEBAL-based estimates of ET were compared with EC measurements during the 2006 season using multiple Landsat 5 TM images. Our results indicate that the SEBAL algorithm is capable to reproducing the seasonal variation in ET of the Amazon-Cerrado Transitional Forest and areas surrounding the EC tower. M.S.B. acknowledges a grant from CAPES (9750/13-4). N.G.M. acknowledges a grant from CAPES (9768/13-0). Partial support was provided by the Remote Sensing Services Laboratory, Department of Civil and Environmental Engineering at Utah State University.

  13. An operational model to estimate hourly and daily crop evapotranspiration in hilly terrain: validation on wheat and oat crops

    NASA Astrophysics Data System (ADS)

    Rana, Gianfranco; Katerji, Nader; Ferrara, Rossana M.; Martinelli, Nicola

    2011-03-01

    In this paper, we present an operational model to estimate the actual evapotranspiration (ET) of crops cultivated on hilly terrains. This new model has the following three characteristics: (1) ET modelling is based on a Penman-Monteith (PM) type equation (Monteith 1965) where canopy resistance is simulated by following an approach already illustrated by Katerji and Perrier (Agronomie 3(6):513-521, 1983); (2) the estimation of ET, by means of the PM equation, is made by using meteorological variables simulated on sloped sites as input; (3) these variables are simulated by using simple relationships linking the variables measured at a reference site on plane to the topographic characteristics of the site (slope, orientation, altitude as difference between reference, and sloped sites). This approach presents two advantages if compared with previously proposed models: Not only computation steps are greatly simplified but also error sources due to the simulation of climatic variables in sloped sites and the ET estimation are well distinguished. This model was validated at hourly and daily scales at four sites cultivated with wheat and oats offering a wide range of slope and orientation values: a reference site on plane, site 1 (9° sloping, NW orientation, 7 m from the reference site in plane), site 2 (6°, SE, 12 m) and site 3 (1°, SE, 18 m). At hourly scale, the new model performed well at all sites studied. The observed slope of the linear relationships between estimated and measured ET values ranged between 0.93 and 1.03, with coefficients of determination, r 2, between 0.80 and 0.98. At daily scale, the slopes of the linear relationships between measured and estimated ET for the sites on plane and the sloped sites were practically the same (0.98 ± 0.01); however, the coefficient of determination r 2 observed in the site on plane was clearly greater (0.98) than that observed in the sloped sites (0.83). The presented analysis does not show any significant

  14. Seasonal estimates of riparian evapotranspiration using remote and in situ measurements

    USGS Publications Warehouse

    Goodrich, D.C.; Scott, R.; Qi, J.; Goff, B.; Unkrich, C.L.; Moran, M.S.; Williams, D.; Schaeffer, S.; Snyder, K.; MacNish, R.; Maddock, T.; Pool, D.; Chehbouni, A.; Cooper, D.I.; Eichinger, W.E.; Shuttleworth, W.J.; Kerr, Y.; Marsett, R.; Ni, W.

    2000-01-01

    In many semi-arid basins during extended periods when surface snowmelt or storm runoff is absent, groundwater constitutes the primary water source for human habitation, agriculture and riparian ecosystems. Utilizing regional groundwater models in the management of these water resources requires accurate estimates of basin boundary conditions. A critical groundwater boundary condition that is closely coupled to atmospheric processes and is typically known with little certainty is seasonal riparian evapotranspiration ET). This quantity can often be a significant factor in the basin water balance in semi-arid regions yet is very difficult to estimate over a large area. Better understanding and quantification of seasonal, large-area riparian ET is a primary objective of the Semi-Arid Land-Surface-Atmosphere (SALSA) Program. To address this objective, a series of interdisciplinary experimental Campaigns were conducted in 1997 in the San Pedro Basin in southeastern Arizona. The riparian system in this basin is primarily made up of three vegetation communities: mesquite (Prosopis velutina), sacaton grasses (Sporobolus wrightii), and a cottonwood (Populus fremontii)/willow (Salix goodingii) forest gallery. Micrometeorological measurement techniques were used to estimate ET from the mesquite and grasses. These techniques could not be utilized to estimate fluxes from the cottonwood/willow (C/W) forest gallery due to the height (20-30 m) and non-uniform linear nature of the forest gallery. Short-term (2-4 days) sap flux measurements were made to estimate canopy transpiration over several periods of the riparian growing season. Simultaneous remote sensing measurements were used to spatially extrapolate tree and stand measurements. Scaled C/W stand level sap flux estimates were utilized to calibrate a Penman-Monteith model to enable temporal extrapolation between Synoptic measurement periods. With this model and set of measurements, seasonal riparian vegetation water use

  15. Thermal and visible remote sensing for estimation of evapotranspiration of rainfed agrosystems and its impact on groundwater in SE Australia

    NASA Astrophysics Data System (ADS)

    Roohi, Rakhshan; Webb, John A.

    2016-05-01

    Rainfed agrosystems are important components of the world's food production system and account for 65-95% of total agriculture. In contrast to irrigated production systems, relatively little attention has been paid to understanding the hydrological interactions between the components of rainfed agrosystems and their impact on water resources, especially groundwater. A new model, the Surface Energy Balance Algorithm for Rainfed Agriculture (SEBARA), has been developed to estimate the spatial pattern of evapotranspiration in these agrosystems using satellite images (thermal, infrared and visible spectra). The model was calibrated for two competing land uses (Eucalyptus globules tree plantations and pastures) in adjacent catchments in western Victoria, southeastern Australia. Using measurements from a flux tower in the pasture catchment and adjusted sapflow measurements in the plantation catchment, an estimation accuracy of 95% was achieved. The tree plantations had higher available net radiation, lower soil heat flux and higher latent heat flux, resulting in 15-20% higher evapotranspirative demand than the pasture, depending upon the age and canopy of plantations. The evapotranspiration rate of plantations declines where groundwater depth is >12m or where shallow groundwater is saline. The shallow root system of the pasture means that it relies solely on soil moisture to meet its water requirements and thus has lower evapotranspiration, which varies according to the pasture species.

  16. Estimation of evapotranspiration in the Rainbow Springs and Silver Springs basins in North-Central Florida

    USGS Publications Warehouse

    Knowles, Leel

    1996-01-01

    Estimates of evapotranspiration (ET) for the Rainbow and Silver Springs ground-water basins in north-central Florida were determined using a regional water-~budget approach and compared to estimates computed using a modified Priestley-Taylor (PT) model calibrated with eddy-correlation data. Eddy-correlation measurements of latent 0~E) and sensible (H) heat flux were made monthly for a few days at a time, and the PT model was used to estimate 3,E between times of measurement during the 1994 water year. A water-budget analysis for the two-basin area indicated that over a 30-year period (196594) annual rainfall was 51.7 inches. Of the annual rainfall, ET accounted for about 37.9 inches; springflow accounted for 13.1 inches; and the remaining 0.7 inch was accounted for by stream-flow, by ground-water withdrawals from the Floridan aquifer system, and by net change in storage. For the same 30-year period, the annual estimate of ET for the Silver Springs basin was 37.6 inches and was 38.5 inches for the Rainbow Springs basin. Wet- and dry-season estimates of ET for each basin averaged between nearly 19 inches and 20 inches, indicating that like rainfall, ET rates during the 4-month wet season were about twice the ET rates during the 8-month dry season. Wet-season estimates of ET for the Rainbow Springs and Silver Springs basins decreased 2.7 inches, and 3.4 inches, respectively, over the 30-year period; whereas, dry-season estimates for the basins decreased about 0.4 inch and1.0 inch, respectively, over the 30-year period. This decrease probably is related to the general decrease in annual rainfall and reduction in net radiation over the basins during the 30-year period. ET rates computed using the modified PT model were compared to rates computed from the water budget for the 1994 water year. Annual ET, computed using the PT model, was 32.0 inches, nearly equal to the ET water-budget estimate of 31.7 inches computed for the Rainbow Springs and Silver Springs basins

  17. Estimates of evapotranspiration or effective moisture in Rocky Mountain watersheds from chloride ion concentrations in stream baseflow

    USGS Publications Warehouse

    Claassen, H.C.; Halm, D.R.

    1996-01-01

    The principle that atmospherically derived chloride is a conservative tracer in many watersheds can be used to calculate average annual evapotranspiration or effective moisture if estimates are available for (1) the average annual chloride input to the watershed, (2) the average annual precipitation, and (3) the baseflow chloride concentration are known. The method assumes that no long-term storage of chloride occurs and there is no lithologic source of chloride, or that such source releases only insignificant amounts to groundwater compared to the atmospheric source. National Atmospheric Deposition Program estimates of chloride wet deposition, watershed precipitation records or hyetal map estimates of precipitation input to watersheds, and a single sample of chloride concentration in base flow were used to calculate evapotranspiration for diverse Rocky Mountain watersheds. This estimate was compared to evapotranspiration determined by subtracting mean discharge from precipitation. Of the 19 watersheds used to test the method, 13 agreed within 10%, 2 appear to have not met the lithology criterion, 1 appears to have not met the flow criterion, and 1 neither criterion. The method's greatest strength is the minimal data requirements and its greatest weakness is that for some watersheds it may be difficult to obtain reliable estimates of precipitation and chloride deposition. If reliable discharge data are available, the method may be used to estimate watershed-average precipitation; this is especially useful in high-altitude mountain watersheds where little or no precipitation data are available.

  18. On the Estimation of Evapotranspiration for Future Climate Change Impacts on Agricultural Water Requirements

    NASA Astrophysics Data System (ADS)

    Aloysius, N. R.

    2005-12-01

    Doubling of atmospheric CO2 concentrations are likely to increase the average global temperature by two to five degrees Celsius and would cause significant changes in climate. Changes in temperature will directly impact water requirements of plants. Since agriculture is the major water consumer, accurate estimates of agricultural crop water requirements are required in order for countries to better plan their future water allocations to different sectors, especially to the agriculture sector. Changes in crop water requirements are indicated by changes in reference evapotranspiration (ET). Procedures for estimating ET should be applicable to all climatic conditions and accurate for both short and long term periods, and should not require data or information that is usually of very limited availability. This is of greater importance when it comes to planning regional and country level agricultural water requirements. Three methods to estimate monthly ET, namely Hargreaves method (ETH), Samani method (ETS) and Food and Agricultural Organization's (FAO) modified Penman-Monteith (FAOETP) method are compared with data obtained for the Indian Sub-continent. While ETH and ETS requires minimum data (minimum and maximum temperatures), FAOETP requires the estimation of net solar radiation and wind velocity in addition to the above two and is physically based. The results are compared with Penman-Monteith ET (ETP) computed from field data. Regression analyses were performed considering ETP as dependant variable and the other three ETs' as independent variables. Results indicates that FAOETP has very high correlation with ETP (average monthly R Square = 0.794, CV = 0.157) compared to ETH (average monthly R Square = 0.709, CV=0.163) and ETS (average monthly R Square = 0.458, CV=0.495). While FAOETP method gives better results and has the capability of incorporating more variables to improve its performance, ETH method is also comparable and provides a simplified procedure. Both

  19. Comparison of Riparian Evapotranspiration Estimated Using Raman LIDAR and Water Balance Based Estimates from a Soil Moisture Sensor Network

    NASA Astrophysics Data System (ADS)

    Solis, J. A.; Rajaram, H.; Whittemore, D. O.; Butler, J. J.; Eichinger, W. E.; Reboulet, E. C.

    2013-12-01

    Riparian evapotranspiration (RET) is an important component of basin-wide evapotranspiration (ET), especially in subhumid to semi-arid regions, with significant impacts on water management and conservation. A common method of measuring ET is using the eddy correlation technique. However, since most riparian zones are narrow, eddy correlation techniques are not applicable because of limited fetch distance. Techniques based on surface-subsurface water balance are applicable in these situations, but their accuracy is not well constrained. In this study, we estimated RET within a 100 meter long and 40 meter wide riparian zone along Rock Creek in the Whitewater Basin in central Kansas using a water balance approach and Raman LIDAR measurements. A total of six soil moisture profiles (with six soil moisture sensors in each profile) and water-table measurements were used to estimate subsurface water storage (total soil moisture, TSM). The Los Alamos National Laboratory (LANL)-University of Iowa (UI) Raman LIDAR was used to measure the water vapor concentrations in three dimensions where the Monin-Obukhov similarity theory was used to obtain the spatially resolved fluxes. The LIDAR system included a 1.064 micron Nd:YAG laser with a Cassagrain telescope with a laser pulse of 50Hz with 25mJ of energy per pulse. Estimates of RET obtained from TSM changes were compared to LIDAR estimates obtained from three-dimensional water vapor concentrations of the atmosphere directly above and downwind of the riparian vegetation. The LIDAR measurements help to validate the TSM based estimates of RET and constrain their accuracy. RET estimates obtained from TSM changes in individual soil moisture profiles exhibited a large variability (up to a factor 8). This variability results from the highly heterogeneous soils in the vadose zone (2-3 m thick), where soil moisture (rather than groundwater) is the major source of water for riparian vegetation. Variable vegetation density and species also

  20. The application of unmanned aerial vehicle to precision agriculture: Chlorophyll, nitrogen, and evapotranspiration estimation

    NASA Astrophysics Data System (ADS)

    Elarab, Manal

    Precision agriculture (PA) is an integration of a set of technologies aiming to improve productivity and profitability while sustaining the quality of the surrounding environment. It is a process that vastly relies on high-resolution information to enable greater precision in the management of inputs to production. This dissertation explored the usage of multispectral high resolution aerial imagery acquired by an unmanned aerial systems (UAS) platform to serve precision agriculture application. The UAS acquired imagery in the visual, near infrared and thermal infrared spectra with a resolution of less than a meter (15--60 cm). This research focused on developing two models to estimate cm-scale chlorophyll content and leaf nitrogen. To achieve the estimations a well-established machine learning algorithm (relevance vector machine) was used. The two models were trained on a dataset of in situ collected leaf chlorophyll and leaf nitrogen measurements, and the machine learning algorithm intelligently selected the most appropriate bands and indices for building regressions with the highest prediction accuracy. In addition, this research explored the usage of the high resolution imagery to estimate crop evapotranspiration (ET) at 15 cm resolution. A comparison was also made between the high resolution ET and Landsat derived ET over two different crop cover (field crops and vineyards) to assess the advantages of UAS based high resolution ET. This research aimed to bridge the information embedded in the high resolution imagery with ground crop parameters to provide site specific information to assist farmers adopting precision agriculture. The framework of this dissertation consisted of three components that provide tools to support precision agriculture operational decisions. In general, the results for each of the methods developed were satisfactory, relevant, and encouraging.

  1. Deriving theoretical boundaries to address scale dependencies of triangle models for evapotranspiration estimation

    NASA Astrophysics Data System (ADS)

    Long, Di; Singh, Vijay P.; Scanlon, Bridget R.

    2012-03-01

    Satellite-based triangle models for evapotranspiration estimation are unique in interpreting the relationship between the normalized difference vegetation index (NDVI)/factional vegetation cover (fc) and surface radiative temperature (Trad) across large heterogeneous areas. However, output and performance of triangle models may depend on the size of the domain being studied and resolution of the satellite images being used. The objective of this study was to assess domain and resolution dependencies of triangle models using progressively larger domains and Landsat Thematic Mapper/Enhanced Thematic Mapper Plus and Moderate Resolution Imaging Spectroradiometer sensors at the Soil Moisture-Atmosphere Coupling Experiment site in central Iowa on days of year 174 and 182 in 2002. Results show domain and resolution dependencies of the triangle models with large uncertainties in evaporative fraction (EF) estimates in terms of a mean absolute percentage difference (MAPD) up to ˜50%. A trapezoid model which requires derivation of theoretical limiting edges of the NDVI-Trad space is proposed to constrain domain and resolution dependencies of triangle models. The theoretical warm edge can be derived by solving for temperatures of the driest bare surface and the fully vegetated surface with the largest water stress implicit in both radiation budget and energy balance equations. Areal average air temperature can be taken as the theoretical cold edge. The triangle model appears to perform well across large areas (˜104 km2) but fails to predict EF over small areas (˜102 km2). The trapezoid model can effectively reduce domain and resolution dependencies and constrain errors of the EF estimates with an MAPD of ˜10%.

  2. Estimating evapotranspiration under warmer climates: Insights from a semiarid riparian system

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This paper presents an approach to quantify evapotranspiration under changing climates, using field observations, theoretical evaporation models and meteorological predictions from global climate models. We analyzed evaporation and meteorological data from three riparian sites located in a semiarid ...

  3. Scaling up stomatal conductance from leaf to canopy using a dual-leaf model for estimating crop evapotranspiration.

    PubMed

    Ding, Risheng; Kang, Shaozhong; Du, Taisheng; Hao, Xinmei; Zhang, Yanqun

    2014-01-01

    The dual-source Shuttleworth-Wallace model has been widely used to estimate and partition crop evapotranspiration (λET). Canopy stomatal conductance (Gsc), an essential parameter of the model, is often calculated by scaling up leaf stomatal conductance, considering the canopy as one single leaf in a so-called "big-leaf" model. However, Gsc can be overestimated or underestimated depending on leaf area index level in the big-leaf model, due to a non-linear stomatal response to light. A dual-leaf model, scaling up Gsc from leaf to canopy, was developed in this study. The non-linear stomata-light relationship was incorporated by dividing the canopy into sunlit and shaded fractions and calculating each fraction separately according to absorbed irradiances. The model includes: (1) the absorbed irradiance, determined by separately integrating the sunlit and shaded leaves with consideration of both beam and diffuse radiation; (2) leaf area for the sunlit and shaded fractions; and (3) a leaf conductance model that accounts for the response of stomata to PAR, vapor pressure deficit and available soil water. In contrast to the significant errors of Gsc in the big-leaf model, the predicted Gsc using the dual-leaf model had a high degree of data-model agreement; the slope of the linear regression between daytime predictions and measurements was 1.01 (R2 = 0.98), with RMSE of 0.6120 mm s-1 for four clear-sky days in different growth stages. The estimates of half-hourly λET using the dual-source dual-leaf model (DSDL) agreed well with measurements and the error was within 5% during two growing seasons of maize with differing hydrometeorological and management strategies. Moreover, the estimates of soil evaporation using the DSDL model closely matched actual measurements. Our results indicate that the DSDL model can produce more accurate estimation of Gsc and λET, compared to the big-leaf model, and thus is an effective alternative approach for estimating and partitioning

  4. Scaling up stomatal conductance from leaf to canopy using a dual-leaf model for estimating crop evapotranspiration.

    PubMed

    Ding, Risheng; Kang, Shaozhong; Du, Taisheng; Hao, Xinmei; Zhang, Yanqun

    2014-01-01

    The dual-source Shuttleworth-Wallace model has been widely used to estimate and partition crop evapotranspiration (λET). Canopy stomatal conductance (Gsc), an essential parameter of the model, is often calculated by scaling up leaf stomatal conductance, considering the canopy as one single leaf in a so-called "big-leaf" model. However, Gsc can be overestimated or underestimated depending on leaf area index level in the big-leaf model, due to a non-linear stomatal response to light. A dual-leaf model, scaling up Gsc from leaf to canopy, was developed in this study. The non-linear stomata-light relationship was incorporated by dividing the canopy into sunlit and shaded fractions and calculating each fraction separately according to absorbed irradiances. The model includes: (1) the absorbed irradiance, determined by separately integrating the sunlit and shaded leaves with consideration of both beam and diffuse radiation; (2) leaf area for the sunlit and shaded fractions; and (3) a leaf conductance model that accounts for the response of stomata to PAR, vapor pressure deficit and available soil water. In contrast to the significant errors of Gsc in the big-leaf model, the predicted Gsc using the dual-leaf model had a high degree of data-model agreement; the slope of the linear regression between daytime predictions and measurements was 1.01 (R2 = 0.98), with RMSE of 0.6120 mm s-1 for four clear-sky days in different growth stages. The estimates of half-hourly λET using the dual-source dual-leaf model (DSDL) agreed well with measurements and the error was within 5% during two growing seasons of maize with differing hydrometeorological and management strategies. Moreover, the estimates of soil evaporation using the DSDL model closely matched actual measurements. Our results indicate that the DSDL model can produce more accurate estimation of Gsc and λET, compared to the big-leaf model, and thus is an effective alternative approach for estimating and partitioning λET.

  5. Scaling Up Stomatal Conductance from Leaf to Canopy Using a Dual-Leaf Model for Estimating Crop Evapotranspiration

    PubMed Central

    Ding, Risheng; Kang, Shaozhong; Du, Taisheng; Hao, Xinmei; Zhang, Yanqun

    2014-01-01

    The dual-source Shuttleworth-Wallace model has been widely used to estimate and partition crop evapotranspiration (λET). Canopy stomatal conductance (Gsc), an essential parameter of the model, is often calculated by scaling up leaf stomatal conductance, considering the canopy as one single leaf in a so-called “big-leaf” model. However, Gsc can be overestimated or underestimated depending on leaf area index level in the big-leaf model, due to a non-linear stomatal response to light. A dual-leaf model, scaling up Gsc from leaf to canopy, was developed in this study. The non-linear stomata-light relationship was incorporated by dividing the canopy into sunlit and shaded fractions and calculating each fraction separately according to absorbed irradiances. The model includes: (1) the absorbed irradiance, determined by separately integrating the sunlit and shaded leaves with consideration of both beam and diffuse radiation; (2) leaf area for the sunlit and shaded fractions; and (3) a leaf conductance model that accounts for the response of stomata to PAR, vapor pressure deficit and available soil water. In contrast to the significant errors of Gsc in the big-leaf model, the predicted Gsc using the dual-leaf model had a high degree of data-model agreement; the slope of the linear regression between daytime predictions and measurements was 1.01 (R2 = 0.98), with RMSE of 0.6120 mm s−1 for four clear-sky days in different growth stages. The estimates of half-hourly λET using the dual-source dual-leaf model (DSDL) agreed well with measurements and the error was within 5% during two growing seasons of maize with differing hydrometeorological and management strategies. Moreover, the estimates of soil evaporation using the DSDL model closely matched actual measurements. Our results indicate that the DSDL model can produce more accurate estimation of Gsc and λET, compared to the big-leaf model, and thus is an effective alternative approach for estimating and

  6. A worldwide evaluation of basin-scale evapotranspiration estimates against the water balance method

    NASA Astrophysics Data System (ADS)

    Liu, Wenbin; Wang, Lei; Zhou, Jing; Li, Yanzhong; Sun, Fubao; Fu, Guobin; Li, Xiuping; Sang, Yan-Fang

    2016-07-01

    Evapotranspiration (ET) plays a critical role in linking the water and energy cycles but is difficult to estimate at regional and basin scales. In this study, we present a worldwide evaluation of nine ET products (three diagnostic products, three land surface model (LSM) simulations and three reanalysis-based products) against reference ET (ETwb) calculated using the water balance method corrected for the water storage change at an annual time scale over the period 1983-2006 for 35 global river basins. The results indicated that there was no significant intra-category discrepancy in the annual ET estimates for the 35 basins calculated using the different products in 35 basins, but some products performed better than others, such as the Global Land surface Evaporation estimated using the Amsterdam Methodology (GLEAM_E) in the diagnostic products, ET obtained from the Global Land Data Assimilation System version 1 (GLDAS 1) with the Community Land Model scheme (GCLM_E) in LSM simulations, and ET from the National Aeronautics and Space Administration (NASA) Modern Era Retrospective-analysis for Research and Applications reanalysis dataset (MERRA_E) in the reanalysis-based products. Almost all ET products (except MERRA_E) reasonably estimated the annual means (especially in the dry basins) but systematically underestimated the inter-annual variability (except for MERRA_E, GCLM_E and ET simulation from the GLDAS 1 with the MOSAIC scheme - GMOS_E) and could not adequately estimate the trends (e.g. GCLM_E and MERRA_E) of ETwb (especially in the energy-limited wet basins). The uncertainties in nine ET products may be primarily attributed to the discrepancies in the forcing datasets and model structural limitations. The enhancements of global forcing data (meteorological data, solar radiation, soil moisture stress and water storage changes) and model physics (reasonable consideration of the water and energy balance and vegetation processes such as canopy interception loss

  7. Evapotranspiration in a cottonwood (Populus fremontii) restoration plantation estimated by sap flow and remote sensing methods

    USGS Publications Warehouse

    Nagler, P.; Jetton, A.; Fleming, J.; Didan, K.; Glenn, E.; Erker, J.; Morino, K.; Milliken, J.; Gloss, S.

    2007-01-01

    Native tree plantations have been proposed for the restoration of wildlife habitat in human-altered riparian corridors of western U.S. rivers. Evapotranspiration (ET) by riparian vegetation is an important, but poorly quantified, term in river water budgets. Native tree restoration plots will potentially increase ET. We used sap flow sensors and satellite imagery to estimate ET in a 8 ha, cottonwood (Populus fremontii) restoration plot on the Lower Colorado River. Biometric methods were used to scale leaf area to whole trees and stands of trees. This technique was used to validate our estimates of ET obtained by scaling from branch level to stand (or plot) level measurements of ET. Cottonwood trees used 6-10 mm day-1 of water during the peak of the growing season as determined by sap flow sensors, and annual rates scaled by time-series MODIS satellite imagery were approximately 1.2 m year-1. Although irrigation was not quantified, the field had been flood irrigated at 2 week intervals during the 3 years prior to the study, receiving approximately 2 m year-1 of water. A frequency-domain electromagnetic induction survey of soil moisture content showed that the field was saturated (26-28% gravimetric water content) at the 90-150 cm soil depth under the field. Trees were apparently rooted into the saturated soil, and considerable saving of water could potentially be achieved by modifying the irrigation regime to take into account that cottonwoods are phreatophytes. The study showed that cottonwood ET can be monitored by remote sensing methods calibrated with ground measurements with an accuracy or uncertainty of 20-30% in western riparian corridors. ?? 2007 Elsevier B.V. All rights reserved.

  8. Deriving Theoretical Boundaries to Address Domain and Resolution Dependencies of Triangle Models for Evapotranspiration Estimation

    NASA Astrophysics Data System (ADS)

    Long, D.; Singh, V. P.; Scanlon, B. R.

    2011-12-01

    Satellite-based triangle models for evapotranspiration (ET) are unique in interpreting the contextual relationship between Normalized Difference Vegetation Index (NDVI)/factional vegetation cover (fc) and surface radiative temperature (Trad) to deduce evaporative fraction (EF) and ET across large heterogeneous areas. The outputs and performance of some satellite-based ET algorithms may be dependent on the domain of a study site being considered and the resolution of satellite imagery being used. These attributes are referred to as domain dependence and resolution dependence. To unravel the domain and resolution dependencies of the triangle models and test the utility of the triangle models using high spatial resolution images, the triangle models were applied to areas with progressively growing domains and to Landsat TM/ETM+ and MODIS sensors, respectively, at the Soil Moisture-Atmosphere Coupling Experiment (SMACEX) site in central Iowa, U.S. on Day of Year (DOY) 174 and 182 in year 2002. Results indicate that the triangle models can be domain-dependent and resolution-dependent, showing large uncertainties in the evaporative fraction estimates in terms of a Mean Absolute Percentage Difference (MAPD) up to ~50%. We derived the theoretical boundaries of the fc-Trad space to restrain the domain and resolution dependencies of the triangle models. The theoretical warm edge was derived by solving for temperatures of the driest bare surface and the fully vegetated surface with the largest water stress implicit in both radiation budget and energy balance equations. The areal average temperature can be taken as the theoretical cold edge. The triangle models appear to perform well across large areas but fail to predict the evaporative fraction over small areas. However, performance of the triangle models across small domains can be improved by incorporating the theoretical boundaries. Combining the triangle models with the theoretical boundaries can effectively reduce

  9. Operational evapotranspiration estimates from SEVIRI in support of sustainable water management

    NASA Astrophysics Data System (ADS)

    Petropoulos, George P.; Ireland, Gareth; Lamine, Salim; Griffiths, Hywel M.; Ghilain, Nicolas; Anagnostopoulos, Vasileios; North, Matthew R.; Srivastava, Prashant K.; Georgopoulou, Hro

    2016-07-01

    This study aimed at evaluating the accuracy of the evapotranspiration (ET) operational estimates from the Meteosat Second Generation (MSG) Spinning Enhanced Visible Infra-Red Imager (SEVIRI) at a range of selected ecosystems in Europe. For this purpose in-situ eddy covariance measurements were used, acquired from 7 selected experimental sites belonging to the CarboEurope ground observational network over 2 full years of observations (2010-2011). Appraisal of ET accuracy was also investigated with respect to land cover, season and each site(s) degree of heterogeneity, the latter being expressed by the fractional vegetation cover (FVC) operational product of SEVIRI. Results indicated a close agreement between the operational product's ET estimates and the tower based in-situ ET measurements for all days of comparison, showing a satisfactory correlation (r of 0.709) with accuracies often comparable to previous analogous studies. For all land cover types, the grassland and cropland sites exhibited the closest agreement (r from 0.705 to 0.759). In terms of seasons the strongest correlations were observed during the summer and autumn (r of 0.714 & 0.685 respectively), and with FVC the highest correlation of 0.735 was observed for the class FVC 0.75-1 when compared against the observed values for the complete monitoring period. Our findings support the potential value of the SEVIRI ET product for regional to mesoscale studies and corroborate its credibility for usage in many practical applications. The latter is of particular importance for water limiting environments, such as those found in the Mediterranean basin, as accurate information on ET rates can provide tremendous support in sustainable water resource management as well as policy and decision making in those areas.

  10. Comparison of satellite-based evapotranspiration estimates over the Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Peng, Jian; Loew, Alexander; Chen, Xuelong; Ma, Yaoming; Su, Zhongbo

    2016-08-01

    The Tibetan Plateau (TP) plays a major role in regional and global climate. The understanding of latent heat (LE) flux can help to better describe the complex mechanisms and interactions between land and atmosphere. Despite its importance, accurate estimation of evapotranspiration (ET) over the TP remains challenging. Satellite observations allow for ET estimation at high temporal and spatial scales. The purpose of this paper is to provide a detailed cross-comparison of existing ET products over the TP. Six available ET products based on different approaches are included for comparison. Results show that all products capture the seasonal variability well with minimum ET in the winter and maximum ET in the summer. Regarding the spatial pattern, the High resOlution Land Atmosphere surface Parameters from Space (HOLAPS) ET demonstrator dataset is very similar to the LandFlux-EVAL dataset (a benchmark ET product from the Global Energy and Water Cycle Experiment), with decreasing ET from the south-east to north-west over the TP. Further comparison against the LandFlux-EVAL over different sub-regions that are decided by different intervals of normalised difference vegetation index (NDVI), precipitation, and elevation reveals that HOLAPS agrees best with LandFlux-EVAL having the highest correlation coefficient (R) and the lowest root mean square difference (RMSD). These results indicate the potential for the application of the HOLAPS demonstrator dataset in understanding the land-atmosphere-biosphere interactions over the TP. In order to provide more accurate ET over the TP, model calibration, high accuracy forcing dataset, appropriate in situ measurements as well as other hydrological data such as runoff measurements are still needed.

  11. Time Series Analysis of Remote Sensing Observations for Citrus Crop Growth Stage and Evapotranspiration Estimation

    NASA Astrophysics Data System (ADS)

    Sawant, S. A.; Chakraborty, M.; Suradhaniwar, S.; Adinarayana, J.; Durbha, S. S.

    2016-06-01

    Satellite based earth observation (EO) platforms have proved capability to spatio-temporally monitor changes on the earth's surface. Long term satellite missions have provided huge repository of optical remote sensing datasets, and United States Geological Survey (USGS) Landsat program is one of the oldest sources of optical EO datasets. This historical and near real time EO archive is a rich source of information to understand the seasonal changes in the horticultural crops. Citrus (Mandarin / Nagpur Orange) is one of the major horticultural crops cultivated in central India. Erratic behaviour of rainfall and dependency on groundwater for irrigation has wide impact on the citrus crop yield. Also, wide variations are reported in temperature and relative humidity causing early fruit onset and increase in crop water requirement. Therefore, there is need to study the crop growth stages and crop evapotranspiration at spatio-temporal scale for managing the scarce resources. In this study, an attempt has been made to understand the citrus crop growth stages using Normalized Difference Time Series (NDVI) time series data obtained from Landsat archives (http://earthexplorer.usgs.gov/). Total 388 Landsat 4, 5, 7 and 8 scenes (from year 1990 to Aug. 2015) for Worldwide Reference System (WRS) 2, path 145 and row 45 were selected to understand seasonal variations in citrus crop growth. Considering Landsat 30 meter spatial resolution to obtain homogeneous pixels with crop cover orchards larger than 2 hectare area was selected. To consider change in wavelength bandwidth (radiometric resolution) with Landsat sensors (i.e. 4, 5, 7 and 8) NDVI has been selected to obtain continuous sensor independent time series. The obtained crop growth stage information has been used to estimate citrus basal crop coefficient information (Kcb). Satellite based Kcb estimates were used with proximal agrometeorological sensing system

  12. Estimation of Regional Evapotranspiration Using Remotely Sensed Land Surface Temperature. Part 1: Measurement of Evapotranspiration at the Environmental Research Center and Determination of Priestley-taylor Parameter

    NASA Technical Reports Server (NTRS)

    Kotada, K.; Nakagawa, S.; Kai, K.; Yoshino, M. M.; Takeda, K.; Seki, K.

    1985-01-01

    In order to study the distribution of evapotranspiration in the humid region using remote sensing technology, the parameter (alpha) in the Priestley-Taylor model was determined. The daily means of the parameter alpha = 1.14 can be available from summer to autumn and alpha = to approximately 2.0 in winter. The results of the satellite and the airborne sensing done on 21st and 22nd January, 1983, are described. Using the vegetation distribution in the Tsukuba Academic New Town, as well as the radiation temperature obtained by remote sensing and the radiation data observed at the ground surface, the evapotranspiration was calculated for each vegetation type by the Priestley-Taylor method. The daily mean evapotranspiration on 22nd January, 1983, was approximately 0.4 mm/day. The differences in evapotranspiration between the vegetation types were not detectable, because the magnitude of evapotranspiration is very little in winter.

  13. Large Scale Evapotranspiration Estimates: An Important Component in Regional Water Balances to Assess Water Availability

    NASA Astrophysics Data System (ADS)

    Garatuza-Payan, J.; Yepez, E. A.; Watts, C.; Rodriguez, J. C.; Valdez-Torres, L. C.; Robles-Morua, A.

    2013-05-01

    Water security, can be defined as the reliable supply in quantity and quality of water to help sustain future populations and maintaining ecosystem health and productivity. Water security is rapidly declining in many parts of the world due to population growth, drought, climate change, salinity, pollution, land use change, over-allocation and over-utilization, among other issues. Governmental offices (such as the Comision Nacional del Agua in Mexico, CONAGUA) require and conduct studies to estimate reliable water balances at regional or continental scales in order to provide reasonable assessments of the amount of water that can be provided (from surface or ground water sources) to supply all the human needs while maintaining natural vegetation, on an operational basis and, more important, under disturbances, such as droughts. Large scale estimates of evapotranspiration (ET), a critical component of the water cycle, are needed for a better comprehension of the hydrological cycle at large scales, which, in most water balances is left as the residual. For operational purposes, such water balance estimates can not rely on ET measurements since they do not exist, should be simple and require the least ground information possible, information that is often scarce or does not exist at all. Given this limitation, the use of remotely sensed data to estimate ET could supplement the lack of ground information, particularly in remote regions In this study, a simple method, based on the Makkink equation is used to estimate ET for large areas at high spatial resolutions (1 km). The Makkink model used here is forced using three remotely sensed datasets. First, the model uses solar radiation estimates obtained from the Geostationary Operational Environmental Satellite (GOES); Second, the model uses an Enhanced Vegetation Index (EVI) obtained from the Moderate-resolution Imaging Spectroradiometer (MODIS) normalized to get an estimate for vegetation amount and land use which was

  14. Estimates of evapotranspiration and CO2 fluxes in a biofiltration system

    NASA Astrophysics Data System (ADS)

    Daly, E.; Niculescu, A.; Beringer, J.; Deletic, A.

    2009-12-01

    Biofiltration systems (or biofilters, bioretention systems or rain gardens) have been adopted to improve the quality of urban aquatic ecosystems and to reduce volumes and peaks of stormwater runoff. Given their good performances, it is likely that the implementation of such systems in urban areas will greatly increase in the future. As an example, the city of Melbourne (Australia) is planning to install 10,000 biofiltration systems within its area by 2013. Because biofiltration systems are commonly installed in urban areas, along roads and highways, their vegetation is often under atmospheric CO2 concentrations higher than average ambient conditions (i.e., above 380 ppm). Additionally, since these systems are designed to receive runoff from large catchment areas (typically around 50-100 times the area of the biofilter), their vegetation rarely experiences water and nitrogen limitations. These surrounding environmental conditions suggest that biofilters might experience high evapotranspiration (ET) rates and CO2 assimilation via photosynthesis, which could potentially provide benefits to the local microclimate in terms of temperature reduction (cooling due to enhanced ET) and CO2 uptake from the atmosphere, in addition to the benefit related to stormwater treatment. These hypotheses have been strengthen by preliminary tests based on laboratory experiments with soil columns vegetated with C.appressa, in which ET has been estimated to be as high as 0.7-0.8 cm per day. To further study these processes, several measurements are being performed in a biofiltration system installed at Monash University, Clayton Campus (Melbourne, VIC). This biofilter receives runoff diverted from a 100% impervious car park and discharges the treated stormwater to an adjacent pond. A chamber that encloses part of the vegetation in the biofilter has been constructed to monitor water and greenhouse gas fluxes. Preliminary results on daily patterns of water and CO2 fluxes within the system in

  15. Remote sensing of energy balance for estimating land evapotranspiration in the semi-arid southwestern USA

    NASA Astrophysics Data System (ADS)

    Mariotto, Isabella

    Modeling spatial variation of evapotranspiration (ET) over heterogeneous landscapes is a difficult task for hydrologists, agronomists, and meteorologists. The application of energy balance algorithms to remotely sensed imagery often fails in properly discriminating ET over spectrally diverse land covers for the complexity of modeling the surface roughness. Furthermore, the assumption of a horizontally homogeneous Lambertian surface reflecting energy equally in all directions affects the albedo and vegetation index calculations. The objective of this study is to improve the accuracy of the Surface Energy Balance Algorithm for Land (SEBAL) for estimating ET from ASTER datasets by analyzing the spatial variation of anisotropic reflectance and surface roughness among different plant species-dominated grasslands, shrublands, and dunelands in Southern New Mexico. The degree to which land cover surfaces are anisotropic is assessed by applying a wavelength-dependent non-Lambertian topographic transformation with the Minnaert function. Surface roughness is modeled using a land cover map in conjunction with the fractional vegetation cover derived from vegetation indices. SEBAL modified for reflectance or for roughness showed stronger agreement with the Eddy-Covariance measurements than the non-modified SEBAL. Furthermore, the former showed higher, intermediate, and lower ET values among grasslands, schrublands, and dunelands respectively, while the latter resulted in more homogeneous ET values among land covers and in overestimation of ET over dunelands and underestimation over grasslands. Multiple pairwise land covers comparisons of ET means showed higher potential of the corrected model in discriminating ET. This study suggests that some assumptions in SEBAL tend to inadvertently homogenize ET on these diverse landscapes.

  16. Global estimates of evapotranspiration and gross primary production based on MODIS and global meteorology data

    USGS Publications Warehouse

    Yuan, W.; Liu, S.; Yu, G.; Bonnefond, J.-M.; Chen, J.; Davis, K.; Desai, A.R.; Goldstein, Allen H.; Gianelle, D.; Rossi, F.; Suyker, A.E.; Verma, S.B.

    2010-01-01

    The simulation of gross primary production (GPP) at various spatial and temporal scales remains a major challenge for quantifying the global carbon cycle. We developed a light use efficiency model, called EC-LUE, driven by only four variables: normalized difference vegetation index (NDVI), photosynthetically active radiation (PAR), air temperature, and the Bowen ratio of sensible to latent heat flux. The EC-LUE model may have the most potential to adequately address the spatial and temporal dynamics of GPP because its parameters (i.e., the potential light use efficiency and optimal plant growth temperature) are invariant across the various land cover types. However, the application of the previous EC-LUE model was hampered by poor prediction of Bowen ratio at the large spatial scale. In this study, we substituted the Bowen ratio with the ratio of evapotranspiration (ET) to net radiation, and revised the RS-PM (Remote Sensing-Penman Monteith) model for quantifying ET. Fifty-four eddy covariance towers, including various ecosystem types, were selected to calibrate and validate the revised RS-PM and EC-LUE models. The revised RS-PM model explained 82% and 68% of the observed variations of ET for all the calibration and validation sites, respectively. Using estimated ET as input, the EC-LUE model performed well in calibration and validation sites, explaining 75% and 61% of the observed GPP variation for calibration and validation sites respectively. Global patterns of ET and GPP at a spatial resolution of 0.5?? latitude by 0.6?? longitude during the years 2000-2003 were determined using the global MERRA dataset (Modern Era Retrospective-Analysis for Research and Applications) and MODIS (Moderate Resolution Imaging Spectroradiometer). The global estimates of ET and GPP agreed well with the other global models from the literature, with the highest ET and GPP over tropical forests and the lowest values in dry and high latitude areas. However, comparisons with observed GPP

  17. Impacts of Reprojection and Sampling of MODIS Satellite Images on Estimating Crop Evapotranspiration Using METRIC model

    NASA Astrophysics Data System (ADS)

    Pun, M.; Kilic, A.; Allen, R.

    2014-12-01

    Landsat satellite images have been used frequently to map evapotranspiration (ET) andbiophysical variables at the field scale with surface energy balance algorithms. Although Landsat images have high spatial resolution with 30m cell size, it has limitations for real time monitoring of crop ET by providing only two to four images per month for an area, which, when encountered with cloudy days, further deteriorates the availability of images and snapshots of ET behavior. Therefore real time monitoring essentially has to include near-daily thermal satellites such as MODIS/VIIRS into the time series. However, the challenge with field scale monitoring with these systems is the large size of the thermal band which is 375 m with VIIRS and 1000 meter with MODIS. To maximize the accuracy of ET estimates during infusion of MODIS products into land surface models for monitoring field scale ET, it is important to assess the geometric accuracy of the various MODIS products, for example, spatial correspondence among the 250 m red and near-infrared bands, the 500 m reflectance bands; and the 1000 m thermal bands and associated products. METRIC model was used with MODIS images to estimate ET from irrigated and rainfed fields in Nebraska. Our objective was to assess geometric accuracy of MODIS image layers and how to correctly handle these data for highest accuracy of estimated ET at the individual field scale during the extensive drought of 2012. For example, the particular tool used to subset and reproject MODIS swath images from level-1 and level-2 products (e.g., using the MRTSwath and other tools), the initial starting location (upper left hand corner), and the projection system all effect how pixel corners of the various resolution bands align. Depending on the approach used, origin of pixel corners can vary from image to image date and therefore impacts the pairing of ET information from multiple dates the consistency and accuracy of sampling ET from within field interiors

  18. A review of models and micrometeorological methods used to estimate wetland evapotranspiration

    USGS Publications Warehouse

    Drexler, J.Z.; Snyder, R.L.; Spano, D.; Paw, U.K.T.

    2004-01-01

    Within the past decade or so, the accuracy of evapotranspiration (ET) estimates has improved due to new and increasingly sophisticated methods. Yet despite a plethora of choices concerning methods, estimation of wetland ET remains insufficiently characterized due to the complexity of surface characteristics and the diversity of wetland types. In this review, we present models and micrometeorological methods that have been used to estimate wetland ET and discuss their suitability for particular wetland types. Hydrological, soil monitoring and lysimetric methods to determine ET are not discussed. Our review shows that, due to the variability and complexity of wetlands, there is no single approach that is the best for estimating wetland ET. Furthermore, there is no single foolproof method to obtain an accurate, independent measure of wetland ET. Because all of the methods reviewed, with the exception of eddy covariance and LIDAR, require measurements of net radiation (Rn) and soil heat flux (G), highly accurate measurements of these energy components are key to improving measurements of wetland ET. Many of the major methods used to determine ET can be applied successfully to wetlands of uniform vegetation and adequate fetch, however, certain caveats apply. For example, with accurate Rn and G data and small Bowen ratio (??) values, the Bowen ratio energy balance method can give accurate estimates of wetland ET. However, large errors in latent heat flux density can occur near sunrise and sunset when the Bowen ratio ?? ??? - 1??0. The eddy covariance method provides a direct measurement of latent heat flux density (??E) and sensible heat flux density (II), yet this method requires considerable expertise and expensive instrumentation to implement. A clear advantage of using the eddy covariance method is that ??E can be compared with Rn-G H, thereby allowing for an independent test of accuracy. The surface renewal method is inexpensive to replicate and, therefore, shows

  19. Estimating the Changes and Impact Factors of Evapotranspiration in the Semi-arid Laohahe Basin, Northeast China

    NASA Astrophysics Data System (ADS)

    Yang, X.; Ren, L.; Yu, Z.

    2011-12-01

    Evapotranspiration (ET) is one important component of hydrological cycle in semi-arid regions, which can not be availably space-based measured. Remote sensors can make spatially resolved measurements over large areas, providing both spatial distribution and visualization of complex processes of evapotranspiration. In this paper, the spatial distribution of daily ET over Laohahe Basin in northeast China with area of 18112 km2 was assessed by using the Surface Energy Balance Algorithm for Land (SEBAL) model. A series of available Moderate-Resolution Imaging Spectroradiometer (MODIS) satellite images on clouds-free days over the growing season (from April to October) in 2008 are used to estimate ET at a spatial resolution of 1 km. Harmonic Analysis of NDVI Time Series (HANTS) is then applied to generate a time series of daily ET over a year period by filling the gaps in the observation series for clouds. Finally, the results were validated with the water balance for the whole study area. The impact of ground parameters on evapotranspiration of the study area was quantified. The result indicates that (1) the SEBAL algorithm can be used to effectively estimate the ET in the Laohahe Basin; (2) The vegetation types, NDVI, and terrain have a direct effect on the spatial distribution of ET. These results can be used to provide current, reliable land use information for management and decision-making in the Laohahe Basin.

  20. Evapotranspiration Estimation over Yangtze River Basin from GRACE satellite measurement and in situ data

    NASA Astrophysics Data System (ADS)

    Li, Qiong; Luo, Zhicai; Zhong, Bo; Wang, Haihong; Zhou, Zebing

    2016-04-01

    As the critical component of hydrologic cycle, evapotranspiration (ET) plays an important role in global water exchanges and energy flow across the hydrosphere, atmosphere and biosphere. Influenced by the Asian monsoon, the Yangtze River Basin (YRB) suffer from the several severe floods and droughts over the last decades due to the significant difference between temporal and spatial distribution terrestrial water storages. As an indispensable part, it is practically important to assessment ET in the YRB accompany with increased population and rapid economic and agriculture development. Average ET over the YRB is computed as the residual of terrestrial water budget using the Gravity Recovery and Climate Experiment (GRACE) satellite-based measurements and the ground-based observations. The GRACE-based ET were well coincidence with the ET from MODIS, with the correlation coefficient of 0.853, and the correlation coefficient is 0.696 while comparing with the ET ground-based observation. The mean monthly average of ET from these various estimates is 56.9 mm/month over the whole YRB, and peak between June and August. Monthly variations of ET reach a maximum in Wujiang with 69.11 mm/month and a minimum in Jinshajiang with 39.01 mm/month. Based on the correlation between ET and independent estimates of near-surface temperature and soil moisture, it is showed that as the temperature increased, the ET of the seven sub-catchment were rising except for the Poyang Lake and Donting Lake. And we also can infer that the midstream of YRB is significant correlated with ESON especially in the Hanjiang basin. The Surface Humidity Index over the YRB was gradually decreased and its variations in each sub-catchment showed a significant decreasing trend in Jinshajiang and Mingjiang. This research has important potential for use in large-scale water budget assessments and intercomparison studies. Acknowledgements: This research is supported by the National Natural Science Foundation of

  1. Modification of evapotranspiration model based on effective resistance to estimate evapotranspiration of maize for seed production in an arid region of northwest China

    NASA Astrophysics Data System (ADS)

    Jiang, Xuelian; Kang, Shaozhong; Tong, Ling; Li, Fusheng

    2016-07-01

    To estimate evapotranspiration (ET) of heterogeneous canopy of maize for seed production accurately, an ET model was developed based on effective resistance after field experiments were conducted from March to September in 2013 and 2014 in an arid region of northwest China. The effective resistance of maize including effective surface (rce) and aerodynamic (rae) resistance was estimated using different methods, and then the Penman-Monteith model (P-M model) based on effective resistance was used to estimate daily ET of maize over the whole growing stage. Results showed that when the fraction cover of the canopy (fc) = 1, the estimated rce by aggregating female and male canopy resistances in parallel, was closer to the measured rce (rcec), which was obtained by inverting the P-M model based on effective resistance using measured ET by the eddy covariance (EC) system. When fc < 1, the calculated rce by aggregating female and male canopy resistances and soil resistance in parallel, weighed by fc, was significantly higher than rcec, but the estimated rce by aggregating female and male canopy resistances and soil resistance in parallel, weighed by leaf area index (LAI), was closer to rcec. The P-M model based on effective resistance by aggregating the plant and soil resistance in parallel, weighed by fc, underestimated ET measured by the EC system (ETEC) at the late stage, while the estimated ET using the P-M model based on effective resistance by aggregating the plant and soil resistances in parallel, weighed by LAI (ETPL), was closer to ETEC over the whole growing stage, with higher coefficient of determination and modified coefficient of efficiency, and lower mean absolute bias error and root mean square error. ETPL was only 2% lower than ETEC in 2013 and 1% higher than ETEC in 2014. Thus the P-M model using the effective resistance by aggregating the plant and soil resistances in parallel, weighed by LAI, is more suitable for estimating water use of maize for seed

  2. A thermal-based remote sensing modeling system for estimating evapotranspiration from field to global scales

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Thermal-infrared remote sensing of land surface temperature provides valuable information for quantifying root-zone water availability, evapotranspiration (ET) and crop condition. This paper describes a robust but relatively simple thermal-based energy balance model that parameterizes the key soil/s...

  3. Estimates of evapotranspiration in alkaline scrub and meadow communities of Owens Valley, California, using the Bowen-ratio, eddy-correlation, and penman-combination methods

    USGS Publications Warehouse

    Duell, Lowell F. W.

    1990-01-01

    In Owens Valley, evapotranspiration (ET) is one of the largest components of outflow in the hydrologic budget and the least understood. ET estimates for December 1983 through October 1985 were made for seven representative locations selected on the basis of geohydrology and the characteristics of phreatophytic alkaline scrub and meadow communities. The Bowen-ratio, eddy-correlation, and Penman-combination methods were used to estimate ET. The results of the analyses appear satisfactory when compared with other estimates of ET. Results by the eddy-correlation method are for a direct and a residual latent-heat flux that is based on sensible-heat flux and energy-budget measurements. Penman-combination potential-ET estimates were determined to be unusable because they overestimated actual ET. Modification of the psychrometer constant of this method to account for differences between heat-diffusion resistance and vapor-diffusion resistance permitted actual ET to be estimated. The methods described in this report may be used for studies in similar semiarid and arid rangeland areas in the Western United States. Meteorological data for three field sites are included in the appendix of this report. Simple linear regression analysis indicates that ET estimates are correlated to air temperature, vapor-density deficit, and net radiation. Estimates of annual ET range from 301 millimeters at a low-density scrub site to 1,137 millimeters at a high-density meadow site. The monthly percentage of annual ET was determined to be similar for all sites studied.

  4. Estimation of crops biomass and evapotranspiration from high spatial and temporal resolutions remote sensing data

    NASA Astrophysics Data System (ADS)

    Claverie, Martin; Demarez, Valérie; Duchemin, Benoît.; Ceschia, Eric; Hagolle, Olivier; Ducrot, Danielle; Keravec, Pascal; Beziat, Pierre; Dedieu, Pierre

    2010-05-01

    Carbon and water cycles are closely related to agricultural activities. Agriculture has been indeed identified by IPCC 2007 report as one of the options to sequester carbon in soil. Concerning the water resources, their consumptions by irrigated crops are called into question in view of demographic pressure. In the prospect of an assessment of carbon production and water consumption, the use of crop models at a regional scale is a challenging issue. The recent availability of high spatial resolution (10 m) optical sensors associated to high temporal resolution (1 day) such as FORMOSAT-2 and, in the future, Venµs and SENTINEL-2 will offer new perspectives for agricultural monitoring. In this context, the objective of this work is to show how multi-temporal satellite observations acquired at high spatial resolution are useful for a regional monitoring of following crops biophysical variables: leaf area index (LAI), aboveground biomass (AGB) and evapotranspiration (ET). This study focuses on three summer crops dominant in South-West of France: maize, sunflower and soybean. A unique images data set (82 FORMOSAT-2 images over four consecutive years, 2006-2009) was acquired for this project. The experimental data set includes LAI and AGB measurements over eight agricultural fields. Two fields were intensively monitored where ET flux were measured with a 30 minutes time step using eddy correlation methods. The modelisation approach is based on FAO-56 method coupled with a vegetation functioning model based on Monteith theory: the SAFY model [5]. The model operates at a daily time step model to provide estimates of plant characteristics (LAI, AGB), soil conditions (soil water content) and water use (ET). As a key linking variable, LAI is deduced from FORMOSAT-2 reflectances images, and then introduced into the SAFY model to provide spatial and temporal estimates of these biophysical variables. Most of the SAFY parameters are crop related and have been fixed according to

  5. Estimated ground-water discharge by evapotranspiration from Death Valley, California, 1997-2001

    USGS Publications Warehouse

    DeMeo, Guy A.; Laczniak, Randell J.; Boyd, Robert A.; Smith, J. LaRue; Nylund, Walter E.

    2003-01-01

    The U.S. Geological Survey, in cooperation with the National Park Service and Inyo County, Calif., collected field data from 1997 through 2001 to accurately estimate the amount of annual ground-water discharge by evapotranspiration (ET) from the floor of Death Valley, California. Multispectral satellite-imagery and National Wetlands Inventory data are used to delineate evaporative ground-water discharge areas on the Death Valley floor. These areas are divided into five general units where ground-water discharge from ET is considered to be significant. Based upon similarities in soil type, soil moisture, vegetation type, and vegetation density; the ET units are salt-encrusted playa (21,287 acres), bare-soil playa (75,922 acres), low-density vegetation (6,625 acres), moderate-density vegetation (5,019 acres), and high-density vegetation (1,522 acres). Annual ET was computed for ET units with micrometeorological data which were continuously measured at six instrumented sites. Total ET was determined at sites that were chosen for their soil- and vegetated-surface conditions, which include salt-encrusted playa (extensive salt encrustation) 0.17 feet per year, bare-soil playa (silt and salt encrustation) 0.21 feet per year, pickleweed (pickleweed plants, low-density vegetation) 0.60 feet per year, Eagle Borax (arrowweed plants and salt grass, moderate-density vegetation) 1.99 feet per year, Mesquite Flat (mesquite trees, high-density vegetation) 2.86 feet per year, and Mesquite Flat mixed grasses (mixed meadow grasses, high-density vegetation) 3.90 feet per year. Precipitation, flooding, and ground-water discharge satisfy ET demand in Death Valley. Ground-water discharge is estimated by deducting local precipitation and flooding from cumulative ET estimates. Discharge rates from ET units were not estimated directly because the range of vegetation units far exceeded the five specific vegetation units that were measured. The rate of annual ground-water discharge by ET for

  6. Crop Evapotranspiration in San Joaquin Valley by Landsat Reflectance-based and Energy-balance Estimation Methods

    NASA Astrophysics Data System (ADS)

    Johnson, L.

    2011-12-01

    Evapotranspiration (ET) estimates are needed to support agricultural and natural resource management. Satellite based measurements offer the potential to efficiently monitor ET over large areas. In this study, two analysis methods were applied to Landsat-5 Thematic Mapper imagery to estimate crop evapotranspiration (ETc) in California's San Joaquin Valley. The Landsat L1T images (path 42, row 35) were collected monthly during the main growing season (Apr-Nov) in 2009. In the first method, the images were transformed to surface reflectance, and subsequently to NDVI. The NDVI was used to estimate mean fractional cover of several major crop types including almond, orange, grape, cotton, corn, alfalfa, and tomato across a total of 115 fields. Prior relationships developed by weighing lysimeter were used to convert fractional cover to a crop coefficient expressing ETc relative to grass reference evapotranspiration (ETo). Measurements of ETo by the California Irrigation Management Information System (CIMIS) were then used to calculate ETc on each overpass date. These reflectance-based estimates were compared with values retrieved by the Surface Energy Balance Algorithm for Land (SEBAL). SEBAL combined spectral radiances in Landsat optical and thermal bands with CIMIS meteorological data to derive ET as a surface energy budget residual by applying radiative, aerodynamic and energy balance physics in 25 computational steps. Reasonably strong agreement resulted, with mean absolute error (MAE) between the two approaches <1 mm/d, and coefficients of determination ranging from 0.78-0.90, for most of the crop types examined. Stronger agreement was found for fields deemed by SEBAL to contain unstressed crop (observed ET at-or-near potential) during satellite overpass, with MAE reductions averaging about 30 percent and coefficients of determination largely of range 0.90-0.94.

  7. Estimating the spatial distribution of evapotranspiration using the water balance model WAVE and fine spatial resolution airborne remote sensing images from the DAIS-sensor: Experimental set-up

    NASA Astrophysics Data System (ADS)

    Verstraeten, W. W.; Veroustraete, F.; Feyen, J.

    2003-04-01

    Actual evapotranspiration (ET) of agricultural land and forestland surfaces play an important role in the redistribution of water on the Earth's surface. Any change in evapotranspiration, either through change in vegetation or climate change, directly effects the available water resources. For quantifying these effects physical models need to be constructed. Most hydrological models have to deal with a lack of good spatial resolution, despite their good temporal information. Remote sensing techniques on the contrary determine the spatial pattern of landscape features and hence are very useful on large scales. The main objective of this research is the combination of the spatial pattern of remote sensing (using visible and thermal infrared spectrum) with the temporal pattern of the water balance model WAVE (Vanclooster et al., 1994 and 1996). To realise this, the following objectives are formulated: (i) relate soil and vegetation surface temperatures to actual evapotranspiration of forest and crops simulated with the water balance model WAVE using remote sensing derived parameters. Three methods will be used and mutually compared. Both airborne and satellite imagery will be implemented; (1) compare the spatial pattern of evapotranspiration, as a result of the three methods, with the energy balance model SEBAL (Bastiaanssen et al., 1998) and finally; (2) subject the up-scaled WAVE and SEBAL models to an uncertainty analysis using the GLUE-approach (Generalised Likelihood Uncertainty Estimate) (Beven en Binley, 1992). To study the behaviour of the model beyond the field-scale (micro-scale), a meso-scale study was conducted at the test-site of DURAS (50°50'38"N, 5°08'50"W, Sint-Truiden). Airborne imagery from the DAIS/ROSIS sensor are available. For the determination of the spatial pattern of actual evapotranspiration the next two methods are considered: (1) relations between surface temperature, surface albedo and vegetation indices are linked with field

  8. Large-eddy Advection in Evapotranspiration Estimates from an Array of Eddy Covariance Towers

    NASA Astrophysics Data System (ADS)

    Lin, X.; Evett, S. R.; Gowda, P. H.; Colaizzi, P. D.; Aiken, R.

    2014-12-01

    Evapotranspiration was continuously measured by an array of eddy covariance systems and large weighting lysimeter in a sorghum in Bushland, Texas in 2014. The advective divergence from both horizontal and vertical directions were measured through profile measurements above canopy. All storage terms were integrated from the depth of soil heat flux plate to the height of eddy covariance measurement. Therefore, a comparison between the eddy covariance system and large weighing lysimeter was conducted on hourly and daily basis. The results for the discrepancy between eddy covariance towers and the lysimeter will be discussed in terms of advection and storage contributions in time domain and frequency domain.

  9. Comparison of equations used for estimating agricultural crop evapotranspiration with field research

    SciTech Connect

    Hill, R.W.; Johns, E.L.; Frevert, D.K.

    1983-10-01

    Research data on alfalfa water use and related yields were obtained for 10 sites in the Western United States. Similar research data was obtained for corn at eight sites. Four different types of research studies were available: lysimeter, line source sprinkler, stress plots, and farm yield. Research alfalfa yields and corresponding ET (evapotranspiration) were assumed to be 20 percent greater than field attained yields and ET, based on experience. Similarly, corn research yields and ET were assumed to be 10 percent greater than field attained yields and ET. Yield versus ET relationships were derived from the available research data.

  10. Estimating Watershed-Averaged Precipitation and Evapotranspiration Fluxes using Streamflow Measurements in a Semi-Arid, High Altitude Montane Catchment

    NASA Astrophysics Data System (ADS)

    Herrington, C.; Gonzalez-Pinzon, R.

    2014-12-01

    Streamflow through the Middle Rio Grande Valley is largely driven by snowmelt pulses and monsoonal precipitation events originating in the mountain highlands of New Mexico (NM) and Colorado. Water managers rely on results from storage/runoff models to distribute this resource statewide and to allocate compact deliveries to Texas under the Rio Grande Compact agreement. Prevalent drought conditions and the added uncertainty of climate change effects in the American southwest have led to a greater call for accuracy in storage model parameter inputs. While precipitation and evapotranspiration measurements are subject to scaling and representativeness errors, streamflow readings remain relatively dependable and allow watershed-average water budget estimates. Our study seeks to show that by "Doing Hydrology Backwards" we can effectively estimate watershed-average precipitation and evapotranspiration fluxes in semi-arid landscapes of NM using fluctuations in streamflow data alone. We tested this method in the Valles Caldera National Preserve (VCNP) in the Jemez Mountains of central NM. This method will be further verified by using existing weather stations and eddy-covariance towers within the VCNP to obtain measured values to compare against our model results. This study contributes to further validate this technique as being successful in humid and semi-arid catchments as the method has already been verified as effective in the former setting.

  11. Estimation of evapotranspiration for a small catchment as an input for rainfall-runoff model

    NASA Astrophysics Data System (ADS)

    Hejduk, Leszek; Banasik, Kazimierz; Krajewski, Adam; Mackiewicz, Marta

    2014-05-01

    One of the methods for determination of floods is application of mathematical rainfall-runoff models. Usually, it is possible to distinguish a number of steps for calculation of hydrograph of the flood. The first step is the calculation of effective rainfall which is a difference between total rainfall and losses (amount of water which do not participate in flood formation like interception, infiltration, evaporation etc.) . One of the most common method for determination of effective rainfall is a USDA-SCS method were losses are connected with type of the soils, vegetation and soil moisture. Those factors includes the Curve Number factor (CN). However there is also different approach for determination of losses were soil moisture is calculated as a function of evapotranspiration. In this study, the meteorological data from year 2002-2012 were used for determination of daily evapotranspiration (ETo) by use of FAO Penmana-Monteitha model for Zagozdzonka river catchment in central Poland. Due to gaps in metrological data, some other simpler methods of ETo calculation were applied like Hargraves model and Grabarczyk (1976) model. Based on received results the uncertainty of ETo was calculated. Grabarczyk S., 1976. Polowe zuzycie wody a czynniki meteorologiczne. Zesz. Probl. Post. Nauk Rol. 181, 495-511 ACKNOWLEDGMENTS The investigation described in the poster is part of the research project KORANET founded by PL-National Center for Research and Development (NCBiR).

  12. Estimates of ground-water discharge as determined from measurements of evapotranspiration, Ash Meadows area, Nye County, Nevada

    SciTech Connect

    Laczniak, R.J.; DeMeo, G.A.; Reiner, S.R.; Smith, J.L.; Nylund, W.E.

    1999-09-30

    Ash Meadows is one of the major discharge areas within the regional Death Valley ground-water flow system of southern Nevada and adjacent California. Ground water discharging at Ash Meadows is replenished from inflow derived from an extensive recharge area that includes the eastern part of the Nevada Test Site. This report presents results of a study to refine the estimate of ground-water discharge at Ash Meadows. The study estimates ground-water discharge from the Ash Meadows area through a rigorous quantification of evapotranspiration (ET). To accomplish this objective, the study identifies areas of ongoing ground-water ET, delineates unique areas of ET defined on the basis of similarities in vegetation and soil-moisture conditions, and computes ET rates for each of the delineated areas. A classification technique using spectral-reflectance characteristics determined from satellite images recorded in 1992 identified seven unique units representing areas of ground-water ET. Micrometeorological data were collected for a minimum of 1 year at each site during 1994 through 1997. Evapotranspiration ranged from 0.6 foot per year in a sparse, dry saltgrass environment to 8.6 feet per year over open water. Mean annual ET from the Ash Meadows area is estimated at 21,000 acre-feet. The estimates given for mean annual ground-water discharge range from 18,000 to 21,000 acre-feet. The range presented is only slightly higher than previous estimates of ground-water discharge from the Ash Meadows area based primarily on springflow measurements.

  13. Comment on 'Shang S. 2012. Calculating actual crop evapotranspiration under soil water stress conditions with appropriate numerical methods and time step. Hydrological Processes 26: 3338-3343. DOI: 10.1002/hyp.8405'

    NASA Technical Reports Server (NTRS)

    Yatheendradas, Soni; Narapusetty, Balachandrudu; Peters-Lidard, Christa; Funk, Christopher; Verdin, James

    2014-01-01

    A previous study analyzed errors in the numerical calculation of actual crop evapotranspiration (ET(sub a)) under soil water stress. Assuming no irrigation or precipitation, it constructed equations for ET(sub a) over limited soil-water ranges in a root zone drying out due to evapotranspiration. It then used a single crop-soil composite to provide recommendations about the appropriate usage of numerical methods under different values of the time step and the maximum crop evapotranspiration (ET(sub c)). This comment reformulates those ET(sub a) equations for applicability over the full range of soil water values, revealing a dependence of the relative error in numerical ET(sub a) on the initial soil water that was not seen in the previous study. It is shown that the recommendations based on a single crop-soil composite can be invalid for other crop-soil composites. Finally, a consideration of the numerical error in the time-cumulative value of ET(sub a) is discussed besides the existing consideration of that error over individual time steps as done in the previous study. This cumulative ET(sub a) is more relevant to the final crop yield.

  14. Estimates of ground-water discharge as determined from measurements of evapotranspiration, Ash Meadows area, Nye County, Nevada

    USGS Publications Warehouse

    Laczniak, R.J.; DeMeo, G.A.; Reiner, S.R.; Smith, Jody L.; Nylund, W.E.

    1999-01-01

    Ash Meadows is one of the major discharge areas within the regional Death Valley ground-water flow system of southern Nevada and adjacent California. Ground water discharging at Ash Meadows is replenished from inflow derived from an extensive recharge area that includes the eastern part of the Nevada Test Site (NTS). Currently, contaminants introduced into the subsurface by past nuclear testing at NTS are the subject of study by the U.S. Department of Energy's Environmental Restoration Program. The transport of any contaminant in contact with ground water is controlled in part by the rate and direction of ground-water flow, which itself depends on the location and quantity of ground water discharging from the flow system. To best evaluate any potential risk associated with these test-generated contaminants, studies were undertaken to accurately quantify discharge from areas downgradient from the NTS. This report presents results of a study to refine the estimate of ground-water discharge at Ash Meadows. The study estimates ground-water discharge from the Ash Meadows area through a rigorous quantification of evapotranspiration (ET). To accomplish this objective, the study identifies areas of ongoing ground-water ET, delineates unique areas of ET defined on the basis of similarities in vegetation and soil-moisture conditions, and computes ET rates for each of the delineated areas. A classification technique using spectral-reflectance characteristics determined from satellite images recorded in 1992 identified seven unique units representing areas of ground-water ET. The total area classified encompasses about 10,350 acres dominated primarily by lush desert vegetation. Each unique area, referred to as an ET unit, generally consists of one or more assemblages of local phreatophytes. The ET units identified range from sparse grasslands to open water. Annual ET rates are computed by energy-budget methods from micrometeorological measurements made at 10 sites within six

  15. Remote Sensing Applications for Planning Irrigation Management. The Use of SEBAL Methodology for Estimating Crop Evapotranspiration in Cyprus

    NASA Astrophysics Data System (ADS)

    Papadavid, George; Perdikou, Skevi; Hadjimitsis, Michalakis; Hadjimitsis, Diofantos

    2012-09-01

    Water allocation to crops has always been of great importance in the agricultural process. In this context, and under the current conditions, where Cyprus is facing a severe drought the last five years, the purpose of this study is basically to estimate the needed crop water requirements for supporting irrigation management and monitoring irrigation on a systematic basis for Cyprus using remote sensing techniques. The use of satellite images supported by ground measurements has provided quite accurate results. Intended purpose of this paper is to estimate the Evapotranspiration (ET) of specific crops which is the basis for irrigation scheduling and establish a procedure for monitoring and managing irrigation water over Cyprus, using remotely sensed data from Landsat TM/ ETM+ and a sound methodology used worldwide, the Surface Energy Balance Algorithm for Land (SEBAL).

  16. Using a data fusion method to estimate daily stand-scale evapotranspiration over a managed pine plantation in North Carolina, USA

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Within the context of a globally changing climate, efficient management of freshwater resource management is becoming an increasingly critical issue. As an indicator of vegetation health and soil moisture status, remotely sensed estimates of evapotranspiration (ET) estimation can provide valuable in...

  17. Estimating the actual ET from a pecan farm using the OPEC energy-balance and Penman- Monteith methods

    NASA Astrophysics Data System (ADS)

    Debele, B.; Bawazir, S. A.

    2006-12-01

    Accurate estimation of ET from field crops/orchards is the basis for better irrigation water management. In areas like Mesilla Valley, NM, where water is scarce, it is even more important to precisely determine the crop ET. An OPEC energy balance system was run for 117 days (June 22 October 14, 2001) in a matured pecan farm at Mesilla Valley, NM. The actual evapotranspiration (ET) from pecan orchards was determined from the surface energy balance as a residual, having measured the net radiation, soil heat flux, and sensible heat components using the OPEC method. Since pecans are large trees, we have also examined the effect of including thermal energies stored in the air (Ga) and plant canopy (Gc), on top of the commonly used thermal energy stored in the soil (Gs), on surface energy balance, and hence ET. The results indicate that incorporating thermal energies stored in the air and canopy has a significant effect on total energy storage for shorter temporal resolutions, such as 30-minutes and an hour. Conversely, for longer temporal resolutions (e.g., diurnal and monthly averages), the effect of including thermal energies stored in the air and vegetation on total thermal energy storage is negligible. Our results also showed that the bulk of the total thermal energy storage (G = Gs + Ga + Gc) in the surface energy balance was stored in the soil (Gs). In addition, we have also determined the crop coefficient (Kc) of pecan by combining the actual ET obtained from the OPEC method and potential ET (ET0) calculated using weather data in the surrounding area. Our average pecan Kc values were comparable with the ones reported by other researchers using different methods. We conclude that the OPEC energy balance method can be used to calculate Kc values for pecan whereby farmers and extension agents use the calculated Kc values in combination with ET0 to determine the consumptive use of pecan trees.

  18. An Overview of the “Triangle Method” for Estimating Surface Evapotranspiration and Soil Moisture from Satellite Imagery

    PubMed Central

    Carlson, Toby

    2007-01-01

    An overview of the ‘triangle’ method for estimating soil surface wetness and evapotranspiration fraction from satellite imagery is presented here. The method is insensitive to initial atmospheric and surface conditions, net radiation and atmospheric correction, yet can yield accuracies comparable to other methods. We describe the method first from the standpoint of the how the triangle is observed as obtained from aircraft and satellite image data and then show how the triangle can be created from a land surface model. By superimposing the model triangle over the observed one, pixel values from the image are determined for all points within the triangle. We further show how the stretched (or ‘universal’) triangle can be used to interpret pixel configurations within the triangle, showing how the temporal trajectories of points uniquely describe patterns of land use change. Finally, we conclude the paper with a brief assessment of the method's limitations.

  19. Evapotranspiration on Western U.S. Rivers Estimated by Remote Sensing and Eddy Covariance Flux Tower Data

    NASA Astrophysics Data System (ADS)

    Nagler, P. L.; Russell, S. L.; Cleverly, J. R.; Westenburg, C.; Glenn, E. P.; Huete, A. R.

    2005-05-01

    Evapotranspiration (ET) rates measured from eight eddy covariance flux towers on three western United States rivers were highly correlated with Enhanced Vegetation Index (EVI) values from Moderate Resolution Imaging Spectrometer sensors on the NASA Terra satellite. Sixteen-day composite values of EVI and maximum daily air temperature (Ta) were combined to predict ET across species and sites (r2 = 0.76). The relationship was then used to estimate ET for 2000-2004 over large river stretches on the Upper San Pedro River, the Middle Rio Grande, and the Lower Colorado River. EVI and ET values were similar across river systems. Measured and estimated ET values tended to be moderate when compared to earlier, and often indirect, estimates, and ranged from 850-1,060 mm yr-1. EVI for individual plant associations, used as a measure of relative ET rates, ranked cottonwood (Populus spp.) and willow (Salix spp.) highest, mesquite (Prosopis glandulosa) and saltcedar (Tamarix ramosissima) intermediate, and giant sacaton (Sporobulus wrightii) and arrowweed (Pluchea sericea) lowest in potential ET. However, saltcedar EVI had a high variance, as this species can grow in sparse to dense stands, depending on water availability. ET rates estimated by remote sensing in this study produced similar values as direct, ground-based measurements on the San Pedro River, but they were much lower than official values estimated for riparian water budgets using crop coefficient methods for the Middle Rio Grande and Lower Colorado River.

  20. Wide-area estimates of evapotranspiration by red gum (Eucalyptus camaldulensis) and associated vegetation in the Murray-Darling River Basin, Australia

    USGS Publications Warehouse

    Nagler, Pamela L.; Doody, Tanya M.; Glenn, Edward P.; Jarchow, Christopher J; Barreto-Munoz, Armando; Didan, Kamel

    2016-01-01

    Floodplain red gum forests (Eucalyptus camaldulensis plus associated grasses, reeds and sedges) are sites of high biodiversity in otherwise arid regions of southeastern Australia. They depend on periodic floods from rivers, but dams and diversions have reduced flood frequencies and volumes, leading to deterioration of trees and associated biota. There is a need to determine their water requirements so environmental flows can be administered to maintain or restore the forests. Their water requirements include the frequency and extent of overbank flooding, which recharges the floodplain soils with water, as well as the actual amount of water consumed in evapotranspiration (ET). We estimated the flooding requirements and ET for a 38 134 ha area of red gum forest fed by the Murrumbidgee River in Yanga National Park, New South Wales. ET was estimated by three methods: sap flux sensors placed in individual trees; a remote sensing method based on the Enhanced Vegetation Index from MODIS satellite imagery and a water balance method based on differences between river flows into and out of the forest. The methods gave comparable estimates yet covered different spatial and temporal scales. We estimated flood frequency and volume requirements by comparing Normalized Difference Vegetation Index values from Landsat images with flood history from 1995 to 2014, which included both wet periods and dry periods. ET during wet years is about 50% of potential ET but is much less in dry years because of the trees' ability to control stomatal conductance. Based on our analyses plus other studies, red gum trees at this location require environmental flows of 2000 GL yr−1 every other year, with peak flows of 20 000 ML d−1, to produce flooding sufficient to keep them in good condition. However, only about 120–200 GL yr−1 of river water is consumed in ET, with the remainder flowing out of the forest where it enters the Murray River system.

  1. A Two-source Energy Balance Model for estimating evapotranspiration over an olive orchard in a semi-arid region of Morocco

    NASA Astrophysics Data System (ADS)

    Ezzahar, Jamal; Chehbouni, Abdelghani; Er-Raki, Salah; Aouade, Ghizlane; Khabba, Said; Merlin, Olivier; Boulet, Gilles; Jarlan, Lionel

    2016-04-01

    In arid and semi-arid regions, about 85% of the available water is used for irrigated agriculture, and therefore a sound and efficient irrigation practice is an important step towards achieving sustainable management of water resources in these regions. In this regard, a better understanding of the water balance is essential for exploring water-saving techniques. One of the most important components of the water balance in semi-arid areas is the evapotranspiration (ET). Therefore, a precise estimation evapotranspiration is of crucial importance for agricultural water management. In this work, a two source energy balance model (TSEB) is used to estimate ET over an irrigated olive orchard located near located near to the Marrakech city (Centre of Morocco). In addition to its simplicity, TSEB does not require a large number of input parameters that are not readily available. Evapotranspiration and micrometeorological parameters were continuously measured during the year 2003 in order to evaluate the performance of TSEB estimates. The comparison between daily estimated and measured evapotranspiration yielded a good agreement although the complexity of the study surface with a correlation coefficient of 0.78 and a root mean square of 61.9wm-².

  2. Evapotranspiration measurement and crop coefficient estimation over a spring wheat Farmland ecosystem in the Loess Plateau.

    PubMed

    Yang, Fulin; Zhang, Qiang; Wang, Runyuan; Zhou, Jing

    2014-01-01

    Evapotranspiration (ET) is an important component of the surface energy balance and hydrological cycle. In this study, the eddy covariance technique was used to measure ET of the semi-arid farmland ecosystem in the Loess Plateau during 2010 growing season (April to September). The characteristics and environmental regulations of ET and crop coefficient (Kc) were investigated. The results showed that the diurnal variation of latent heat flux (LE) was similar to single-peak shape for each month, with the largest peak value of LE occurring in August (151.4 W m(-2)). The daily ET rate of the semi-arid farmland in the Loess Plateau also showed clear seasonal variation, with the maximum daily ET rate of 4.69 mm day(-1). Cumulative ET during 2010 growing season was 252.4 mm, and lower than precipitation. Radiation was the main driver of farmland ET in the Loess Plateau, which explained 88% of the variances in daily ET (p<0.001). The farmland Kc values showed the obvious seasonal fluctuation, with the average of 0.46. The correlation analysis between daily Kc and its major environmental factors indicated that wind speed (Ws), relative humidity (RH), soil water content (SWC), and atmospheric vapor pressure deficit (VPD) were the major environmental regulations of daily Kc. The regression analysis results showed that Kc exponentially decreased with Ws increase, an exponentially increased with RH, SWC increase, and a linearly decreased with VPD increase. An experiential Kc model for the semi-arid farmland in the Loess Plateau, driven by Ws, RH, SWC and VPD, was developed, showing a good consistency between the simulated and the measured Kc values. PMID:24941017

  3. Evapotranspiration Measurement and Crop Coefficient Estimation over a Spring Wheat Farmland Ecosystem in the Loess Plateau

    PubMed Central

    Yang, Fulin; Zhang, Qiang; Wang, Runyuan; Zhou, Jing

    2014-01-01

    Evapotranspiration (ET) is an important component of the surface energy balance and hydrological cycle. In this study, the eddy covariance technique was used to measure ET of the semi-arid farmland ecosystem in the Loess Plateau during 2010 growing season (April to September). The characteristics and environmental regulations of ET and crop coefficient (Kc) were investigated. The results showed that the diurnal variation of latent heat flux (LE) was similar to single-peak shape for each month, with the largest peak value of LE occurring in August (151.4 W m−2). The daily ET rate of the semi-arid farmland in the Loess Plateau also showed clear seasonal variation, with the maximum daily ET rate of 4.69 mm day−1. Cumulative ET during 2010 growing season was 252.4 mm, and lower than precipitation. Radiation was the main driver of farmland ET in the Loess Plateau, which explained 88% of the variances in daily ET (p<0.001). The farmland Kc values showed the obvious seasonal fluctuation, with the average of 0.46. The correlation analysis between daily Kc and its major environmental factors indicated that wind speed (Ws), relative humidity (RH), soil water content (SWC), and atmospheric vapor pressure deficit (VPD) were the major environmental regulations of daily Kc. The regression analysis results showed that Kc exponentially decreased with Ws increase, an exponentially increased with RH, SWC increase, and a linearly decreased with VPD increase. An experiential Kc model for the semi-arid farmland in the Loess Plateau, driven by Ws, RH, SWC and VPD, was developed, showing a good consistency between the simulated and the measured Kc values. PMID:24941017

  4. Evapotranspiration measurement and crop coefficient estimation over a spring wheat Farmland ecosystem in the Loess Plateau.

    PubMed

    Yang, Fulin; Zhang, Qiang; Wang, Runyuan; Zhou, Jing

    2014-01-01

    Evapotranspiration (ET) is an important component of the surface energy balance and hydrological cycle. In this study, the eddy covariance technique was used to measure ET of the semi-arid farmland ecosystem in the Loess Plateau during 2010 growing season (April to September). The characteristics and environmental regulations of ET and crop coefficient (Kc) were investigated. The results showed that the diurnal variation of latent heat flux (LE) was similar to single-peak shape for each month, with the largest peak value of LE occurring in August (151.4 W m(-2)). The daily ET rate of the semi-arid farmland in the Loess Plateau also showed clear seasonal variation, with the maximum daily ET rate of 4.69 mm day(-1). Cumulative ET during 2010 growing season was 252.4 mm, and lower than precipitation. Radiation was the main driver of farmland ET in the Loess Plateau, which explained 88% of the variances in daily ET (p<0.001). The farmland Kc values showed the obvious seasonal fluctuation, with the average of 0.46. The correlation analysis between daily Kc and its major environmental factors indicated that wind speed (Ws), relative humidity (RH), soil water content (SWC), and atmospheric vapor pressure deficit (VPD) were the major environmental regulations of daily Kc. The regression analysis results showed that Kc exponentially decreased with Ws increase, an exponentially increased with RH, SWC increase, and a linearly decreased with VPD increase. An experiential Kc model for the semi-arid farmland in the Loess Plateau, driven by Ws, RH, SWC and VPD, was developed, showing a good consistency between the simulated and the measured Kc values.

  5. Actual and Estimated Energy Savings Comparison for Deep Energy Retrofits in the Pacific Northwest

    SciTech Connect

    Blanchard, Jeremy; Widder, Sarah H.; Giever, Elisabeth L.; Baechler, Michael C.

    2012-10-01

    Seven homes from the Pacific Northwest were selected to evaluate the differences between estimated and actual energy savings achieved from deep energy retrofits. The energy savings resulting from these retrofits were estimated, using energy modeling software, to save at least 30% on a whole-house basis. The modeled pre-retrofit energy use was trued against monthly utility bills. After the retrofits were completed, each of the homes was extensively monitored, with the exception of one home which was monitored pre-retrofit. This work is being conducted by Pacific Northwest National Laboratory (PNNL) for the U.S. Department of Energy Building Technologies Program as part of the Building America Program. This work found many discrepancies between actual and estimated energy savings and identified the potential causes for the discrepancies. The differences between actual energy use and modeled energy use also suggest improvements to improve model accuracy. The difference between monthly whole-house actual and estimated energy savings ranged from 75% more energy saved than predicted by the model to 16% less energy saved for all the monitored homes. Similarly, the annual energy savings difference was between 36% and -14%, which was estimated based on existing monitored savings because an entire year of data is not available. Thus, on average, for all six monitored homes the actual energy use is consistently less than estimates, indicating home owners are saving more energy than estimated. The average estimated savings for the eight month monitoring period is 43%, compared to an estimated savings average of 31%. Though this average difference is only 12%, the range of inaccuracies found for specific end-uses is far greater and are the values used to directly estimate energy savings from specific retrofits. Specifically, the monthly post-retrofit energy use differences for specific end-uses (i.e., heating, cooling, hot water, appliances, etc.) ranged from 131% under

  6. Penman-Monteith approaches for estimating crop evapotranspiration in screenhouses--a case study with table-grape.

    PubMed

    Pirkner, Moran; Dicken, Uri; Tanny, Josef

    2014-07-01

    In arid and semi-arid regions many crops are grown under screens or in screenhouses to protect them from excessive radiation, strong winds, hailstorms and insects, and to reduce crop water requirements. Screens modify the crop microclimate, which means that it is necessary to accurately estimate crop water use under screens in order to improve the irrigation management and thereby increase water-use efficiency. The goal of the present study was to develop a set of calibrated relationships between inside and outside climatic variables, which would enable growers to predict crop water use under screens, based on standard external meteorological measurements and evapotranspiration (ET) models. Experiments were carried out in the Jordan Valley region of eastern Israel in a table-grape vineyard that was covered with a transparent screen providing 10% shading. An eddy covariance system was deployed in the middle of the vineyard and meteorological variables were measured inside and outside the screenhouse. Two ET models were evaluated: a classical Penman-Monteith model (PM) and a Penman-Monteith model modified for screenhouse conditions by the inclusion of an additional boundary-layer resistance (PMsc). Energy-balance closure analysis, presented as a linear relation between half-hourly values of available and consumed energy (1,344 data points), yielded the regression Y=1.05X-9.93 (W m(-2)), in which Y=sum of latent and sensible heat fluxes, and X=net radiation minus soil heat flux, with R2=0.81. To compensate for overestimation of the eddy fluxes, ET was corrected by forcing the energy balance closure. Average daily ET under the screen was 5.4±0.54 mm day(-1), in general agreement with the model estimates and the applied irrigation. The results showed that measured ET under the screen was, on average, 34% lower than that estimated outside, indicating significant potential water saving through screening irrigated vineyards. The PM model was somewhat more accurate than

  7. Does the accuracy of fine-scale water level measurements by vented pressure transducers permit for diurnal evapotranspiration estimation?

    NASA Astrophysics Data System (ADS)

    Gribovszki, Zoltán; Kalicz, Péter; Szilágyi, József

    2013-04-01

    Evapotranspiration (ET) estimation methods based on diurnal water level (surface or groundwater) fluctuations are sensitive to measurement accuracy (McLaughlin and Cohen, 2011; Cuevas et al., 2010). Water level fluctuations are often measured by pressure transducers of varying design and precision. Available total pressure transducers require a compensation for barometric pressure change supplied by barometric pressure transducers. Recently McLaughlin and Cohen (2011) as well as Cuevas et al. (2010) analyzed the 'thermal artifacts' of such transducer-pair data questioning the applicability of sub-daily water level measurements in non-buffered thermal mode for diurnal ET estimation. Similar problems should not, in principle, occur for so-called vented pressure transducers. With the help of ancillary manual measurements, this study verifies the accuracy of vented pressure transducer obtained ultra-fine scale (temporal resolution of 1-10 min) stream- and groundwater level data. Thermal effects were examined by a statistical analysis of concurrent water level and temperature data. The results support the thermal artifact-free nature of vented pressure transducers and therefore their suitability for diurnal ET estimation purposes when proper maintenance and periodic calibrations are provided. In the lack of such measures, diurnal temperature changes can induce errors in vented pressure transducer readings as well.

  8. Comparison of ELM, GANN, WNN and empirical models for estimating reference evapotranspiration in humid region of Southwest China

    NASA Astrophysics Data System (ADS)

    Feng, Yu; Cui, Ningbo; Zhao, Lu; Hu, Xiaotao; Gong, Daozhi

    2016-05-01

    Reference evapotranspiration (ET0) is an essential component in hydrological ecological processes and agricultural water management. Accurate estimation of ET0 is of importance in improving irrigation efficiency, water reuse and irrigation scheduling. FAO-56 Penman-Monteith (P-M) model is recommended as the standard model to estimate ET0. Nevertheless, its application is limited due to the lack of required meteorological data. In this study, trained extreme learning machine (ELM), backpropagation neural networks optimized by genetic algorithm (GANN) and wavelet neural networks (WNN) models were developed to estimate ET0, and the performances of ELM, GANN, WNN, two temperature-based (Hargreaves and modified Hargreaves) and three radiation-based (Makkink, Priestley-Taylor and Ritchie) ET0 models in estimating ET0 were evaluated in a humid area of Southwest China. Results indicated that among the new proposed models, ELM and GANN models were much better than WNN model, and the temperature-based ELM and GANN models had better performance than Hargreaves and modified Hargreaves models, radiation-based ELM and GANN models had higher precision than Makkink, Priestley-Taylor and Ritchie models. Both of radiation-based ELM (RMSE ranging 0.312-0.332 mm d-1, Ens ranging 0.918-0.931, MAE ranging 0.260-0.300 mm d-1) and GANN models (RMSE ranging 0.300-0.333 mm d-1, Ens ranging 0.916-0.941, MAE ranging 0.2580-0.303 mm d-1) could estimate ET0 at an acceptable accuracy level, and are highly recommended for estimating ET0 without adequate meteorological data.

  9. Decision support system for estimation of potential evapo-transpiration in Pangani Basin

    NASA Astrophysics Data System (ADS)

    Moges, S. A.; Katambara, Z.; Bashar, K.

    A decision support system for estimation water loss through evaporation was developed for Pangani basin. The model was envisaged to estimate reference potential evapotranspiratiom (PET) at ungauged locations, estimate average catchment PET and can be used to filling missing data for hydrological and agricultural planning purposes. It was designed to make use of the existing limited data in estimation of PET by using anyone of the available evaporation methods (E-methods). Six evaporation methods are imbedded in the model--Penman, Penman-Montieth, Kimberly-Penman (combination method), Hargreaves (temperature based), Priestly and Taylor and Turc (radiation based). Stochastic time series model was used to transfer information from gauged to ungauged location. The model was effectively used to estimate catchment average PET for HEC-HMS model and filling missing data.

  10. Estimating Evapotranspiration over Heterogeneously Vegetated Surfaces using Large Aperture Scintillometer, LiDAR, and Airborne Multispectral Imagery

    NASA Astrophysics Data System (ADS)

    Geli, H. M.; Neale, C. M.; Pack, R. T.; Watts, D. R.; Osterberg, J.

    2011-12-01

    Estimates of evapotranspiration (ET) over heterogeneous areas is challenging especially in water-limited sparsely vegetated environments. New techniques such as airborne full-waveform LiDAR (Light Detection and Ranging) and high resolution multispectral and thermal imagery can provide enough detail of sparse canopies to improve energy balance model estimations as well as footprint analysis of scintillometer data. The objectives of this study were to estimate ET over such areas and develop methodologies for the use of these airborne data technologies. Because of the associated heterogeneity, this study was conducted over the Cibola National wildlife refuge, southern California on an area dominated with tamarisk (salt cedar) forest (90%) interspersed with arrowweed and bare soil (10%). A set of two large aperture scintillometers (LASs) were deployed over the area to provide estimates of sensible heat flux (HLAS). The LASs were distributed over the area in a way that allowed capturing different surface spatial heterogeneity. Bowen ratio systems were used to provide hydrometeorological variables and surface energy balance fluxes (SEBF) (i.e. Rn, G, H, and LE) measurements. Scintillometer-based estimates of HLAS were improved by considering the effect of the corresponding 3D footprint and the associated displacement height (d) and the roughness length (z0) following Geli et al. (2011). The LiDAR data were acquired using the LASSI Lidar developed at Utah State University (USU). The data was used to obtain 1-m spatial resolution DEM's and vegetation canopy height to improve the HLAS estimates. The BR measurements of Rn and G were combined with LAS estimates, HLAS, to provide estimates of LELASas a residual of the energy balance equation. A thermal remote sensing model namely the two source energy balance (TSEB) of Norman et al. (1995) was applied to provide spatial estimates of SEBF. Four airborne images at 1-4 meter spatial resolution acquired using the USU airborne

  11. Quantifying Uncertainties of Seasonal and Regional Evapotranspiration Estimates from Operational Simplified Surface Energy Balance Model in the Contiguous USA

    NASA Astrophysics Data System (ADS)

    Chen, M.; Senay, G. B.; Verdin, J. P.; Bohms, S.

    2015-12-01

    An operational simplified surface energy balance (SSEBop) model can provide site to regional and daily to seasonal evapotranspiration (ET) estimation. Like other ET models, SSEBop model also faces a challenging issue—uncertainty from inevitable input errors, poorly defined parameters, and inadequate model structures. Recent uncertainty assessment at multiple Ameriflux tower sites showed the uncertainties of seasonal ET estimates by the SSEBop model were within a reasonable range (less than 20%). In this study, we further quantified the uncertainties of seasonal SSEBop ET estimates at 1-km pixel resolution for the contiguous U.S.A. (CONUS) from 2001 to 2014. The uncertainty analysis focused on quantifying uncertainties from errors of key parameters (i.e., difference between cold and hot temperature boundaries (dT)) and primary driving forces, including the 8-day composite 1-km Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST) data, Global Land Data Assimilation System daily air temperature data, and USGS/EROS daily short grass reference ET data. The sensitivity analysis indicated that relative errors of ET estimates from errors of input data and parameters were less than 20% in most areas of CONUS, except for western mountain areas with complex topography, southwestern bare desert areas with high albedo and dry climate conditions, and southeastern areas with high emissivity and humid climate conditions. The relative errors of ET estimates were around 30% in those specific areas where the large ET errors stemmed from errors of input data and parameters, such as LST data with errors over 1.5K, and dT with errors over 2.5K. The uncertainty assessment showed that SSEBop model is a reliable method for wide-area ET calculation. Reduction of errors from input variables (e.g., LST from MODIS) and key parameters (e.g., dT) in topographically complex areas and high albedo and emissivity surfaces can significantly improve the ET calculation

  12. Estimates of evapotranspiration from the Ruby Lake National Wildlife Refuge area, Ruby Valley, northeastern Nevada, May 1999-October 2000

    USGS Publications Warehouse

    Berger, David L.; Johnson, Michael J.; Tumbusch, Mary L.; Mackay, Jeffrey

    2001-01-01

    The Ruby Lake National Wildlife Refuge in Ruby Valley, Nevada, contains the largest area of perennial wetlands in northeastern Nevada and provides habitat to a large number of migratory and nesting waterfowl. The long-term preservation of the refuge depends on the availability of sufficient water to maintain optimal habitat conditions. In the Ruby Valley water budget, evapotranspiration (ET) from the refuge is one of the largest components of natural outflow. To help determine the amount of inflow needed to maintain wetland habitat, estimates of ET for May 1999 through October 2000 were made at major habitats throughout the refuge. The Bowen-ratio method was used to estimate daily ET at four sites: over open water, in a moderate-to-dense cover of bulrush marsh, in a moderate cover of mixed phreatophytic shrubs, and in a desert-shrub upland. The eddy-correlation method was used to estimate daily ET for periods of 2 to 12 weeks at a meadow site and at four sites in a sparse-to-moderate cover of phreatophytic shrubs. Daily ET rates ranged from less than 0.010 inch per day at all of the sites to a maximum of 0.464 inch per day at the open-water site. Average daily ET rates estimated for open water and a bulrush marsh were about four to five times greater than in areas of mixed phreatophytic shrubs, where the depth to ground water is less than 5 feet. Based on the seasonal distribution of major habitats in the refuge and on winter and summer ET rates, an estimated total of about 89,000 acre-feet of water was consumed by ET during October 1999-September 2000 (2000 water year). Of this total, about 49,800 acre-feet was consumed by ET in areas of open water and bulrush marsh.

  13. Comparison of terrestrial evapotranspiration estimates using the mass transfer and Penman-Monteith equations in land surface models

    NASA Astrophysics Data System (ADS)

    Chen, Jing; Chen, Baozhang; Black, T. Andrew; Innes, John L.; Wang, Guangyu; Kiely, Gerard; Hirano, Takashi; Wohlfahrt, Georg

    2013-12-01

    The mass transfer (MT) equation and the Penman-Monteith (PM) equation are two common approaches used in various land surface models for simulating evapotranspiration (ET). Yet assessments are rarely conducted to determine how well these structurally differing equations simulate ET across various biomes and climatic environments with different canopy upscaling strategies. We evaluated the capacity of models to estimate ET using the MT equation with the one-leaf strategy in the Community Land Model version 4 and the PM equation in the Dynamic Land Model using the one-leaf and two-leaf upscaling approaches for 22 selected eddy covariance flux towers representing 10 typical plant functional types. Overall, across half-hourly, daily, monthly, and seasonal scales, the MT equation performed less robust than the PM equation in forests. The former had 8-15% higher root-mean-square error and 1-4% lower index of agreement and a large uncertainty in warm and wet seasons for several sites. It leaves a doubt about its application of estimating ET across regional to global scales. Considering the net radiation available on the surface of leaf/soil and adopting the two-leaf approach made the PM equation closer to the EC measurements on average but still could not capture the variation during the cold season. We suggest that further improvements in simulation of ET require seasonal variation of some key parameters and quantification of spatial heterogeneity.

  14. Estimation of Daily Reference Evapotranspiration using Temperature Based Models and Remotely Sensed Data over Indian River Basin

    NASA Astrophysics Data System (ADS)

    R, Shwetha H.; D, Nagesh Kumar

    2015-04-01

    Reference evapotranspiration (ETo) is the most significant component of the hydrological budget. Accurate quantification of ETo is vital for proper water management, efficient agricultural activities, irrigation planning and irrigation scheduling. FAO Penman Montieth (FAO-PM) is the widely accepted and used method for the ETo estimation under all climatic conditions, but needs numerous inputs which are difficult to acquire in developing countries. In such conditions, temperature based models such as Hargreaves-Samani (HS) equation and Penman Montieth temperature (PMT) can be used, where only maximum and minimum temperatures are required. Spatial interpolation of meteorological parameters to calculate spatial variation of ETo results in inaccurate estimations at lowly densed weather stations. Hence, there is a necessity of simple and easy method to estimate spatial distribution of ETo. In this regard, remotely sensed data provides viable alternative approach to obtain continuous spatio-temporal ETo. In this study, we used temperature based ETo models with remotely sensed LST data to estimate spatio-temporal variation of ETo. Day and night LST (MYD11A1) data of the year 2010 for the Cauvery basin on a daily basis were obtained from MODIS sensor of Aqua satellite. Firstly, day and night land surface temperatures (LST) with HS and PMT methods were applied to estimate ETo. Secondly, maximum and minimum air temperatures were estimated from day and night LST respectively using simple linear regression and these air temperature data were used to estimate ETo. Estimated results were validated with the ETo calculated using meteorological data obtained from Automatic Weather Stations (AWS) by applying standard FAO-PM. The preliminary results revealed that, HS method with LST overestimated ETo in the study region. Statistical analysis showed PMT method with both LST and air temperatures performed better than the HS method. These two temperature based methods are often used for

  15. Use of geostationary satellite imagery in optical and thermal bands for the estimation of soil moisture status and land evapotranspiration

    NASA Astrophysics Data System (ADS)

    Ghilain, N.; Arboleda, A.; Gellens-Meulenberghs, F.

    2009-04-01

    For water and agricultural management, there is an increasing demand to monitor the soil water status and the land evapotranspiration. In the framework of the LSA-SAF project (http://landsaf.meteo.pt), we are developing an energy balance model forced by remote sensing products, i.e. radiation components and vegetation parameters, to monitor in quasi real-time the evapotranspiration rate over land (Gellens-Meulenberghs et al, 2007; Ghilain et al, 2008). The model is applied over the full MSG disk, i.e. including Europe and Africa. Meteorological forcing, as well as the soil moisture status, is provided by the forecasts of the ECMWF model. Since soil moisture is computed by a forecast model not dedicated to the monitoring of the soil water status, inadequate soil moisture input can occur, and can cause large effects on evapotranspiration rates, especially over semi-arid or arid regions. In these regions, a remotely sensed-based method for the soil moisture retrieval can therefore be preferable, to avoid too strong dependency in ECMWF model estimates. Among different strategies, remote sensing offers the advantage of monitoring large areas. Empirical methods of soil moisture assessment exist using remotely sensed derived variables either from the microwave bands or from the thermal bands. Mainly polar orbiters are used for this purpose, and little attention has been paid to the new possibilities offered by geosynchronous satellites. In this contribution, images of the SEVIRI instrument on board of MSG geosynchronous satellites are used. Dedicated operational algorithms were developed for the LSA-SAF project and now deliver images of land surface temperature (LST) every 15-minutes (Trigo et al, 2008) and vegetations indices (leaf area index, LAI; fraction of vegetation cover, FVC; fraction of absorbed photosynthetically active radiation, FAPAR) every day (Garcia-Haro et al, 2005) over Africa and Europe. One advantage of using products derived from geostationary

  16. Daily evapotranspiration estimates by scaling instantaneous latent heat flux derived from a two-source model

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Radiometric brightness temperature can be used in energy balance models that estimate sensible and latent heat fluxes of the land surface. However, brightness temperature is usually available only at one time of day when acquired from aircraft, fine-scale satellite platforms, or infrared thermometer...

  17. Modeling Evapotranspiration in Subtropical Climate

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Evapotranspiration loss is estimated at about 80% of annual precipitation in south Florida. Accurate prediction of evapotranspiration is important during and beyond the implementation of the Comprehensive Everglades Restoration Project(CERP). In the USDA’s Everglades Agro-Hydrology Model (EAHM) the...

  18. A Simple Statistical Model for Estimating Evapotranspiration of Tallgrass Prairies in the Central United States Using MODIS Data

    NASA Astrophysics Data System (ADS)

    Wagle, P.; Xiao, X.; Gowda, P. H.; Basara, J. B.

    2015-12-01

    Accurate estimation of evapotranspiration (ET) across space and time is of great significance for quantifying global water cycle and improving land and water resources management. The Moderate Resolution Imaging Spectroradiometer (MODIS)-derived enhanced vegetation index (EVI) and ground-based climatic variables were integrated with eddy covariance tower-based ET (ETEC) at six AmeriFlux tallgrass prairie sites in the Central United States to develop a simple and robust statistical model for predicting tallgrass prairie ET. The EVI tracked the seasonal variation of ETEC well at both individual (R2 > 0.70) and across six (R2 = 0.76) sites, suggesting that the EVI could be used to estimate ET. The inclusion of photosynthetically active radiation (PAR) measured at tower sites further improved the ET-EVI relationship (R2 = 0.86). Based on this result, we aggregated ETEC, EVI, and PAR (MJ m-2 d-1) data from four sites (15 site-years) to develop a statistical model (ET = 0.11 Rg + 5.49 EVI - 1.43, adj. R2 = 0.86, P < 0.0001) for predicting ET (mm d-1) at 8-day intervals. This predictive model was evaluated against additional two years of ETEC data from one of the four model development sites and two independent sites. The predicted ET (ETEVI+PAR) captured the seasonal patterns and magnitudes of ETEC, and correlated well with ETEC, with R2 of 0.87-0.96 and RMSE of 0.35-0.49 mm d-1, and it was significantly improved compared to the standard MODIS ET product and ET estimates from two remote sensing ET models (Coupling Photosynthesis and Transpiration Model and Vegetation Transpiration Model). Overall, the results from this study demonstrated that tallgrass prairie ET can be accurately predicted using a multiple regression model that uses EVI and PAR which can be readily derived from remote sensing data.

  19. Using satellite-based estimates of evapotranspiration and groundwater changes to determine anthropogenic water fluxes in land surface models

    NASA Astrophysics Data System (ADS)

    Anderson, R. G.; Lo, M.-H.; Swenson, S.; Famiglietti, J. S.; Tang, Q.; Skaggs, T. H.; Lin, Y.-H.; Wu, R.-J.

    2015-04-01

    Irrigation is a widely used water management practice that is often poorly parameterized in land surface and climate models. Previous studies have addressed this issue via use of irrigation area, applied water inventory data, or soil moisture content. These approaches have a variety of drawbacks including data latency, accurately prescribing irrigation intensity, and conservation of water volume for soil moisture approach. In this study, we parameterize irrigation fluxes using satellite observations of evapotranspiration (ET) against ET from a suite of land surface models without irrigation. We then apply this water flux into the Community Land Model (CLM) and use an iterative approach to estimate groundwater recharge and partition the water flux between groundwater and surface water. The ET simulated by CLM with irrigation matches the magnitude and seasonality of observed satellite ET well, with a mean difference of 6.3 mm month-1 and a correlation of 0.95. Differences between the new CLM ET values and observed ET values are always less than 30 mm month-1 and the differences show no pattern with respect to seasonality. The results reinforce the importance of accurately parameterizing anthropogenic hydrologic fluxes into land surface and climate models to assess environmental change under current and future climates and land management regimes.

  20. Catchment scale estimation of evapotranspiration from remote sensing data based on an energy balance approach: A validation study for the Rur catchment, Germany

    NASA Astrophysics Data System (ADS)

    Ali, Muhammad; Montzka, Carsten; Graf, Alexander; Jonard, Francois; Vereecken, Harry

    2014-05-01

    Being a major component of the hydrological cycle, evapotranspiration (ET) and its spatial and temporal distribution are of major importance for hydrological and meteorological applications. Owing to its dependency on the amount and duration of incoming solar radiations and other meteorological parameters, changes in ET may occur on short time scales (less than an hour). Therefore, monitoring the temporal and spatial anomalies in evapotranspiration is very important. Conventional methods for ET estimation are restricted to local measurements, and hence unable to capture the spatial distribution of ET on heterogeneous surfaces. However, they are useful for validating ET derived from remote sensing data over large areas. To estimate evapotranspiration on a regional scale, two main approaches are available i) Application of a water balance approach to ground-based catchment-scale measurements and ii) Application of an energy balance approach to remote sensing data. The energy balance approach is based on the distribution of energy on the earth surface and the availability of the amount of latent heat to cause evapotranspiration (transpiration and evaporation) from plants and soil surface. Several approaches have been presented in literature but in this study we used a two source model (TSM) approach to calculate surface energy fluxes (e.g., latent heat, sensible heat and ground heat fluxes) for canopy and soil. The TSM assumes that soil and vegetation affect the microclimate within the soil-canopy system and therefore separate resistances are calculated for heat exchange from canopy and soil. In TSM net radiations are partitioned in to soil and canopy components (Rns, Rnc) and have been revised several times for improving shortwave and longwave radiation exchange between canopy and soil. TSM uses satellite derived directional radiometric surface temperature [TR(θ)] as composite of the soil and canopy temperatures (TS and TC respectively). In this study

  1. Satellite-Based Estimates of Evapotranspiration Compared with Estimates from Land Surface Models and Flux Towers: Drivers of Discrepancies and their Spatial and Temporal Patterns

    NASA Astrophysics Data System (ADS)

    Lipton, A.; Liang, P.; Galantowicz, J. F.; Moncet, J.; Jimenez, C.; Prigent, C.; Aires, F.; Unmin, G.

    2013-12-01

    Monthly-average estimates of latent heat flux and evapotranspiration have been derived from a combination of satellite-derived microwave emissivities, day-night differences in land surface temperature (from microwave AMSR-E), downward solar and infrared fluxes from ISCCP cloud analysis, and MODIS visible and near-infrared surface reflectances. The estimates are produced by a neural network. These estimates have been compared with data from the NOAH land surface model, as produced for GLDAS-2, and we have analyzed areas with persistent, substantial discrepancies between the satellite and model products. Some of these discrepancies persist year-to-year, while others relate to different responses of the satellite/NN product and the model to anomalous conditions. Data from flux towers have been used to identify model and data deficiencies responsible for these discrepancies. The satellite-derived products are compared also with latent heat flux estimates derived by Jung et al., who used model tree ensembles to upscale Fluxnet tower data to the global scale.

  2. Determining vertical leakage from the Great Artesian Basin, Australia, through up-scaling field estimates of phreatic evapotranspiration

    NASA Astrophysics Data System (ADS)

    Costelloe, J. F.; Matic, V.; Western, A. W.; Walker, J. P.; Tyler, M.

    2015-10-01

    Understanding the water balance of large groundwater systems is fundamental for the sustainable management of the resource. The vertical leakage (i.e. discharge to upper aquifers or the unconfined water table) component of the Great Artesian Basin (GAB) is an example of a poorly constrained but large component of the water balance of Australia's largest groundwater resource. Field estimates of phreatic evapotranspiration (ET) were made at discharge zones along the southwestern margin of the GAB using eddy covariance station and micro-lysimeter measurements, and inversion of chloride/isotope soil profile measurements. The field estimates were assigned to three major landforms associated with areas of increasingly higher evaporative discharge and progressively decreasing depths to the water table. These landforms were mapped using remote sensing and digital elevation data, with characteristically higher soil moisture, salt precipitation, and lower surface temperature compared to areas distal to discharge zones. Based on the field measurements, broad ranges of phreatic ET (0.5-10, 10-100 and 100-300 mm y-1) were assigned to the major land-types. The higher phreatic ET discharge zones mapped by supervised classification of satellite data are 8-28% of the total regional vertical leakage component estimated by numerical modelling of the GAB. In comparison, the higher discharge zones estimated by landform mapping are 73-251% of the total vertical leakage component estimated by modelling. The mapped distribution of the high discharge areas has important implications for modelling of the GAB. In the western sub-basin, most of the estimated recharge can be accounted for by phreatic ET in the high discharge zones located around the Basin margins, implying that vertical leakage rates distal to the margins are very low and that discharge may exceed current recharge. In contrast, the results for the eastern sub-basin suggest that vertical leakage rates around the South

  3. Comprehensive Evaluation of Attitude and Orbit Estimation Using Actual Earth Magnetic Field Data

    NASA Technical Reports Server (NTRS)

    Deutschmann, Julie K.; Bar-Itzhack, Itzhack Y.

    2000-01-01

    A single, augmented Extended Kalman Filter (EKF), which simultaneously and autonomously estimates spacecraft attitude and orbit has been developed and successfully tested with real magnetometer and gyro data only. Because the earth magnetic field is a function of time and position, and because time is known quite precisely, the differences between the computed and measured magnetic field components, as measured by the magnetometers throughout the entire spacecraft orbit, are a function of both orbit and attitude errors. Thus, conceivably these differences could be used to estimate both orbit and attitude; an observability study validated this assumption. The results of testing the EKF with actual magnetometer and gyro data, from four satellites supported by the NASA Goddard Space Flight Center (GSFC) Guidance, Navigation, and Control Center, are presented and evaluated. They confirm the assumption that a single EKF can estimate both attitude and orbit when using gyros and magnetometers only.

  4. Estimation of evapotranspiration by reed canarygrass using field observations and model simulations

    USGS Publications Warehouse

    Schilling, K.E.; Kiniry, J.R.

    2007-01-01

    Reed canarygrass (Phalaris arundinacea) commonly invades meadow wetlands, effectively dominating water use and outcompeting native plants. Objectives of this study were to (i) estimate daily, seasonal and annual water use by reed canarygrass using shallow water table fluctuations; and (ii) calibrate the ALMANAC (Agricultural Land Management Alternative with Numerical Assessment Criteria) model to accurately simulate water uptake by this grass. Using a groundwater well, the water table under an area in Iowa dominated by reed canarygrass was monitored hourly. Differences between water level measurements taken each hour were averaged to determine the hourly water table change in each month. Using these estimates of water use, the ALMANAC model was then calibrated to simulate plant transpiration values close to these water table use rates. Average monthly calculated daily plant water use rates were 3.3 mm d-1 in July and 2.3-2.8 mm d-1 in May, June, August, and September. Simulated bimonthly values for measured water use and plant transpiration simulated by the ALMANAC model differed by 14% or less. From May to October the mean ratio of measured to simulated values was 94%. Thus, the similarity between simulated plant transpiration and water use from the water table showed promise that this process-based model can realistically simulate water use under such grassland systems. ?? 2007 Elsevier B.V. All rights reserved.

  5. Ground-water discharge determined from estimates of evapotranspiration, Death Valley regional flow system, Nevada and California

    USGS Publications Warehouse

    Laczniak, Randell J.; Smith, J. LaRue; Elliott, Peggy E.; DeMeo, Guy A.; Chatigny, Melissa A.; Roemer, Gaius J.

    2001-01-01

    The Death Valley regional flow system (DVRFS) is one of the larger ground-water flow systems in the southwestern United States and includes much of southern Nevada and the Death Valley region of eastern California. Centrally located within the ground-water flow system is the Nevada Test Site (NTS). The NTS, a large tract covering about 1,375 square miles, historically has been used for testing nuclear devices and currently is being studied as a potential repository for the long-term storage of high-level nuclear waste generated in the United States. The U.S. Department of Energy, as mandated by Federal and State regulators, is evaluating the risk associated with contaminants that have been or may be introduced into the subsurface as a consequence of any past or future activities at the NTS. Because subsurface contaminants can be transported away from the NTS by ground water, components of the ground-water budget are of great interest. One such component is regional ground-water discharge. Most of the ground water leaving the DVRFS is limited to local areas where geologic and hydrologic conditions force ground water upward toward the surface to discharge at springs and seeps. Available estimates of ground-water discharge are based primarily on early work done as part of regional reconnaissance studies. These early efforts covered large, geologically complex areas and often applied substantially different techniques to estimate ground-water discharge. This report describes the results of a study that provides more consistent, accurate, and scientifically defensible measures of regional ground-water losses from each of the major discharge areas of the DVRFS. Estimates of ground-water discharge presented in this report are based on a rigorous quantification of local evapotranspiration (ET). The study identifies areas of ongoing ground-water ET, delineates different ET areas based on similarities in vegetation and soil-moisture conditions, and determines an ET rate for

  6. Application of the water table fluctuation method for estimating evapotranspiration at two phreatophyte-dominated sites under hyper-arid environments

    NASA Astrophysics Data System (ADS)

    Wang, Ping; Grinevsky, Sergey O.; Pozdniakov, Sergey P.; Yu, Jingjie; Dautova, Dina S.; Min, Leilei; Du, Chaoyang; Zhang, Yichi

    2014-11-01

    Shallow groundwater is primarily discharged via evapotranspiration (ETg) in arid and semi-arid riparian systems; however, the quantification of ETg remains a challenge in regional water resource assessments of such systems. In this study, the diagnostic indicators of groundwater evapotranspiration processes and the principles of applying the water table fluctuation (WTF) method to estimate ETg based on seasonal groundwater level changes were presented. These techniques were then used to investigate groundwater evapotranspiration processes at two sites dominated by phreatophytes (Tamarix ramosissima and Populus euphratica) within hyper-arid desert environments in northwestern China for the period 2010-2012. The results indicate that steady declines in the water table, which are commonly attributed to groundwater evapotranspiration, occurred at both sites during the growing season. Based on the proposed WTF method, the estimated ETg was 0.63-0.73 mm/d at the Tamarix ramosissima site and 1.89-2.33 mm/d at the Populus euphratica site during the summer months (June-August). Numerical simulations using a one-dimensional root water uptake model indicate that the seasonal variations in ETg at both sites were primarily dependent on the potential evaporation rates. Comparisons with previous studies on plant transpiration at similar sites in this area show that these results are reasonable. It is apparent that the WTF method can provide a simple and relatively inexpensive method of estimating ETg on a large scale in arid/semi-arid regions. However, there are significant uncertainties associated with time-dependent lateral flow rates, which creates a challenge when applying this method. In addition, the selection of calculation periods that show steady declines in the groundwater level can be somewhat subjective. To enhance the performance of the WTF method based on seasonal water table declines, further research on the estimation of lateral flow rates should be performed

  7. Actual evapotranspiration (water use) assessment of the Colorado River Basin at the Landsat resolution using the operational Simplified Surface Energy Balance Model.

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Accurately estimating consumptive water use in the Colorado River Basin (CRB) is important for assessing and managing limited water resources in the basin. Increasing water demand from various sectors may threaten long-term sustainability of the water supply in the arid southwestern United States. L...

  8. Estimating spatially distributed monthly evapotranspiration rates by linear transformations of MODIS daytime land surface temperature data

    NASA Astrophysics Data System (ADS)

    Szilagyi, J.; Jozsa, J.

    2009-05-01

    Under simplifying conditions catchment-scale vapor pressure at the drying land surface can be calculated as a function of its watershed-representative temperature () by the wet-surface equation (WSE, similar to the wet-bulb equation in meteorology for calculating the dry-bulb thermometer vapor pressure) of the Complementary Relationship of evaporation. The corresponding watershed ET rate, , is obtained from the Bowen ratio with the help of air temperature, humidity and percent possible sunshine data. The resulting (,) pair together with the wet-environment surface temperature () and ET rate (ETw), obtained by the Priestley-Taylor equation, define a linear transformation on a monthly basis by which spatially distributed ET rates can be estimated as a sole function of MODIS daytime land surface temperature, Ts, values within the watershed. The linear transformation preserves the mean which is highly desirable. , in the lack of significant open water surfaces within the study watershed (Elkhorn, Nebraska), was obtained as the mean of the smallest MODIS Ts values each month. The resulting period-averaged (2000-2007) catchment-scale ET rate of 624 mm/yr is very close to the water-balance derived ET rate of about 617 mm/yr. The latter is a somewhat uncertain value due to the effects of (a) observed groundwater depletion of about 1m over the study period caused by extensive irrigation, and; (b) the uncertain rate of net regional groundwater supply toward the watershed. The spatially distributed ET rates correspond well with soil/aquifer properties and the resulting land use type (i.e. rangeland versus center-pivot irrigated crops).

  9. Estimating spatially distributed monthly evapotranspiration rates by linear transformations of MODIS daytime land surface temperature data

    NASA Astrophysics Data System (ADS)

    Szilagyi, J.; Jozsa, J.

    2009-03-01

    Under simplifying conditions catchment-scale vapor pressure at the drying land surface can be calculated as a function of its watershed-representative temperature () by the wet-surface equation (WSE, similar to the wet-bulb equation in meteorology for calculating the dry-bulb thermometer vapor pressure) of the complementary relationship of evaporation. The corresponding watershed ET rate, , is obtained from the Bowen ratio with the help of air temperature, humidity and percent possible sunshine data. The resulting (, ) pair together with the wet-environment surface temperature () and ET rate (ETw), obtained by the Priestley-Taylor equation, define a linear transformation on a monthly basis by which spatially distributed ET rates can be estimated as a sole function of MODIS daytime land surface temperature, Ts, values within the watershed. The linear transformation preserves the mean which is highly desirable. , in the lack of significant open water surfaces within the study watershed (Elkhorn, Nebraska), was obtained as the mean of the smallest MODIS Ts values each month. The resulting period-averaged (2000-2007) catchment-scale ET rate of 624 mm/yr is very close to the water-balance derived ET rate of about 617 mm/yr. The latter is a somewhat uncertain value due to the effects of (a) observed groundwater depletion of about 1m over the study period caused by extensive irrigation, and; (b) the uncertain rate of net regional groundwater supply toward the watershed. The spatially distributed ET rates correspond well with soil/aquifer properties and the resulting land use type (i.e., rangeland versus center-pivot irrigated crops).

  10. Uncertainty Analysis on an Operational Simplified Surface Energy Balance algorithm for Estimation of Evapotranspiration at Multiple Flux Tower Sites

    NASA Astrophysics Data System (ADS)

    Chen, M.; Senay, G. B.; Verdin, J. P.; Rowland, J.

    2014-12-01

    Current regional to global and daily to annual Evapotranspiration ( ET) estimation mainly relies on surface energy balance (SEB) ET models or statistical empirical methods driven by remote sensing data and various meteorology databases. However, these ET models face challenging issues—large uncertainties from inevitable input errors, poorly defined parameters, and inadequate model structures. The eddy covariance measurements on water, energy, and carbon fluxes at globally available FLUXNET tower sites provide a feasible opportunity to assess the ET modelling uncertainties. In this study, we focused on uncertainty analysis on an operational simplified surface energy balance (SSEBop) algorithm for ET estimation at multiple Ameriflux tower sites with diverse land cover characteristics and climatic conditions. The input land surface temperature (LST) data of the algorithm were adopted from the 8-day composite1-km Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature. The other input data were taken from the Ameriflux database. Results of statistical analysis indicated that uncertainties or random errors from input variables and parameters of SSEBop led to daily and seasonal ET estimates with relative errors around 20% across multiple flux tower sites distributed across different biomes. This uncertainty of SSEBop lies in the error range of 20-30% of similar SEB-based ET algorithms, such as, Surface Energy Balance System and Surface Energy Balance Algorithm for Land. The R2 between daily and seasonal ET estimates by SSEBop and ET eddy covariance measurements at multiple Ameriflux tower sites exceed 0.7, and even up to 0.9 for croplands, grasslands, and forests, suggesting systematic error or bias of the SSEBop is acceptable. In summary, the uncertainty assessment verifies that the SSEBop is a reliable method for wide-area ET calculation and especially useful for detecting drought years and relative drought severity for agricultural production

  11. Estimating Evapotranspiration Demands of Different Land Cover Using Diurnal Signals in Dry Season Stream Discharge

    NASA Astrophysics Data System (ADS)

    Bhalla, R. S.; K, K.; Srinivas, V.; Krishnaswamy, J.; Chappell, N. A.; Jones, T.

    2015-12-01

    We use a paired catchment approach to compare the dry season flows between natural grasslands and introduced plantations of black wattle (Acacia mearnsii) in the Nilgiri South range forest which lies in the southern parts of the Western Ghat mountain range in Sothern India, a global biodiversity hot-spot. Discharges were measured using a portable flume and a weir fitted with capacitance probes logging water levels every five minutes in two adjacent catchments. Sensor artefacts in the data were filtered out before analysis. Diurnal variations in dry season flows from March 1st to April 15th, 2014 were used to estimate the daily ET based on Boronina et al. 2005 (Hyd. Proc. 19, 20, pp. 4055-4068.) using the equation 1. : E T daily = ∑ i=1 24 ( Q max - Q i ) Δ t , where E T daily is the daily loss of water from the catchment through ET, Q max is the daily maximum flow rate in the river, Q i is the average flow rate for every hour of the day and Δ t is one hour. Our results show that land use conversion from grasslands to wattle has increased ET by 40.97mm which is to the order of 60% during the period of the study (table 1). This has immediate relevance for dry season flows in the region. Nilgiris provide 40% of the total hydro-power generation for the state of Tamil Nadu and these streams sustain biodiversity and are tributaries of the Cauvery river, the largest the state. They also highlight the potential consequences of programmes such as the National Mission for Greening India which explicitly targets conversions of 10m ha of degraded forests, scrub and grasslands to tree cover and forest. Grassland Wattle Difference 1st Qu. 1.14 1.36 -1.33 Median 1.94 2.04 0.28 Mean 2.06 2.97 0.91 3rd Qu. 2.66 3.51 2.43 Sum 92.63 133.60 40.97 Table 1: Summary statistics for daily dry season ET for catchment under grassland, wattle and the daily differences between the two in mm per day.

  12. Anisotropic reflectance is a major correction to energy-balance estimates of evapotranspiration in a semi-arid landscape

    NASA Astrophysics Data System (ADS)

    Mariotto, I.; Gutschick, V. P.; Clason, D. L.

    2009-12-01

    Modeling spatial variation of evapotranspiration (ET) over heterogeneous landscapes is a difficult task for hydrologists, agronomists, and meteorologists. The application of energy balance algorithms to remotely sensed imagery often fails in properly discriminating ET over spectrally diverse land covers for the complexity of modeling the surface roughness. Furthermore, the assumption of a horizontally homogeneous Lambertian surface reflecting energy equally in all directions affects the albedo and vegetation index calculations. The objective of this study is to improve the accuracy of the Surface Energy Balance Algorithm for Land (SEBAL) for estimating ET from ASTER datasets by analyzing the spatial variation of anisotropic reflectance and surface roughness among different plant species-dominated grasslands, shrublands, and dunelands in Southern New Mexico. The degree to which land cover surfaces are anisotropic is assessed by applying a wavelength-dependent non-Lambertian topographic transformation with the Minnaert function. Surface roughness is modeled using a land cover map in conjunction with the fractional vegetation cover derived from MSAVI. SEBAL with one or both modifications showed stronger agreement with the Eddy-Covariance measurements than the non-modified SEBAL. Furthermore, the former showed higher, intermediate, and lower ET values among grasslands, schrublands, and dunelands respectively, while the latter resulted in more homogeneous ET values among land covers and in overestimation of ET over dunelands and underestimation over grasslands. Multiple pairwise land covers comparisons of ET means showed higher potential of the corrected model in discriminating ET. This study suggests that some assumptions in SEBAL tend to inadvertently homogenize ET on these diverse landscapes.

  13. A comparison of continental actual evaporation estimates for Africa to improve hydrological drought forecasting

    NASA Astrophysics Data System (ADS)

    Trambauer, Patricia; Maskey, Shreedhar; Werner, Micha

    2013-04-01

    Evaporation is a key process in the development of hydrological and agricultural droughts. Although distributed drought indicators are often calculated using estimates of evaporation or soil moisture, the estimation of continental evaporation fluxes is complex and typically relies on continental-scale hydrological or land-surface models. However, it appears that most global or continental-scale hydrological models underestimate evaporative fluxes in some regions of Africa, and as a result overestimate stream flows. On the other hand, other studies suggest that land-surface models may overestimate evaporative fluxes. In this study, we computed actual evaporation for the African continent using a continental version of the global hydrological model PCR-GLOBWB, which is based on a water balance approach. Results are compared with other independently computed evaporation products; the evaporation results from the HTESSEL model and ERA-Interim (both based on the energy balance approach), both the MOD16 evaporation product (largely derived from MODIS remote sensing images), and the GLEAM product (derived from satellite observations). Three alternative versions of the PCR-GLOBWB hydrological model were also considered. In the first the model structure was amended by introducing an irrigation scheme, while in the second and third forcing data (precipitation and potential evaporation) were modified to assess the impact that the choice of forcing has on the actual evaporation fluxes simulated by the model. This resulted in eight products of actual evaporation, and derived drought indices were compared in distinct regions of the African continent spanning different climatic regimes. Annual totals, spatial patterns and seasonality were studied and compared through visual inspection and using statistical methods. The comparison indicated that the representation of irrigation areas has an insignificant contribution to the actual evaporation at a continental scale with a 0.5

  14. An original interpretation of the surface temperature-albedo space to estimate crop evapotranspiration (SEB-1S)

    NASA Astrophysics Data System (ADS)

    Merlin, O.

    2013-05-01

    The space defined by the pair surface temperature (T) and surface albedo (α), and the space defined by the pair T and fractional green vegetation cover (fvg) have been extensively used to estimate evaporative fraction (EF) from optical remote sensing data. In both space-based approaches, evapotranspiration (ET) is estimated as remotely sensed EF times the available energy. For a given data point in the T - α space or in the T - fvg space, EF is derived as the ratio of the distance separating the point from the line identified as the dry edge to the distance separating the dry edge and the line identified as the wet edge. The dry and wet edges are classically defined as the upper and lower limit of the spaces, respectively. When side-by-side investigating the T - α and the T - fvg spaces, one observes that the range covered by T values on the (classically determined) wet edge is different for both spaces. In addition, when extending the wet and dry lines of the T - α space, both lines cross at α ≈ 0.4 although the wet and dry edges of the T - fvg space never cross for 0 ≤ fvg < 1. In this paper, a new ET (EF) model (SEB-1S) is derived by revisiting the classical physical interpretation of the T - α space to make its wet edge consistent with that of the T - fvg space. SEB-1S is tested over a 16 km by 10 km irrigated area in northwestern Mexico during the 2007-2008 agricultural season. The classical T - α space-based model is implemented as benchmark to evaluate the performance of SEB-1S. Input data are composed of ASTER (Advanced Spaceborne Thermal Emission and Reflection radiometer) thermal infrared, Formosat-2 shortwave, and station-based meteorological data. The fluxes simulated by SEB-1S and the classical T - α space-based model are compared on seven ASTER overpass dates with the in situ measurements collected at six locations within the study domain. The ET simulated by SEB-1S is significantly more accurate and robust than that predicted by the

  15. A thermal-based remote sensing modeling system for estimating daily evapotranspiration from field to global scales

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Thermal-infrared (TIR) remote sensing of land surface temperature (LST) provides valuable information for quantifying root-zone water availability, evapotranspiration (ET) and crop condition as well as providing useful information for constraining prognostic land surface models. This presentation d...

  16. Daily stand-scale evapotranspiration estimation over a managed pine plantation in North Carolina, USA, using multisatellite data fusion

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Evapotranspiration (ET) over agricultural land surfaces represents the rate at which soil water is consumed in growing crops. Maps of ET,produced at high spatial and temporal resolution using satellite imagery, can provide detailed information about daily vegetation water use and soil moisture statu...

  17. A comparison between evapotranspiration estimates based on remotely sensed surface energy balance and ground-based soil water balance analyses

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Remotely sensed and in-situ data were used to investigate dynamics of root zone soil moisture and evapotranspiration (ET) at four Mesonet stations in north-central Oklahoma over an 11-year period (2000-2010). Two moisture deficit indicators based on soil matric potential had spatial and temporal pat...

  18. Evapotranspiration analysis based on topography algorithm in the Yellow River Delta

    NASA Astrophysics Data System (ADS)

    Ning, Jicai; Gao, Zhiqiang; Shi, Runhe; Gao, Wei

    2013-09-01

    A remote sensing regional evapotranspiration (ET) model was built on the basis of topography correction (slope, aspect and elevation), herein. A variety of satellite data which have visible, near-infrared and thermal infrared remote sensing data can be used by this improved model. Combined with conventional ground meteorological information, it can estimate regional distribution of ET under different climate and terrain conditions, expanding the scope of application. Taking into account the terrain factors, we modified the algorithm of SEBAL model. Results showed that, the modified inversion method of evapotranspiration can better reflect actual evapotranspiration condition. Evapotranspiration changes were consistent with land use types. This research indicates that application of medium or high resolution satellite data to calculate regional ET under undulating landform should consider the impact of terrain. It improves the accuracy of ET estimates and has important reference value for the work of the regional water balance and regional agricultural climate research.

  19. Evapotranspiration and remote sensing

    NASA Technical Reports Server (NTRS)

    Schmugge, T. J.; Gurney, R.

    1982-01-01

    There are three things required for evapotranspiration to occur: (1) energy (580 cal/gm) for the change of phase of the water; (2) a source of the water, i.e., adequate soil moisture in the surface layer or in the root zone of the plant; and (3) a sink for the water, i.e., a moisture deficit in the air above the ground. Remote sensing can contribute information to the first two of these conditions by providing estimates of solar insolation, surface albedo, surface temperature, vegetation cover, and soil moisture content. In addition there have been attempts to estimate precipitation and shelter air temperature from remotely sensed data. The problem remains to develop methods for effectively using these sources of information to make large area estimates of evapotranspiration.

  20. Actual Versus Estimated Utility Factor of a Large Set of Privately Owned Chevrolet Volts

    SciTech Connect

    John Smart; Thomas Bradley; Stephen Schey

    2014-04-01

    In order to determine the overall fuel economy of a plug-in hybrid electric vehicle (PHEV), the amount of operation in charge depleting (CD) versus charge sustaining modes must be determined. Mode of operation is predominantly dependent on customer usage of the vehicle and is therefore highly variable. The utility factor (UF) concept was developed to quantify the distance a group of vehicles has traveled or may travel in CD mode. SAE J2841 presents a UF calculation method based on data collected from travel surveys of conventional vehicles. UF estimates have been used in a variety of areas, including the calculation of window sticker fuel economy, policy decisions, and vehicle design determination. The EV Project, a plug-in electric vehicle charging infrastructure demonstration being conducted across the United States, provides the opportunity to determine the real-world UF of a large group of privately owned Chevrolet Volt extended range electric vehicles. Using data collected from Volts enrolled in The EV Project, this paper compares the real-world UF of two groups of Chevrolet Volts to estimated UF's based on J2841. The actual observed fleet utility factors (FUF) for the MY2011/2012 and MY2013 Volt groups studied were observed to be 72% and 74%, respectively. Using the EPA CD ranges, the method prescribed by J2841 estimates a FUF of 65% and 68% for the MY2011/2012 and MY2013 Volt groups, respectively. Volt drivers achieved higher percentages of distance traveled in EV mode for two reasons. First, they had fewer long-distance travel days than drivers in the national travel survey referenced by J2841. Second, they charged more frequently than the J2841 assumption of once per day - drivers of Volts in this study averaged over 1.4 charging events per day. Although actual CD range varied widely as driving conditions varied, the average CD ranges for the two Volt groups studied matched the EPA CD range estimates, so CD range variation did not affect FUF results.

  1. Partitioning evapotranspiration fluxes using atmometer

    NASA Astrophysics Data System (ADS)

    Orsag, Matej; Fischer, Milan; Trnka, Miroslav; Kucera, Jiri; Zalud, Zdenek

    2013-04-01

    This effort is aimed to derive a simple tool for separating soil evaporation and transpiration from evapotranspiration, measured by Bowen ration energy balance method (BREB) in short rotation coppice (SRC). The main idea is to utilize daily data of actual evapotranspiration (ETa) measured above bare soil (spring 2010 - first year following harvest), reference evapotranspiration (ETo) measured by atmometer ETgage and precipitation data, in order to create an algorithm for estimation evaporation from bare soil. This approach is based on the following assumption: evaporation of wetted bare soil same as the ETo from atmometer is assumed to be identical in days with rain. In first and further days with no rain (and e.g. high evaporative demand) the easily evaporable soil water depletes and ETa so as crop coefficient of bare soil (Kcb) decreases in a way similar to decreasing power function. The algorithm represents a parameterized function of daily cumulated ETo (ETc) measured by atmometer in days elapsed from last rain event (Kcb = a*ETc^b). After each rain event the accumulation of ETo starts again till next rain event (e. g. only days with no rain are cumulated). The function provides decreasing Kcb for each day without rain. The bare soil evaporation can be estimated when the atmometer-recorded value is multiplied by Kcb for particular day without rain. In days with rain Kcb is assumed to be back at 1. This method was successfully tested for estimating evaporation from bare soil under closed canopy of poplar-based SRC. When subtracting the estimated soil evaporation from total ETa flux, measured above the canopy using BREB method, it is possible to obtain transpiration flux of the canopy. There is also possibility to test this approach on the contrary - subtracting transpiration derived from sap-flow measurement from total ETa flux is possible to get soil evaporation as well. Acknowledgements: The present experiment is made within the frame of project Inter

  2. Single-source surface energy balance algorithms to estimate evapotranspiration from satellite-based remotely sensed data

    NASA Astrophysics Data System (ADS)

    Bhattarai, Nishan

    The flow of water and energy fluxes at the Earth's surface and within the climate system is difficult to quantify. Recent advances in remote sensing technologies have provided scientists with a useful means to improve characterization of these complex processes. However, many challenges remain that limit our ability to optimize remote sensing data in determining evapotranspiration (ET) and energy fluxes. For example, periodic cloud cover limits the operational use of remotely sensed data from passive sensors in monitoring seasonal fluxes. Additionally, there are many remote sensing-based single-source surface energy balance (SEB) models, but no clear guidance on which one to use in a particular application. Two widely used models---surface energy balance algorithm for land (SEBAL) and mapping ET at high resolution with internalized calibration (METRIC)---need substantial human-intervention that limits their applicability in broad-scale studies. This dissertation addressed some of these challenges by proposing novel ways to optimize available resources within the SEB-based ET modeling framework. A simple regression-based Landsat-Moderate Resolution Imaging Spectroradiometer (MODIS) fusion model was developed to integrate Landsat spatial and MODIS temporal characteristics in calculating ET. The fusion model produced reliable estimates of seasonal ET at moderate spatial resolution while mitigating the impact that cloud cover can have on image availability. The dissertation also evaluated five commonly used remote sensing-based single-source SEB models and found the surface energy balance system (SEBS) may be the best overall model for use in humid subtropical climates. The study also determined that model accuracy varies with land cover type, for example, all models worked well for wet marsh conditions, but the SEBAL and simplified surface energy balance index (S-SEBI) models worked better than the alternatives for grass cover. A new automated approach based on

  3. Estimating the actual dose delivered by intravascular coronary brachytherapy using geometrically correct 3D modeling

    NASA Astrophysics Data System (ADS)

    Wahle, Andreas; Lopez, John J.; Pennington, Edward C.; Meeks, Sanford L.; Braddy, Kathleen C.; Fox, James M.; Brennan, Theresa M. H.; Buatti, John M.; Rossen, James D.; Sonka, Milan

    2003-05-01

    Intravascular brachytherapy has shown to reduce re-occurrence of in-stent restenosis in coronary arteries. For beta radiation, application time is determined from source activity and the angiographically estimated vessel diameter. Conventionally used dosing models assume a straight vessel with the catheter centered and a constant-diameter circular cross section. Aim of this study was to compare the actual dose delivered during in-vivo intravascular brachytherapy with the target range determined from the patient's prescribed dose. Furthermore, differences in dose distribution between a simplified tubular model (STM) and a geometrically correct 3-D model (GCM) obtained from fusion between biplane angiography and intravascular ultrasound were quantified. The tissue enclosed by the segmented lumen/plaque and media/adventitia borders was simulated using a structured finite-element mesh. The beta-radiation sources were modeled as 3-D objects in their angiographically determined locations. The accumulated dose was estimated using a fixed distance function based on the patient-specific radiation parameters. For visualization, the data was converted to VRML with the accumulated doses represented by color encoding. The statistical comparison between STM and GCM models in 8 patients showed that the STM significantly underestimates the dose delivered and its variability. The analysis revealed substantial deviations from the target dose range in curved vessels.

  4. Estimating evapotranspiration over agricultural landscapes with thermal infrared data: comparison of two approaches using Simple Energy Budget and SVAT modeling.

    NASA Astrophysics Data System (ADS)

    Bigeard, G.; Coudert, B.; Jarlan, L.; Er-Raki, S.; Khabba, S.

    2012-04-01

    Evapotranspiration (ET) monitoring presents wide range of applications from agriculture and water resources management to meteorology. Several approaches have been developed to retrieve ET based on a joint use of remote sensing data and land surface modeling, in particular with a SVAT (Soil Vegetation Atmosphere Transfers) model or a SEB (Surface Energy Budget) model. The objective of our work is to estimate spatialized ET fluxes from Thermal Infra-Red (TIR) imagery, focusing on simulating fluxes at low spatial resolution with 2 methodologies: 1. Simulating with a SEB model directly at low resolution (landscape scale: 4km) with TIR forcing. 2. Aggregating high resolution (agricultural field scale) estimates from a SVAT model constrained by TIR data and based on a high spatial resolution database (landcover, LAI, vegetation height, meteorological forcing and irrigation). In a first part we sum up previous results about in-situ capabilities of a SEB model (TSEB, Norman & al. 1995) versus a SVAT model (SEtHyS, described by Coudert & al. 2006) over crops. TSEB is driven directly with TIR forcing and does not consider soil water transfers. SEtHyS doesn't rely on TIR data availability but it has more parameters and requires more inputs for initialization. Simulations of both models were compared to in-situ Eddy-Correlation (EC) fluxes, with data from 3 sites in southern France and Morocco, covering several kinds of cultures, various vegetative states and various meteorological conditions. A sensitivity analysis on inputs was used to better characterize their capabilities and behaviors, and quantify error ranges induced by spatialization. Globally, models provide estimations of latent heat flux (LE) with RMSD of around 55W/m2 for TSEB and 45W/m2 for SEtHyS. Energy fluxes partition in TSEB was shown to be relatively less sensitive to some inputs when using only a single set of parameters. However it has lower performances on rising vegetation and stressed vegetation

  5. A one-layer satellite surface energy balance for estimating evapotranspiration rates and crop water stress indexes.

    PubMed

    Barbagallo, Salvatore; Consoli, Simona; Russo, Alfonso

    2009-01-01

    Daily evapotranspiration fluxes over the semi-arid Catania Plain area (Eastern Sicily, Italy) were evaluated using remotely sensed data from Landsat Thematic Mapper TM5 images. A one-source parameterization of the surface sensible heat flux exchange using satellite surface temperature has been used. The transfer of sensible and latent heat is described by aerodynamic resistance and surface resistance. Required model inputs are brightness, temperature, fractional vegetation cover or leaf area index, albedo, crop height, roughness lengths, net radiation, air temperature, air humidity and wind speed. The aerodynamic resistance (r(ah)) is formulated on the basis of the Monin-Obukhov surface layer similarity theory and the surface resistance (r(s)) is evaluated from the energy balance equation. The instantaneous surface flux values were converted into evaporative fraction (EF) over the heterogeneous land surface to derive daily evapotranspiration values. Remote sensing-based assessments of crop water stress (CWSI) were also made in order to identify local irrigation requirements. Evapotranspiration data and crop coefficient values obtained from the approach were compared with: (i) data from the semi-empirical approach "K(c) reflectance-based", which integrates satellite data in the visible and NIR regions of the electromagnetic spectrum with ground-based measurements and (ii) surface energy flux measurements collected from a micrometeorological tower located in the experiment area. The expected variability associated with ET flux measurements suggests that the approach-derived surface fluxes were in acceptable agreement with the observations.

  6. A One-Layer Satellite Surface Energy Balance for Estimating Evapotranspiration Rates and Crop Water Stress Indexes

    PubMed Central

    Barbagallo, Salvatore; Consoli, Simona; Russo, Alfonso

    2009-01-01

    Daily evapotranspiration fluxes over the semi-arid Catania Plain area (Eastern Sicily, Italy) were evaluated using remotely sensed data from Landsat Thematic Mapper TM5 images. A one-source parameterization of the surface sensible heat flux exchange using satellite surface temperature has been used. The transfer of sensible and latent heat is described by aerodynamic resistance and surface resistance. Required model inputs are brightness, temperature, fractional vegetation cover or leaf area index, albedo, crop height, roughness lengths, net radiation, air temperature, air humidity and wind speed. The aerodynamic resistance (rah) is formulated on the basis of the Monin-Obukhov surface layer similarity theory and the surface resistance (rs) is evaluated from the energy balance equation. The instantaneous surface flux values were converted into evaporative fraction (EF) over the heterogeneous land surface to derive daily evapotranspiration values. Remote sensing-based assessments of crop water stress (CWSI) were also made in order to identify local irrigation requirements. Evapotranspiration data and crop coefficient values obtained from the approach were compared with: (i) data from the semi-empirical approach “Kc reflectance-based”, which integrates satellite data in the visible and NIR regions of the electromagnetic spectrum with ground-based measurements and (ii) surface energy flux measurements collected from a micrometeorological tower located in the experiment area. The expected variability associated with ET flux measurements suggests that the approach-derived surface fluxes were in acceptable agreement with the observations. PMID:22389585

  7. Estimation of Actual Crop ET of Paddy Using the Energy Balance Model SMARET and Validation with Field Water Balance Measurements and a Crop Growth Model (ORYZA)

    NASA Astrophysics Data System (ADS)

    Nallasamy, N. D.; Muraleedharan, B. V.; Kathirvel, K.; Narasimhan, B.

    2014-12-01

    Sustainable management of water resources requires reliable estimates of actual evapotranspiration (ET) at fine spatial and temporal resolution. This is significant in the case of rice based irrigation systems, one of the major consumers of surface water resources and where ET forms a major component of water consumption. However huge tradeoff in the spatial and temporal resolution of satellite images coupled with lack of adequate number of cloud free images within a growing season act as major constraints in deriving ET at fine spatial and temporal resolution using remote sensing based energy balance models. The scale at which ET is determined is decided by the spatial and temporal scale of Land Surface Temperature (LST) and Normalized Difference Vegetation Index (NDVI), which form inputs to energy balance models. In this context, the current study employed disaggregation algorithms (NL-DisTrad and DisNDVI) to generate time series of LST and NDVI images at fine resolution. The disaggregation algorithms aimed at generating LST and NDVI at finer scale by integrating temporal information from concurrent coarse resolution data and spatial information from a single fine resolution image. The temporal frequency of the disaggregated images is further improved by employing composite images of NDVI and LST in the spatio-temporal disaggregation method. The study further employed half-hourly incoming surface insolation and outgoing long wave radiation obtained from the Indian geostationary satellite (Kalpana-1) to convert the instantaneous ET into daily ET and subsequently to the seasonal ET, thereby improving the accuracy of ET estimates. The estimates of ET were validated with field based water balance measurements carried out in Gadana, a subbasin predominated by rice paddy fields, located in Tamil Nadu, India.

  8. A Researcher's Dilemma: A Comparison of Estimated versus Actual College G.P.A.

    ERIC Educational Resources Information Center

    Herman, William E.; Nelson, Gena C.

    2009-01-01

    This study compared college student reported grade point averages (GPA) with actual GPA as recorded at the Registrar's Office to determine the accuracy of student reported GPA. Results indicated that, on average, students reported slightly higher GPA than their actual GPA. Additionally, females were virtually as accurate as males and students with…

  9. Remote sensing applications for estimating changes on crop evapotranspiration of the most water intensive crops, due to climate change in Cyprus

    NASA Astrophysics Data System (ADS)

    Papadavid, G.; Neocleous, D.; Stylianou, A.; Markou, M.; Kountios, G.; Hadjimitsis, D.

    2016-08-01

    Water allocation to crops, and especially to the most water intensive ones, has always been of great importance in agricultural process. Deficit or excess water irrigation quantities could create either crop health related problems or water over-consumption situation which lead to stored water reduction and toxic material depletion to deeper ground layers, respectively. In this context, and under the current conditions, where Cyprus is facing effects of climate changes, purpose of this study is basically to estimate the needed crop water requirements of the past (1995-2004) and the corresponding ones of the present (2005-2015) in order to test if there were any significant changes regarding the crop water requirements of the most water intensive trees in Cyprus. Mediterranean region has been identified as the region that will suffer the most from climate change. Thus the paper refers to effects of climate changes on crop evapotranspiration (ETc) using remotely sensed data from Landsat TM/ ETM+ / OLI employing a sound methodology used worldwide, the Surface Energy Balance Algorithm for Land (SEBAL). Though the general feeling is that of changes on climate will consequently affect ETc, the results have indicated that there is no significant effect of climate change on crop evapotranspiration, despite the fact that some climatic factors have changed. Applying Student's T-test, the mean values for the most water intensive trees in Cyprus of the 1994-2004 decade have shown no statistical difference from the mean values of 2005-2015 decade's for all the cases, concluding that the climate change taking place the last decades in Cyprus have either not affected the crop evapotranspiration or the crops have manage to adapt into the new environmental conditions through time.

  10. Comparing three approaches of evapotranspiration estimation in mixed urban vegetation; field-based, remote sensing-based and observational-based methods

    USGS Publications Warehouse

    Nouri, Hamideh; Glenn, Edward P.; Beecham, Simon; Chavoshi Boroujeni, Sattar; Sutton, Paul; Alaghmand, Sina; Nagler, Pamela L.; Noori, Behnaz

    2016-01-01

    Despite being the driest inhabited continent, Australia has one of the highest per capita water consumptions in the world. In addition, instead of having fit-for-purpose water supplies (using different qualities of water for different applications), highly treated drinking water is used for nearly all of Australia’s urban water supply needs, including landscape irrigation. The water requirement of urban landscapes, and particularly urban parklands, is of growing concern. The estimation of ET and subsequently plant water requirements in urban vegetation needs to consider the heterogeneity of plants, soils, water and climate characteristics. Accurate estimation of evapotranspiration (ET), which is the main component of a plant’s water requirement, in urban parks is highly desirable because this water maintains the health of green infrastructure and this in turn provides essential ecosystem services. This research contributes to a broader effort to establish sustainable irrigation practices within the Adelaide Parklands in Adelaide, South Australia.

  11. Vegetation monitoring and estimation of evapotranspiration using remote sensing-based models in heterogeneous areas with patchy natural vegetation and crops

    NASA Astrophysics Data System (ADS)

    Carpintero, Elisabet; Andreu, Ana; Gonzalez-Dugo, Maria P.

    2015-04-01

    The integration of remotely sensed data into models for estimating evapotranspiration (ET) has increased significantly in recent years, allowing the extension of these models application from point to regional scale. Remote sensors provide distributed information about the status of vegetation and allow for a regular monitoring of water consumption. Currently, there are two types of approaches for estimating ET based either on the soil water balance, or surface energy balance. The first one uses the reflectance of vegetated surfaces in the visible and near infrared regions of the electromagnetic spectrum (VIS / NIR) to characterize the vegetation and its role in the water balance (Gonzalez-Dugo and Mateos, 2008). On the other hand, thermal-based energy balance models use the radiometric surface temperature registered by the sensor on thermal infrared (TIR) bands as the primary boundary condition for estimating ET (Kustas and Norman, 1996). The aim of this work is to carry out, using Landsat-8 satellite images, a continuous monitoring of growth and evapotranspiration of the different vegetation types, both natural and cultivated, in a region located in Southern Spain during the season August 2013 / September 2014. The region, with about 13800 ha, is marked by strong contrasts in the physical environment, with significant altitudinal gradient combined with a great variety of soil types and vegetation. It is characterized by a variation of grassland, scrubs, conifers, oaks and irrigated crops. In this work, a daily soil water balance has been applied using the vegetation index-basal crop coefficient approach (RSWB). This model is based on FAO-56 methodology (Allen et al., 1998), which determines the evapotranspiration of vegetation with the concepts of crop coefficient and reference ET. The crop coefficient accounts for the influence of the plants on the evapotranspiration, considering the effect of changes in canopy biophysical properties throughout the growth cycle

  12. Comparison of Statistically Modeled Contaminated Soil Volume Estimates and Actual Excavation Volumes at the Maywood FUSRAP Site - 13555

    SciTech Connect

    Moore, James; Hays, David; Quinn, John; Johnson, Robert; Durham, Lisa

    2013-07-01

    As part of the ongoing remediation process at the Maywood Formerly Utilized Sites Remedial Action Program (FUSRAP) properties, Argonne National Laboratory (Argonne) assisted the U.S. Army Corps of Engineers (USACE) New York District by providing contaminated soil volume estimates for the main site area, much of which is fully or partially remediated. As part of the volume estimation process, an initial conceptual site model (ICSM) was prepared for the entire site that captured existing information (with the exception of soil sampling results) pertinent to the possible location of surface and subsurface contamination above cleanup requirements. This ICSM was based on historical anecdotal information, aerial photographs, and the logs from several hundred soil cores that identified the depth of fill material and the depth to bedrock under the site. Specialized geostatistical software developed by Argonne was used to update the ICSM with historical sampling results and down-hole gamma survey information for hundreds of soil core locations. The updating process yielded both a best guess estimate of contamination volumes and a conservative upper bound on the volume estimate that reflected the estimate's uncertainty. Comparison of model results to actual removed soil volumes was conducted on a parcel-by-parcel basis. Where sampling data density was adequate, the actual volume matched the model's average or best guess results. Where contamination was un-characterized and unknown to the model, the actual volume exceeded the model's conservative estimate. Factors affecting volume estimation were identified to assist in planning further excavations. (authors)

  13. 12 CFR Appendix M3 to Part 226 - Sample Calculations of Generic Repayment Estimates and Actual Repayment Disclosures

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 12 Banks and Banking 3 2010-01-01 2010-01-01 false Sample Calculations of Generic Repayment Estimates and Actual Repayment Disclosures M3 Appendix M3 to Part 226 Banks and Banking FEDERAL RESERVE SYSTEM (CONTINUED) BOARD OF GOVERNORS OF THE FEDERAL RESERVE SYSTEM TRUTH IN LENDING (REGULATION Z)...

  14. Drought assessment by evapotranspiration mapping in Twente

    NASA Astrophysics Data System (ADS)

    Eden, U.; Timmermans, J.; van der Velde, R.; Su, Z.

    2012-04-01

    Drought is a reoccurring worldwide problem with impacts ranging from food production to infrastructure. Droughts are different from other natural hazards (floods, hurricanes, and earthquakes) because the effects can only be witnessed slowly and with a time delay. Effects of droughts are diverse, like famine and migration of people. Droughts are caused by natural causes but also by interaction between the natural events and water demand. Not only typical dry regions, like the Horn of Africa, are affected, but even semi-humid environments, like Europe. Temperature rise and precipitation deficit in the summers of 2003 and 2006 caused substantial crop losses in the agricultural sector in the Netherlands. In addition increased river water temperatures and low water levels caused cooling problems for power plants. Heat waves and prolonged absence of precipitation is expected to increase due to climate change. Therefore assessing and monitoring drought in the Netherlands is thus very important. Various drought indices are available to assess the severity, duration and spatial extend of the drought. Some of the commonly indices used are Standardized precipitation index (SPI) and the Palmer Drought Severity Index (PDSI). However each of these indices do not take into account the actual state of the land surface in respect to the dryness. By analysing drought through actual evapotranspiration (ET) estimations from remote sensing this can be circumvented. The severity of the droughts was quantified by ET-mapping from 2003-2010. The assessment was based on the spatial and temporal distribution of ET using the Evapotranspiration Deficit Index (ETDI) drought index. Surface energy fluxes, like ET, were estimated using WACMOS methodology. The input data consisted of remote sensing products like land surface temperature, LAI, and albedo from MODIS; and meteorological data like air-temperature, humidity and wind speed from the European Centre for Medium weather forecast (ECMWF

  15. Using satellite-based estimates of evapotranspiration and groundwater changes to determine anthropogenic water fluxes in land surface models

    NASA Astrophysics Data System (ADS)

    Anderson, R. G.; Lo, M.-H.; Swenson, S.; Famiglietti, J. S.; Tang, Q.; Skaggs, T. H.; Lin, Y.-H.; Wu, R.-J.

    2015-10-01

    Irrigation is a widely used water management practice that is often poorly parameterized in land surface and climate models. Previous studies have addressed this issue via use of irrigation area, applied water inventory data, or soil moisture content. These approaches have a variety of drawbacks including data latency, accurately prescribing irrigation intensity, and a lack of conservation of water volume for models using a prescribed soil moisture approach. In this study, we parameterize irrigation fluxes using satellite observations of evapotranspiration (ET) compared to ET from a suite of land surface models without irrigation. We then incorporate the irrigation flux into the Community Land Model (CLM) and use a systematic trial-and-error procedure to determine the ground- and surface-water withdrawals that are necessary to balance the new irrigation flux. The resulting CLM simulation with irrigation produces ET that matches the magnitude and seasonality of observed satellite ET well, with a mean difference of 6.3 mm month-1 and a correlation of 0.95. Differences between the new CLM ET values and satellite-observed ET values are always less than 30 mm month-1 and the differences show no pattern with respect to seasonality. The results reinforce the importance of accurately parameterizing anthropogenic hydrologic fluxes into land surface and climate models to assess environmental change under current and future climates and land management regimes.

  16. Evapotranspiration Retrieval through Optical/Thermal Satellite Imagery and Ground Measurements in the Green River Basin, Wyoming

    NASA Astrophysics Data System (ADS)

    Pradhan, N.; Hendrickx, J. M.; Ogden, F. L.; Wollf, S. W.

    2010-12-01

    Remote sensing methods are increasingly employed in combination with modeling for evapotranspiration estimation because they can provide multi-temporal, spatially-distributed estimates of key variables based on spatially distributed measurements. The approach for estimating evapotranspiration with remotely sensed data couples thermal and optical remote sensing with energy balance models such as: SEBAL, Surface Energy Balance Algorithms for Land, and METRICtm, Mapping Evapotranspiration at high Resolution using Internalized Calibration. The objective of this study is to investigate how ground measurements and satellite imagery at different scales can be combined to retrieve actual evapotranspiration over large watersheds. Scales of ground measurements are: (1) point scale that is typical for regular meteorological measurements such as air temperature, relative humidity, solar radiation, and wind speed; (2) footprint scale that varies from about 5,000 m2 for eddy-covariance measurements of sensible and latent heat fluxes to about 5,000,000 m2 for scintillometer sensible heat flux measurements when optical/thermal Landsat and MODIS satellites pass over around 10 am. In our analysis, we focused on evapotranspiration or consumptive use associated with irrigated agriculture in the Green River Basin in Wyoming that is the main headwater tributary of the entire Colorado River Basin. Ground-based meteorological stations, eddy-covariance and large-aperture scintillometers were set up in Pinedale, Green River basin, Wyoming to conduct the research. METRIC is used to retrieve evapotranspiration estimates from Landsat5 (30-120 m resolution) and MODIS (250-1000 m resolution) imagery.

  17. Quantifying the Effect of Thinning Vegetation on Evapotranspiration in a Mountainous Watershed through Remote Sensing: Improving Water Balance Estimates for Managed Aquifer Recharge

    NASA Astrophysics Data System (ADS)

    Revelle, P.; Hendrickx, J. M. H.

    2015-12-01

    A long-term water balance study in an experimental watershed of the Sacramento Mountains in New Mexico monitors the impact of thinning vegetation on groundwater recharge. The study objective is to evaluate if thinning forest vegetation will increase groundwater recharge in the mountains to provide larger regional flows to aquifers in surrounding basins. In the semi-arid Southwest, evapotranspiration (ET) makes up 75 to 95% or more of the total water budget. The variability of daily vegetation transpiration and solar radiation with time of year and the effects of complex terrain create a seasonal and spatial variability of ET that is not well quantified in mountainous regions. Through applying the remote sensing model METRIC (Mapping Evapotranspiration with High Resolution and Internalized Calibration) to satellite imagery from the LANDSAT satellite, we calculate high-resolution maps of ET for the Sacramento Mountains watershed area to quantify spatially-distributed estimates of ET before and after thinning to provide improved estimates for determining the water balance and the effect on recharge. METRIC calculates ET through applying an energy balance spatially across an image to estimate ET for each pixel (30m x 30m). Differences in ET are calculated between thinned and control plots in the watershed before and after thinning with the net impact of thinning on ET for an image determined with standard statistical tests following a Before-After Control-Impact (BACI) approach commonly used in environmental impact assessment studies. Estimates of ET from METRIC indicate a net decrease in ET in the first year after thinning for all of the thinned plots but show significant variability (~2 - 12 %) between areas with different terrain characteristics. The impact of surface parameters such as slope, aspect, or albedo among others are currently being examined using multivariate statistical analysis methods to improve the understanding of the spatial and temporal

  18. Do estimated and actual species phylogenies match? Evaluation of East African cichlid radiations.

    PubMed

    Huang, Huateng; Tran, Lucy A P; Knowles, L Lacey

    2014-09-01

    A large number of published phylogenetic estimates are based on a single locus or the concatenation of multiple loci, even though genealogies of single or concatenated loci may not accurately reflect the true history of species diversification (i.e., the species tree). The increased availability of genomic data, coupled with new computational methods, improves resolution of species relationships beyond what was possible in the past. Such developments will no doubt benefit future phylogenetic studies. It remains unclear how robust phylogenies that predate these developments (i.e., the bulk of phylogenetic studies) are to departures from the assumption of strict gene tree-species tree concordance. Here, we present a parametric bootstrap (PBST) approach that assesses the reliability of past phylogenetic estimates in which gene tree-species tree discord was ignored. We focus on a universal cause of discord-the random loss of gene lineages from genetic drift-and apply the method in a meta-analysis of East African cichlids, a group encompassing historical scenarios that are particularly challenging for phylogenetic estimation. Although we identify some evolutionary relationships that are robust to gene tree discord, many past phylogenetic estimates of cichlids are not. We discuss the utility of the PBST method for evaluating the robustness of gene tree-based phylogenetic estimations in general as well as for testing the clade-specific performance of species tree estimation methods and designing sampling strategies that increase the accuracy of estimated species relationships.

  19. Relationship between evapotranspiration and precipitation pulses in a semiarid rangeland estimated by moisture flux towers and MODIS vegetation indices

    USGS Publications Warehouse

    Nagler, P.L.; Glenn, E.P.; Kim, H.; Emmerich, W.; Scott, R.L.; Huxman, T. E.; Huete, A.R.

    2007-01-01

    We used moisture Bowen ratio flux tower data and the enhanced vegetation index (EVI) from the moderate resolution imaging spectrometer (MODIS) on the Terra satellite to measure and scale evapotranspiration (ET) over sparsely vegetated grassland and shrubland sites in a semiarid watershed in southeastern Arizona from 2000 to 2004. The grassland tower site had higher mean annual ET (336 mm yr-1) than the shrubland tower site (266 mm yr-1) (P<0.001). ET measured at the individual tower sites was strongly correlated with EVI (r=0.80-0.94). ET was moderately correlated with precipitation (P), and only weakly correlated with net radiation or air temperature. The strong correlation between ET and EVI, as opposed to the moderate correlation with rainfall, suggests that transpiration (T) is the dominant process controlling ET at these sites. ET could be adequately predicted from EVI and P across seasons and tower sites (r2 = 0.74) by a single multiple regression equation. The regression equation relating ET to EVI and P was used to scale ET over 25 km2 areas of grassland and shrubland around each tower site. Over the study, ratios of T to ET ranged from 0.75 to 1.0. Winter rains stimulated spring ET, and a large rain event in fall, 2000, stimulated ET above T through the following year, indicating that winter rain stored in the soil profile can be an important component of the plants' water budget during the warm season in this ecosystem. We conclude that remotely sensed vegetation indices can be used to scale ground measurements of ET over larger landscape units in semiarid ranglelands, and that the vegetation communities in this landscape effectively harvest the available precipitation over a period of years, even though precipitation patterns are variably seasonally and interannually. ?? 2007 Elsevier Ltd. All rights reserved.

  20. A gap-filling model for eddy covariance latent heat flux: Estimating evapotranspiration of a subtropical seasonal evergreen broad-leaved forest as an example

    NASA Astrophysics Data System (ADS)

    Chen, Yi-Ying; Chu, Chia-Ren; Li, Ming-Hsu

    2012-10-01

    SummaryIn this paper we present a semi-parametric multivariate gap-filling model for tower-based measurement of latent heat flux (LE). Two statistical techniques, the principal component analysis (PCA) and a nonlinear interpolation approach were integrated into this LE gap-filling model. The PCA was first used to resolve the multicollinearity relationships among various environmental variables, including radiation, soil moisture deficit, leaf area index, wind speed, etc. Two nonlinear interpolation methods, multiple regressions (MRS) and the K-nearest neighbors (KNNs) were examined with random selected flux gaps for both clear sky and nighttime/cloudy data to incorporate into this LE gap-filling model. Experimental results indicated that the KNN interpolation approach is able to provide consistent LE estimations while MRS presents over estimations during nighttime/cloudy. Rather than using empirical regression parameters, the KNN approach resolves the nonlinear relationship between the gap-filled LE flux and principal components with adaptive K values under different atmospheric states. The developed LE gap-filling model (PCA with KNN) works with a RMSE of 2.4 W m-2 (˜0.09 mm day-1) at a weekly time scale by adding 40% artificial flux gaps into original dataset. Annual evapotranspiration at this study site were estimated at 736 mm (1803 MJ) and 728 mm (1785 MJ) for year 2008 and 2009, respectively.

  1. Evaluation of actual and estimated hydraulic conductivity of sands with different gradation and shape.

    PubMed

    Cabalar, Ali Firat; Akbulut, Nurullah

    2016-01-01

    Hydraulic conductivities of sands with different gradation and grain shape were estimated experimentally at a relative density (Dr) of about 40 % and a 22 ± 2 °C of constant temperature. Narli Sand (NS) with 0.67 of sphericity (S) and 0.72 of roundness (R), and Crushed Stone Sand (CSS) with 0.55 of S and 0.15 of R values were artificially graded into sixteen different grain-size fractions (4.75-2, 2-1.18, 1.18-0.6, 0.6-0.425, 0.425-0.3, 0.3-0.075, 4.75-0.075, 2-0.075, 1.18-0.075, 0.6-0.075, 0.425-0.075, 4.75-0.6, 2-0.6, 4.75-0.425, 2-0.425, 1.18-0.425 mm). Hydraulic conductivities of the NS estimated by use of constant head test ranged from 1.61 to 0.01 cm/s, whilst those of the CSS estimated by the same test ranged from 2.45 to 0.012 cm/s. It was observed that the hydraulic conductivity values of the NS are lower than those of the CSS samples, which is likely to be the result of differences in shape, particularly in R values. The results clearly demonstrated that the hydraulic conductivity can be significantly influenced by grading characteristics (d10, d20, d30, d50, d60, cu, cc, n, Io). Furthermore, comparisons between results obtained in the present study and hydraulic conductivity estimated with other formulas available in the literature were made. The comparisons indicated that the best estimation of hydraulic conductivity changes based on the gradation and shape properties of the sands tested.

  2. Evaluation of actual and estimated hydraulic conductivity of sands with different gradation and shape.

    PubMed

    Cabalar, Ali Firat; Akbulut, Nurullah

    2016-01-01

    Hydraulic conductivities of sands with different gradation and grain shape were estimated experimentally at a relative density (Dr) of about 40 % and a 22 ± 2 °C of constant temperature. Narli Sand (NS) with 0.67 of sphericity (S) and 0.72 of roundness (R), and Crushed Stone Sand (CSS) with 0.55 of S and 0.15 of R values were artificially graded into sixteen different grain-size fractions (4.75-2, 2-1.18, 1.18-0.6, 0.6-0.425, 0.425-0.3, 0.3-0.075, 4.75-0.075, 2-0.075, 1.18-0.075, 0.6-0.075, 0.425-0.075, 4.75-0.6, 2-0.6, 4.75-0.425, 2-0.425, 1.18-0.425 mm). Hydraulic conductivities of the NS estimated by use of constant head test ranged from 1.61 to 0.01 cm/s, whilst those of the CSS estimated by the same test ranged from 2.45 to 0.012 cm/s. It was observed that the hydraulic conductivity values of the NS are lower than those of the CSS samples, which is likely to be the result of differences in shape, particularly in R values. The results clearly demonstrated that the hydraulic conductivity can be significantly influenced by grading characteristics (d10, d20, d30, d50, d60, cu, cc, n, Io). Furthermore, comparisons between results obtained in the present study and hydraulic conductivity estimated with other formulas available in the literature were made. The comparisons indicated that the best estimation of hydraulic conductivity changes based on the gradation and shape properties of the sands tested. PMID:27390660

  3. Consumer estimation of recommended and actual calories at fast food restaurants.

    PubMed

    Elbel, Brian

    2011-10-01

    Recently, localities across the United States have passed laws requiring the mandatory labeling of calories in all chain restaurants, including fast food restaurants. This policy is set to be implemented at the federal level. Early studies have found these policies to be at best minimally effective in altering food choice at a population level. This paper uses receipt and survey data collected from consumers outside fast food restaurants in low-income communities in New York City (NYC) (which implemented labeling) and a comparison community (which did not) to examine two fundamental assumptions necessary (though not sufficient) for calorie labeling to be effective: that consumers know how many calories they should be eating throughout the course of a day and that currently customers improperly estimate the number of calories in their fast food order. Then, we examine whether mandatory menu labeling influences either of these assumptions. We find that approximately one-third of consumers properly estimate that the number of calories an adult should consume daily. Few (8% on average) believe adults should be eating over 2,500 calories daily, and approximately one-third believe adults should eat lesser than 1,500 calories daily. Mandatory labeling in NYC did not change these findings. However, labeling did increase the number of low-income consumers who correctly estimated (within 100 calories) the number of calories in their fast food meal, from 15% before labeling in NYC increasing to 24% after labeling. Overall knowledge remains low even with labeling. Additional public policies likely need to be considered to influence obesity on a large scale.

  4. Consumer estimation of recommended and actual calories at fast food restaurants.

    PubMed

    Elbel, Brian

    2011-10-01

    Recently, localities across the United States have passed laws requiring the mandatory labeling of calories in all chain restaurants, including fast food restaurants. This policy is set to be implemented at the federal level. Early studies have found these policies to be at best minimally effective in altering food choice at a population level. This paper uses receipt and survey data collected from consumers outside fast food restaurants in low-income communities in New York City (NYC) (which implemented labeling) and a comparison community (which did not) to examine two fundamental assumptions necessary (though not sufficient) for calorie labeling to be effective: that consumers know how many calories they should be eating throughout the course of a day and that currently customers improperly estimate the number of calories in their fast food order. Then, we examine whether mandatory menu labeling influences either of these assumptions. We find that approximately one-third of consumers properly estimate that the number of calories an adult should consume daily. Few (8% on average) believe adults should be eating over 2,500 calories daily, and approximately one-third believe adults should eat lesser than 1,500 calories daily. Mandatory labeling in NYC did not change these findings. However, labeling did increase the number of low-income consumers who correctly estimated (within 100 calories) the number of calories in their fast food meal, from 15% before labeling in NYC increasing to 24% after labeling. Overall knowledge remains low even with labeling. Additional public policies likely need to be considered to influence obesity on a large scale. PMID:21779085

  5. Consumer Estimation of Recommended and Actual Calories at Fast Food Restaurants

    PubMed Central

    Elbel, Brian

    2013-01-01

    Recently, localities across the United States have passed laws requiring the mandatory labeling of calories in all chain restaurants, including fast food restaurants. This policy is set to be implemented at the federal level. Early studies have found these policies to be at best minimally effective in altering food choice at a population level. This paper uses receipt and survey data collected from consumers outside fast food restaurants in low-income communities in New York City (NYC) (which implemented labeling) and a comparison community (which did not) to examine two fundamental assumptions necessary (though not sufficient) for calorie labeling to be effective: that consumers know how many calories they should be eating throughout the course of a day and that currently customers improperly estimate the number of calories in their fast food order. Then, we examine whether mandatory menu labeling influences either of these assumptions. We find that approximately one-third of consumers properly estimate that the number of calories an adult should consume daily. Few (8% on average) believe adults should be eating over 2,500 calories daily, and approximately one-third believe adults should eat lesser than 1,500 calories daily. Mandatory labeling in NYC did not change these findings. However, labeling did increase the number of low-income consumers who correctly estimated (within 100 calories) the number of calories in their fast food meal, from 15% before labeling in NYC increasing to 24% after labeling. Overall knowledge remains low even with labeling. Additional public policies likely need to be considered to influence obesity on a large scale. PMID:21779085

  6. Making appropriate comparisons of estimated and actual costs of reducing SO{sub 2} emissions under Title IV

    SciTech Connect

    Smith, A.E.

    1998-12-31

    A current sentiment within some parts of the environmental policy community is that market-based regulatory approaches such as emissions trading have proven so effective that actual costs will be only a small fraction of what ex ante cost estimation procedures would project. With this line of reasoning, some have dismissed available cost estimates for major proposed new regulations, such as the new PM and ozone NAAQS, as not meaningful for policy decisions. The most commonly used evidence in support of this position is the experience with SO{sub 2} reductions under Title IV of the 1990 Clean Air Act Amendments. In Title IV, a market for emissions allowances has been used to achieve reductions in sulfur dioxides (SO{sub 2}) to ameliorate acid rain. It is commonly asserted today that the cost of achieving the SO{sub 2} emissions reductions has been only one-tenth or less of what Title IV was originally expected to cost. This paper demonstrates that, to the contrary, actual costs for SO{sub 2} reductions remain roughly in line with original estimates associated with Title IV. Erroneous conclusions about Title IV`s costs are due to inappropriate comparisons of a variety of different measures that appear to be comparable only because they are all stated in dollars per ton. Program cost estimates include the total costs of a fully-implemented regulatory program. The very low costs of Title IV that are commonly cited today are neither directly reflective of a fully implemented Title IV, (which is still many years away) nor reflective of all the costs already incurred. Further, a careful review of history finds that the initial cost estimates that many cite were never associated with Title IV. Technically speaking, people are comparing the estimated control costs for the most-costly power plant associated with earlier acid rain regulatory proposals with prices from a market that do not directly reflect total costs.

  7. Estimation of annual forest evapotranspiration from a coniferous plantation watershed in Japan (2): Comparison of eddy covariance, water budget and sap-flow plus interception loss

    NASA Astrophysics Data System (ADS)

    Shimizu, Takanori; Kumagai, Tomo'omi; Kobayashi, Masahiro; Tamai, Koji; Iida, Shin'ichi; Kabeya, Naoki; Ikawa, Reo; Tateishi, Makiko; Miyazawa, Yoshiyuki; Shimizu, Akira

    2015-03-01

    Evapotranspiration (ET) was estimated from a planted coniferous forest in southwestern Japan by applying three methods: the eddy covariance method; the measurement of rainfall (P) and runoff (Q) in a small watershed; and a combination of rainfall interception loss (IC), upper canopy transpiration based on a sap-flux density measurement in Japanese cedar (Cryptomeria Japonica D. Don) stands (EUC), and modeled sub-canopy ET (ESC). After inverse multiplication of the energy imbalance ratio, ET by the eddy covariance method (ETEC) was 839.9 mm in 2007 and 811.8 mm in 2008. The yearly values of P-Q were partially affected by P in the previous autumn. After continuous data collection for more than 5 years, P-Q became stable. The 9-year (2000-2008) average P-Q, which was considered most reliable in this study, was 897.5 mm y-1. The cumulative ETEC during the daylight hours from the right stream bank, covered mainly with large Japanese cedars, was 894.1 mm from April 2007 to March 2008. The value was almost the same as that calculated as the components sum (ETCOMP = IC + EUC + ESC: 911.4 mm), and the comparison suggested that the annual totals of ETEC with an energy imbalance correction provide a reliable estimate of ET in a forest stand on a complex topography. Spatial variation in the watershed was likely caused by differences in soil water retention at each slope position. The slight difference in annual ETEC in 2007 compared with 2008 was attributed to differences in the radiative energy input. In the monthly-weekly analysis, ETCOMP was frequently higher than ETEC after heavy rainfall, while ETEC was higher under dry conditions and during active ET. Even under dry canopy conditions, daily ETEC was often higher than EUC + ESC. The results suggested a time-lag in evaporation from the ecosystem and/or under-estimated ETEC after rainfall.

  8. Multi-scales and multi-satellites estimates of evapotranspiration with a residual energy balance model in the Muzza agricultural district in Northern Italy

    NASA Astrophysics Data System (ADS)

    Corbari, C.; Bissolati, M.; Mancini, M.

    2015-05-01

    Evapotranspiration estimates were performed with a residual energy balance model (REB) over an agricultural area using remote sensing data. REB uses land surface temperature (LST) as main input parameter so that energy fluxes were computed instantaneously at the time of data acquisition. Data from MODIS and SEVIRI sensors were used and downscaling techniques were implemented to improve their spatial resolutions. Energy fluxes at the original spatial resolutions (1000 m for MODIS and 5000 m for SEVIRI) as well as at the downscaled resolutions (250 m for MODIS and 1000 m for SEVIRI) were calculated with the REB model. Ground eddy covariance data and remote sensing information from the Muzza agricultural irrigation district in Italy from 2010 to 2012 gave the opportunity to validate and compare spatially distributed energy fluxes. The model outputs matched quite well ground observations when ground LST data were used, while differences increased when MODIS and SEVIRI LST were used. The spatial analysis revealed significant differences between the two sensors both in term of LST (around 2.8 °C) and of latent heat fluxes with values (around 100 W m-2).

  9. Evaluating five remote sensing based single-source surface energy balance models for estimating daily evapotranspiration in a humid subtropical climate

    NASA Astrophysics Data System (ADS)

    Bhattarai, Nishan; Shaw, Stephen B.; Quackenbush, Lindi J.; Im, Jungho; Niraula, Rewati

    2016-07-01

    In the last two decades, a number of single-source surface energy balance (SEB) models have been proposed for mapping evapotranspiration (ET); however, there is no clear guidance on which models are preferable under different conditions. In this paper, we tested five models-Surface Energy Balance Algorithm for Land (SEBAL), Mapping ET at high Resolution with Internalized Calibration (METRIC), Simplified Surface Energy Balance Index (S-SEBI), Surface Energy Balance System (SEBS), and operational Simplified Surface Energy Balance (SSEBop)-to identify the single-source SEB models most appropriate for use in the humid southeastern United States. ET predictions from these models were compared with measured ET at four sites (marsh, grass, and citrus surfaces) for 149 cloud-free Landsat image acquisition days between 2000 and 2010. The overall model evaluation statistics showed that SEBS generally outperformed the other models in terms of estimating daily ET from different land covers (e.g., the root mean squared error (RMSE) was 0.74 mm day-1). SSEBop was consistently the worst performing model and overestimated ET at all sites (RMSE = 1.67 mm day-1), while the other models typically fell in between SSEBop and SEBS. However, for short grass conditions, SEBAL, METRIC, and S-SEBI appear to work much better than SEBS. Overall, our study suggests that SEBS may be the best SEB model in humid regions, although it may require modifications to work better over short vegetation.

  10. A Satellite-Based Estimation of Evapotranspiration Using Vegetation Index-Temperature Trapezoid Concept: A Case Study in Southern Florida, U.S.A.

    NASA Astrophysics Data System (ADS)

    Yagci, A. L.; Santanello, J. A., Jr.; Jones, J. W.

    2015-12-01

    One of the key surface variables for hydrological applications, monitoring of natural and anthropogenic water consumption, closing energy balance and water budgets and drought identification is evapotranspiration (ET). There is currently a strong need for high temporal and spatial resolution ET products for climate and hydrological modelers. A satellite-based retrieval method based on vegetation index-temperature trapezoid (VITT) concept has been developed. This model has the ability to generate accurate ET estimates at high temporal and spatial resolutions by taking advantage of key remotely sensed parameters such as vegetation indices (VIs) and land surface temperature (LST) acquired by satellites as well as routinely-measured meteorological variables such as air temperature (Ta) and net radiation. For local-scale applications, the model has been successfully implemented in Python programming language and tested using Landsat satellite products at an eddy covariance flux tower in Florida. It is fully functional and automated such that there is no need of user intervention to run the model. The model development for continental-scale applications using VI and LST products from NASA satellites such as the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Visible Infrared Imaging Radiometer Suite (VIIRS) is currently in progress. The results for local-scale application and early results for continental-scale (US) will be presented and discussed.

  11. Using a data fusion method to estimate daily stand-scale evapotranspiration over a managed pine plantation in North Carolina, USA

    NASA Astrophysics Data System (ADS)

    Yang, Y.; Anderson, M. C.; Gao, F.; Hain, C.; Kustas, W. P.; Noormets, A.; Wynne, R. H.; Thomas, V. A.; Sun, G.

    2015-12-01

    Within the context of a globally changing climate, efficient management of freshwater resource management is becoming an increasingly critical issue. As an indicator of vegetation health and soil moisture status, remotely sensed estimates of evapotranspiration (ET) estimation can provide valuable information about water usage in managed landscapes. The two source energy balance (TSEB) model has been widely applied to quantify field scale ET over agricultural systems using thermal infrared remote sensing data. However, limitations on the spatial and temporal resolution of the satellite data combined with the effects of cloud contamination constrain the amount of detail that a single satellite can provide. Fusing multi-satellite data with varying spatial and temporal resolutions can give a more continuous estimation of daily ET at field scale. In this study, we used the regional TSEB modeling system (Atmosphere-Land Exchange Inverse; ALEXI) to map ET at 4-km resolution over the continental U.S. using imagery from geostationary satellites. These 4-km regional estimates were disaggregated to 1-km (daily timesteps) using Moderate Resolution Imaging Spectroradiometer (MODIS) input data and down to 30-m with Landsat data 8 scenes during the growing season) using the disaggregation scheme DisALEXI, applied over a managed pine plantation in North Carolina, USA. The MODIS and Landsat ET retrievals were then combined using the Spatial-Temporal Adaptive Reflectance Fusion Model (STARFM) to estimate daily ET estimates at 30-m resolution. The modeled daily ET was in good agreement compared with observations at two Ameriflux eddy covariance flux tower sites (US-NC2, mid-rotation site and US-NC3, recently clear cut site). Seasonal water use patterns varied significantly with stand age, with higher rates of ET from mid-rotation stands in comparison with younger stands. Water use also varies with land cover types, with higher rates of ET from forested areas than from agricultural

  12. Wetlands Evapotranspiration Using Remotely Sensed Solar Radiation

    NASA Astrophysics Data System (ADS)

    Jacobs, J. M.; Myers, D. A.; Anderson, M. C.

    2001-12-01

    The application of remote sensing methods to estimate evapotranspiration has the advantage of good spatial resolution and excellent spatial coverage, but may have the disadvantage of infrequent sampling and considerable expense. The GOES satellites provide enhanced temporal resolution with hourly estimates of solar radiation and have a spatial resolution that is significantly better than that available from most ground-based pyranometer networks. As solar radiation is the primary forcing variable in wetland evapotranspiration, the opportunity to apply GOES satellite data to wetland hydrologic analyses is great. An accuracy assessment of the remote sensing product is important and the subsequent validation of the evapotranspiration estimates are a critical step for the use of this product. A wetland field experiment was conducted in the Paynes Prairie Preserve, North Central Florida during a growing season characterized by significant convective activity. Evapotranspiration and other surface energy balance components of a wet prairie community dominated by Panicum hemitomon (maiden cane), Ptilimnium capillaceum (mock bishop's weed), and Eupatorium capillifolium (dog fennel) were investigated. Incoming solar radiation derived from GOES-8 satellite observations, in combination with local meteorological measurements, were used to model evapotranspiration from a wetland. The satellite solar radiation, derived net radiation and estimated evapotranspiration estimates were compared to measured data at 30-min intervals and daily times scales.

  13. Evapotranspiration from the Lower Walker River Basin, West-Central Nevada, Water Years 2005-07

    USGS Publications Warehouse

    Allander, Kip K.; Smith, J. LaRue; Johnson, Michael J.

    2009-01-01

    evapotranspiration station in a saltcedar grove, measurements indicated a possible decrease in evapotranspiration of about 50 percent due to defoliation of the saltcedar by the saltcedar leaf beetle. Total evapotranspiration from the evapotranspiration units identified in the Lower Walker River basin was about 231,000 acre-feet per year (acre-ft/yr). Of this amount, about 45,000 acre-ft/yr originated from direct precipitation, resulting in net evapotranspiration of about 186,000 acre-ft/yr. More than 80 percent of net evapotranspiration in the Lower Walker River basin was through evaporation from Walker Lake. Total evaporation from Walker Lake was about 161,000 acre-ft/yr and net evaporation was about 149,000 acre-ft/yr. Some previous estimates of evaporation from Walker Lake based on water-budget analysis actually represent total evaporation minus ground-water inflow to the lake. Historical evaporation rates determined on the basis of water budget analysis were less than the evaporation rate measured directly during this study. The difference could represent ground-water inflow to Walker Lake of 16,000 to 26,000 acre-ft/yr or could indicate that ground-water inflow to Walker Lake is decreasing over time as the lake perimeter recedes.

  14. Sensitivity of future continental United States water deficit projections to general circulation models, the evapotranspiration estimation method, and the greenhouse gas emission scenario

    NASA Astrophysics Data System (ADS)

    Chang, Seungwoo; Graham, Wendy D.; Hwang, Syewoon; Muñoz-Carpena, Rafael

    2016-08-01

    Projecting water deficit under various possible future climate scenarios depends on the choice of general circulation model (GCM), reference evapotranspiration (ET0) estimation method, and Representative Concentration Pathway (RCP) trajectory. The relative contribution of each of these factors must be evaluated in order to choose an appropriate ensemble of future scenarios for water resources planning. In this study variance-based global sensitivity analysis and Monte Carlo filtering were used to evaluate the relative sensitivity of projected changes in precipitation (P), ET0, and water deficit (defined here as P-ET0) to choice of GCM, ET0 estimation method, and RCP trajectory over the continental United States (US) for two distinct future periods: 2030-2060 (future period 1) and 2070-2100 (future period 2). A total of 9 GCMs, 10 ET0 methods, and 3 RCP trajectories were used to quantify the range of future projections and estimate the relative sensitivity of future projections to each of these factors. In general, for all regions of the continental US, changes in future precipitation are most sensitive to the choice of GCM, while changes in future ET0 are most sensitive to the choice of ET0 estimation method. For changes in future water deficit, the choice of GCM is the most influential factor in the cool season (December-March), and the choice of ET0 estimation method is most important in the warm season (May-October) for all regions except the Southeast US, where GCMs and ET0 have approximately equal influence throughout most of the year. Although the choice of RCP trajectory is generally less important than the choice of GCM or ET0 method, the impact of RCP trajectory increases in future period 2 over future period 1 for all factors. Monte Carlo filtering results indicate that particular GCMs and ET0 methods drive the projection of wetter or drier future conditions much more than RCP trajectory; however, the set of GCMs and ET0 methods that produce wetter or

  15. Use of Empirical Mode Decomposition based Denoised NDVI in Extended Three-Temperature Model to estimate Evapotranspiration in Northeast Indian Ecosystems

    NASA Astrophysics Data System (ADS)

    Padhee, S. K.

    2015-12-01

    Evapotranspiration (ET) is an essential component involved in the energy balance and water budgeting methods, and its precise assessment are crucial for estimation of various hydrological parameters. Traditional point estimation methods for ET computation offer quantitative analysis, but lag in spatial distribution. The use of Remote Sensing (RS) data with good spatial, spectral and temporal resolution having broad spatial coverage, could lead the estimations with some advantages. However, approaches which requires data rich environment, demands time and resources. The estimation of spatially distributed soil evaporation (Es) and transpiration from canopy (Ec) by RS data, followed by their combination to provide the total ET, could be a simpler approach for accurate estimates of ET flux at macro-scale level. The 'Extended Three Temperature Model' (Extended 3T Model) is an established model based on same approach and is capable to compute ET and its partition of Es and Ec within the same algorithm. A case study was conducted using Extended 3T Model and MODIS products for the Brahmaputra river basin within the Northeast India for years 2000-2010. The extended 3T model was used by including its pre-requisite the land surface temperature (Ts), which was separated into the surface temperature of dry soil (Tsm) and the surface temperature of vegetation (Tcm), decided by a derivative of vegetation index (NDVI) called fractional vegetation cover (f). However, NDVI time series which is nonlinear and nonstationary can be decomposed by the Empirical Mode Decomposition (EMD) into components called intrinsic mode functions (IMFs), based on inherent temporal scales. The highest frequency component which was found to represent noise was subtracted from the original NDVI series to get the denoised product from which f was derived. The separated land surface temperatures (Tsm and Tcm) were used to calculate the Es and Ec followed by estimation of total ET. The spatiotemporal

  16. Technique of estimation of actual strength of a gas pipeline section at its deformation in landslide action zone

    SciTech Connect

    Tcherni, V.P.

    1996-12-31

    The technique is given which permits determination of stress and strain state (SSS) and estimation of actual strength of a section of a buried main gas pipeline (GP) in the case of its deformation in a landslide action zone. The technique is based on the use of three-dimensional coordinates of axial points of the deformed GP section. These coordinates are received by a full-scale survey. The deformed axis of the surveyed GP section is described by the polynomial. The unknown coefficients of the polynomial can be determined from the boundary conditions at points of connection with contiguous undeformed sections as well as by use of minimization methods in mathematical processing of full-scale survey results. The resulting form of GP section`s axis allows one to determine curvatures and, accordingly, bending moments along all the length of the considered section. The influence of soil resistance to longitudinal displacements of a pipeline is used to determine longitudinal forces. Resulting values of bending moments and axial forces as well as the known value of internal pressure are used to analyze all necessary components of an actual SSS of pipeline section and to estimate its strength by elastic analysis.

  17. Daily High Spatial Resolution Evapotranspiration Estimation Using Multi-Satellite Data Fusion Approach in Agricultural and Forested Sites in the U.S.

    NASA Astrophysics Data System (ADS)

    Yang, Y.; Anderson, M. C.; Semmens, K. A.; Gao, F.; Kustas, W. P.; Hain, C.; Schull, M. A.

    2014-12-01

    Evapotranspiration (ET), as a major part of the water balance, is a key indicator of vegetation stress and also represents various types of water usage strategies. High spatial and temporal resolution ET mapping can provide detailed information about daily vegetation water use and soil moisture status at finer scales, which is important to water management and vegetation condition monitoring. This research employs a multi-scale ET modeling system which is based on the two source surface energy balance (TSEB) model. We discuss the utility of applying this modeling system over an irrigated agriculture area in California and a forested site in North Carolina. The multi-scale ET modeling system integrates the Atmosphere-Land Exchange Inverse model and associated disaggregation scheme (ALEXI/DisALEXI) and fuses the ET estimations from both MODIS (1km, daily) and Landsat (30m, bi-weekly). The Spatial and Temporal Adaptive Reflective Fusion Model (STARFM) is used to retrieve high spatial and temporal resolution ET. A Data Mining Sharpener (DMS) methodology is used in the system to sharpen the native Landsat thermal infrared band (TIR) to 30m resolution. Comparing with Landsat only ET retrievals, this ET modeling system can optimize the usage of multi-satellite data, which are in different temporal and spatial resolution, to maximize the utility of high spatial and temporal ET estimation. Daily high spatial resolution ET retrievals are compared with observations from local flux towers. Determining how model output of daily water use information can be employed in irrigation and forest management applications will be discussed.

  18. Shift of annual water balance in the Budyko space for catchments with groundwater-dependent evapotranspiration

    NASA Astrophysics Data System (ADS)

    Wang, Xu-Sheng; Zhou, Yangxiao

    2016-09-01

    The Budyko framework represents the general relationship between the evapotranspiration ratio (F) and the aridity index (φ) for the mean annual steady-state water balance at the catchment scale. It is interesting to investigate whether this standard F - φ space can also be applied to capture the shift of annual water balance in catchments with varying dryness. Previous studies have made significant progress in incorporating the storage effect into the Budyko framework for the non-steady conditions, whereas the role of groundwater-dependent evapotranspiration was not investigated. This study investigates how groundwater-dependent evapotranspiration causes the shift of the annual water balance in the standard Budyko space. A widely used monthly hydrological model, the ABCD model, is modified to incorporate groundwater-dependent evapotranspiration into the zone with a shallow water table and delayed groundwater recharge into the zone with a deep water table. This model is applied in six catchments in the Erdos Plateau, China, to estimate the actual annual evapotranspiration. Results show that the variations in the annual F value with the aridity index do not satisfy the standard Budyko formulas. The shift of the annual water balance in the standard Budyko space is a combination of the Budyko-type response in the deep groundwater zone and the quasi-energy limited condition in the shallow groundwater zone. Excess evapotranspiration (F > 1) could occur in dry years, which is contributed by the significant supply of groundwater for evapotranspiration. Use of groundwater for irrigation can increase the frequency of the F > 1 cases.

  19. EVAPOTRANSPIRATION RATES AND CROP COEFFICIENTS FOR LOWBUSH BLUEBERRY (Vaccinium angustifolium)

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Lowbush blueberry (Vaccinium angustifolium) yield is strongly influenced by water availability; however, growers need more specific irrigation recommendations in order to optimize water use efficiency. Weighing lysimeters were used to determine actual evapotranspiration (ET) rates of lowbush bluebe...

  20. Estimates of evapotranspiration for riparian sites (Eucalyptus) in the Lower Murray -Darling Basin using ground validated sap flow and vegetation index scaling techniques

    NASA Astrophysics Data System (ADS)

    Doody, T.; Nagler, P. L.; Glenn, E. P.

    2014-12-01

    Water accounting is becoming critical globally, and balancing consumptive water demands with environmental water requirements is especially difficult in in arid and semi-arid regions. Within the Murray-Darling Basin (MDB) in Australia, riparian water use has not been assessed across broad scales. This study therefore aimed to apply and validate an existing U.S. riparian ecosystem evapotranspiration (ET) algorithm for the MDB river systems to assist water resource managers to quantify environmental water needs over wide ranges of niche conditions. Ground-based sap flow ET was correlated with remotely sensed predictions of ET, to provide a method to scale annual rates of water consumption by riparian vegetation over entire irrigation districts. Sap flux was measured at nine locations on the Murrumbidgee River between July 2011 and June 2012. Remotely sensed ET was calculated using a combination of local meteorological estimates of potential ET (ETo) and rainfall and MODIS Enhanced Vegetation Index (EVI) from selected 250 m resolution pixels. The sap flow data correlated well with MODIS EVI. Sap flow ranged from 0.81 mm/day to 3.60 mm/day and corresponded to a MODIS-based ET range of 1.43 mm/day to 2.42 mm/day. We found that mean ET across sites could be predicted by EVI-ETo methods with a standard error of about 20% across sites, but that ET at any given site could vary much more due to differences in aquifer and soil properties among sites. Water use was within range of that expected. We conclude that our algorithm developed for US arid land crops and riparian plants is applicable to this region of Australia. Future work includes the development of an adjusted algorithm using these sap flow validated results.

  1. Automated calculation of the evapotranspiration and crop coefficients for a large number of peatland sites using diurnal groundwater table fluctuations

    NASA Astrophysics Data System (ADS)

    Maurer, Eike; Bechtold, Michel; Dettmann, Ullrich; Tiemeyer, Bärbel

    2014-05-01

    Evapotranspiration is one of the main processes controlling peatland hydrology. Greenhouse gas (GHG) emissions from peatlands are in turn strongly controlled by the groundwater table. Through the increasing political and scientific interest to reduce GHG emissions, monitoring and modelling strategies to optimize re-wetting strategies and to quantify GHG emissions are needed. To achieve these aims, an accurate determination of the evapotranspiration as an essential part of the water balance is required. Many different approaches are known to determine the evapotranspiration. They are mostly either expensive or hard to parameterize. Plant specific crop coefficients (Kc-values) are an option to calculate plant-specific evapotranspiration but due to the lack of Kc-values for typical peatland vegetation types more data on evapotranspiration from peatlands in the temperate zone are required. Furthermore, simple methods to estimate evapotranspiration are needed especially for monitoring projects. Diurnal groundwater table fluctuations caused by root water uptake and groundwater inflow can be used to calculate daily evapotranspiration rates. This approach was first described by White (1932) who compared groundwater recovery rates at night to the decline during daytime. Besides the groundwater table data only the specific yield (Sy) is needed to calculate evapotranspiration. However, the method has some limitations because not all days can be evaluated which leads to data gaps during rainy and very dry or very wet periods. This study presents an automated method to calculate the specific yield, evapotranspiration and crop coefficients for a large number of sites covering all major peatland types and their typical land uses in Germany. As an input for our method, only groundwater level, precipitation and grass reference evapotranspiration (ET0) data is required. In a first step, the groundwater level data was smoothed by a LOESS function. In a second step, site-specific SY

  2. Heterogeneous terrain: a challenge to derive evapotranspiration with remote sensing and scintillometry

    NASA Astrophysics Data System (ADS)

    Thiem, Christina; Sun, Liya; Müller, Benjamin; Bernhardt, Matthias; Schulz, Karsten

    2014-05-01

    Despite the importance of evapotranspiration for Meteorology, Hydrology and Agronomy, obtaining area-averaged evapotranspiration estimates is cost as well as maintenance intensive: usually area-averaged evapotranspiration estimates are obtained by distributed sensor networks or remotely sensed with a scintillometer. A low cost alternative for evapotranspiration estimates are satellite images, as many of them are freely available. This approach has been proven to be worthwhile above homogeneous terrain, and typically evapotranspiration data obtained with scintillometry are applied for validation. We will extend this approach to heterogeneous terrain: evapotranspiration estimates from ASTER 2013 images will be compared to scintillometer derived evapotranspiration estimates. The goodness of the correlation will be presented as well as an uncertainty estimation for both the ASTER derived and the scintillometer derived evapotranspiration.

  3. How accurately can students estimate their performance on an exam and how does this relate to their actual performance on the exam?

    NASA Astrophysics Data System (ADS)

    Rebello, N. Sanjay

    2012-02-01

    Research has shown students' beliefs regarding their own abilities in math and science can influence their performance in these disciplines. I investigated the relationship between students' estimated performance and actual performance on five exams in a second semester calculus-based physics class. Students in a second-semester calculus-based physics class were given about 72 hours after the completion of each of five exams, to estimate their individual and class mean score on each exam. Students were given extra credit worth 1% of the exam points for estimating their score correct within 2% of the actual score and another 1% extra credit for estimating the class mean score within 2% of the correct value. I compared students' individual and mean score estimations with the actual scores to investigate the relationship between estimation accuracies and exam performance of the students as well as trends over the semester.

  4. Variation of Evapotranspiration as Function of Surface Type

    NASA Astrophysics Data System (ADS)

    Ringgaard, R.; Herbst, M.; Friborg, T.; Soegaard, H.

    2009-12-01

    Evapotranspiration is tightly coupled with vegetation type and coverage. Many studies examining the partitioning of evapotranspiration into soil evaporation and plant transpiration have found that transpiration may account for up to 90% of total evapotranspiration depending on leaf area index and stomatal conductance. This is especially true in temperate humid climates, where conditions favor development of high-LAI vegetation and a large soil moisture pool from which the plants can draw water during most of the growing season. This makes explicit treatment of surface type/evapotranspiration relationships an important part of large-scale water balance and hydrological studies. The present study is part of the catchment-scale hydrological observatory “HOBE” situated on the west coast of Denmark. The main goals of the observatory is to better the scientific understating of large scale hydrological processes and to examine in detail the issue of scaling plot measurements to catchment scale. To estimate actual evapotranspiration, eddy-covariance systems have been installed on the most important surface types in the catchment - at an agricultural site (68% of the total area), over a spruce plantation (16%) and over wet grassland (7%). This presentation will introduce the first full-year time series of evapotranspiration from the three sites, with special emphasis on the difference in evaporative response through the seasons from the different surface types. The catchment covers about 2500km2 extending inland ca. 65 km. The landscape is very flat throughout the catchment, rising to only about 80 meters furthest inland. The geology is dominated by loose glacial and melt water deposits, with soils being comprised mostly of coarse sand. The climate can be characterized as maritime with winter temperatures around 1°C and summer temperatures around 16°C. Mean annual precipitation is around 800 mm. The weather is dominated by the prevailing westerlies from the Atlantic

  5. Satellite passive microwave remote sensing for estimating diurnal variation of leaf water content, as a proxy of evapotranspiration, in the Dry Chaco Forest, Argentina

    NASA Astrophysics Data System (ADS)

    Barraza Bernadas, V.; Grings, F.; Ferrazzoli, P.; Carbajo, A.; Fernandez, R.; Karszenbaum, H.

    2012-12-01

    Evapotranspiration (ET) is a key component of water cycle, which is strongly linked with environmental condition and vegetation functioning. Since it is very difficult to robustly estimate it from remote sensing data at regional scale it is usually inferred from other proxies using water balance. This work describes a procedure to estimate ET in a dry forest by monitoring diurnal variation of leaf water content (LWC), using multitemporal passive microwave remote sensing observations. Hourly observations provide the opportunity to monitor repetitive diurnal variations of passive microwave observations, which can only be accounted by changes in LWC (which is itself related to water vapor that enters to the atmosphere from land surface). To this end, we calculated the vegetation frequency index (FI) as FI= 2*(TBKa-TBX)/ ((TBKa +TBX)), where TBKa and TBX indicate brightness temperatures at 37 and 10.6 GHz respectively. There is both theoretical and experimental evidence that link this index to microwave to LWC. The index was computed for vertical polarization, because it presents higher correlation with vegetation state. At diurnal temporal scale, changes in LWC are commonly very small. Nevertheless, it was previously shown that passive remote sensing data (FI computed using Ku and Ka bands) acquired at different hours can be used to estimate the seasonal changes in ET. In this work, we present a procedure based on the hourly changes of FI, which are interpreted as changes in LWC. In order to present a quantitative estimation, the discrete forest model described in (Ferrazzoli and Guerriero, 1996) has been used to simulate the variations of FI with LWC. To illustrate the procedure, AMSR-E and WINDSAT data from 2007-2009 at X and Ka bands were used, and up to four observations per day at four different local times (2.30 am, 7.00 am, 2.30 pm and 7.00 pm) were analyzed. The region addressed is the area of the Dry Chaco forest located in Bermejo River Basin in Argentina

  6. Airborne and ground-based remote sensing for the estimation of evapotranspiration and yield of bean, potato, and sugar beet crops

    NASA Astrophysics Data System (ADS)

    Jayanthi, Harikishan

    The focus of this research was two-fold: (1) extend the reflectance-based crop coefficient approach to non-grain (potato and sugar beet), and vegetable crops (bean), and (2) develop vegetation index (VI)-yield statistical models for potato and sugar beet crops using high-resolution aerial multispectral imagery. Extensive crop biophysical sampling (leaf area index and aboveground dry biomass sampling) and canopy reflectance measurements formed the backbone of developing of canopy reflectance-based crop coefficients for bean, potato, and sugar beet crops in this study. Reflectance-based crop coefficient equations were developed for the study crops cultivated in Kimberly, Idaho, and subsequently used in water availability simulations in the plant root zone during 1998 and 1999 seasons. The simulated soil water profiles were compared with independent measurements of actual soil water profiles in the crop root zone in selected fields. It is concluded that the canopy reflectance-based crop coefficient technique can be successfully extended to non-grain crops as well. While the traditional basal crop coefficients generally expect uniform growth in a region the reflectance-based crop coefficients represent the actual crop growth pattern (in less than ideal water availability conditions) in individual fields. Literature on crop canopy interactions with sunlight states that there is a definite correspondence between leaf area index progression in the season and the final yield. In case of crops like potato and sugar beet, the yield is influenced not only on how early and how quickly the crop establishes its canopy but also on how long the plant stands on the ground in a healthy state. The integrated area under the crop growth curve has shown excellent correlations with hand-dug samples of potato and sugar beet crops in this research. Soil adjusted vegetation index-yield models were developed, and validated using multispectral aerial imagery. Estimated yield images were

  7. Estimating Evapotranspiration Over Agricultural Landscapes with Thermal Infrared Data: Towards the Comparison of Two Approaches Using Simple Energy Budget and Svat Modeling

    NASA Astrophysics Data System (ADS)

    Bigeard, G.; Coudert, B.; Jarlan, L.

    2011-12-01

    Evapotranspiration (ET) monitoring presents wide range of applications from agriculture and water resources management to meteorology. Several approaches have been developed to retrieve ET based on a joint use of remote sensing data and land surface modeling, in particular with a SVAT (Soil Vegetation Atmosphere Transfers) model or a SEB (Surface Energy Budget) model. The objective of our work is to estimate spatialized ET fluxes from Thermal Infra-Red (TIR) imagery. We will focus on simulating fluxes at low resolution with 2 methodologies: 1- Simulating with a SEB model directly at low resolution (landscape scale: 4km) with TIR forcing. 2- Aggregating high resolution (agricultural field scale) estimates from a SVAT model constrained by TIR data and forced by a spatialized database (landcover, LAI, vegetation height and meteorological forcing). By doing a sensitivity analysis and comparing both approaches we will point out mechanisms that govern scale switching, and how high resolution "informations" and aggregation scenarios impact low resolution estimates. Within this preliminary study, we compare in-situ potentialities of a SEB model (TSEB) versus a SVAT model (SEtHyS). TSEB (Two Sources Equation Balance) is a model of turbulent exchange (Norman & al. 1995) partitioning the available energy between soil and vegetation and driven directly via remote sensing TIR sensors. SEtHyS (French acronym for soil moisture monitoring) is a SVAT model (described by Coudert & al. 2006) which is physically based and has more inputs and parameters requirements. Besides fluxes, it outputs brightness temperatures which can be compared and constrained with TIR data. Models fluxes simulations are compared to in-situ Eddy-Correlation (EC) fluxes measurement stations. Models are then compared performing a sensitivity analysis on their inputs and parameters so as to characterize their capabilities and behaviors, and quantify error ranges that will be induced by spatialization over

  8. Evapotranspiration from areas of native vegetation in west-central Florida

    USGS Publications Warehouse

    Bidlake, W.R.; Woodham, W.M.; Lopez, Miguel Angel

    1996-01-01

    The micrometeorological methods of energy-balance Bowen ratio and eddy correlation probably are suitable for determining evapotranspiration from unforested sites, but the aerodynamic effects of tall tree canopies need to be considered when the methods are used for forested sites. Potential evapotranspiration methods might not yield reliable estimates of evapotranspiration for all areas of native vegetation. Estimates of annual evapotranspiration ranged from 970 millimeters for a cypress swamp site to 1,060 millimeters for a pine flatwood site.

  9. Use of finite-difference arrays of observation wells to estimate evapotranspiration from ground water in the Arkansas River Valley, Colorado

    USGS Publications Warehouse

    Weeks, Edwin P.; Sorey, M.L.

    1973-01-01

    A method to determine evapotranspiration from ground water was tested at four sites in the flood plain of the Arkansas River in Colorado. Approximate ground-water budgets were obtained by analyzing water-level data from observation wells installed in five-point arrays. The analyses were based on finite difference approximations of the differential equation describing ground-water flow. Data from the sites were divided into two groups by season. It was assumed that water levels during the dormant season were unaffected by evapotranspiration of ground water or by recharge, collectively termed 'accretion.' Regression analyses of these data were made to provide an equation for separating the effects of changes in aquifer storage and of aquifer heterogeneity from those due to accretion during the growing season. The data collected during the growing season were thus analyzed to determine accretion.

  10. Water Footprint of a Super-intensive Olive Grove Under Mediterranean Climate using Ground-based Evapotranspiration Measurements and Remote Sensing

    NASA Astrophysics Data System (ADS)

    Nogueira, A. M.; Paço, T. A.; Silvestre, J. C.; Gonzalez, L. F.; Santos, F. L.; Pereira, L. S.

    2012-04-01

    measurements were used to calculate water footprint instead of the common procedure (using evapotranspiration estimates), this might have also introduced some differences. The potential of using remote sensing techniques for the assessment of water footprint of crops has been discussed in recent literature. It can provide estimates of actual evapotranspiration, of precipitation, of surface runoff and of irrigation needs when associated with modelling. In this study we further compare the water footprint estimates using in situ evapotranspiration measurements and water footprint estimates using remote sensing techniques. A comparison with the irrigation records for this particular olive orchard will be used to validate the approaches.

  11. Evapotranspiration and microclimate at a low-level radioactive-waste disposal site in northwestern Illinois

    USGS Publications Warehouse

    Healy, R.W.; DeVries, M.P.; Sturrock, Alex M.

    1989-01-01

    From July 1982 through June 1984, a study was made of the evapotranspiration and microclimate at a low-level radioactive-waste disposal site near Sheffield, Bureau County, Illinois. Vegetation at the site consists of mixed pasture grasses, primarily awnless brome (Bromus inermis) and red clover (Trifoleum pratense). Three methods were used to estimate evapotranspiration: (1) an energy budget with the Bowen ratio, (2) an aerodynamic profile, and (3) a soil-based water budget. For the aerodynamic-profile method, sensible-heat flux was estimated by a profile equation and evapotranspiration was then calculated as the residual in the energy-balance equation. Estimates by the energy-budget and aerodynamic-profile methods were computed from hourly data and then summed by days and months. Yearly estimates (for March through November) by these methods were in close agreement: 648 and 626 millimeters, respectively. Daily estimates reach a maximum of about 6 millimeters. The water-budget method produced only monthly estimates based on weekly or biweekly soil-moisture content measurements. The yearly evapotranspiration estimated by this method (which actually included only the months of April through October) was 655 millimeters. The March-through-November average for the three methods of 657 millimeters was equivalent to 70 percent of total precipitation. Continuous measurements were made of incoming and reflected shortwave radiation, incoming and emitted longwave radiation, net radiation, soil-heat flux, soil temperature, horizontal windspeed, and wet- and dry-bulb air temperature. Windspeed and air temperature were measured at heights of 0.5 and 2.0 meters (and also at 1.0 meter after September 1983). Soilmoisture content of the soil zone was measured with a gamma-attenuation gage. Annual precipitation (938 millimeters) and average temperature (10.8 degrees Celsius) at the Sheffield site were virtually identical to long-term averages from nearby National Weather Service

  12. Data-driven regionalization of river discharges and emergent land cover-evapotranspiration relationships across Sweden

    NASA Astrophysics Data System (ADS)

    Velde, Ype; Lyon, Steve W.; Destouni, Georgia

    2013-03-01

    in river discharge and river water quality, due to climate change and other drivers such as land cover change, pose both societal and ecosystem threats. Analyses of measured terrestrial river fluxes are key for identifying the drivers and quantifying the magnitudes of such riverine changes. In this paper, we develop and apply a data-driven regionalization approach using the dense network of discharge measurements in Sweden. The developed regionalization approach facilitates detailed mapping of discharges (Q) and change trends in Q across Sweden. Combining these with estimates of precipitation (P) and change trends in P, we estimated actual evapotranspiration (AET) and change trends in AET via catchment-scale water balance constraints. We identified characteristic land cover-evapotranspiration relationships by plotting water use efficiency (AET/P) against energy use efficiency (AET/potential ET) for areas with unique land cover across Sweden. Our results show that wetlands have clearly lower water and energy use efficiencies compared to open waters, forests, and agriculture, and that agriculture has water and energy use efficiencies closest to those of open waters. We further compared the data-driven regionalization estimates of different water balance components with estimates of regional climate models (RCMs). The RCMs do not describe well the observed change trends in Sweden. In particular, for evapotranspiration, the observed change trends are not reproduced by any of the investigated 24 RCMs.

  13. Estimating shortwave solar radiation using net radiation and meteorological measurements

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Shortwave radiation has a wide variety of uses in land-atmosphere interactions research. Actual evapotranspiration estimation that involves stomatal conductance models like Jarvis and Ball-Berry require shortwave radiation to estimate photon flux density. However, in most weather stations, shortwave...

  14. Evapotranspiration in Subtropical Climate: Measurements and predictions

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Evapotranspiration (ET) loss is estimated at about 80-85% of annual precipitation in South Florida. Accurate prediction of ET is an important part of the implementation of the Comprehensive Everglades Restoration Plan (CERP). In the USDA's Everglades Agro-Hydrology Model (EAHM), the daily soil root...

  15. Long-term lysimeter data on evapotranspiration

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Long term crop evapotranspiration (ET) data measured using large weighing lysimeters have only been gathered in a few places in the world, yet are of great importance for ground truthing of many models of plant water use, mesoscale climate, remote sensing estimation of ET, climate change and climate...

  16. Potential evapotranspiration and continental drying

    NASA Astrophysics Data System (ADS)

    Milly, P. C. D.; Dunne, K. A.

    2016-10-01

    By various measures (drought area and intensity, climatic aridity index, and climatic water deficits), some observational analyses have suggested that much of the Earth’s land has been drying during recent decades, but such drying seems inconsistent with observations of dryland greening and decreasing pan evaporation. `Offline’ analyses of climate-model outputs from anthropogenic climate change (ACC) experiments portend continuation of putative drying through the twenty-first century, despite an expected increase in global land precipitation. A ubiquitous increase in estimates of potential evapotranspiration (PET), driven by atmospheric warming, underlies the drying trends, but may be a methodological artefact. Here we show that the PET estimator commonly used (the Penman-Monteith PET for either an open-water surface or a reference crop) severely overpredicts the changes in non-water-stressed evapotranspiration computed in the climate models themselves in ACC experiments. This overprediction is partially due to neglect of stomatal conductance reductions commonly induced by increasing atmospheric CO2 concentrations in climate models. Our findings imply that historical and future tendencies towards continental drying, as characterized by offline-computed runoff, as well as other PET-dependent metrics, may be considerably weaker and less extensive than previously thought.

  17. Evapotranspiration and microclimate at a low-level radioactive-waste disposal site in northwestern Illinois

    SciTech Connect

    Healy, R.W.; deVries, M.P.; Sturrock, A.M. Jr.

    1989-01-01

    Theory, methods, and results of a 2-yr study of microclimate and evapotranspiration of vegetated trench caps, conducted at the disposal site near Sheffield, Illinois, are presented in the report. Three methods were used to estimate evapotranspiration: energy-budget, aerodynamic-profile, and water-budget. Daily evapotranspiration ranged from 0 to 6 mm. The yearly average for the three methods of 657 mm was equivalent to 70% of precipitation and 75% of potential evapotranspiration.

  18. Mothers' and Teachers' Estimations of First Graders' Literacy Level and Their Relation to the Children's Actual Performance in Different SES Groups

    ERIC Educational Resources Information Center

    Korat, Ofra

    2011-01-01

    The relationship between mothers' and teachers' estimations of 60 children's literacy level and their actual performance were investigated in two different socio-economic status (SES) groups: low (LSES) and high (HSES). The children's reading (fluency, accuracy and comprehension) and spelling levels were measured. The mothers evaluated their own…

  19. Drought trends indicated by evapotranspiration deficit over the contiguous United States during 1896-2013

    NASA Astrophysics Data System (ADS)

    Kim, Daeha; Rhee, Jinyoung

    2016-04-01

    Evapotranspiration (ET) has received a great attention in drought assessment as it is closely related to atmospheric water demand. The hypothetical potential ET (ETp) has been predominantly used, nonetheless it does not actually exist in the hydrologic cycle. In this work, we used a complementary method for ET estimation to obtain wet-environment ET (ETw) and actual ET (ETa) from routinely observed climatic data. By combining ET deficits (ETw minus ETa) and the structure of the Standardized Precipitation-Evapotranspiration Index (SPEI), we proposed a novel ET-based drought index, the Standardized Evapotranspiration Deficit Index (SEDI). We carried out historical drought identification for the contiguous United States using temperature datasets of the PRISM Climate Group. SEDI presented spatial distributions of drought areas similar to the Palmer Drought Severity Index (PDSI) and Standardized Precipitation Index (SPI) for major drought events. It indicates that SEDI can be used for validating other drought indices. Using the non-parametric Mann-Kendall test, we found a significant decreasing trend of SEDI (increasing drought risk) similar to PDSI and SPI in the western United States. This study suggests a potential of ET-based indices for drought quantification even with no involvement of precipitation data.

  20. Evapotranspiration and microclimate at a low-level radioactive-waste disposal site in northwestern Illinois

    USGS Publications Warehouse

    Healy, R.W.; DeVries, M.P.; Sturrock, A.M.

    1987-01-01

    From July 1982 through June 1984, a study was made of the microclimate and evapotranspiration at a low-level radioactive-waste disposal site near Sheffield, Bureau County, Illinois. Vegetation at the site consists of mixed pasture grasses, primarily brome (Bromus inermis) and red clover (Trifoleum pratense). Three methods were used to estimate evapotranspiration: (1) an energy-budget with the Bowen ratio, (2) an aerodynamic-profile, and (3) a soil-based water-budget. For the aerodynamic-profile method, sensible-heat flux was estimated by a profile equation and evapotranspiration was then calculated as the residual in the energy-balance equation. Estimates by the energy-budget and aerodynamic-profile methods were computed from hourly data, then summed by days and months. Yearly estimates for March through November, by these methods, were quite close--648 and 626 millimeters, respectively. Daily estimates range up to a maximum of about 6 millimeters. The water-budget method produced only monthly estimates based on weekly or biweekly soil-moisture content measurements. The yearly evapotranspiration estimated by this method (which actually included only the months of April through October) was 655 millimeters. The March-through-November average for the three methods of 657 millimeters was equivalent to 70 percent of precipitation. Continuous measurements were made of incoming and reflected shortwave radiation, incoming and emitted longwave radiation, net radiation, soil-heat flux, soil temperature, horizontal windspeed, and wet- and dry-bulb air temperature. Windspeed and air temperature were measured at heights of 0.5 and 2.0 meters (and also at 1.0 meter after September 1983). Soil-moisture content of the soil zone was measured with a gamma-attenuation gage. Annual precipitation (938 millimeters) and average temperature (10.8 degrees Celsius) were virtually identical to long-term averages from nearby National Weather Service stations. Solar radiation averaged 65

  1. Timescales of Land Surface Evapotranspiration Response

    NASA Technical Reports Server (NTRS)

    Scott, Russell; Entekhabi, Dara; Koster, Randal; Suarez, Max

    1997-01-01

    Soil and vegetation exert strong control over the evapotranspiration rate, which couples the land surface water and energy balances. A method is presented to quantify the timescale of this surface control using daily general circulation model (GCM) simulation values of evapotranspiration and precipitation. By equating the time history of evaporation efficiency (ratio of actual to potential evapotranspiration) to the convolution of precipitation and a unit kernel (temporal weighting function), response functions are generated that can be used to characterize the timescales of evapotranspiration response for the land surface model (LSM) component of GCMS. The technique is applied to the output of two multiyear simulations of a GCM, one using a Surface-Vegetation-Atmosphere-Transfer (SVAT) scheme and the other a Bucket LSM. The derived response functions show that the Bucket LSM's response is significantly slower than that of the SVAT across the globe. The analysis also shows how the timescales of interception reservoir evaporation, bare soil evaporation, and vegetation transpiration differ within the SVAT LSM.

  2. Evapotranspiration-based irrigation scheduling of lettuce and broccoli

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Estimation of crop evapotranspiration supports efficient irrigation water management, which in turn supports water conservation, mitigation of groundwater depletion/degradation, energy savings, and crop quality maintenance. Past research in California has revealed strong relationships between fract...

  3. Wavelet-based Evapotranspiration Forecasts

    NASA Astrophysics Data System (ADS)

    Bachour, R.; Maslova, I.; Ticlavilca, A. M.; McKee, M.; Walker, W.

    2012-12-01

    Providing a reliable short-term forecast of evapotranspiration (ET) could be a valuable element for improving the efficiency of irrigation water delivery systems. In the last decade, wavelet transform has become a useful technique for analyzing the frequency domain of hydrological time series. This study shows how wavelet transform can be used to access statistical properties of evapotranspiration. The objective of the research reported here is to use wavelet-based techniques to forecast ET up to 16 days ahead, which corresponds to the LANDSAT 7 overpass cycle. The properties of the ET time series, both physical and statistical, are examined in the time and frequency domains. We use the information about the energy decomposition in the wavelet domain to extract meaningful components that are used as inputs for ET forecasting models. Seasonal autoregressive integrated moving average (SARIMA) and multivariate relevance vector machine (MVRVM) models are coupled with the wavelet-based multiresolution analysis (MRA) results and used to generate short-term ET forecasts. Accuracy of the models is estimated and model robustness is evaluated using the bootstrap approach.

  4. Recharge and Evapotranspiration Assessment In Kalahari

    NASA Astrophysics Data System (ADS)

    Lubczynski, M.; Obakeng, O.

    2006-12-01

    Sustainability of groundwater resources in Kalahri is constrained not only by recharge to the aquifers but also by discharge from them. Natural groundwater discharge takes place in 3 different ways, as aquifer groundwater outflow, direct tree root water uptake called groundwater transpiration (Tg) and as upward vapor-liquid water movement called groundwater evaporation (Eg), the latter two called groundwater evapotranspiration (ETg). The evaluation of ETg and recharge was the main goal of this study. Due to generally large depth of groundwater table in Kalahari, >60 m, Eg was assumed as negligible component of groundwater balances while in contrast Tg has been considered significant already since 90-ties. This was because of fragments of tree roots of Boscia albitrunca and Acacia erioloba found in borehole cores at depth of >60 m. Some of those roots reach groundwater, which allow them to remain green throughout dry seasons. This study was carried out using hydrological monitoring consisting of 10 multi-sensor towers and 17 groundwater monitoring points. Soil moisture movement was investigated by profile monitoring. The deepest profile was down to 76 m depth. The soil moisture results revealed complicated pattern characterized by a combination of diffuse and preferential flow. The actual evapotranspiration was estimated by the Bowen-ratio and temperature-profile methods which provided overestimated results as compared with rainfall so the recharge could not be deduced directly. Therefore recharge was derived indirectly, through 1D lumped parameter model that used rainfall and PET as input and heads as calibration reference. That model indicated recharge 0-50 mm/yr. For understanding tree impact upon groundwater recharge, tree sap velocity was monitored for 2 years using the Granier method on 41 trees of 9 species in 8 plots of 30x30m. The estimated plot transpirations showed large spatio-temporal variability, 3-71 mm/yr and occasionally exceeded recharge. In order

  5. Evapotranspiration and soil heterogeneity

    SciTech Connect

    Luxmoore, R J; Sharma, M L

    1982-01-01

    In a previous computer simulation study of a grassland catchment in Oklahoma, evapotranspiration was predicted to increase up to 25% for soils with finer textures than the silt loam reference soil. Results are further analyzed to illustrate plant water responses to scaled soil physical characteristics from the simulations with the Terrestrial Ecosystem Hydrology Model. Finer soils were shown to have higher soil water capacities over wider ranges of soil matric pressures than the reference soil which increased the water supply to vegetation. The water potential and stomatal conductance of foliage were generally higher on soils with higher soil water capacities. The analysis suggests that areal variation in soil hydraulic characteristics may significantly influence areal evapotranspiration.

  6. Global investigation of vegetation impact on mean annual catchment evapotranspiration

    NASA Astrophysics Data System (ADS)

    Peel, Murray C.; McMahon, Thomas A.; Finlayson, Brian L.

    2010-05-01

    Historically, relationships between catchment vegetation type, evapotranspiration and runoff have been assessed primarily through paired catchment studies. The literature contains results from over 200 of these studies from around the world but two factors limit the applicability of the results to the wider domain. Firstly, catchment areas are generally small (<10 km2). Secondly, the range of climate types is narrow, with temperate (Köppen C) and cold (Köppen D) climate types in the majority. Here we present results from a global assessment of the impact of vegetation type on mean annual catchment evapotranspiration for a large, spatially and climatically diverse dataset of 699 catchments. This assessment is based on analysis of areal precipitation, temperature, runoff, and land cover information from each catchment, which differs from the paired catchment methodology where streamflow responses to a controlled land cover change are assessed. When catchments are grouped by vegetation type, any evidence of differing vegetation impact on actual evapotranspiration will be observed through differences in mean annual actual evapotranspiration, defined as precipitation minus runoff. Stratifying catchments by climate type was observed to be important when assessing the vegetation impact on evapotranspiration. Tropical and temperate forested catchments had significantly higher median evapotranspiration (~170mm and ~130mm, respectively) than non-forested catchments. Cold forested catchments unexpectedly had significantly lower median evapotranspiration (~90mm) than non-forested catchments. No significant difference in median evapotranspiration was found between temperate evergreen and deciduous forested catchments, though sample sizes were small. Temperate evergreen needleleaf forested catchments had significantly higher median evapotranspiration than evergreen broadleaf forested catchments, though again sample sizes were small. The significant difference in median

  7. Estimation of potential evapotranspiration from extraterrestrial radiation, air temperature and humidity to assess future climate change effects on the vegetation of the Northern Great Plains, USA

    USGS Publications Warehouse

    King, David A.; Bachelet, Dominique M.; Symstad, Amy J.; Ferschweiler, Ken; Hobbins, Michael

    2014-01-01

    The potential evapotranspiration (PET) that would occur with unlimited plant access to water is a central driver of simulated plant growth in many ecological models. PET is influenced by solar and longwave radiation, temperature, wind speed, and humidity, but it is often modeled as a function of temperature alone. This approach can cause biases in projections of future climate impacts in part because it confounds the effects of warming due to increased greenhouse gases with that which would be caused by increased radiation from the sun. We developed an algorithm for linking PET to extraterrestrial solar radiation (incoming top-of atmosphere solar radiation), as well as temperature and atmospheric water vapor pressure, and incorporated this algorithm into the dynamic global vegetation model MC1. We tested the new algorithm for the Northern Great Plains, USA, whose remaining grasslands are threatened by continuing woody encroachment. Both the new and the standard temperature-dependent MC1 algorithm adequately simulated current PET, as compared to the more rigorous PenPan model of Rotstayn et al. (2006). However, compared to the standard algorithm, the new algorithm projected a much more gradual increase in PET over the 21st century for three contrasting future climates. This difference led to lower simulated drought effects and hence greater woody encroachment with the new algorithm, illustrating the importance of more rigorous calculations of PET in ecological models dealing with climate change.

  8. Assessment of actual transpiration rate in olive tree field combining sap-flow, leaf area index and scintillometer measurements

    NASA Astrophysics Data System (ADS)

    Agnese, C.; Cammalleri, C.; Ciraolo, G.; Minacapilli, M.; Provenzano, G.; Rallo, G.; de Bruin, H. A. R.

    2009-09-01

    Models to estimate the actual evapotranspiration (ET) in sparse vegetation area can be fundamental for agricultural water managements, especially when water availability is a limiting factor. Models validation must be carried out by considering in situ measurements referred to the field scale, which is the relevant scale of the modelled variables. Moreover, a particular relevance assumes to consider separately the components of plant transpiration (T) and soil evaporation (E), because only the first is actually related to the crop stress conditions. Objective of the paper was to assess a procedure aimed to estimate olive trees actual transpiration by combining sap flow measurements with the scintillometer technique at field scale. The study area, located in Western Sicily (Italy), is mainly cultivated with olive crop and is characterized by typical Mediterranean semi-arid climate. Measurements of sap flow and crop actual evapotranspiration rate were carried out during 2008 irrigation season. Crop transpiration fluxes, measured on some plants by means of sap flow sensors, were upscaled considering the leaf area index (LAI). The comparison between evapotranspiration values, derived by displaced-beam small-aperture scintillometer (DBSAS-SLS20, Scintec AG), with the transpiration fluxes obtained by the sap flow sensors, also allowed to evaluate the contribute of soil evaporation in an area characterized by low vegetation coverage.

  9. Estimation of evaporation over the upper Blue Nile basin by combining observations from satellites and river flow gauges

    NASA Astrophysics Data System (ADS)

    Allam, Mariam M.; Jain Figueroa, Anjuli; McLaughlin, Dennis B.; Eltahir, Elfatih A. B.

    2016-02-01

    Reliable estimates of regional evapotranspiration are necessary to improve water resources management and planning. However, direct measurements of evaporation are expensive and difficult to obtain. Some of the difficulties are illustrated in a comparison of several satellite-based estimates of evapotranspiration for the Upper Blue Nile (UBN) basin in Ethiopia. These estimates disagree both temporally and spatially. All the available data products underestimate evapotranspiration leading to basin-scale mass balance errors on the order of 35 percent of the mean annual rainfall. This paper presents a methodology that combines satellite observations of rainfall, terrestrial water storage as well as river-flow gauge measurements to estimate actual evapotranspiration over the UBN basin. The estimates derived from these inputs are constrained using a one-layer soil water balance and routing model. Our results describe physically consistent long-term spatial and temporal distributions of key hydrologic variables, including rainfall, evapotranspiration, and river-flow. We estimate an annual evapotranspiration over the UBN basin of about 2.55 mm per day. Spatial and temporal evapotranspiration trends are revealed by dividing the basin into smaller subbasins. The methodology described here is applicable to other basins with limited observational coverage that are facing similar future challenges of water scarcity and climate change.

  10. Riparian evapotranspiration in Nebraska

    USGS Publications Warehouse

    Hall, Brent M.; Rus, David L.

    2013-01-01

    With increasing demands being placed on the water resources of Nebraska, characterizing evapotranspiration (ET) from riparian vegetation has gained importance to water users and managers. This report summarizes and compares the results from several studies of the ET from cottonwood-dominated riparian forests, riparian grasslands, and common reed, Phragmites australis, in Nebraska. Reported results show that the highest seasonal ET amounts were associated with Phragmites australis, followed by riparian forests, with riparian grasslands experiencing the lowest total ET of the studied vegetation communities.

  11. Investigating Landsat-derived forest evapotranspiration in the Amazon

    NASA Astrophysics Data System (ADS)

    Khand, K. B.; Numata, I.; Kjaersgaard, J.; Cochrane, M. A.

    2015-12-01

    Nearly half of annual rainfall in the Amazon rainforest region is returned to the atmosphere through evapotranspiration (ET). However, this land-atmosphere water vapor feedback in Amazonia has been continuously disturbed by anthropogenic influence and climate change such as severe drought events. While forest ET dynamics in the Amazon have been studied from both point estimates (or in-situ measurements) and regional land-surface models as well as coarse-spatial satellite data, finer spatial data is required to address the spatial variability of forest ET associated with both forest disturbances and extreme climate events. We use Landsat-based METRIC (Mapping Evapotranspiration at high Resolution with Internalized Calibration) model to generate high-resolution (30 m) ET products and investigate its potential to characterize local and regional ET behavior by comparison to ET calculated from flux tower data. METRIC estimates actual ET as residual of the surface energy balance and is applied to capture the spatial variability of forest ET. The flux tower data were collected at two sites with different forest types: Para with wet equatorial forest and Rondônia with seasonally dry tropical forest. Our study was conducted on the dry season of the years 2003 and 2005 for Para, and 2000 through 2002 for Rondônia as a function of data availability of both cloud-free Landsat images and meteorological data for METRIC processing. Daily gridded actual ET estimates from METRIC during the dry season were obtained using a cubic spline interpolation of ETrF (fraction of reference ET) values between the satellite image dates and multiplying by daily reference ET. Across the all study years, differences between the daily ET estimates for the selected image dates from METRIC and the flux towers were less than 1.2 mm/day, while on monthly basis, these averaged daily ET differences were much lower (< 0.5 mm). At Para, the correlation (R2) between the daily ET rates from METRIC and the

  12. Remote sensing of evapotranspiration using automated calibration: Development and testing in the state of Florida

    NASA Astrophysics Data System (ADS)

    Evans, Aaron H.

    Thermal remote sensing is a powerful tool for measuring the spatial variability of evapotranspiration due to the cooling effect of vaporization. The residual method is a popular technique which calculates evapotranspiration by subtracting sensible heat from available energy. Estimating sensible heat requires aerodynamic surface temperature which is difficult to retrieve accurately. Methods such as SEBAL/METRIC correct for this problem by calibrating the relationship between sensible heat and retrieved surface temperature. Disadvantage of these calibrations are 1) user must manually identify extremely dry and wet pixels in image 2) each calibration is only applicable over limited spatial extent. Producing larger maps is operationally limited due to time required to manually calibrate multiple spatial extents over multiple days. This dissertation develops techniques which automatically detect dry and wet pixels. LANDSAT imagery is used because it resolves dry pixels. Calibrations using 1) only dry pixels and 2) including wet pixels are developed. Snapshots of retrieved evaporative fraction and actual evapotranspiration are compared to eddy covariance measurements for five study areas in Florida: 1) Big Cypress 2) Disney Wilderness 3) Everglades 4) near Gainesville, FL. 5) Kennedy Space Center. The sensitivity of evaporative fraction to temperature, available energy, roughness length and wind speed is tested. A technique for temporally interpolating evapotranspiration by fusing LANDSAT and MODIS is developed and tested. The automated algorithm is successful at detecting wet and dry pixels (if they exist). Including wet pixels in calibration and assuming constant atmospheric conductance significantly improved results for all but Big Cypress and Gainesville. Evaporative fraction is not very sensitive to instantaneous available energy but it is sensitive to temperature when wet pixels are included because temperature is required for estimating wet pixel

  13. Global daily reference evapotranspiration modeling and evaluation

    USGS Publications Warehouse

    Senay, G.B.; Verdin, J.P.; Lietzow, R.; Melesse, Assefa M.

    2008-01-01

    Accurate and reliable evapotranspiration (ET) datasets are crucial in regional water and energy balance studies. Due to the complex instrumentation requirements, actual ET values are generally estimated from reference ET values by adjustment factors using coefficients for water stress and vegetation conditions, commonly referred to as crop coefficients. Until recently, the modeling of reference ET has been solely based on important weather variables collected from weather stations that are generally located in selected agro-climatic locations. Since 2001, the National Oceanic and Atmospheric Administration's Global Data Assimilation System (GDAS) has been producing six-hourly climate parameter datasets that are used to calculate daily reference ET for the whole globe at 1-degree spatial resolution. The U.S. Geological Survey Center for Earth Resources Observation and Science has been producing daily reference ET (ETo) since 2001, and it has been used on a variety of operational hydrological models for drought and streamflow monitoring all over the world. With the increasing availability of local station-based reference ET estimates, we evaluated the GDAS-based reference ET estimates using data from the California Irrigation Management Information System (CIMIS). Daily CIMIS reference ET estimates from 85 stations were compared with GDAS-based reference ET at different spatial and temporal scales using five-year daily data from 2002 through 2006. Despite the large difference in spatial scale (point vs. ???100 km grid cell) between the two datasets, the correlations between station-based ET and GDAS-ET were very high, exceeding 0.97 on a daily basis to more than 0.99 on time scales of more than 10 days. Both the temporal and spatial correspondences in trend/pattern and magnitudes between the two datasets were satisfactory, suggesting the reliability of using GDAS parameter-based reference ET for regional water and energy balance studies in many parts of the world

  14. The Role of Evapotranspiration on Soil Moisture Depletion in a Small Alaskan Subarctic Farm

    NASA Astrophysics Data System (ADS)

    Ruairuen, W.; Fochesatto, G. J.; Sparrow, E. B.; Schnabel, W.; Zhang, M.

    2013-12-01

    At high latitudes the period for agriculture production is very short (110 frost-free days) and strongly depends on the availability of soil water content for vegetables to grow. In this context the evapotranspiration (ET) cycle is key variable underpinning mass and energy balance modulating therefore moisture gradients and soil dryness. Evapotranspiration (ET) from field-grown crops water stress is virtually unknown in the subarctic region. Understanding ET cycles in high latitude agricultural ecosystem is essential in terms of water management and sustainability and projection of agricultural activity. To investigate the ET cycle in farming soils a field experiment was conducted in the summer of 2012 and 2013 at the University of Alaska Fairbanks Agricultural and Forestry Experiment Station combining micrometeorological and hydrological measurements. In this case experimental plots of lettuce (Lactuca sativa) plants were grown. The experiment evaluated several components of the ET cycle such as actual evapotranspiration, reference evaporation, pan evaporation as well as soil water content and temperature profiles to link them to the vegetable growing functions. We investigated the relationship of soil moisture content and crop water use across the growing season as a function of the ET cycle. Soil water depletion was compared to daily estimates of water loss by ET during dry and wet periods. We also investigated the dependence of ET on the atmospheric boundary layer flow patterns set by the synoptic large scale weather patterns.

  15. Effect of Microclimates on Evapotranspiration Rates, Energy Balance, and Water Use Estimation in the Sacramento-San Joaquin Delta, California, USA

    NASA Astrophysics Data System (ADS)

    Anderson, F.; Bergamaschi, B. A.; Von Dessonneck, T.; Keating, K.; Verfaillie, J. G.; Hatala, J.; Knox, S.; Baldocchi, D. D.; Fujii, R.

    2012-12-01

    Research involving the atmospheric-surface exchange of greenhouse gases in California's Sacramento-San Joaquin Delta (Delta) has primarily focused on peat oxidation and resulting subsidence from over a century of agricultural land management practices. Currently there is a network of flux towers used to investigate management plans to mitigate subsidence and, in some cases, increase land elevation. Nevertheless, Delta land elevations have decreased by over 10m and water resources are largely allocated to maintain levee stability and prevent salt-water intrusion into the Delta, the source of fresh water to over to 22 million Southern Californians. These water allocations are potentially modeled using outdated evapotranspiration (ET) rates. The network of flux towers in the Delta has provided researchers the ability to calculate the atmospheric exchange of water vapor from a variety of land surfaces. From these results, ET rates are found to be reduced compared to the same land surface measurements outside the Delta region and are most likely due to the Delta's unique microclimate. In the summertime, this area is an oasis of cool, moist air (Delta Breeze) when compared to other areas in the Sacramento and San Joaquin Valleys, where daytime high temperatures are often 5 to 10°C higher. The air mass that influences the delta region is formed from a complex interaction between the sub-tropical Pacific High pressure system, upwelling along the California coast, upper atmospheric westerlies, and the unique break in the California Coastal range (i.e. the San Francisco Bay). In general, ET rates are lower than the surrounding geography, as the onset of the "Delta Breeze" occurs in the afternoons, increasing the sensible heat exchange and reducing the energy available for latent heat. Current ET rates were calculated using eddy covariance flux systems for a variety of land uses within the Delta: agricultural crops (corn, rice, alfalfa, and irrigated pasture), a newly

  16. Estimation of rainfall interception in grassland using eddy flux measurements

    NASA Astrophysics Data System (ADS)

    Maruyama, A.; Miyazawa, Y.; Inoue, A.

    2014-12-01

    Rainfall interception plays an important role in the water cycle in natural ecosystems. Interception by the forest canopies have been widely observed or estimated over various ecosystems, such as tropical rainforest, evergreen forest and deciduous forest. However interception by the short canopies, e.g. shrubby plant, grassland and crop, has been rarely observed since it has been difficult to obtain reliable precipitation measurements under the canopy. In this study, we estimated monthly and annual rainfall interception in grassland using evapotranspiration data of eddy flux measurements. Experiments were conducted in grassland (Italian ryegrass) from 2010 to 2012 growing season in Kumamoto, Japan. Evapotranspiration (latent heat flux) were observed throughout the year based on the eddy covariance technique. A three dimensional sonic anemometer and an open path CO2/H2O analyzer were used to calculate 30 min flux. Other meteorological factors, such as air temperature, humidity and solar radiation, were also observed. Rainfall interception was estimated as follows. 1) Using evapotranspiration data during dry period, environmental response of surface conductance (gc) was inversely calculated based on the big-leaf model. 2) Evapotranspiration without interception during precipitation period was estimated using above model and environmental response of gc. 3) Assuming that evaporation of intercepted rainfall is equal to the difference in evapotranspiration between above estimation and actual measurements, rainfall interception was estimated over experimental period. The account of rainfall interception in grassland using this technique will be presented at the meeting.

  17. Regional ground-water evapotranspiration and ground-water budgets, Great Basin, Nevada

    USGS Publications Warehouse

    Nichols, William D.

    2000-01-01

    PART A: Ground-water evapotranspiration data from five sites in Nevada and seven sites in Owens Valley, California, were used to develop equations for estimating ground-water evapotranspiration as a function of phreatophyte plant cover or as a function of the depth to ground water. Equations are given for estimating mean daily seasonal and annual ground-water evapotranspiration. The equations that estimate ground-water evapotranspiration as a function of plant cover can be used to estimate regional-scale ground-water evapotranspiration using vegetation indices derived from satellite data for areas where the depth to ground water is poorly known. Equations that estimate ground-water evapotranspiration as a function of the depth to ground water can be used where the depth to ground water is known, but for which information on plant cover is lacking. PART B: Previous ground-water studies estimated groundwater evapotranspiration by phreatophytes and bare soil in Nevada on the basis of results of field studies published in 1912 and 1932. More recent studies of evapotranspiration by rangeland phreatophytes, using micrometeorological methods as discussed in Chapter A of this report, provide new data on which to base estimates of ground-water evapotranspiration. An approach correlating ground-water evapotranspiration with plant cover is used in conjunction with a modified soil-adjusted vegetation index derived from Landsat data to develop a method for estimating the magnitude and distribution of ground-water evapotranspiration at a regional scale. Large areas of phreatophytes near Duckwater and Lockes in Railroad Valley are believed to subsist on ground water discharged from nearby regional springs. Ground-water evapotranspiration by the Duckwater phreatophytes of about 11,500 acre-feet estimated by the method described in this report compares well with measured discharge of about 13,500 acre-feet from the springs near Duckwater. Measured discharge from springs near Lockes

  18. Evapotranspiration from areas of native vegetation in west-central Florida

    USGS Publications Warehouse

    Bidlake, W.R.; Woodham, W.M.; Lopez, M.A.

    1993-01-01

    A study was made to examine the suitability of three different micrometeorological methods for estimating evapotranspiration from selected areas of native vegetation in west-central Florida and to estimate annual evapotranspiration from those areas. Evapotranspiration was estimated using the energy- balance Bowen ratio and eddy correlation methods. Potential evapotranspiration was computed using the Penman equation. The energy-balance Bowen ratio method was used to estimate diurnal evapotrans- piration at unforested sites and yielded reasonable results; however, measurements indicated that the magnitudes of air temperature and vapor-pressure gradients above the forested sites were too small to obtain reliable evapotranspiration measurements with the energy balance Bowen ratio system. Analysis of the surface energy-balance indicated that sensible and latent heat fluxes computed using standard eddy correlation computation methods did not adequately account for available energy. Eddy correlation data were combined with the equation for the surface energy balance to yield two additional estimates of evapotranspiration. Daily potential evapotranspiration and evapotranspira- tion estimated using the energy-balance Bowen ratio method were not correlated at a unforested, dry prairie site, but they were correlated at a marsh site. Estimates of annual evapotranspiration for sites within the four vegetation types, which were based on energy-balance Bowen ratio and eddy correlation measurements, were 1,010 millimeters for dry prairie sites, 990 millimeters for marsh sites, 1,060 millimeters for pine flatwood sites, and 970 millimeters for a cypress swamp site.

  19. Estimating the economic impact of a repository from scenario-based surveys: Models of the relation of stated intent to actual behavior

    SciTech Connect

    Easterling, D.; Morwitz, V.; Kunreuther, H.

    1990-12-01

    The task of estimating the economic impact of a facility as novel and long-lived as a high-level nuclear waste (HLNW) repository is fraught with uncertainty. One approach to the forecasting problems is to survey economic agents as to how they would respond when confronted with hypothetical repository scenarios. A series of such studies conducted for the state of Nevada have examined the potential impact of a Yucca Mountain repository on behavior such as planning conventions, attending conventions, vacationing, outmigration, immigration, and business location. In each case, respondents drawn from a target population report on whether a particular repository event (either some form of an accident, or simply the presence of the facility) would cause them to act any differently than they otherwise would. The responses to such a survey provide an indication of whether or not economic behavior would be altered. However, the analysis is inevitably plagued with the question of how much credence to place in the reports of intended behavior; can we believe what people report they would do in a hypothetical situation? The present study examines a more precise version of this question regarding the validity of stated intent data. After reviewing a variety of literature in the area of intent versus actual behavior, we provide an answer to the question, ``What levels of actual behavior are consistent with the intent data that have been observed in the repository surveys?`` More formally, we assume that we are generally interested in predicting the proportion of a sample who will actually perform a target behavior. 86 refs., 6 figs., 9 tabs.

  20. First insights into disassembled "evapotranspiration"

    NASA Astrophysics Data System (ADS)

    Chormański, Jarosław; Kleniewska, Małgorzata; Berezowski, Tomasz; Szporak-Wasilewska, Sylwia; Okruszko, Tomasz; Szatyłowicz, Jan; Batelaan, Okke

    2015-04-01

    In this work we present an initial data analysis obtained from a complex tool for measuring water fluxes in wetland ecosystems. The tool was designed to quantify processes related to interception storage on plants leafs. The measurements are conducted by combining readings from various instruments, including: eddy covariance tower (EC), field spectrometer, SapFlow system, rain gauges above and under canopy, soil moisture probes and other. The idea of this set-up is to provide continuous measurement of overall water flux from the ecosystem (EC tower), intercepted water volume and timing (field spectrometers), through-fall (rain gauges above and under canopy), transpiration (SapFlow), evaporation and soil moisture (soil moisture probes). Disassembling the water flux to the above components allows giving more insight to the interception related processes and differentiates them fromthe total evapotranspiration. The measurements are conducted in the Upper Biebrza Basin (NE Poland). The study area is part of the valley and is covered by peat soils (mainly peat moss with the exception of areas near the river) and receives no inundations waters of the Biebrza. The plant community of Agrostietum-Carici caninae has a dominant share here creating an up to 0.6 km wide belt along the river. The area is covered also by Caricion lasiocarpae as well as meadows and pastures Molinio-Arrhenatheretea, Phragmitetum communis. Sedges form a hummock pattern characteristic for the sedge communities in natural river valleys with wetland vegetation. The main result of the measurement set-up will be the analyzed characteristics and dynamics of interception storage for sedge ecosystems and a developed methodology for interception monitoring by use spectral reflectance technique. This will give a new insight to processes of evapotranspiration in wetlands and its component transpiration, evaporation from interception and evaporation from soil. Moreover, other important results of this project

  1. Subdaily evapotranspiration rate calculation from streamflow summer diel signal

    NASA Astrophysics Data System (ADS)

    Gribovszki, Z.; Kalicz, P.; Szilágyi, J.

    2009-04-01

    Diel signal of hydrological variables (e.g., shallow groundwater level or streamflow rate) are rarely investigated in the hydrologic literature although these short-term fluctuations may incorporate useful information for the characterization of hydro-ecological systems. Riparian vegetation (especially forest) typically has a great influence on groundwater level and groundwater-sustained baseflow, therefore calculation of the correct evapotranspiration rates is very important for natural protection tasks and water resources management. Recently a new technique was developed by us to calculate daily or even subdaily evapotranspiration rates from groundwater-level measurements, and that method now is modified to estimate evapotranspiration rates from the baseflow diel signal only. The method was successfully tested with hydro-meteorological data from the Hidegvíz Valley experimental catchment in the Sopron Hills at the western border of Hungary. The evapotranspiration rates calculated from the groundwater signal only, are typically (a magnitude) higher than those obtained with an already existing method. With the application of our new technique exploiting the baseflow diel signal of the stream, evapotranspiration rates, very similar to those gained from groundwater level readings and the Penman-Monteith equation, can be obtained. Keywords: baseflow diel signal, evapotranspiration, riparian zone

  2. Geostatistical improvements of evapotranspiration spatial information using satellite land surface and weather stations data

    NASA Astrophysics Data System (ADS)

    de Carvalho Alves, Marcelo; de Carvalho, Luiz Gonsaga; Vianello, Rubens Leite; Sediyama, Gilberto C.; de Oliveira, Marcelo Silva; de Sá Junior, Arionaldo

    2013-07-01

    The objective of the present study was to use the simple cokriging methodology to characterize the spatial variability of Penman-Monteith reference evapotranspiration and Thornthwaite potential evapotranspiration methods based on Moderate Resolution Imaging Spetroradiometer (MODIS) global evapotranspiration products and high-resolution surfaces of WordClim temperature and precipitation data. The climatic element data referred to 39 National Institute of Meteorology climatic stations located in Minas Gerais state, Brazil and surrounding states. The use of geostatistics and simple cokriging technique enabled the characterization of the spatial variability of the evapotranspiration providing uncertainty information on the spatial prediction pattern. Evapotranspiration and precipitation surfaces were implemented for the climatic classification in Minas Gerais. Multivariate geostatistical determined improvements of evapotranspiration spatial information. The regions in the south of Minas Gerais derived from the moisture index estimated with the MODIS evapotranspiration (2000-2010), presented divergence of humid conditions when compared to the moisture index derived from the simple kriged and cokriged evapotranspiration (1961-1990), indicating climate change in this region. There was stronger pattern of crossed covariance between evapotranspiration and precipitation rather than temperature, indicating that trends in precipitation could be one of the main external drivers of the evapotranspiration in Minas Gerais state, Brazil.

  3. Modeling landscape evapotranspiration by integrating land surface phenology and a water balance algorithm

    USGS Publications Warehouse

    Senay, Gabriel B.

    2008-01-01

    The main objective of this study is to present an improved modeling technique called Vegetation ET (VegET) that integrates commonly used water balance algorithms with remotely sensed Land Surface Phenology (LSP) parameter to conduct operational vegetation water balance modeling of rainfed systems at the LSP’s spatial scale using readily available global data sets. Evaluation of the VegET model was conducted using Flux Tower data and two-year simulation for the conterminous US. The VegET model is capable of estimating actual evapotranspiration (ETa) of rainfed crops and other vegetation types at the spatial resolution of the LSP on a daily basis, replacing the need to estimate crop- and region-specific crop coefficients.

  4. Estimating hourly crop ET using a two-source energy balance model and multispectral airborne imagery

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Efficient water use through improved irrigation scheduling is expected to moderate fast declining groundwater levels and improve sustainability of the Ogallala Aquifer. Thus, an accurate estimation of spatial actual evapotranspiration (ET) is needed for this purpose. Therefore, during 2007, the Bush...

  5. Spatial and temporal variation in evapotranspiration using Raman lidar

    NASA Astrophysics Data System (ADS)

    Eichinger, W. E.; Cooper, D. I.; Hipps, L. E.; Kustas, W. P.; Neale, C. M. U.; Prueger, J. H.

    2006-02-01

    The Los Alamos Raman lidar has been used to make high resolution (25 m) estimates of the evapotranspiration rate over adjacent corn and soybean canopies. The lidar makes three-dimensional measurements of the water vapor content of the atmosphere directly above the canopy that are inverted using Monin-Obukhov similarity theory. This may be used to examine the relationship between evapotranspiration and surface moisture/soil type. Lidar estimates of evapotranspiration reveal a high degree of spatial variability over corn and soybean fields that may be associated with small elevation changes in the area. The spatial structure of the variability is characterized using a structure function and correlation function approach. The power law relationship found by other investigators for soil moisture is not clear in the data for evapotranspiration, nor is the data a straight line over the measured lags. The magnitude of the structure function and the slope changes with time of day, with a probable connection to the amount of evapotranspiration and the spatial variability of the water vapor source. The data used was taken during the soil moisture-atmosphere coupling experiment (SMACEX) conducted in the Walnut Creek Watershed near Ames, Iowa in June and July 2002.

  6. Combining surface reanalysis and remote sensing data for monitoring evapotranspiration

    NASA Astrophysics Data System (ADS)

    Marshall, M.; Tu, K.; Funk, C.; Michaelsen, J.; Williams, P.; Williams, C.; Ardö, J.; Marie, B.; Cappelaere, B.; Grandcourt, A.; Nickless, A.; Nouvellon, Y.; Scholes, R.; Kutsch, W.

    2012-02-01

    Climate change is expected to have the greatest impact on the world's poor. In the Sahel, a climatically sensitive region where rain-fed agriculture is the primary livelihood, expected decreases in water supply will increase food insecurity. Studies on climate change and the intensification of the water cycle in sub-Saharan Africa are few. This is due in part to poor calibration of modeled actual evapotranspiration (AET), a key input in continental-scale hydrologic models. In this study, a model driven by dynamic canopy AET was combined with the Global Land Data Assimilation System realization of the NOAH Land Surface Model (GNOAH) wet canopy and soil AET for monitoring purposes in sub-Saharan Africa. The performance of the hybrid model was compared against AET from the GNOAH model and dynamic model using eight eddy flux towers representing major biomes of sub-Saharan Africa. The greatest improvements in model performance are at humid sites with dense vegetation, while performance at semi-arid sites is poor, but better than individual models. The reduction in errors using the hybrid model can be attributed to the integration of a dynamic vegetation component with land surface model estimates, improved model parameterization, and reduction of multiplicative effects of uncertain data.

  7. Combining surface reanalysis and remote sensing data for monitoring evapotranspiration

    USGS Publications Warehouse

    Marshall, M.; Tu, K.; Funk, C.; Michaelsen, J.; Williams, Pat; Williams, C.; Ardö, J.; Marie, B.; Cappelaere, B.; Grandcourt, A.; Nickless, A.; Noubellon, Y.; Scholes, R.; Kutsch, W.

    2012-01-01

    Climate change is expected to have the greatest impact on the world's poor. In the Sahel, a climatically sensitive region where rain-fed agriculture is the primary livelihood, expected decreases in water supply will increase food insecurity. Studies on climate change and the intensification of the water cycle in sub-Saharan Africa are few. This is due in part to poor calibration of modeled actual evapotranspiration (AET), a key input in continental-scale hydrologic models. In this study, a model driven by dynamic canopy AET was combined with the Global Land Data Assimilation System realization of the NOAH Land Surface Model (GNOAH) wet canopy and soil AET for monitoring purposes in sub-Saharan Africa. The performance of the hybrid model was compared against AET from the GNOAH model and dynamic model using eight eddy flux towers representing major biomes of sub-Saharan Africa. The greatest improvements in model performance are at humid sites with dense vegetation, while performance at semi-arid sites is poor, but better than individual models. The reduction in errors using the hybrid model can be attributed to the integration of a dynamic vegetation component with land surface model estimates, improved model parameterization, and reduction of multiplicative effects of uncertain data.

  8. Evapotranspiration Estimates for Deficit Irrigated Corn

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Water deficits must be imposed on crops during non-critical growth periods to maximize net economic output per unit of water consumed by the plant. The reference ET-crop coefficient procedure widely used for managing fully irrigated crops would be easiest to implement for irrigation management of d...

  9. Dynamics of heat storage in evapotranspiration estimate

    Technology Transfer Automated Retrieval System (TEKTRAN)

    One of the widely discussed reasons for a lack of surface energy balance closure when using eddy covariance is neglect of storage term elements. Storage as related to the surface energy balance refers to all heat stored below the observation level of eddies. It represents the sum of several componen...

  10. Seasonal energy and evapotranspiration partitioning in a desert vineyard

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The challenge of partitioning energy and evapotranspiration (ET) components was addressed over a season (bud break till harvest) in a wine grape vineyard located in an extreme arid region. A below canopy energy balance approach was applied to continuously estimate evaporation from the soil (E) while...

  11. Evapotranspiration (ET) covers.

    PubMed

    Rock, Steve; Myers, Bill; Fiedler, Linda

    2012-01-01

    Evapotranspiration (ET) cover systems are increasingly being used at municipal solid waste (MSW) landfills, hazardous waste landfills, at industrial monofills, and at mine sites. Conventional cover systems use materials with low hydraulic permeability (barrier layers) to minimize the downward migration of water from the surface to the waste (percolation), ET cover systems use water balance components to minimize percolation. These cover systems rely on soil to capture and store precipitation until it is either transpired through vegetation or evaporated from the soil surface. Compared to conventional membrane or compacted clay cover systems, ET cover systems are expected to cost less to construct. They are often aesthetic because they employ naturalized vegetation, require less maintenance once the vegetative system is established, including eliminating mowing, and may require fewer repairs than a barrier system. All cover systems should consider the goals of the cover in terms of protectiveness, including the pathways of risk from contained material, the lifecycle of the containment system. The containment system needs to be protective of direct contact of people and animals with the waste, prevent surface and groundwater water pollution, and minimize release of airborne contaminants. While most containment strategies have been based on the dry tomb strategy of keeping waste dry, there are some sites where adding or allowing moisture to help decompose organic waste is the current plan. ET covers may work well in places where complete exclusion of precipitation is not needed. The U.S. EPA Alternative Cover Assessment Program (ACAP), USDOE, the Nuclear Regulatory Commission, and others have researched ET cover design and efficacy, including the history of their use, general considerations in their design, performance, monitoring, cost, current status, limitations on their use, and project specific examples. An on-line database has been developed with information

  12. Satellite-based monitoring of cotton evapotranspiration

    NASA Astrophysics Data System (ADS)

    Dalezios, Nicolas; Dercas, Nicholas; Tarquis, Ana Maria

    2016-04-01

    Water for agricultural use represents the largest share among all water uses. Vulnerability in agriculture is influenced, among others, by extended periods of water shortage in regions exposed to droughts. Advanced technological approaches and methodologies, including remote sensing, are increasingly incorporated for the assessment of irrigation water requirements. In this paper, remote sensing techniques are integrated for the estimation and monitoring of crop evapotranspiration ETc. The study area is Thessaly central Greece, which is a drought-prone agricultural region. Cotton fields in a small agricultural sub-catchment in Thessaly are used as an experimental site. Daily meteorological data and weekly field data are recorded throughout seven (2004-2010) growing seasons for the computation of reference evapotranspiration ETo, crop coefficient Kc and cotton crop ETc based on conventional data. Satellite data (Landsat TM) for the corresponding period are processed to estimate cotton crop coefficient Kc and cotton crop ETc and delineate its spatiotemporal variability. The methodology is applied for monitoring Kc and ETc during the growing season in the selected sub-catchment. Several error statistics are used showing very good agreement with ground-truth observations.

  13. Evapotranspiration studies for protective barriers: Experimental plans

    SciTech Connect

    Link, S.O.; Waugh, W.J.

    1989-11-01

    This document describes a general theory and experimental plans for predicting evapotranspiration in support of the Protective Barrier Program. Evapotranspiration is the combined loss of water from plants and soil surfaces to the atmosphere. 45 refs., 1 fig., 4 tabs.

  14. An original interpretation of the wet edge of the surface temperature-albedo space to estimate crop evapotranspiration (SEB-1S), and its validation over an irrigated area in northwestern Mexico

    NASA Astrophysics Data System (ADS)

    Merlin, O.

    2013-09-01

    The space defined by the pair surface temperature (T) and surface albedo (α), and the space defined by the pair T and fractional green vegetation cover (fvg) have been extensively used to estimate evaporative fraction (EF) from solar/thermal remote sensing data. In both space-based approaches, evapotranspiration (ET) is estimated as remotely sensed EF times the available energy. For a given data point in the T-α space or in the T-fvg space, EF is derived as the ratio of the distance separating the point from the line identified as the dry edge to the distance separating the dry edge and the line identified as the wet edge. The dry and wet edges are classically defined as the upper and lower limit of the spaces, respectively. When investigating side by side the T-α and the T-fvg spaces, one observes that the range covered by T values on the (classically determined) wet edge is different for both spaces. In addition, when extending the wet and dry lines of the T-α space, both lines cross at α ≈ 0.4 although the wet and dry edges of the T-fvg space never cross for 0 ≤ fvg < 1. In this paper, a new ET (EF) model (SEB-1S) is derived by revisiting the classical physical interpretation of the T-α space to make its wet edge consistent with that of the T-fvg space. SEB-1S is tested over a 16 km by 10 km irrigated area in northwestern Mexico during the 2007-2008 agricultural season. The classical T-α space-based model is implemented as benchmark to evaluate the performance of SEB-1S. Input data are composed of ASTER (Advanced Spaceborne Thermal Emission and Reflection radiometer) thermal infrared, Formosat-2 shortwave, and station-based meteorological data. The fluxes simulated by SEB-1S and the classical T-α space-based model are compared on seven ASTER overpass dates with the in situ measurements collected at six locations within the study domain. The ET simulated by SEB-1S is significantly more accurate and robust than that predicted by the classical T

  15. Potential Evapotranspiration on Tutuila, American Samoa

    USGS Publications Warehouse

    Izuka, Scott K.; Giambelluca, Thomas W.; Nullet, Michael A.

    2005-01-01

    Data from nine widely distributed climate stations were used to assess the distribution of potential evapotranspiration on the tropical South Pacific island of Tutuila, American Samoa. Seasonal patterns of climate data in this study differed in detail from available long-term data because the monitoring period of each station in this study was only 1 to 5 years, but overall climate conditions during the monitoring period (1999-2004) are representative of normal conditions. Potential evapotranspiration shows a diurnal pattern. On average, potential evapotranspiration in the daytime, when net radiation is the dominant controlling factor, constitutes 90 percent or more of the total daily potential evapotranspiration at each station. Positive heat advection from the ocean contributes to potential evapotranspiration at at least one station, and possibly other stations, in this study. Seasonal variation of potential evapotranspiration is linked to seasonal daylight duration. Spatial variation of potential evapotranspiration, however, is linked primarily to orographic cloud cover. Potential evapotranspiration on Tutuila is lowest in the interior of the island, where rainfall is higher, cloud cover is more frequent, and net radiation is lower than along the coasts. Potential evapotranspiration is highest along the southern and eastern coasts of the island, where rainfall is lower and cloud cover less frequent. The gradient from areas of high to low potential evapotranspiration is steepest in November and December, when island-wide potential evapotranspiration is highest, and less steep in June and July, when island-wide potential evapotranspiration is lowest. Comparison of potential evapotranspiration to rainfall indicates that evapotranspiration processes on Tutuila have the potential to remove from 23 to 61 percent of the water brought by rainfall. In lower-rainfall coastal locations, potential evapotranspiration can be 50 percent or more of rainfall, whereas in higher

  16. Daily evapotranspiration assessment by means of residual surface energy balance modeling: A critical analysis under a wide range of water availability

    NASA Astrophysics Data System (ADS)

    Cammalleri, C.; Ciraolo, G.; La Loggia, G.; Maltese, A.

    2012-07-01

    SummaryAn operational use of the actual evapotranspiration assessed by remote sensing approaches requires the integration of instantaneous fluxes to daily values. This is commonly achieved under the hypotheses of daytime self-preservation of evaporative fraction and negligible daily ground heat flux. The aim of this study is to evaluate the effect of these assumptions on estimate daily evapotranspiration over a full phenological cycle, including phases characterized by significant changes both in net radiation and vegetation cover. To assess the reliability of these hypotheses, the observations made by a flux tower, installed within a homogeneous field of cereal located in the valley part of the Imera Meridionale basin, were analyzed. Additionally, the widely-known SEBAL (Surface Energy Balance Algorithm for Land) model was applied on the same study area by means of four MODIS (MODerate-resolution Imaging Spectroradiometer) images selected across a three-rainfall events period in March-April 2007 with the aim to analyze the consistency of its estimates in an operational study case under different conditions of water availability. The analysis of in situ data highlights errors on 24-h evapotranspiration characterized by an average value of 20% due to daily soil heat flux neglecting; whereas, the hypothesis of evaporative fraction self-preservation causes an average error equal to -16%. Moreover, the analysis of the observations suggests that a compensation effect of the errors related to each hypothesis occurs in most cases (56%), and this makes suitable the approach for practical daily integration purposes. The application of the SEBAL model at basin scale shows a good capability to detect the increase of the actual 24-h evapotranspiration under the tested hypotheses, also in the case of instantaneous evaporative fraction and daily net radiation not derived form in situ observations.

  17. Potential Evapotranspiration as a Source of Uncertainty and Bias in Hydrologic Impact Analyses

    NASA Astrophysics Data System (ADS)

    Milly, P. C. D.

    2015-12-01

    The diversity of commonly used potential evapotranspiration (PET) models contributes uncertainty in the estimation of hydrologic response to anthropogenic climate change. The temperature sensitivity of six commonly used PET equations (Hamon, Oudin, Penman-Monteith, Priestley-Taylor, Samani-Hargreaves, and Thornthwaite) is readily shown to vary by almost an order of magnitude, with energy-unconstrained (i.e., temperature-based) methods showing the largest sensitivity. The change in annual multimodel (Coupled Model Intercomparison Project, Phase 5) PET under Representative Concentration Pathway 8.5 from 1981-2000 to 2081-2100 is typically 10-20% (20-40%) in the low (high) latitudes according to the physics-based Penman-Monteith (ASCE Standardized Reference Evapotranspiration) equation, but 20-40% (20-80%) according to the empirical, temperature-based Hamon equation. Radiation-based Priestley-Taylor changes are smaller than both of these, while empirical, temperature-based Thornthwaite changes are larger than both. These differences in PET change translate to large differences in change of water availability; when combined with a form of the Budyko water-balance relation, the PET methods predict a wide range of runoff changes. Furthermore, all PET methods result in bias that indicates drier conditions globally than those computed by the climate models themselves, and all PET methods overestimate the changes in actual evapotranspiration in non-water-stressed seasons/regions relative to the changes in the climate models. We conclude that use of PET methods that are inappropriate for climate-change applications is a source not only of uncertainty, but also of more drying than suggested by climate models, in hydrologic impact analyses. In view of the bias, it is advised that a no-PET-change analysis be used to define a wet upper bound on potential hydrologic impacts.

  18. Evapotranspiration from successional vegetation in a deforested area of the Lake Wales Ridge, Florida

    USGS Publications Warehouse

    Sumner, D.M.

    1996-01-01

    The suitability of three evapotranspiration models (Penman-Monteith, Penman, and a modified Priestley-Taylor) was evaluated at a site ofsuccessional vegetation in a deforested area of theLake Wales Ridge, Florida. Eddy correlation mea surements of evapotranspiration made during 22approximately 1-day periods at a temporal resolu tion of 20 minutes from September 1993 to August 1994 were used to calibrate the evapotranspiration models. Three variants of the eddy correlation method that ascribe measurement error to three different sources were considered in the analysis. The Penman-Monteith and modified Priestley- Taylor models were successful in approximating measured 20-minute values of evapotranspiration (r2  0.918). The most suc cessful approaches were the modified Priestley-Taylor model (r2 = 0.972) and a nontraditional and simplified form of the Penman-Monteith model (r2 = 0.967). The Penman approach was unsuccessful as a predictor of evapotranspiration. The evapotranspiration models were used to estimate evapotranspiration between measure ments. When evapotranspiration values measured with a Bowen ratio variant of the eddy correlation method were used for model calibration, estimated daily evapotranspiration rates varied sea sonally ranging from 0.2 millimeters per day (0.008 inch per day) in late December 1993 to5 millimeter per day (0.2 inch per day) in mid-July 1994. Annual evapotranspiration (September 15, 1993, to September 15, 1994) was estimated to be about 680 millimeters (27 inches).Evapotranspiration models calibrated to the stan dard eddy correlation method and to an energy- balance residual variant provided estimates ofannual evapotranspiration that were about 10 per cent lower and higher, respectively. These dataindicate that of the 1,320 millimeters (52 inches)of precipitation during the 1-year period, about 570 to 700 millimeters (22 to 28 inches) recharged the surficial aquifer. Evapotranspiration at this study site probably defines the lower

  19. Dominant controls of diel discharge fluctuations: viscosity changes vs. evapotranspiration

    NASA Astrophysics Data System (ADS)

    Schwab, Michael; Klaus, Julian; Pfister, Laurent; Weiler, Markus

    2016-04-01

    Diel fluctuations in stream discharge are a long known but rarely investigated phenomena that is known to be driven by various processes, such as precipitation, evapotranspiration, freeze-thawing cycles and sometimes viscosity fluctuations. Improving our understanding of how these processes control diel discharge fluctuations is actually key to solving other questions related to diel cycles of biogeochemicals as well as the temporal variability of fundamental hydrological functions in a catchment. In the forested Weierbach catchment (0.47 km2) in Luxembourg we showed that seasonal changes in the relative importance of viscosity fluctuations of inflowing water to the creek and evapotranspiration are the key controls of diel discharge fluctuations. In the dormant season, we observed daily discharge maxima in the afternoon, albeit temperatures remained persistently above zero and no snow cover was present, which excludes freeze-thawing cycles as the driving factor. However, we showed that diel water temperature fluctuations in the subsurface and therefore viscosity fluctuations in the upper layer of the riparian zone can be an explanation for the daily discharge maxima in the afternoon. In the transition period between dormant and growing season, the counteracting viscosity and evapotranspiration processes cancel each other out resulting in no diel discharge fluctuations. Subsequently, during the growing season, the higher relative importance of evapotranspiration is guiding the diel discharge pattern; nevertheless, the viscosity effect might still be invisibly present. We believe this finding to be of relevance for better understanding hydrological functions in catchments and for analyzing daily fluctuations of biogeochemicals in stream water.

  20. Statistical Analysis of Meteorological Data to Assess Evapotranspiration and Infiltration at the Rifle Site, CO, USA

    NASA Astrophysics Data System (ADS)

    Faybishenko, B.; Long, P. E.; Tokunaga, T. K.; Christensen, J. N.

    2015-12-01

    Net infiltration to the vadose zone, especially in arid or semi-arid climates, is an important control on microbial activity and solute and green house gas fluxes. To assess net infiltration, we performed a statistical analysis of meteorological data as the basis for hydrological and climatic investigations and predictions for the Rifle site, Colorado, USA, located within a floodplain in a mountainous region along the Colorado River, with a semi-arid climate. We carried out a statistical analysis of meteorological 30-year time series data (1985-2015), including: (1) precipitation data, taking into account the evaluation of the snowmelt, (2) evaluation of the evapotranspiration (reference and actual), (3) estimation of the multi-time-scalar Standardized Precipitation-Evapotranspiration Index (SPEI), (4) evaluation of the net infiltration rate, and (5) corroborative analysis of calculated net infiltration rate and groundwater recharge from radioisotopic measurements from samples collected in 2013. We determined that annual net infiltration percentage of precipitation varies from 4.7% to ~18%, with a mean of ~10%, and concluded that calculations of net infiltration based on long-term meteorological data are comparable with those from strontium isotopic investigations. The evaluation of the SPEI showed the intermittent pattern of droughts and wet periods over the past 30 years, with a detectable decreasein the duration of droughts with time. Local measurements within the floodplain indicate a recharge gradient with increased recharge closer to the Colorado River.

  1. Surface Energy Balance Based Evapotranspiration Mapping in the Texas High Plains

    PubMed Central

    Gowda, Prasanna H.; Chávez, José L.; Howell, Terry A.; Marek, Thomas H.; New, Leon L.

    2008-01-01

    Agriculture on the Texas High Plains (THP) uses approximately 89% of groundwater withdrawals from the Ogallala Aquifer. Consequently, groundwater levels are declining faster than the recharge rate. Therefore, efficient agricultural water use is essential for economic viability and sustainability of the THP. Accurate regional evapotranspiration (ET) maps would provide valuable information on actual crop water use. In this study, METRIC (Mapping Evapotranspiration at High Resolution using Internalized Calibration), a remote sensing based ET algorithm, was evaluated for mapping ET in the THP. Two Landsat 5 Thematic Mapper images acquired on 27 June (DOY 178) and 29 July (DOY 210) 2005 were used for this purpose. The performance of the ET model was evaluated by comparing the predicted daily ET with values derived from soil moisture budget at four commercial agricultural fields. Daily ET estimates resulted with a prediction error of 12.7±8.1% (mean bias error ± root mean square error) on DOY 178 and -4.7±9.4% on DOY 210 when compared with ET derived from measured soil moisture through the soil water balance. These results are good considering the prevailing advective conditions in the THP. METRIC have the potential to be used for mapping regional ET in the THP region. However, more evaluation is needed under different agroclimatological conditions.

  2. Mapping Evapotranspiration in Hawai';i

    NASA Astrophysics Data System (ADS)

    Giambelluca, T. W.; Shuai, X.; Barnes, M.; Longman, R. J.; Miura, T.; Chen, Q.; Alliss, R. J.; Frazier, A. G.

    2013-12-01

    The hydrological cycle in Hawai';i determines the timing and amount of water flows that affect aquatic and near-shore marine ecosystems, and provides water for domestic and industrial uses. Rainfall and fog interception are the principal water sources, while evaporation and transpiration reduce the amount available for streamflow and groundwater recharge. Evapotranspiration (ET) is controlled by climate, vegetation, soil, and water availability, and hence is highly variable in space and time. Understanding of the magnitude and variability of ET is essential for protecting Hawai';i's ecosystems and planning for water resource development and utilization. In this study, ET was estimated at high spatial resolution (250 m), for each hour of the mean diurnal cycle of each month, using the Penman-Monteith approach. Soil evaporation, wet canopy evaporation, and transpiration were estimated separately and summed to get ET. Solar and net radiation were estimated using cloudiness and surface characteristics from satellite remote sensing, clear-sky radiation simulations, and ground-based observations. Other spatial data sets developed or acquired for use in estimating ET included air temperature, relative humidity, wind speed, soil moisture, fractional canopy wetness, fractional vegetation cover, vegetation height, leaf area index, land cover type, and maximum stomatal conductance. More than 12,000 digital maps were produced of climate and hydrological variables in including evapotranspiration and its components. Results show that across the State of Hawai';i mean annual solar radiation varies from 130 to 296 W m-2. Low solar radiation is found along cloudy windward slopes below the trade-wind inversion level and in terrain-shaded valleys, while the highest values occur at the high mountain summits of Mauna Kea and Mauna Loa. ET has a complex spatial pattern reflecting variations in net radiation, moisture availability, and vegetation characteristics. With a few exceptions

  3. Divergence of reference evapotranspiration observations with windy tropical conditions

    NASA Astrophysics Data System (ADS)

    Anderson, R. G.; Wang, D.; Tirado-Corbalá, R.; Zhang, H.; Ayars, J. E.

    2014-06-01

    Standardized reference evapotranspiration (ET) and ecosystem-specific vegetation coefficients are frequently used to estimate actual ET. However, equations for calculating reference ET have not been well validated in tropical environments. We measured ET (ETEC) using Eddy Covariance (EC) towers at two irrigated sugarcane fields on the leeward (dry) side of Maui, Hawaii, USA in contrasting climates. We calculated reference ET at the fields using the short (ET0) and tall (ETr) vegetation versions of the American Society for Civil Engineers (ASCE) equation. The ASCE equations were compared to the Priestley-Taylor ET (ETPT) and ETEC. Reference ET from the ASCE approaches exceeded ETEC during the mid-period (when vegetation coefficients suggest ETEC should exceed reference ET). At the windier tower site, cumulative ETr exceeded ETEC by 854 mm over the course of the mid-period (267 days). At the less windy site, mid-period ETr still exceeded ETEC, but the difference was smaller (443 mm). At both sites, ETPT approximated mid-period ETEC more closely than the ASCE equations ((ETPT-ETEC) < 170 mm). Analysis of applied water and precipitation, soil moisture, leaf stomatal resistance, and canopy cover suggest that the lower observed ETEC was not the result of water stress or reduced vegetation cover. Use of a custom calibrated bulk canopy resistance improved the reference ET estimate and reduced seasonal ET discrepancy relative to ETPT and ETEC for the less windy field and had mixed performance at the windier field. These divergences suggest that modifications to reference ET equations may be warranted in some tropical regions.

  4. Daily lsa-saf evapotranspiration product

    NASA Astrophysics Data System (ADS)

    Arboleda Rodallega, Alirio; Ghilain, Nicolas; Meulenberghs, Francoise

    2010-05-01

    In the framework of the EUMETSAT's Satellite Application Facility on Land Surface Analysis (LSA-SAF), some models have been implemented in view to characterize continental surfaces by using information obtained from MSG and EPS satellites. In this context a method has been developed in order to monitor the flux of water (Evapotranspiration) between the land surface and the atmosphere. The method is based on a physical approach in which radiative data derived from Meteosat Second Generation (MSG) satellites together with land-cover information are used to constrain a physical model of energy exchange between the soil-vegetation system and the atmosphere. The implemented algorithm provides instantaneous ET estimates over four regions defined in the MSG FOV (the defined regions cover Europe, Africa and the west of south America), with MSG spatial resolution (3km at sub satellite point) and a temporal time step of 30 minutes. The scope of the method is limited to evaporation from terrestrial surfaces rather than from lakes or oceans. The instantaneous product has been validated over different vegetation cover and climatic conditions, providing evidence that the algorithm is able to reproduce ET estimates with accuracy equivalent to the accuracy of ET obtained from observations. In 2009 the instantaneous ET product has been declared pre-operational by EUMETSAT, allowing the product to be disseminated to a larger community of users (http://landsaf.meteo.pt). In some areas like agriculture, hydrology, water management, ecology and climate studies the main concern is not instantaneous but accumulated values over days, months or longer periods. To encompass the need for these community of users, a daily ET product in which daily evapotranspiration is obtained as temporal integration of instantaneous values has been developed. In this contribution we will present the methodology used to obtain instantaneous ET estimates and the procedure applied to derive daily

  5. Assessing reference evapotranspiration in a subhumid climate in NE Austria

    NASA Astrophysics Data System (ADS)

    Nolz, Reinhard; Eitzinger, Josef; Cepuder, Peter

    2015-04-01

    Computing reference evapotranspiration and multiplying it with a specific crop coefficient as recommended by the Food and Agriculture Organization of the United Nations (FAO) is the most widely accepted approach to estimate plant water requirements. The standardized form of the well-known FAO Penman-Monteith equation, published by the Environmental and Water Resources Institute of the American Society of Civil Engineers (ASCE-EWRI), is recommended as a standard procedure for calculating reference evapotranspiration. Applied and validated under different climatic conditions it generally achieved good results compared to other methods. However, several studies documented deviations between measured and calculated reference evapotranspiration depending on local environmental conditions. Consequently, it seems advisable to evaluate the model under local environmental conditions. Evapotranspiration was determined at a subhumid site in Austria (48°12'N, 16°34'E; 157 m asl) using a large weighing lysimeter operated at (limited) reference conditions and compared with calculations according to ASCE-EWRI. The lysimeter had an inner diameter of 1.9 m and a hemispherical bottom with a maximum depth of 2.5 m. Seepage water was measured at a free draining outlet using a tipping bucket. Lysimeter mass changes were sensed by a weighing facility with an accuracy of ±0.1 mm. Both rainfall and evapotranspiration were determined directly from lysimeter data using a simple water balance equation. Meteorological data for the ASCE-EWRI model were obtained from a weather station of the Central Institute for Meteorology and Geodynamics, Austria (ZAMG). The study period was from 2005 to 2010, analyses were based upon daily time steps. Daily calculated reference evapotranspiration was generally overestimated at small values, whereas it was rather underestimated when evapotranspiration was large, which is supported also by other studies. In the given case, advection of sensible heat proved

  6. [Evapotranspiration of winter wheat field in North China Plain].

    PubMed

    Guo, Jiaxuan; Li, Yuzhong; Yan, Chang-Rong; Zhao, Quansheng; Mei, Xurong

    2006-12-01

    By using eddy covariance and remote sensing techniques, the relationships between winter wheat soil moisture content and farmland evapotranspiration or canopy temperature were analyzed at field scale under various environmental conditions in the North China Plain. The results showed that when the soil moisture content was below 65% of field capacity, the evaporative fraction under full canopy was low and stable during the middle part of clear days. Under clear sky condition, there was a good non-linear correlation between latent heat flux and crop canopy temperature with diurnal and seasonal patterns. The temperature difference between crop canopy and air as well as the relative evapotranspiration had a close link to the relative moisture content of 0 - 100 cm soil layer. Based on the in situ measurements of daily evapotranspiration amount (ET(d)), daily net radiation flux (Rn(d), mm), average canopy temperature (T(e), degrees C) from 13 : 30 to 14: 00, and daily maximum air temperature (T(a max), degrees C) during the field experiment, the parameters of simplified estimation model for daily evapotranspiration were established.

  7. Evapotranspiration parameterizations at a grass site in Florida, USA

    USGS Publications Warehouse

    Rizou, M.; Sumner, David M.; Nnadi, F.

    2007-01-01

    In spite of the fact that grasslands account for about 40% of the ice-free global terrestrial land cover, their contribution to the surface exchanges of energy and water in local and regional scale is so far uncertain. In this study, the sensitivity of evapotranspiration (ET) and other energy fluxes to wetness variables, namely the volumetric Soil Water Content (SWC) and Antecedent Precipitation Index (API), over a non-irrigated grass site in Central Florida, USA (28.049 N, 81.400 W) were investigated. Eddy correlation and soil water content measurements were taken by USGS (U.S. Geological Survey) at the grass study site, within 100 m of a SFWMD (South Florida Water Management District) weather station. The soil is composed of fine sands and it is mainly covered by Paspalum notatum (bahia grass). Variable soil wetness conditions with API bounds of about 2 to 160 mm and water table levels of 0.03 to 1.22 m below ground surface, respectively, were observed throughout the year 2004. The Bowen ratio exhibited an average of 1 and values larger than 2 during few dry days. The daytime average ET was classified into two stages, first stage (energy-limited) and second stage (water- limited) based on the water availability. The critical values of API and SWC were found to be about 56 mm and 0.17 respectively, with the second one being approximately 33% of the SWC at saturation. The ET values estimated by the simple Priestley-Taylor (PT) method were compared to the actual values. The PT coefficient varied from a low bound of approximately 0.4 to a peak of 1.21. Simple relationships for the PT empirical factor were employed in terms of SWC and API to improve the accuracy of the second stage observations. The results of the ET parameterizations closely match eddy-covariance flux values on daily and longer time steps.

  8. Geohydrology and evapotranspiration at Franklin Lake Playa, Inyo County, California

    SciTech Connect

    1990-12-01

    Franklin Lake playa is one of the principal discharge areas of the Furnace Creek Ranch-Alkali Flat ground-water-flow system in southern Nevada and adjacent California. Yucca Mountain, Nevada, located within this flow system, is being evaluated by the US Department of Energy to determine its suitability as a potential site for a high-level nuclear-waste repository. To assist the US Department of Energy with its evaluation of the Yucca Mountain site, the US Geological Survey developed a parameter-estimation model of the Furnace Creek Ranch-Alkali Flat ground-water-flow system. Results from sensitivity analyses made using the parameter-estimation model indicated that simulated rates of evapotranspiration at Franklin Lake playa had the largest effect on the calculation of transmissivity values at Yucca Mountain of all the model-boundary conditions and, therefore, that evapotranspiration required careful definition. 72 refs., 59 figs., 26 tab.

  9. Geohydrology and evapotranspiration at Franklin Lake playa, Inyo County, California

    SciTech Connect

    Czarnecki, J.B.

    1997-12-31

    Franklin Lake playa is one of the principal discharge areas of the Furnace Creek Ranch-Alkali Flat ground-water-flow system in southern Nevada and adjacent California. Yucca Mountain, Nevada, located within this flow system, is being evaluated by the US Department of Energy to determine its suitability as a potential site for a high-level nuclear-waste repository. To assist the U.S. Department of Energy with its evaluation of the Yucca Mountain site, the US Geological Survey developed a parameter-estimation model of the Furnace Creek Ranch-Alkali Flat ground-water-flow system. Results from sensitivity analyses made using the parameter-estimation model indicated that simulated rates of evapotranspiration at Franklin Lake playa had the largest effect on the calculation of transmissivity values at Yucca Mountain of all the model-boundary conditions and, therefore, that evapotranspiration required careful definition.

  10. Soil moisture and evapotranspiration predictions using Skylab data

    NASA Technical Reports Server (NTRS)

    Myers, V. I. (Principal Investigator); Moore, D. G.; Horton, M. L.; Russell, M. J.

    1975-01-01

    The author has identified the following significant results. Multispectral reflectance and emittance data from the Skylab workshop were evaluated for prediction of evapotranspiration and soil moisture for an irrigated region of southern Texas. Wavelengths greater than 2.1 microns were required to spectrally distinguish between wet and dry fallow surfaces. Thermal data provided a better estimate of soil moisture than did data from the reflective bands. Thermal data were dependent on soil moisture but not on the type of agricultural land use. The emittance map, when used in conjunction with existing models, did provide an estimate of evapotranspiration rates. Surveys of areas of high soil moisture can be accomplished with space altitude thermal data. Thermal data will provide a reliable input into irrigation scheduling.

  11. Use of the Aquacrop model for the simulation of wheat evapotranspiration in north-eastern Tunisia

    NASA Astrophysics Data System (ADS)

    Aloui, A.; Masmoudi, M.; Jacob, F.; Ben Mechlia, N.

    2012-04-01

    Improvement of rainfed cropping systems is based on the use of rainfall water for crop transpiration. This could be achieved by the appropriate partitioning of rainfall between green water and blue water. Under semiarid conditions, the AquaCrop model which has a driving engine based on the direct link between dry matter production and crop evapotranspiration, seems to be a powerful tool to perform this task. For this purposes, an experimental work was conducted on the wheat crop, grown under various farming conditions, to determine how simulation modeling could be used to monitor canopy changes and actual crop evapotranspiration. The study area -CapBon- is located in north eastern Tunisia where rainfall is about 500 mm and ET0 around 1200mm Field monitoring consisted in regular measurements of the leaf area index (LAI), vegetation cover changes (CC) and soil moisture content profiles over the cropping season December 2009-April 2010. The usefulness of using hemispherical and standard images to determine LAI and CC was also investigated for their adoption as a standard methods for the assessment of these important parameter as input data. Results show that good estimates of LAI and CC could be obtained from digital images. Fairly reliable linear relationships were obtained between measurements on samples using a leaf area meter and indirect assessments (r2 = 0.78) Aqua-Crop simulations where also mostly accurate in estimating soil moisture temporal variations and soil water content of well textured soils. However for soils with high clay content, important differences were observed between simulation outputs and direct gravimetric measurements.

  12. Influence of potential evapotranspiration on the water balance of sugarcane fields in Maui, Hawaii

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The year-long warm temperatures and other climatic characteristics of the Pacific Ocean Islands have made Hawaii an optimum place for growing sugarcane; however, irrigation is essential to satisfy the large water demand of sugarcane. Under the Hawaiian tropical weather, actual evapotranspiration (A...

  13. Evapotranspiration from a cypress and pine forest subjected to natural fires, Volusia County, Florida, 1998-99

    USGS Publications Warehouse

    Sumner, D.M.

    2001-01-01

    Daily values of evapotranspiration from a watershed in Volusia County, Florida, were estimated for a 2-year period (January 1998 through December 1999) by using an energy-budget variant of the eddy correlation method and a Priestley-Taylor model. The watershed consisted primarily of pine flatwood uplands interspersed within cypress wetlands. A drought-induced fire in spring 1998 burned about 40 percent of the watershed, most of which was subsequently logged. The model reproduced the 449 measured values of evapotranspiration reasonably well (r2=0.90) over a wide range of seasonal and surface-cover conditions. Annual evapotranspiration from the watershed was estimated to be 916 millimeters (36 inches) for 1998 and 1,070 millimeters (42 inches) for 1999. Evapotranspiration declined from near potential rates in the wet conditions of January 1998 to less than 50 percent of potential evapotranspiration after the fire and at the peak of the drought in June 1998. After the drought ended in early July 1998 and water levels returned to near land-surface, evapotranspiration increased sharply; however, the evapotranspiration rate was only about 60 percent of the potential rate in the burned areas, compared to about 90 percent of the potential rate in the unburned areas. This discrepancy can be explained as a result of fire damage to vegetation. Beginning in spring 1999, evapotranspiration from burned areas increased sharply relative to unburned areas, sometimes exceeding unburned evapotranspiration by almost 100 percent. Possible explanations for the dramatic increase in evapotranspiration from burned areas could include phenological changes associated with maturation or seasonality of plants that emerged after the fire or successional changes in composition of plant community within burned areas. Variations in daily evapotranspiration are primarily the result of variations in surface cover, net radiation, photosynthetically active radiation, air temperature, and water

  14. Harmonizing multiple methods for reconstructing historical potential and reference evapotranspiration

    USGS Publications Warehouse

    Belaineh, Getachew; Sumner, David; Carter, Edward; Clapp, David

    2013-01-01

    Potential evapotranspiration (PET) and reference evapotranspiration (RET) data are usually critical components of hydrologic analysis. Many different equations are available to estimate PET and RET. Most of these equations, such as the Priestley-Taylor and Penman- Monteith methods, rely on detailed meteorological data collected at ground-based weather stations. Few weather stations collect enough data to estimate PET or RET using one of the more complex evapotranspiration equations. Currently, satellite data integrated with ground meteorological data are used with one of these evapotranspiration equations to accurately estimate PET and RET. However, earlier than the last few decades, historical reconstructions of PET and RET needed for many hydrologic analyses are limited by the paucity of satellite data and of some types of ground data. Air temperature stands out as the most generally available meteorological ground data type over the last century. Temperature-based approaches used with readily available historical temperature data offer the potential for long period-of-record PET and RET historical reconstructions. A challenge is the inconsistency between the more accurate, but more data intensive, methods appropriate for more recent periods and the less accurate, but less data intensive, methods appropriate to the more distant past. In this study, multiple methods are harmonized in a seamless reconstruction of historical PET and RET by quantifying and eliminating the biases of the simple Hargreaves-Samani method relative to the more complex and accurate Priestley-Taylor and Penman-Monteith methods. This harmonization process is used to generate long-term, internally consistent, spatiotemporal databases of PET and RET.

  15. Recent decline in the global land evapotranspiration trend due to limited moisture supply.

    PubMed

    Jung, Martin; Reichstein, Markus; Ciais, Philippe; Seneviratne, Sonia I; Sheffield, Justin; Goulden, Michael L; Bonan, Gordon; Cescatti, Alessandro; Chen, Jiquan; de Jeu, Richard; Dolman, A Johannes; Eugster, Werner; Gerten, Dieter; Gianelle, Damiano; Gobron, Nadine; Heinke, Jens; Kimball, John; Law, Beverly E; Montagnani, Leonardo; Mu, Qiaozhen; Mueller, Brigitte; Oleson, Keith; Papale, Dario; Richardson, Andrew D; Roupsard, Olivier; Running, Steve; Tomelleri, Enrico; Viovy, Nicolas; Weber, Ulrich; Williams, Christopher; Wood, Eric; Zaehle, Sönke; Zhang, Ke

    2010-10-21

    More than half of the solar energy absorbed by land surfaces is currently used to evaporate water. Climate change is expected to intensify the hydrological cycle and to alter evapotranspiration, with implications for ecosystem services and feedback to regional and global climate. Evapotranspiration changes may already be under way, but direct observational constraints are lacking at the global scale. Until such evidence is available, changes in the water cycle on land−a key diagnostic criterion of the effects of climate change and variability−remain uncertain. Here we provide a data-driven estimate of global land evapotranspiration from 1982 to 2008, compiled using a global monitoring network, meteorological and remote-sensing observations, and a machine-learning algorithm. In addition, we have assessed evapotranspiration variations over the same time period using an ensemble of process-based land-surface models. Our results suggest that global annual evapotranspiration increased on average by 7.1 ± 1.0 millimetres per year per decade from 1982 to 1997. After that, coincident with the last major El Niño event in 1998, the global evapotranspiration increase seems to have ceased until 2008. This change was driven primarily by moisture limitation in the Southern Hemisphere, particularly Africa and Australia. In these regions, microwave satellite observations indicate that soil moisture decreased from 1998 to 2008. Hence, increasing soil-moisture limitations on evapotranspiration largely explain the recent decline of the global land-evapotranspiration trend. Whether the changing behaviour of evapotranspiration is representative of natural climate variability or reflects a more permanent reorganization of the land water cycle is a key question for earth system science.

  16. Changes in reference evapotranspiration over an agricultural region in the Qinghai-Tibetan plateau, China

    NASA Astrophysics Data System (ADS)

    Zhang, Cungui; Shen, Yanjun; Liu, Fenggui; Meng, Lei

    2016-01-01

    Reference evapotranspiration (ET0), as an estimate of the evaporative demand of the atmosphere, has been receiving extensive attention in researches on hydrological cycle. Sensitivity of ET0 to major climatic variables has significant applications in climatology, hydrology, and agrometeorology and is also important to improve our understanding of the connections between climatic conditions and ET0 variability. In this study, we used the Penman-Monteith equation to calculate ET0 and adopted a nondimensional sensitivity coefficient formula to analyze sensitivities of ET0 to four climatic variables based on daily meteorological data from eight meteorological sites in the Huangshui River basin and surrounding areas during 1961-2010. The results indicated that (1) strong correlations with R 2 up to 0.76 exist between observed E pan and calculated annual ET0; (2) ET0 had a decreasing trend in the Huangshui River basin (HRB) during 1961-2010; (3) Spatially, distribution of ET0 was largely correlated with altitude, for instance, the average annual ET0 was larger in low-altitude areas than in high-altitude areas; (4) ET0 was more sensitive to actual vapor pressure in high-altitude areas while it was more sensitive to temperature in low-altitude areas; and (5) ET0 showed a decreasing trend and was consistent with the decreases in net radiation and wind speed at seasonal and annual time scales in HRB during 1961-2010. Sensitivity analysis of ET0 to major climatic variables revealed that temperature was primarily responsible for changes in ET0 in the growing season while actual vapor pressure was the dominating factor causing changes in ET0 in the nongrowing season. However, annual averaged ET0 was more sensitive to actual vapor pressure ( R 2 = 0.63), indicating that actual vapor pressure was possibly the primary climatic variable that causes changes in annual ET0.

  17. Simple analytical model of evapotranspiration in the presence of roots

    NASA Astrophysics Data System (ADS)

    Cejas, Cesare; Castaing, Jean-Christophe; Hough, Larry; Fretigny, Christian; Dreyfus, Remi; Compass Team

    2015-03-01

    Water is essential for plant growth. The loss of water via evaporation in soil remains to be an important limiting factor for root growth and consists of well-debated mechanisms. The presence of a plant also provides an additional pathway for water transport in the form of transpiration. Prediction of total evapotranspiration flux permits estimation of the remaining quantity of water in the soil. Using a controlled visual 2D model set-up, we perform evaporation experiments with real root systems under different relative humidity conditions. We use the results on mass loss and evaporation front positions to develop a simple model, based on basic principles of evaporation flux, which predicts the position of the evaporating front and the total mass of water that is lost from the evapotranspiration of water out of the granular medium. The model also helps predict the lifetime of the plant - an important application in agriculture.

  18. Assessment of aquifer properties, evapotranspiration, and the effects of ditching in the Stoney Brook watershed, Fond du Lac Reservation, Minnesota, 2006-9

    USGS Publications Warehouse

    Jones, Perry M.; Tomasek, Abigail A.

    2015-01-01

    Daily fluctuations in water levels in two wells indicated that the evapotranspiration extinction depth in the Stoney Brook watershed is approximately 4.6 to 6 feet below the land surface. A polynomial regression fit of the daily evapotranspiration rates during 2006–9 for well 1 produced a total evapotranspiration estimate of 16.1 inches from June 26 to October 6 for every year. Evapotranspiration estimated from daily water-level fluctuations in wells near ditches is relatively high. The ditch-water surface allowed for relatively high evap

  19. Uncertainties in Measuring and Modeling Evapotranspiration in Open Savanna Ecosystems in West-Africa

    NASA Astrophysics Data System (ADS)

    Falk, Ulrike; Hendrickx, Jan M. H.; Conrad, Christopher; Vlek, Paul

    2010-05-01

    In recent years, several methods have been developed to estimate the spatial distribution of actual evapotranspiration (ET) by the means of remote sensing (RS). One frequently used approach is to calculate ET from latent heat fluxes modeled as residuum of the surface energy balance. For this purpose, ground heat fluxes and sensible heat fluxes are subtracted from the energy available on the land surface. One of these methods is the Surface Energy Balance Algorithm for Land (SEBAL), which has been applied to many ecosystems and different sensors. ET mapping from remotely sensed satellite images is critical for water management since the estimation of spatial and temporal ET distributions over large areas is impossible using only ground measurements. A major difficulty for the calibration and validation of operational ET RS algorithms is the validation against ground measurements of ET at a scale similar to the spatial resolution of the remote sensing image. The spatial length scale of remote sensing images covers a range from 30 m (Landsat) to 1000 m (MODIS). Direct methods to measure the latent heat flux (W/m2) -i.e. the evapotranspiration rate (mm/day) multiplied by the latent heat for vaporization- such as eddy covariance (EC) only provide measurements at a scale that may be considerably smaller than the estimate obtained from a remote sensing method. The Large Aperture Scintillometer (LAS) flux footprint area is larger (here about 1 km²) and its spatial extent better constraint than that of EC systems. Nevertheless, it is only an indirect method for estimation of ET. A detailed footprint analysis and its changes during the day is therefore necessary as well as uncertainties introduced by the different temporal scales. Overflight missions for mapping land surface properties were carried out to bridge the gap between the different spatial scales. The objective of this contribution is to present our experiences with time series of ET mapping using ground

  20. The Significance of Accounting Order for Evapotranspiration and Recharge in Monthly and Daily Threshold-Type Water Budgets

    USGS Publications Warehouse

    Oki, Delwyn S.

    2008-01-01

    Most threshold-type water-budget models account for the loss of water by evapotranspiration before accounting for recharge. Recharge estimates can differ substantially, depending on whether recharge is counted before or after evapotranspiration in the water budget. This disparity is the source of uncertainty and is most pronounced for areas where soil-moisture storage capacity is small or for water budgets computed using a large time interval (such as monthly). Water budgets that account for recharge before evapotranspiration provide higher estimates of recharge and lower estimates of evapotranspiration relative to water budgets that account for evapotranspiration before recharge. The choice of accounting method is less significant for a daily computation interval than for a monthly computation interval. In general, uncertainty in recharge estimates is least for water budgets computed using the shortest computation interval that the data allow and that is consistent with the physical processes being represented. If the data only allow for long (weekly or monthly) computation intervals, then selecting the appropriate accounting order for the study area may be critical. For monthly water budgets, accounting for recharge before evapotranspiration is most appropriate in areas where rainfall occurs infrequently, whereas accounting for evapotranspiration before recharge is most appropriate where rainfall occurs relatively uniformly throughout the month.

  1. Mapping daily evapotranspiration at Landsat spatial scales during the BEAREX'08 field campaign

    NASA Astrophysics Data System (ADS)

    Anderson, Martha C.; Kustas, William P.; Alfieri, Joseph G.; Gao, Feng; Hain, Christopher; Prueger, John H.; Evett, Steven; Colaizzi, Paul; Howell, Terry; Chávez, José L.

    2012-12-01

    Robust spatial information about environmental water use at field scales and daily to seasonal timesteps will benefit many applications in agriculture and water resource management. This information is particularly critical in arid climates where freshwater resources are limited or expensive, and groundwater supplies are being depleted at unsustainable rates to support irrigated agriculture as well as municipal and industrial uses. Gridded evapotranspiration (ET) information at field scales can be obtained periodically using land-surface temperature-based surface energy balance algorithms applied to moderate resolution satellite data from systems like Landsat, which collects thermal-band imagery every 16 days at a resolution of approximately 100 m. The challenge is in finding methods for interpolating between ET snapshots developed at the time of a clear-sky Landsat overpass to provide complete daily time-series over a growing season. This study examines the efficacy of a simple gap-filling algorithm designed for applications in data-sparse regions, which does not require local ground measurements of weather or rainfall, or estimates of soil texture. The algorithm relies on general conservation of the ratio between actual ET and a reference ET, generated from satellite insolation data and standard meteorological fields from a mesoscale model. The algorithm was tested with ET retrievals from the Atmosphere-Land Exchange Inverse (ALEXI) surface energy balance model and associated DisALEXI flux disaggregation technique, which uses Landsat-scale thermal imagery to reduce regional ALEXI maps to a finer spatial resolution. Daily ET at the Landsat scale was compared with lysimeter and eddy covariance flux measurements collected during the Bushland Evapotranspiration and Agricultural Remote sensing EXperiment of 2008 (BEAREX08), conducted in an irrigated agricultural area in the Texas Panhandle under highly advective conditions. The simple gap-filling algorithm performed

  2. Mapping Seasonal Evapotranspiration and Root Zone Soil Moisture using a Hybrid Modeling Approach over Vineyards

    NASA Astrophysics Data System (ADS)

    Geli, H. M. E.

    2015-12-01

    Estimates of actual crop evapotranspiration (ETa) at field scale over the growing season are required for improving agricultural water management, particularly in water limited and drought prone regions. Remote sensing data from multiple platforms such as airborne and Landsat-based sensors can be used to provide these estimates. Combining these data with surface energy balance models can provide ETa estimates at sub- field scale as well as information on vegetation stress and soil moisture conditions. However, the temporal resolution of airborne and Landsat data does not allow for a continuous ETa monitoring over the course of the growing season. This study presents the application of a hybrid ETa modeling approach developed for monitoring daily ETa and root zone available water at high spatial resolutions. The hybrid ETa modeling approach couples a thermal-based energy balance model with a water balance-based scheme using data assimilation. The two source energy balance (TSEB) model is used to estimate instantaneous ETa which can be extrapolated to daily ETa using a water balance model modified to use the reflectance-based basal crop coefficient for interpolating ETa in between airborne and/or Landsat overpass dates. Moreover, since it is a water balance model, the soil moisture profile is also estimated. The hybrid ETa approach is applied over vineyard fields in central California. High resolution airborne and Landsat imagery were used to drive the hybrid model. These images were collected during periods that represented different vine phonological stages in 2013 growing season. Estimates of daily ETa and surface energy balance fluxes will be compared with ground-based eddy covariance tower measurements. Estimates of soil moisture at multiple depths will be compared with measurements.

  3. Estimating the spatio-temporal distribution of surface water availability across India

    NASA Astrophysics Data System (ADS)

    Singh, R.; Kumar, R.

    2015-12-01

    Quantifying the spatio-temporal variation of future surface water availability across India is critical for water resources planning and management in the water stressed region. However, this remains a challenge as long-term streamflow data is scarce and there is significant uncertainty regarding unmonitored withdrawals. We present a framework to estimate long-term (surface) water availability and its vulnerability to climate change across India using hydro-climatic variables based on long-term precipitation, potential and actual evapotranspiration. We derive estimates of actual evapotranspiration through a probabilistic Budyko framework which further allows us to obtain uncertainty bounds on surface water availability. We define vulnerability as a relative change in long-term surface water availability for a unit change in long-term precipitation. Based on this, we present vulnerability maps for India which shows the spatio-temporal variation of vulnerability of surface water resources to climate change across India.

  4. Potential Evapotranspiration Trends over South America

    NASA Astrophysics Data System (ADS)

    Maske, B. B.; Goncalves, L.

    2013-05-01

    Evapotranspiration (ET) is a key variable for energy and mass flux estimation from the land surface, and consequent water balance over regional to global scales. It also affects the atmosphere dynamics from weather to climate scales due to its link between the hydrological and energy cycles. Many studies investigating global ET trends have found a consistently positive signal in the period between 1982-1997 followed by a decline until 2008, which proved consistent with the acceleration of the hydrological cycle, caused by the global increase of temperature and radiative forcing. The large El nino in 1998, for instance, resulted in a negative trend of ET due in part to the limitation of soil moisture availability. However some researchers emphasize the importance of treating ET trends regionally and thus already found two distinct scenarios with inclusion of the regional dimension of evapotranspiration drivers for global studies: one where ET decreases following decreasing in pan evaporation in regions with ample supply of water and, the other scenario with a positive trend in observed ET following decreasing in pan evaporation, with indication of the latter being induced only by the tendency of precipitation. Studies about ET trend in the western United States, using data from the hydrologic model Variable Infiltration Capacity (VIC), also found significant seasonal variations associated with changes of temperature, snow accumulation and melting. Moreover, Canada researchers indicate strong correlation between ET variations and temperature, although temperature alone can not be related to changes of ET, since it not considers the heat flux in soil and cycles of freezing and melting of snow. Considering the importance of understanding variations of ET regionally, this study aims to analyze ET trends over South America. The data used are potential evapotranspiration estimated by the Penman-Monteith method, computed using data from meteorological stations for the

  5. NASA GLDAS Evapotranspiration Data and Climatology

    NASA Technical Reports Server (NTRS)

    Rui, Hualan; Beaudoing, Hiroko Kato; Teng, William L.; Vollmer, Bruce; Rodell, Matthew

    2012-01-01

    Evapotranspiration (ET) is the water lost to the atmosphere by evaporation and transpiration. ET is a shared component in the energy and water budget, therefore, a critical variable for global energy and water cycle and climate change studies. However, direct ET measurements and data acquisition are difficult and expensive, especially at the global level. Therefore, modeling is one common alternative for estimating ET. With the goal to generate optimal fields of land surface states and fluxes, the Global Land Data Assimilation System (GLDAS) has been generating quality-controlled, spatially and temporally consistent, terrestrial hydrologic data, including ET and other variables that affect evaporation and transpiration, such as temperature, precipitation, humidity, wind, soil moisture, heat flux, and solar radiation. This poster presents the long-term ET climatology (mean and monthly), derived from the 61-year GLDAS-2 monthly 1.0 deg x 1.0 deg. NOAH model Experiment-1 data, and describes the basic characteristics of spatial and seasonal variations of the climatology. The time series of GLDAS-2 precipitation and radiation, and ET are also discussed to show the improvement of GLDAS-2 forcing data and model output over those from GLDAS-1.

  6. Evaluating reference evapotranspiration in mountain areas

    NASA Astrophysics Data System (ADS)

    Calanca, P.; Philipona, R.; Bretscher, D.; Rohrer, M.; Sanabria, J.; Trebejo, I.; Alarcón Velazco, C.; Smith, P.

    2010-09-01

    The so-called reference evapotranspiration (ETo) is one of the key variables for the assessment of crop water requirements and irrigation needs. Standard methods are available for computing ETo as well as for the pre-processing of the meteorological data. Many of them have been developed and tested with respect to stations situated at low altitudes. In the context of climate change and its impacts on agriculture there is, however, an increasing necessity for applying these methods to mountain areas. These have been identified as among the most vulnerable environments and have for this reason become the focus of several research programmes such as e.g. the Climate Change Adaptation Programme in Peru (PACC), initiated by the Swiss Agency for Development and Cooperation (SDC) in 2008, and the EU funded project ACQWA. In this contribution we discuss practical aspects related to the evaluation of ETo in mountain areas. As the availability of weather data is generally more limited than in low altitude regions, we examine approaches for the generation of input data with examples from the Swiss Alps and the Peruvian Andes. In particular we consider the estimation of net radiation (NR), as this is the main driver of the heat exchange at the earth surface and controls the evaporative demand of the atmosphere. Empirical approaches for computing NR are examined in the light of data from the Alpine Surface Radiation Budget (ASRB) network and discussed in relation to the implications for ETo.

  7. Multiyear Riparian Evapotranspiration and Groundwater Use for the Upper San Pedro Basin 1915

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Riparian evapotranspiration (ET) is a major component of the surface and subsurface water balance for many semiarid watersheds. Measurement or model-based estimates of ET are often made on a local scale, but spatially distributed estimates are needed to determine ET over catchments. In this paper,...

  8. Remote Sensing of Snow and Evapotranspiration

    NASA Technical Reports Server (NTRS)

    Schmugge, T. (Editor)

    1985-01-01

    The use of snowmelt runoff models from both the U.S. and Japan for simulating discharge on basins in both countries is discussed as well as research in snowpack properties and evapotranspiration using remotely sensed data.

  9. Mapping evapotranspiration in the Texas Panhandle

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Agriculture in the Texas High Plains accounts for approximately 92% of groundwater withdrawals. Because groundwater levels are declining in the region, efficient agricultural water use is imperative for sustainability and regional economic viability. Accurate regional evapotranspiration (ET) maps ...

  10. The effect of different evapotranspiration methods on portraying soil water dynamics and ET partitioning in a semi-arid environment in Northwest China

    NASA Astrophysics Data System (ADS)

    Yu, Lianyu; Zeng, Yijian; Su, Zhongbo; Cai, Huanjie; Zheng, Zhen

    2016-03-01

    Different methods for assessing evapotranspiration (ET) can significantly affect the performance of land surface models in portraying soil water dynamics and ET partitioning. An accurate understanding of the impact a method has is crucial to determining the effectiveness of an irrigation scheme. Two ET methods are discussed: one is based on reference crop evapotranspiration (ET0) theory, uses leaf area index (LAI) for partitioning into soil evaporation and transpiration, and is denoted as the ETind method; the other is a one-step calculation of actual soil evaporation and potential transpiration by incorporating canopy minimum resistance and actual soil resistance into the Penman-Monteith model, and is denoted as the ETdir method. In this study, a soil water model, considering the coupled transfer of water, vapor, and heat in the soil, was used to investigate how different ET methods could affect the calculation of the soil water dynamics and ET partitioning in a crop field. Results indicate that for two different ET methods this model varied concerning the simulation of soil water content and crop evapotranspiration components, but the simulation of soil temperature agreed well with lysimeter observations, considering aerodynamic and surface resistance terms improved the ETdir method regarding simulating soil evaporation, especially after irrigation. Furthermore, the results of different crop growth scenarios indicate that the uncertainty in LAI played an important role in estimating the relative transpiration and evaporation fraction. The impact of maximum rooting depth and root growth rate on calculating ET components might increase in drying soil. The influence of maximum rooting depth was larger late in the growing season, while the influence of root growth rate dominated early in the growing season.

  11. [An operational remote sensing algorithm of land surface evapotranspiration based on NOAA PAL dataset].

    PubMed

    Hou, Ying-Yu; He, Yan-Bo; Wang, Jian-Lin; Tian, Guo-Liang

    2009-10-01

    Based on the time series 10-day composite NOAA Pathfinder AVHRR Land (PAL) dataset (8 km x 8 km), and by using land surface energy balance equation and "VI-Ts" (vegetation index-land surface temperature) method, a new algorithm of land surface evapotranspiration (ET) was constructed. This new algorithm did not need the support from meteorological observation data, and all of its parameters and variables were directly inversed or derived from remote sensing data. A widely accepted ET model of remote sensing, i. e., SEBS model, was chosen to validate the new algorithm. The validation test showed that both the ET and its seasonal variation trend estimated by SEBS model and our new algorithm accorded well, suggesting that the ET estimated from the new algorithm was reliable, being able to reflect the actual land surface ET. The new ET algorithm of remote sensing was practical and operational, which offered a new approach to study the spatiotemporal variation of ET in continental scale and global scale based on the long-term time series satellite remote sensing images.

  12. [An operational remote sensing algorithm of land surface evapotranspiration based on NOAA PAL dataset].

    PubMed

    Hou, Ying-Yu; He, Yan-Bo; Wang, Jian-Lin; Tian, Guo-Liang

    2009-10-01

    Based on the time series 10-day composite NOAA Pathfinder AVHRR Land (PAL) dataset (8 km x 8 km), and by using land surface energy balance equation and "VI-Ts" (vegetation index-land surface temperature) method, a new algorithm of land surface evapotranspiration (ET) was constructed. This new algorithm did not need the support from meteorological observation data, and all of its parameters and variables were directly inversed or derived from remote sensing data. A widely accepted ET model of remote sensing, i. e., SEBS model, was chosen to validate the new algorithm. The validation test showed that both the ET and its seasonal variation trend estimated by SEBS model and our new algorithm accorded well, suggesting that the ET estimated from the new algorithm was reliable, being able to reflect the actual land surface ET. The new ET algorithm of remote sensing was practical and operational, which offered a new approach to study the spatiotemporal variation of ET in continental scale and global scale based on the long-term time series satellite remote sensing images. PMID:20077694

  13. Improving evapotranspiration in a land surface model using biophysical variables derived from MSG/SEVIRI satellite

    NASA Astrophysics Data System (ADS)

    Ghilain, N.; Arboleda, A.; Sepulcre-Cantò, G.; Batelaan, O.; Ardö, J.; Gellens-Meulenberghs, F.

    2012-08-01

    Monitoring evapotranspiration over land is highly dependent on the surface state and vegetation dynamics. Data from spaceborn platforms are desirable to complement estimations from land surface models. The success of daily evapotranspiration monitoring at continental scale relies on the availability, quality and continuity of such data. The biophysical variables derived from SEVIRI on board the geostationary satellite Meteosat Second Generation (MSG) and distributed by the Satellite Application Facility on Land surface Analysis (LSA-SAF) are particularly interesting for such applications, as they aimed at providing continuous and consistent daily time series in near-real time over Africa, Europe and South America. In this paper, we compare them to monthly vegetation parameters from a database commonly used in numerical weather predictions (ECOCLIMAP-I), showing the benefits of the new daily products in detecting the spatial and temporal (seasonal and inter-annual) variability of the vegetation, especially relevant over Africa. We propose a method to handle Leaf Area Index (LAI) and Fractional Vegetation Cover (FVC) products for evapotranspiration monitoring with a land surface model at 3-5 km spatial resolution. The method is conceived to be applicable for near-real time processes at continental scale and relies on the use of a land cover map. We assess the impact of using LSA-SAF biophysical variables compared to ECOCLIMAP-I on evapotranspiration estimated by the land surface model H-TESSEL. Comparison with in-situ observations in Europe and Africa shows an improved estimation of the evapotranspiration, especially in semi-arid climates. Finally, the impact on the land surface modelled evapotranspiration is compared over a north-south transect with a large gradient of vegetation and climate in Western Africa using LSA-SAF radiation forcing derived from remote sensing. Differences are highlighted. An evaluation against remote sensing derived land surface temperature

  14. Investigating effects of different evapotranspiration (ET) schemes on soil water dynamics and ET partitioning: a large lysimeter case of summer maize in a semi-arid environment northwest of China

    NASA Astrophysics Data System (ADS)

    Yu, L.; Zeng, Y.; Su, Z.; Cai, H.; Zheng, Z.

    2015-09-01

    Different evapotranspiration (ET) schemes can affect significantly the performance of land surface models in capturing the soil water dynamics and ET partitioning over various land cover and climates, the accurate understanding of which is crucial to determine the effective irrigation. In this study, a land model considering the coupled transfer of water, vapor and heat in the soil, with two alternative ET schemes, was used to investigate how the coupled mechanism can affect the soil water dynamics in a crop field and how the ET partitioning was influenced. There are two different evapotranspiration (ET) schemes, one is based on reference crop evapotranspiration (ET0) and use LAI to partition into soil evaporation and transpiration, denoted as the ETind scheme; the other is one-step calculation of actual soil evaporation and potential transpiration by incorporating canopy minimum resistance and actual soil resistance into Penman-Monteith model, denoted as the ETdir scheme. Results indicated that the coupled model with the two different ET schemes differed in simulating soil water content and crop evapotranspiration components while agreed well for the simulation of soil temperature. Considering the aerodynamic and surface resistance terms made the ETdir scheme better in simulating soil evaporation especially after irrigations. Furthermore, the results of different crop growth scenarios indicated that the uncertainty in LAI played an important role in estimating the relative transpiration and evaporation fraction. The soil drying seemed to intensify the disturbance of maximum rooting depth and root growth rate in calculating ET components. The former was more important at the late growing season while the latter dominated at the early growing season.

  15. Estimation of radiation budget and water balance with satellite data for savanna monitoring

    NASA Astrophysics Data System (ADS)

    Amram, Olivier; Flouzat, Guy; Cherchali, S.

    1995-01-01

    This paper presents a functional characterization of West Africa's ecological systems using satellite data. It shows the capability of spatio-temporal determination of the hydrological budget well fitted to the chlorophyllian phenology. The method includes two parts: estimation of radiation budget at the earth surface, and actual evapotranspiration and, in addition, estimation of one hydrological budget and its capability to describe and possibly to predict growth process. The estimation of evaportranspiration is made with simplified relationships proposed by Jackson and Seguin. These descriptions need a limited number of input data, and their parametrization can be deduced from the main classes of vegetation. A hydrological budget model is then established using evapotranspiration, rainfall measurement, and the estimation of ground contribution at a suitable scale. In this model, we assume that the phenological state of the plant at a given time depends on the efficient stock of water during the months preceding the state development. The results show that the concept of the estimation of radiation budget at the earth surface and actual evapotranspiration can be applied generally for large areas at fine spatial resolution and the model of efficient water shows a good adjustment with the cycle normalized difference vegetation index.

  16. Remote Sensing of Evapotranspiration and Carbon Uptake at Harvard Forest

    NASA Technical Reports Server (NTRS)

    Min, Qilong; Lin, Bing

    2005-01-01

    A land surface vegetation index, defined as the difference of microwave land surface emissivity at 19 and 37 GHz, was calculated for a heavily forested area in north central Massachusetts. The microwave emissivity difference vegetation index (EDVI) was estimated from satellite SSM/I measurements at the defined wavelengths and used to estimate land surface turbulent fluxes. Narrowband visible and infrared measurements and broadband solar radiation observations were used in the EDVI retrievals and turbulent flux estimations. The EDVI values represent physical properties of crown vegetation such as vegetation water content of crown canopies. The collocated land surface turbulent and radiative fluxes were empirically linked together by the EDVI values. The EDVI values are statistically sensitive to evapotranspiration fractions (EF) with a correlation coefficient (R) greater than 0.79 under all-sky conditions. For clear skies, EDVI estimates exhibit a stronger relationship with EF than normalized difference vegetation index (NDVI). Furthermore, the products of EDVI and input energy (solar and photosynthetically-active radiation) are statistically significantly correlated to evapotranspiration (R=0.95) and CO2 uptake flux (R=0.74), respectively.

  17. Assessment of aquifer properties, evapotranspiration, and the effects of ditching in the Stoney Brook watershed, Fond du Lac Reservation, Minnesota, 2006-9

    USGS Publications Warehouse

    Jones, Perry M.; Tomasek, Abigail A.

    2015-01-01

    Daily fluctuations in water levels in two wells indicated that the evapotranspiration extinction depth in the Stoney Brook watershed is approximately 4.6 to 6 feet below the land surface. A polynomial regression fit of the daily evapotranspiration rates during 2006–9 for well 1 produced a total evapotranspiration estimate of 16.1 inches from June 26 to October 6 for every year. Evapotranspiration estimated from daily water-level fluctuations in wells near ditches is relatively high. The ditch-water surface allowed for relatively high evaporation compared to the land surface, which, with a good hydraulic connection to surrounding groundwater, resulted in relatively high fluctuations in daily groundwater levels near ditches, resulting in high evapotranspiration estimates.

  18. Assessment of Evapotranspiration and Soil Moisture Content Across Different Scales of Observation

    PubMed Central

    Verstraeten, Willem W.; Veroustraete, Frank; Feyen, Jan

    2008-01-01

    The proper assessment of evapotranspiration and soil moisture content are fundamental in food security research, land management, pollution detection, nutrient flows, (wild-) fire detection, (desert) locust, carbon balance as well as hydrological modelling; etc. This paper takes an extensive, though not exhaustive sample of international scientific literature to discuss different approaches to estimate land surface and ecosystem related evapotranspiration and soil moisture content. This review presents: (i)a summary of the generally accepted cohesion theory of plant water uptake and transport including a shortlist of meteorological and plant factors influencing plant transpiration;(ii)a summary on evapotranspiration assessment at different scales of observation (sap-flow, porometer, lysimeter, field and catchment water balance, Bowen ratio, scintillometer, eddy correlation, Penman-Monteith and related approaches);(iii)a summary on data assimilation schemes conceived to estimate evapotranspiration using optical and thermal remote sensing; and(iv)for soil moisture content, a summary on soil moisture retrieval techniques at different spatial and temporal scales is presented. Concluding remarks on the best available approaches to assess evapotranspiration and soil moisture content with and emphasis on remote sensing data assimilation, are provided.

  19. Evapotranspiration Cycles in a High Latitude Agroecosystem: Potential Warming Role

    PubMed Central

    Ruairuen, Watcharee

    2015-01-01

    As the acreages of agricultural lands increase, changes in surface energetics and evapotranspiration (ET) rates may arise consequently affecting regional climate regimes. The objective of this study was to evaluate summertime ET dynamics and surface energy processes in a subarctic agricultural farm in Interior Alaska. The study includes micrometeorological and hydrological data. Results covering the period from June to September 2012 and 2013 indicated consistent energy fractions: LE/Rnet (67%), G/Rnet (6%), H/Rnet (27%) where LE is latent heat flux, Rnet is the surface net radiation, G is ground heat flux and H is the sensible heat flux. Additionally actual surface evapotranspiration from potential evaporation was found to be in the range of 59 to 66%. After comparing these rates with those of most prominent high latitude ecosystems it is argued here that if agroecosystem in high latitudes become an emerging feature in the land-use, the regional surface energy balance will significantly shift in comparison to existing Arctic natural ecosystems. PMID:26368123

  20. Improved seasonal drought forecasts using reference evapotranspiration anomalies

    NASA Astrophysics Data System (ADS)

    McEvoy, Daniel J.; Huntington, Justin L.; Mejia, John F.; Hobbins, Michael T.

    2016-01-01

    A novel contiguous United States (CONUS) wide evaluation of reference evapotranspiration (ET0; a formulation of evaporative demand) anomalies is performed using the Climate Forecast System version 2 (CFSv2) reforecast data for 1982-2009. This evaluation was motivated by recent research showing ET0 anomalies can accurately represent drought through exploitation of the complementary relationship between actual evapotranspiration and ET0. Moderate forecast skill of ET0 was found up to leads of 5 months and was consistently better than precipitation skill over most of CONUS. Forecasts of ET0 during drought events revealed high categorical skill for notable warm-season droughts of 1988 and 1999 in the central and northeast CONUS, with precipitation skill being much lower or absent. Increased ET0 skill was found in several climate regions when CFSv2 forecasts were initialized during moderate-to-strong El Niño-Southern Oscillation events. Our findings suggest that ET0 anomaly forecasts can improve and complement existing seasonal drought forecasts.

  1. Concerning the relationship between evapotranspiration and soil moisture

    NASA Technical Reports Server (NTRS)

    Wetzel, Peter J.; Chang, Jy-Tai

    1987-01-01

    The relationship between the evapotranspiration and soil moisture during the drying, supply-limited phase is studied. A second scaling parameter, based on the evapotranspirational supply and demand concept of Federer (1982), is defined; the parameter, referred to as the threshold evapotranspiration, occurs in vegetation-covered surfaces just before leaf stomata close and when surface tension restricts moisture release from bare soil pores. A simple model for evapotranspiration is proposed. The effects of natural soil heterogeneities on evapotranspiration computed from the model are investigated. It is observed that the natural variability in soil moisture, caused by the heterogeneities, alters the relationship between regional evapotranspiration and the area average soil moisture.

  2. Evapotranspiration from selected fallowed agricultural fields on the Tule Lake National Wildlife Refuge, California, during May to October 2000

    USGS Publications Warehouse

    Bidlake, W.R.

    2002-01-01

    An investigation of evapotranspiration, vegetation quantity and composition, and depth to the water table below the land surface was made at three sites in two fallowed agricultural lots on the 15,800-hectare Tule Lake National Wildlife Refuge in northern California during the 2000 growing season. All three sites had been farmed during 1999, but were not irrigated since the 1999 growing season. Vegetation at the lot C1B and lot 6 stubble sites included weedy species and small grain plants. The lot 6 cover crop site supported a crop of cereal rye that had been planted during the previous winter. Percentage of coverage by live vegetation ranged from 0 to 43.2 percent at the lot C1B site, from approximately 0 to 63.2 percent at the lot 6 stubble site, and it was estimated to range from 0 to greater than 90 percent at the lot 6 cover crop site. Evapotranspiration was measured using the Bowen ratio energy balance technique and it was estimated using a model that was based on the Priestley-Taylor equation and a model that was based on reference evapotranspiration with grass as the reference crop. Total evapotranspiration during May to October varied little among the three evapotranspiration measurement sites, although the timing of evapotranspiration losses did vary among the sites. Total evapotranspiration from the lot C1B site was 426 millimeters, total evapotranspiration from the lot 6 stubble site was 444 millimeters, and total evapotranspiration from the lot 6 cover crop site was 435 millimeters. The months of May to July accounted for approximately 78 percent of the total evapotranspiration from the lot C1B site, approximately 63 percent of the evapotranspiration from the lot 6 stubble site, and approximately 86 percent of the total evapotranspiration from the lot 6 cover crop site. Estimated growing season precipitation accounted for 16 percent of the growing-season evapotranspiration at the lot C1B site and for 17 percent of the growing-season evapotranspiration

  3. Effect of root distribution on modelling percolation and groundwater evapotranspiration

    NASA Astrophysics Data System (ADS)

    Orellana, F. A.; Daly, E.

    2011-12-01

    In groundwater-dependent ecosystems, vegetation is able to extend its root system deep in the soil to wet zones strongly influenced by the water table. As a result, either part or all transpired water is supplied by groundwater. In many models, roots are assumed to be submerged in groundwater; however, this is not the case for many species. We analised the effect of using different root systems in estimating evapotranspiration and recharge in groundwater-dependent ecosystems. A 2D finite-elements model was developed using the program SEEPW to simulate the interaction between saturated and unsaturated soil in a riparian area. The domain of the model consists in a soil layer 8 meters deep and 100 meters long, with a constant water table outside of the vegetated area and a variable water table in the opposite side, controlled by the stage level of a river. Five root distributions were simulated: homogeneous in the saturated zone, homogeneous in the unsaturated zone, concentrated in the top layer of the soil, concentrated in the capillary fringe and a dimorphic distribution. The water-table level in the vegetated zone is always close to three meter depth; therefore, the direct evaporation from groundwater is neglected. Preliminary results show a significant impact of differing root distributions on the modelled water-table levels. The daily pattern of transpiration produces daily fluctuations in the water-table level, whose amplitude is higher when the total transpiration is uptaken from groundwater, and is considerably smaller when the root system is only in the unsaturated zone. These differences are also reflected in the net recharge and groundwater evapotranspiration. When transpiration comes directly from groundwater, most of the infiltrated water reaches the water table. However, when roots are distributed in the unsaturated zone, they are able to intercep part of the infiltration, with a decrease in percolation. Likewise, groundwater evapotranspiration reduces

  4. Sources of variability of evapotranspiration in California

    USGS Publications Warehouse

    Hidalgo, H.G.; Cayan, D.R.; Dettinger, M.D.

    2005-01-01

    The variability (1990-2002) of potential evapotranspiration estimates (ETo) and related meteorological variables from a set of stations from the California Irrigation Management System (CIMIS) is studied. Data from the National Climatic Data Center (NCDC) and from the Department of Energy from 1950 to 2001 were used to validate the results. The objective is to determine the characteristics of climatological ETo and to identify factors controlling its variability (including associated atmospheric circulations). Daily ETo anomalies are strongly correlated with net radiation (Rn) anomalies, relative humidity (RH), and cloud cover, and less with average daily temperature (Tavg). The highest intraseasonal variability of ETo daily anomalies occurs during the spring, mainly caused by anomalies below the high ETo seasonal values during cloudy days. A characteristic circulation pattern is associated with anomalies of ETo and its driving meteorological inputs, Rn, RH, and Tavg, at daily to seasonal time scales. This circulation pattern is dominated by 700-hPa geopotential height (Z700) anomalies over a region off the west coast of North America, approximately between 32?? and 44?? latitude, referred to as the California Pressure Anomaly (CPA). High cloudiness and lower than normal ETo are associated with the lowheight (pressure) phase of the CPA pattern. Higher than normal ETo anomalies are associated with clear skies maintained through anomalously high Z700 anomalies offshore of the North American coast. Spring CPA, cloudiness, maximum temperature (Tmax), pan evaporation (Epan), and ETo conditions have not trended significantly or consistently during the second half of the twentieth century in California. Because it is not known how cloud cover and humidity will respond to climate change, the response of ETo in California to increased greenhouse-gas concentrations is essentially unknown; however, to retain the levels of ETo in the current climate, a decline of Rn by about 6

  5. Spatial interpolation of daily reference evapotranspiration in the Texas High Plains

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The Texas High Plains Evapotranspiration (ET) Network collects meteorological data from 18 grass reference weather stations at hourly intervals and estimates hourly and daily reference ET using the American Society of Civil Engineers (ASCE) Standardized Reference ET equation. Producers in the Texas ...

  6. Quantifying variability in field scale evapotranspiration measurements in an irrigated agricultural region under advection

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This study compares the evapotranspiration (ET) measurements from eddy covariance, lysimetry, and water balance using a network of neutron probe sensors and investigates the role of within-field variability in the vegetation density in explaining the differences among the ET estimates from the vario...

  7. Spatial interpolation of daily evapotranspiration data in the Texas High Plains

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The Texas High Plains Evapotranspiration (ET) Network collects meteorological data from grass-referenced weather stations at hourly intervals and estimates hourly and daily reference ET using the American Society of Civil Engineers (ASCE) Standardized Reference ET equation. Producers in the Texas Hi...

  8. The Pattern Across the Continental United States of Evapotranspiration Variability Associated with Water Availability

    NASA Astrophysics Data System (ADS)

    Koster, Randal; Salvucci, Guido; Rigden, Angela; Jung, Martin; Collatz, G.; Schubert, Siegfried

    2015-07-01

    The spatial pattern across the continental United States of the interannual variance of warm-season water-dependent evapotranspiration, a pattern of relevance to land-atmosphere feedback, cannot be measured directly. Alternative and indirect approaches to estimating the pattern, however, do exist, and given the uncertainty of each, we use several such approaches here. We first quantify the water-dependent evapotranspiration variance pattern inherent in two derived evapotranspiration datasets available from the literature. We then search for the pattern in proxy geophysical variables (air temperature, streamflow, and NDVI) known to have strong ties to evapotranspiration. The variances inherent in all of the different (and mostly independent) data sources show some differences but are generally strongly consistent - they all show a large variance signal down the center of the U.S., with lower variances toward the east and (for the most part) toward the west. The robustness of the pattern across the datasets suggests that it indeed represents the pattern operating in nature. Using Budyko’s hydroclimatic framework, we show that the pattern can largely be explained by the relative strength of water and energy controls on evapotranspiration across the continent.

  9. The Pattern Across the Continental United States of Evapotranspiration Variability Associated with Water Availability

    NASA Technical Reports Server (NTRS)

    Koster, Randal D.; Salvucci, Guido D.; Rigden, Angela J.; Jung, Martin; Collatz, G. James; Schubert, Siegfried D.

    2015-01-01

    The spatial pattern across the continental United States of the interannual variance of warm season water-dependent evapotranspiration, a pattern of relevance to land-atmosphere feedback, cannot be measured directly. Alternative and indirect approaches to estimating the pattern, however, do exist, and given the uncertainty of each, we use several such approaches here. We first quantify the water dependent evapotranspiration variance pattern inherent in two derived evapotranspiration datasets available from the literature. We then search for the pattern in proxy geophysical variables (air temperature, stream flow, and NDVI) known to have strong ties to evapotranspiration. The variances inherent in all of the different (and mostly independent) data sources show some differences but are generally strongly consistent they all show a large variance signal down the center of the U.S., with lower variances toward the east and (for the most part) toward the west. The robustness of the pattern across the datasets suggests that it indeed represents the pattern operating in nature. Using Budykos hydroclimatic framework, we show that the pattern can largely be explained by the relative strength of water and energy controls on evapotranspiration across the continent.

  10. Evapotranspiration and canopy resistance at an undeveloped prairie in a humid subtropical climate

    USGS Publications Warehouse

    Bidlake, W.R.

    2002-01-01

    Reliable estimates of evapotranspiration from areas of wildland vegetation are needed for many types of water-resource investigations. However, little is known about surface fluxes from many areally important vegetation types, and relatively few comparisons have been made to examine how well evapotranspiration models can predict evapotranspiration for soil-, climate-, or vegetation-types that differ from those under which the models have been calibrated. In this investigation at a prairie site in west-central Florida, latent heat flux (??E) computed from the energy balance and alternatively by eddy covariance during a 15-month period differed by 4 percent and 7 percent on hourly and daily time scales, respectively. Annual evapotranspiration computed from the energy balance and by eddy covariance were 978 and 944 mm, respectively. An hourly Penman-Monteith (PM) evapotranspiration model with stomatal control predicated on water-vapor-pressure deficit at canopy level, incoming solar radiation intensity, and soil water deficit was developed and calibrated using surface fluxes from eddy covariance. Model-predicted ??E agreed closely with ??E computed from the energy balance except when moisture from dew or precipitation covered vegetation surfaces. Finally, an hourly PM model developed for an Amazonian pasture predicted ??E for the Florida prairie with unexpected reliability. Additional comparisons of PM-type models that have been developed for differing types of short vegetation could aid in assessing interchangeability of such models.

  11. Form and Actuality

    NASA Astrophysics Data System (ADS)

    Bitbol, Michel

    A basic choice underlies physics. It consists of banishing actual situations from theoretical descriptions, in order to reach a universal formal construct. Actualities are then thought of as mere local appearances of a transcendent reality supposedly described by the formal construct. Despite its impressive success, this method has left major loopholes in the foundations of science. In this paper, I document two of these loopholes. One is the problem of time asymmetry in statistical thermodynamics, and the other is the measurement problem of quantum mechanics. Then, adopting a broader philosophical standpoint, I try to turn the whole picture upside down. Here, full priority is given to actuality (construed as a mode of the immanent reality self-reflectively being itself) over formal constructs. The characteristic aporias of this variety of "Copernican revolution" are discussed.

  12. Comparison of two simple tools (TSEB and FAO-56) to retrieve evapotranspiration of irrigated agriculture in semi-arid areas.

    NASA Astrophysics Data System (ADS)

    Diarra, Alhousseine; Jarlan, Lionel; Er-Raki, Salah; Le Page, Michel; Khabba, Said; Boulet, Gilles

    2016-04-01

    In a context of climate change and an increasing water demand, the semi-arid climate region face heightened pressure on the availability of water resources. About 85% of available water is used for irrigation in these regions. There is thus a crucial need to develop tools for a better management of irrigation through accurate estimates of crop water requirement. The objective of this study was to adapt and evaluate two parsimonious modeling approaches feeded by remote sensing observations, which have potential for the operational monitoring of evapotranspiration (ET): the two-source surface energy balance (TSEB) model developed by Norman et al. (1995) and the FAO-56 dual crop coefficient method (Allen et al., 1998), through the SAMIR tool (Simonneaux et al., 2009). At the field scale, both models were evaluated on four sites located in the Haouz plain (Marrakech, Morocco) during two agricultural seasons: wheat and sugar beet in 2012 and two other wheat crops in 2013; all belonging to an irrigated perimeter of 2800 ha. A time series of 12 high spatial resolution images acquired by SPOT-5 and ASTER images was collected during the growing seasons of wheat and sugar beet. The simulation results showed that both models offer fair performances of ET compared to measured one by eddy covariance with an average root mean square error (RMSE) lower than 1 mm/day for the sugar beet where the simulation are lower by the FAO-56 approach due to water inputs are uncertain. By contrast, the TSEB model, which not needs the water supply as input, offers smoother performances in all cases. At the scale of the perimeter, both approaches show similar spatial patterns because of homogeneous water conditions at the date of remote sensing image acquisitions. The partition of evapotranspiration between soil evaporation and transpiration from vegetation is estimated indirectly by confrontation between simulated soil evaporation and surface (0-5 cm) soil moisture acquired spatially with Theta

  13. Annual evapotranspiration retrieved from satellite vegetation indices for the eastern Mediterranean at 250 m spatial resolution

    NASA Astrophysics Data System (ADS)

    Helman, D.; Givati, A.; Lensky, I. M.

    2015-11-01

    We present a model to retrieve actual evapotranspiration (ET) from satellites' vegetation indices (Parameterization of Vegetation Indices for ET estimation model, or PaVI-E) for the eastern Mediterranean (EM) at a spatial resolution of 250 m. The model is based on the empirical relationship between satellites' vegetation indices (normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI) from MODIS) and total annual ET (ETAnnual) estimated at 16 FLUXNET sites, representing a wide range of plant functional types and ETAnnual. Empirical relationships were first examined separately for (a) annual vegetation systems (i.e. croplands and grasslands) and (b) systems with combined annual and perennial vegetation (i.e. woodlands, forests, savannah and shrublands). Vegetation indices explained most of the variance in ETAnnual in those systems (71 % for annuals, and 88 % for combined annual and perennial systems), while adding land surface temperature data in a multiple-variable regression and a modified version of the Temperature and Greenness model did not result in better correlations (p > 0.1). After establishing empirical relationships, PaVI-E was used to retrieve ETAnnual for the EM from 2000 to 2014. Models' estimates were highly correlated (R = 0.92, p < 0.01) with ETAnnual calculated from water catchment balances along rainfall gradient of the EM. They were also comparable to the coarser-resolution ET products of the Land Surface Analysis Satellite Applications Facility (LSA-SAF MSG ETa, 3.1 km) and MODIS (MOD16, 1 km) at 148 EM basins with R of 0.75 and 0.77 and relative biases of 5.2 and -5.2 %, respectively (p < 0.001 for both). In the absence of high-resolution (< 1 km) ET models for the EM the proposed model is expected to contribute to the hydrological study of this region, assisting in water resource management, which is one of the most valuable resources of this region.

  14. Comparison of evapotranspiration rates for flatwoods and ridge citrus

    USGS Publications Warehouse

    Jia, X.; Swancar, A.; Jacobs, J.M.; Dukes, M.D.; Morgan, K.

    2007-01-01

    Florida citrus groves are typically grown in two regions of the state: flatwoods and ridge. The southern flatwoods citrus area has poorly drained fine textured sands with low organic matter in the shallow root zone. Ridge citrus is located in the northern ridge citrus zone and has fine to coarse textured sands with low water-holding capacity. Two commercial citrus groves, selected from each region, were studied from 15 July 2004 to 14 July 2005. The flatwoods citrus (FC) grove had a grass cover and used drainage ditches to remove excess water from the root zone. The ridge citrus (RC) grove had a bare soil surface with weeds periodically eliminated by tillage. Citrus crop evapotranspiration (ETc) rates at the two citrus groves were measured by the eddy correlation method, and components in the energy balance were also examined and compared. The study period had higher than average rainfall, and as a result, the two locations had similar annual ETc rates (1069 and 1044 mm for RC and FC, respectively). The ETc rates were 59% (RC) and 47% (FC) of the rainfall amounts during the study period. The annual reference crop evapotranspiration (ETo) rates were 1180 mm for RC and 1419 mm for FC, estimated using the standardized reference evapotranspiration equation. The citrus crop coefficients (Kc, ratio of ETc to ET o) were different between the two locations because of differences in latitude, ground cover, and rainfall amounts. The Kc values ranged from 0.70 between December and March to 1.05 between July and November for RC, and from 0.65 between November and May to 0.85 between June and October for FC. The results are consistent with other Kc values reported from field studies on citrus in both Florida and elsewhere using these and alternate methods.

  15. EBBR Observation and fluctuation of evapotranspiration in a Cambodian evergreen forest

    NASA Astrophysics Data System (ADS)

    Shimizu, A.; Tanaka, K.; Nobuhiro, T.; Kabeya, N.; Tamai, K.; Chann, S.; Keth, N.

    2006-12-01

    In the Mekong River basin, the increase in farming associated with a rapidly growing population has lead to a dramatic reduction in forest area. The incidence of illegal logging and wood collection is also increasing throughout the entire Asian Monsoon area, including Cambodia. According to Cambodian government statistics, the proportion of forested area in Cambodia has declined from 74% in the 1970s to 58% in 1993. Despite this reduction, the area covered by forests in Cambodia remains high compared to that in adjacent countries. We measured several meteorological elements associated with evapotranspiration, runoff, and precipitation in the broadleaf forest watersheds in Kampong Thom Province of central Cambodia. The topography of the watershed studied was relatively gentle. Meteorological factors were observed with a 60-m-high meteorological observation tower to determine the amount of evapotranspiration. The Energy Balance Bowen Ratio (EBBR) system was used to calculate the energy budget above the forest canopy for estimating evapotranspiration. Moreover, an automatic rain gauge was placed at the top of the observation tower and an interception plot was established for calculating the rainfall interception ratio by forest coverage near the tower. The main vegetation species at the research site were Vatica odorata and Myristica iners. The mean tree height in the upper crown layer at the research site was 27 m, and the maximum tree height was 45 m. Meteorological data for estimation of evapotranspiration were collected from October 2003 to September 2004. The SPAC model, used for analyzing characteristics of evapotranspiration variation, is a multilayer model considering factors such as Reynolds stress, temperature and H2O exchanges of leaves and ground surface, radiation transfer within the canopy, atmospheric diffusion within and above the canopy, energy balance for leaves and ground surface, interception of rainfall, and water budget for leaves. Several

  16. Decreasing reference evapotranspiration in a warming climate - A case of Changjiang (Yangtze) River catchment during 1970-2000

    NASA Astrophysics Data System (ADS)

    Xu, C. Y.; Gong, L. B.; Tong, J.; Chen, D. L.

    2006-07-01

    This study deals with temporal trends in the Penman-Monteith reference evapotranspiration estimated from standard meteorological observations, observed pan evaporation, and four related meteorological variables during 1970-2000 in the Yangtze River catchment. Relative contributions of the four meteorological variables to changes in the reference evapotranspiration are quantified. The results show that both the reference evapotranspiration and the pan evaporation have significant. decreasing trends in the upper, the middle as well as in the whole Changjiang (Yangtze) River catchment at the 5% significance level, while the air temperature shows a significant increasing trend. The decreasing trend detected in the reference evapotranspiration can be attributed to the significant decreasing trends in the net radiation and the wind speed.

  17. Vegetation impact on mean annual evapotranspiration at a global catchment scale

    NASA Astrophysics Data System (ADS)

    Peel, Murray C.; McMahon, Thomas A.; Finlayson, Brian L.

    2010-09-01

    Research into the role of catchment vegetation within the hydrologic cycle has a long history in the hydrologic literature. Relationships between vegetation type and catchment evapotranspiration and runoff were primarily assessed through paired catchment studies during the 20th century. Results from over 200 paired catchment studies from around the world have been reported in the literature. Two constraints on utilizing the results from paired catchment studies in the wider domain have been that the catchment areas studied are generally (1) small (<10 km2) and (2) from a narrow range of climate types. The majority of reported paired catchment studies are located in the USA (˜47%) and Australia (˜27%) and experience mainly temperate (Köppen C) and cold (Köppen D) climate types. In this paper we assess the impact of vegetation type on mean annual evapotranspiration through a large, spatially, and climatically diverse data set of 699 catchments from around the world. These catchments are a subset of 861 unregulated catchments considered for the analysis. Spatially averaged precipitation and temperature data, in conjunction with runoff and land cover information, are analyzed to draw broad conclusions about the vegetation impact on mean annual evapotranspiration. In this analysis any vegetation impact signal is assessed through differences in long-term catchment average actual evapotranspiration, defined as precipitation minus runoff, between catchments grouped by vegetation type. This methodology differs from paired catchment studies where vegetation impact is assessed through streamflow responses to a controlled, within catchment, land cover change. The importance of taking the climate type experienced by the catchments into account when assessing the vegetation impact on evapotranspiration is demonstrated. Tropical and temperate forested catchments are found to have statistically significant higher median evapotranspiration, by about 170 mm and 130 mm

  18. Quantifying evapotranspiration from urban green roofs: a comparison of chamber measurements with commonly used predictive methods.

    PubMed

    Marasco, Daniel E; Hunter, Betsy N; Culligan, Patricia J; Gaffin, Stuart R; McGillis, Wade R

    2014-09-01

    Quantifying green roof evapotranspiration (ET) in urban climates is important for assessing environmental benefits, including stormwater runoff attenuation and urban heat island mitigation. In this study, a dynamic chamber method was developed to quantify ET on two extensive green roofs located in New York City, NY. Hourly chamber measurements taken from July 2009 to December 2009 and April 2012 to October 2013 illustrate both diurnal and seasonal variations in ET. Observed monthly total ET depth ranged from 0.22 cm in winter to 15.36 cm in summer. Chamber results were compared to two predictive methods for estimating ET; namely the Penman-based ASCE Standardized Reference Evapotranspiration (ASCE RET) equation, and an energy balance model, both parametrized using on-site environmental conditions. Dynamic chamber ET results were similar to ASCE RET estimates; however, the ASCE RET equation overestimated bottommost ET values during the winter months, and underestimated peak ET values during the summer months. The energy balance method was shown to underestimate ET compared the ASCE RET equation. The work highlights the utility of the chamber method for quantifying green roof evapotranspiration and indicates green roof ET might be better estimated by Penman-based evapotranspiration equations than energy balance methods.

  19. Effective crop evapotranspiration measurement using time-domain reflectometry technique in a sub-humid region

    NASA Astrophysics Data System (ADS)

    Srivastava, R. K.; Panda, R. K.; Halder, Debjani

    2016-06-01

    The primary objective of this study was to evaluate the performance of the time-domain reflectometry (TDR) technique for daily evapotranspiration estimation of peanut and maize crop in a sub-humid region. Four independent methods were used to estimate crop evapotranspiration (ETc), namely, soil water balance budgeting approach, energy balance approach—(Bowen ratio), empirical methods approach, and Pan evaporation method. The soil water balance budgeting approach utilized the soil moisture measurement by gravimetric and TDR method. The empirical evapotranspiration methods such as combination approach (FAO-56 Penman-Monteith and Penman), temperature-based approach (Hargreaves-Samani), and radiation-based approach (Priestley-Taylor, Turc, Abetw) were used to estimate the reference evapotranspiration (ET0). The daily ETc determined by the FAO-56 Penman-Monteith, Priestley-Taylor, Turc, Pan evaporation, and Bowen ratio were found to be at par with the ET values derived from the soil water balance budget; while the methods Abetw, Penman, and Hargreaves-Samani were not found to be ideal for the determination of ETc. The study illustrates the in situ applicability of the TDR method in order to make it possible for a user to choose the best way for the optimum water consumption for a given crop in a sub-humid region. The study suggests that the FAO-56 Penman-Monteith, Turc, and Priestley-Taylor can be used for the determination of crop ETc using TDR in comparison to soil water balance budget.

  20. Estimation of Soil Type Effects on Water Demand for Cultivated Wheat Fields Using RS and GIS

    NASA Astrophysics Data System (ADS)

    Ozcan, O.; Musaoglu, N.; Ormeci, C.; Seker, D. Z.

    2011-12-01

    The loss of water by evaporation as both transpiration from plants and evaporation from the underlying soil is an important factor in water resources and hydrological studies and for estimating irrigation water requirements when planning, designing, and scheduling irrigation systems, especially in arid and semi-arid conditions such as the large regions of South-Eastern Anatolia in Turkey. Improved irrigation water management requires accurate scheduling of irrigations which in turn requires an accurate calculation of daily crop evapotranspiration. Components of a satellite-based system for estimating the crop water requirements of the study area have been combined, applied, and tested against field data. Calculated reference crop evapotranspiration and crop coefficients provide a practical method for estimating actual crop evapotranspiration (Et) throughout a growing season. The aim of the study is to determine the relationship between different soil groups and water demands in different cultivated wheat fields by estimating actual crop evapotranspiration of wheat crop by using Remote Sensing and Geographical Information System (GIS) techniques. Data used in this study have been obtained from real-time monitoring areas for wheat in the area of South-Eastern Anatolia region (Turkey), describing crop growth stages with leaf area index (LAI). In the study, the SPOT 5 images for different months of growing season were used to determine the Normalized Difference Vegetation Index (NDVI) and Soil Adjusted Vegetation Index (SAVI) for areas under wheat crop. The relationship between vegetation indices and crop coefficients (Kc) of wheat for corresponding months were developed and crop coefficients were generated for each month of wheat crop season. A spectral crop coefficient for wheat that applies over a wide range of agricultural soil reflectance, obtained from SAVI provides to estimate the amount of water removed by the crop from the active root zone. Daily reference

  1. Regional evaluation of evapotranspiration in the Everglades

    USGS Publications Warehouse

    German, E.R.

    2000-01-01

    Nine sites in the Florida Everglades were selected and instrumented for collection of data necessary for evapotranspiration-determination using the Bowen-ratio energy-budget method. The sites were selected to represent the sawgrass or cattail marshes, wet prairie, and open-water areas that constitute most of the natural Everglades system. At each site, measurements necessary for evapotranspiration (ET) calculation and modeling were automatically made and stored on-site at 15- or 30-minute intervals. Data collected included air temperature and humidity at two heights, wind speed and direction, incoming solar radiation, net solar radiation, water level and temperature, soil moisture content, soil temperature, soil heat flux, and rainfall. Data summarized in this report were collected from January 1996 through December 1997, and the development of site-specific and regional models of ET for this period is described. Latent heat flux is the energy flux density equivalent of the ET rate. Modified Priestley-Taylor models of latent heat flux as a function of selected independent variables were developed at each site. These models were used to fill in periods of missing latent heat flux measurement, and to develop regional models of the entire Everglades region. The regional models may be used to estimate ET in wet prairie, sawgrass or cattail marsh, and open-water portions of the natural Everglades system. The models are not applicable to forested areas or to the brackish areas adjacent to Florida Bay. Two types of regional models were developed. One type of model uses measurements of available energy at a site, together with incoming solar energy and water depth, to estimate hourly ET. This available-energy model requires site data for net radiation, water heat storage, and soil heat flux, as well as data for incoming solar radiation and water depth. The other type of model requires only incoming solar energy, air temperature, and water depth data to provide estimates of

  2. Monitoring drought occurrences using MODIS evapotranspiration data: Direct impacts on agricultural productivity in Southern Brazil

    NASA Astrophysics Data System (ADS)

    Ruhoff, Anderson

    2014-05-01

    Evapotranspiration (ET), including water loss from plant transpiration and land evaporation, is of vital importance for understanding hydrological processes and climate dynamics and remote sensing is considered as the most important tool for estimate ET over large areas. The Moderate Resolution Imaging Spectroradiometer (MODIS) offers an interesting opportunity to evaluate ET with spatial resolution of 1 km. The MODIS global evapotranspiration algorithm (MOD16) considers both surface energy fluxes and climatic constraints on ET (water or temperature stress) to predict plant transpiration and soil evaporation based on Penman-Monteith equation. The algorithm is driven by remotely sensed and reanalysis meteorological data. In this study, MOD16 algorithm was applied to Southern Brazil to evaluate drought occurrences and its impacts over the agricultural production. Drought is a chronic potential natural disaster characterized by an extended period of time in which less water is available than expected, typically classified as meteorological, agricultural, hydrological and socioeconomic. With human-induced climate change, increases in the frequency, duration and severity of droughts are expected, leading to negative impacts in several sectors, such as agriculture, energy, transportation, urban water supply, among others. The current drought indicators are primarily based on precipitation, however only a few indicators incorporate ET and soil moisture components. ET and soil moisture play an important role in the assessment of drought severity as sensitive indicators of land drought status. To evaluate the drought occurrences in Southern Brazil from 2000 to 2012, we used the Evaporative Stress Index (ESI). The ESI, defined as 1 (one) minus the ratio of actual ET to potential ET, is one of the most important indices denoting ET and soil moisture responses to surface dryness with effects over natural ecosystems and agricultural areas. Results showed that ESI captured major

  3. Realizing actual feedback control of complex network

    NASA Astrophysics Data System (ADS)

    Tu, Chengyi; Cheng, Yuhua

    2014-06-01

    In this paper, we present the concept of feedbackability and how to identify the Minimum Feedbackability Set of an arbitrary complex directed network. Furthermore, we design an estimator and a feedback controller accessing one MFS to realize actual feedback control, i.e. control the system to our desired state according to the estimated system internal state from the output of estimator. Last but not least, we perform numerical simulations of a small linear time-invariant dynamics network and a real simple food network to verify the theoretical results. The framework presented here could make an arbitrary complex directed network realize actual feedback control and deepen our understanding of complex systems.

  4. Improving evapotranspiration processes in distrubing hydrological models using Remote Sensing derived ET products.

    NASA Astrophysics Data System (ADS)

    Abitew, T. A.; van Griensven, A.; Bauwens, W.

    2015-12-01

    Evapotranspiration is the main process in hydrology (on average around 60%), though has not received as much attention in the evaluation and calibration of hydrological models. In this study, Remote Sensing (RS) derived Evapotranspiration (ET) is used to improve the spatially distributed processes of ET of SWAT model application in the upper Mara basin (Kenya) and the Blue Nile basin (Ethiopia). The RS derived ET data is obtained from recently compiled global datasets (continuously monthly data at 1 km resolution from MOD16NBI,SSEBop,ALEXI,CMRSET models) and from regionally applied Energy Balance Models (for several cloud free days). The RS-RT data is used in different forms: Method 1) to evaluate spatially distributed evapotransiration model resultsMethod 2) to calibrate the evotranspiration processes in hydrological modelMethod 3) to bias-correct the evapotranpiration in hydrological model during simulation after changing the SWAT codesAn inter-comparison of the RS-ET products shows that at present there is a significant bias, but at the same time an agreement on the spatial variability of ET. The ensemble mean of different ET products seems the most realistic estimation and was further used in this study.The results show that:Method 1) the spatially mapped evapotranspiration of hydrological models shows clear differences when compared to RS derived evapotranspiration (low correlations). Especially evapotranspiration in forested areas is strongly underestimated compared to other land covers.Method 2) Calibration allows to improve the correlations between the RS and hydrological model results to some extent.Method 3) Bias-corrections are efficient in producing (sesonal or annual) evapotranspiration maps from hydrological models which are very similar to the patterns obtained from RS data.Though the bias-correction is very efficient, it is advised to improve the model results by better representing the ET processes by improved plant/crop computations, improved

  5. Simple analytical model of evapotranspiration in the presence of roots.

    PubMed

    Cejas, Cesare M; Hough, L A; Castaing, Jean-Christophe; Frétigny, Christian; Dreyfus, Rémi

    2014-10-01

    Evaporation of water out of a soil involves complicated and well-debated mechanisms. When plant roots are added into the soil, water transfer between the soil and the outside environment is even more complicated. Indeed, plants provide an additional process of water transfer. Water is pumped by the roots, channeled to the leaf surface, and released into the surrounding air by a process called transpiration. Prediction of the evapotranspiration of water over time in the presence of roots helps keep track of the amount of water that remains in the soil. Using a controlled visual setup of a two-dimensional model soil consisting of monodisperse glass beads, we perform experiments on actual roots grown under different relative humidity conditions. We record the total water mass loss in the medium and the position of the evaporating front that forms within the medium. We then develop a simple analytical model that predicts the position of the evaporating front as a function of time as well as the total amount of water that is lost from the medium due to the combined effects of evaporation and transpiration. The model is based on fundamental principles of evaporation fluxes and includes empirical assumptions on the quantity of open stomata in the leaves, where water transpiration occurs. Comparison between the model and experimental results shows excellent prediction of the position of the evaporating front as well as the total mass loss from evapotranspiration in the presence of roots. The model also provides a way to predict the lifetime of a plant. PMID:25375532

  6. Simple analytical model of evapotranspiration in the presence of roots

    NASA Astrophysics Data System (ADS)

    Cejas, Cesare M.; Hough, L. A.; Castaing, Jean-Christophe; Frétigny, Christian; Dreyfus, Rémi

    2014-10-01

    Evaporation of water out of a soil involves complicated and well-debated mechanisms. When plant roots are added into the soil, water transfer between the soil and the outside environment is even more complicated. Indeed, plants provide an additional process of water transfer. Water is pumped by the roots, channeled to the leaf surface, and released into the surrounding air by a process called transpiration. Prediction of the evapotranspiration of water over time in the presence of roots helps keep track of the amount of water that remains in the soil. Using a controlled visual setup of a two-dimensional model soil consisting of monodisperse glass beads, we perform experiments on actual roots grown under different relative humidity conditions. We record the total water mass loss in the medium and the position of the evaporating front that forms within the medium. We then develop a simple analytical model that predicts the position of the evaporating front as a function of time as well as the total amount of water that is lost from the medium due to the combined effects of evaporation and transpiration. The model is based on fundamental principles of evaporation fluxes and includes empirical assumptions on the quantity of open stomata in the leaves, where water transpiration occurs. Comparison between the model and experimental results shows excellent prediction of the position of the evaporating front as well as the total mass loss from evapotranspiration in the presence of roots. The model also provides a way to predict the lifetime of a plant.

  7. Reference Crop Evapotranspiration obtained from the geostationary satellite MSG (METEOSAT).

    NASA Astrophysics Data System (ADS)

    de Bruin, H. A. R.; Trigo, I. F.; Lorite, I. J.; Cruz-Blanco, M.; Gavilán, P.

    2012-04-01

    Among others, the scope of the Land Surface Analysis Satellite Applications Facility (LSA SAF) is to increase benefit from the EUMETSAT geostationary Satellites MSG data related to land, land-atmosphere interactions and biophysical applications. This is achieved by developing techniques, products and algorithms that will allow an effective use of MSG data, if needed, combined with data from numerical weather prediction models (e.g., ECMWF). Although directly designed to improve the observation of meteorological systems, the spectral characteristics, time resolution and area coverage offered by MSG allow for their use in a broad spectrum of other applications, for instance in agro- and hydrometeorology. This study concerns a method to determine how much water is needed for irrigation. Note that this is complementary to the actual evapotranspiration LSA SAF product. The objective of this study is to present a novel semi-empirical method to determine the Reference Crop Evapotranspiration (ET0) from the down-welling shortwave radiation and air temperature obtained through LSF SAF. ET0 is defined in the FAO Irrigation and Drainage report 56 (FAO56) and it is used to determine water requirements of agricultural crops in irrigated regions. It is evaluated with a special version of the Penman-Monteith equation (PM_FAO56) using data of a weather station installed over non-stressed grass. Such stations are expensive and very labor consuming. We developed our method for semi-arid regions where appropriate weather stations needed for FAO56 ET0 are missing. This concerns huge areas in the world. High-quality FAO-grass station near Cordoba, Spain were used, where, besides all input for PM-FAO56, independent lysimeter data are collected. In addition, it will be shown that significant errors in ET0 can occur if meteorological gathered over dry terrain will be used as input of PM-FAO56. For this purpose data sets obtained in different semi-arid regions will be analyzed.

  8. A calibration-free evapotranspiration mapping technique

    NASA Astrophysics Data System (ADS)

    Szilagyi, J.

    2010-12-01

    With the availability of Moderate Resolution Imaging Spectroradiometer (MODIS) data the spatial distribution of the resulting daytime land surface temperature (Ts) can be tracked at a resolution of about 1-km. A simple, self-calibrating linear transformation of the Ts values into evapotranspiration (ET) rates is possible if the following criteria are met: a) the vertical gradient of the air temperature near the surface is directly proportional to Ts; b) net energy available for sensible and latent heat transfer at the surface is quasi-constant in space; c) heat conduction into the soil is negligible, and; d) land-surface properties do not change drastically over space. The validity of a) has been proved by such models as SEBAL and METRIC. Requirement b) is fulfilled over a flat or rolling terrain provided the probability distribution of the surface albedo values of the MODIS cells has a narrow spread, which is the case for the two study areas (Hungary and Nebraska) with a characteristic vegetation-period mean of about 16% and a standard deviation of 1.4%. Heat conduction into the soil can be considered negligible for periods longer than a day, thus the 8-day composited Ts values employed in the present study comply with this requirement. Finally, for periods longer than a day, the assumption of near-neutral atmospheric conditions is justified which entails that spatial variations in surface properties have a significantly dampened effect on the flux-transfer coefficient (i.e., aerodynamic resistance) value which therefore can be considered as quasi-constant in space. The linear transformation of the Ts values into ET rates in this study has been performed on a monthly basis. The transformation requires specifying two anchor points in the Ts - ET plane with the help of standard atmospheric variables, such as air temperature and humidity, as well as incident global radiation, or in lieu of it, sunshine duration. From March to November ET has been mapped for Hungary

  9. Intercomparison of Evapotranspiration Over the Savannah Volta Basin in West Africa Using Remote Sensing Data

    PubMed Central

    Opoku-Duah, S.; Donoghue, D.N.M.; Burt, T. P.

    2008-01-01

    This paper compares evapotranspiration estimates from two complementary satellite sensors – NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) and ESA's ENVISAT Advanced Along-Track Scanning Radiometer (AATSR) over the savannah area of the Volta basin in West Africa. This was achieved through solving for evapotranspiration on the basis of the regional energy balance equation, which was computationally-driven by the Surface Energy Balance Algorithm for Land algorithm (SEBAL). The results showed that both sensors are potentially good sources of evapotranspiration estimates over large heterogeneous landscapes. The MODIS sensor measured daily evapotranspiration reasonably well with a strong spatial correlation (R2=0.71) with Landsat ETM+ but underperformed with deviations up to ∼2.0 mm day-1, when compared with local eddy correlation observations and the Penman-Monteith method mainly because of scale mismatch. The AATSR sensor produced much poorer correlations (R2=0.13) with Landsat ETM+ and conventional ET methods also because of differences in atmospheric correction and sensor calibration over land.

  10. Evaluation of the relation between evapotranspiration and normalized difference vegetation index for downscaling the simplified surface energy balance model

    USGS Publications Warehouse

    Haynes, Jonathan V.; Senay, Gabriel B.

    2012-01-01

    The Simplified Surface Energy Balance (SSEB) model uses satellite imagery to estimate actual evapotranspiration (ETa) at 1-kilometer resolution. SSEB ETa is useful for estimating irrigation water use; however, resolution limitations restrict its use to regional scale applications. The U.S. Geological Survey investigated the downscaling potential of SSEB ETa from 1 kilometer to 250 meters by correlating ETa with the Normalized Difference Vegetation Index (NDVI) from the Moderate Resolution Imaging Spectroradiometer instrument (MODIS). Correlations were studied in three arid to semiarid irrigated landscapes of the Western United States (Escalante Valley near Enterprise, Utah; Palo Verde Valley near Blythe, California; and part of the Columbia Plateau near Quincy, Washington) during several periods from 2002 to 2008. Irrigation season ETa-NDVI correlations were lower than expected, ranging from R2 of 0.20 to 0.61 because of an eastward 2-3 kilometer shift in ETa data. The shift is due to a similar shift identified in the land-surface temperature (LST) data from the MODIS Terra satellite, which is used in the SSEB model. Further study is needed to delineate the Terra LST shift, its effect on SSEB ETa, and the relation between ETa and NDVI.

  11. Predicting interannual variability in evapotranspiration rates

    NASA Astrophysics Data System (ADS)

    Schultz, Colin

    2011-11-01

    The amount of evapotranspiration (ET), the sum of all the water that evaporates from the surface or is drawn up through plants and vented as vapor, is a strong controlling factor for the amount of water left over for other purposes, such as groundwater recharge or surface runoff. Understanding how ET rates vary from year to year is challenging, because the change is inherently controlled by small-scale variations in vegetation type and density, soil properties, and meteorological conditions. Yet there has been some success understanding variations in ET at the watershed scale. Analyzing daily measurements of evapotranspiration for 547 watersheds across the United States from 1983 to 2006, Cheng et al. identified a strong linear relationship between two slightly different ratios: the ratio between the watershed's potential evapotranspiration (PET) and precipitation and that between observed ET and precipitation. This is surprising because many previous studies suggested a nonlinear relationship between the two ratios by following the Budyko framework, a dominant approach in water cycle modeling that relates ET rates to the amount of energy and water in the system.

  12. Anthropogenic influence on multidecadal changes in reconstructed global evapotranspiration

    NASA Astrophysics Data System (ADS)

    Douville, H.; Ribes, A.; Decharme, B.; Alkama, R.; Sheffield, J.

    2013-01-01

    Global warming is expected to intensify the global hydrological cycle, with an increase of both evapotranspiration (EVT) and precipitation. Yet, the magnitude and spatial distribution of this global and annual mean response remains highly uncertain. Better constraining land EVT in twenty-first-century climate scenarios is critical for predicting changes in surface climate, including heatwaves and droughts, evaluating impacts on ecosystems and water resources, and designing adaptation policies. Continental scale EVT changes may already be underway, but have never been attributed to anthropogenic emissions of greenhouse gases and sulphate aerosols. Here we provide global gridded estimates of annual EVT and demonstrate that the latitudinal and decadal differentiation of recent EVT variations cannot be understood without invoking the anthropogenic radiative forcings. In the mid-latitudes, the emerging picture of enhanced EVT confirms the end of the dimming decades and highlights the possible threat posed by increasing drought frequency to managing water resources and achieving food security in a changing climate.

  13. Estimating sugarcane water requirements for biofuel feedstock production in Maui, Hawaii using satellite imagery

    NASA Astrophysics Data System (ADS)

    Zhang, H.; Anderson, R. G.; Wang, D.

    2011-12-01

    Water availability is one of the limiting factors for sustainable production of biofuel crops. A common method for determining crop water requirement is to multiply daily potential evapotranspiration (ETo) calculated from meteorological parameters by a crop coefficient (Kc) to obtain actual crop evapotranspiration (ETc). Generic Kc values are available for many crop types but not for sugarcane in Maui, Hawaii, which grows on a relatively unstudied biennial cycle. In this study, an algorithm is being developed to estimate sugarcane Kc using normalized difference vegetation index (NDVI) derived from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imagery. A series of ASTER NDVI maps were used to depict canopy development over time or fractional canopy cover (fc) which was measured with a handheld multispectral camera in the fields during satellite overpass days. Canopy cover was correlated with NDVI values. Then the NDVI based canopy cover was used to estimate Kc curves for sugarcane plants. The remotely estimated Kc and ETc values were compared and validated with ground-truth ETc measurements. The approach is a promising tool for large scale estimation of evapotranspiration of sugarcane or other biofuel crops.

  14. The groundwater recharge response and hydrologic services of tropical humid forest ecosystems to use and reforestation: Support for the “infiltration-evapotranspiration trade-off hypothesis”

    NASA Astrophysics Data System (ADS)

    Krishnaswamy, Jagdish; Bonell, Michael; Venkatesh, Basappa; Purandara, Bekal K.; Rakesh, K. N.; Lele, Sharachchandra; Kiran, M. C.; Reddy, Veerabasawant; Badiger, Shrinivas

    2013-08-01

    The hydrologic effects of forest use and reforestation of degraded lands in the humid tropics has implications for local and regional hydrologic services but such issues have been relatively less studied when compared to the impacts of forest conversion. In particular, the “infiltration-evapotranspiration trade-off” hypothesis which predicts a net gain or loss to baseflow and dry-season flow under both, forest degradation or reforestation depending on conditions has not been tested adequately. In the Western Ghats of India, we examined the hydrologic responses and groundwater recharge and hydrologic services linked with three ecosystems, (1) remnant tropical evergreen forest (NF), (2) heavily-used former evergreen forest which now has been converted to tree savanna, known as degraded forest(DF), and (3) exotic Acacia plantations (AC, Acacia auriculiformis) on degraded former forest land. Instrumented catchments ranging from 7 to 23 ha representing these three land-covers (3 NF, 4 AC and 4 DF, in total 11 basins), were established and maintained between 2003 and 2005 at three sites in two geomorphological zones, Coastal and Up-Ghat (Malnaad). Four larger (1-2 km2) catchments downstream of the head-water catchments in the Malnaad with varying proportions of different land-cover and providing irrigation water for areca-nut and paddy rice were also measured for post-monsoon baseflow. Daily hydrological and climate data was available at all the sites. In addition, 36 min data was available at the Coastal site for 41 days as part of the opening phase of the summer monsoon, June-July 2005. Low potential and actual evapotranspiration rates during the monsoon that are similar across all land-cover ensures that the main control on the extent of groundwater recharge during the south-west monsoon is the proportion of rainfall that is converted into quick flow rather than differences in evapotranspiration between the different land cover types. The Flow duration curves

  15. RIPGIS-NET: a GIS tool for riparian groundwater evapotranspiration in MODFLOW.

    PubMed

    Ajami, Hoori; Maddock, Thomas; Meixner, Thomas; Hogan, James F; Guertin, D Phillip

    2012-01-01

    RIPGIS-NET, an Environmental System Research Institute (ESRI's) ArcGIS 9.2/9.3 custom application, was developed to derive parameters and visualize results of spatially explicit riparian groundwater evapotranspiration (ETg), evapotranspiration from saturated zone, in groundwater flow models for ecohydrology, riparian ecosystem management, and stream restoration. Specifically RIPGIS-NET works with riparian evapotranspiration (RIP-ET), a modeling package that works with the MODFLOW groundwater flow model. RIP-ET improves ETg simulations by using a set of eco-physiologically based ETg curves for plant functional subgroups (PFSGs), and separates ground evaporation and plant transpiration processes from the water table. The RIPGIS-NET program was developed in Visual Basic 2005, .NET framework 2.0, and runs in ArcMap 9.2 and 9.3 applications. RIPGIS-NET, a pre- and post-processor for RIP-ET, incorporates spatial variability of riparian vegetation and land surface elevation into ETg estimation in MODFLOW groundwater models. RIPGIS-NET derives RIP-ET input parameters including PFSG evapotranspiration curve parameters, fractional coverage areas of each PFSG in a MODFLOW cell, and average surface elevation per riparian vegetation polygon using a digital elevation model. RIPGIS-NET also provides visualization tools for modelers to create head maps, depth to water table (DTWT) maps, and plot DTWT for a PFSG in a polygon in the Geographic Information System based on MODFLOW simulation results.

  16. Observing Seasonal and Diurnal Hydrometeorological Variability Within a Tropical Alpine Valley: Implications for Evapotranspiration

    NASA Astrophysics Data System (ADS)

    Hellstrom, R. A.; Mark, B. G.

    2007-12-01

    Conditions of glacier recession in the seasonally dry tropical Peruvian Andes motivate research to better constrain the hydrological balance in alpine valleys. There is an outstanding need to better understand the impact of the pronounced tropical hygric seasonality on energy and water budgets within pro-glacial valleys that channel glacier runoff to stream flow. This paper presents a novel embedded network installed in the glacierized Llanganuco valley of the Cordillera Blanca (9°S) comprising eight low-cost, discrete temperature and humidity microloggers ranging from 3470 to 4740 masl and an automatic weather station at 3850 masl. Data are aggregated into distinct dry and wet periods sampled from two full annual cycles (2004-2006) to explore patterns of diurnal and seasonal variability. The magnitude of diurnal solar radiation varies little within the valley between the dry and wet periods, while wet season near-surface air temperatures are cooler. Seasonally characteristic diurnal fluctuations in lapse rate partially regulate convection and humidity. Steep lapse rates during the wet season afternoon promote up-slope convection of warm, moist air and nocturnal rainfall events. Standardized grass reference evapotranspiration (ET0) was estimated using the FAO-56 algorithm of the United Nations Food and Agriculture Organization and compared with estimates of actual ET from the process-based BROOK90 model that incorporates more realistic vegetation parameters. Comparisons of composite diurnal cycles of ET for the wet and dry periods suggest about twice the daily ET0 during the dry period, attributed primarily to the 500% higher vapor pressure deficit and 20% higher daily total solar irradiance. Conversely, the near absence of rainfall during the dry season diminishes actual ET below that of the wet season by two orders of magnitude. Nearly cloud-free daylight conditions are critical for ET during the wet season. We found significant variability of ET with elevation

  17. Evapotranspiration crop coefficients for mixed riparian plant community and transpiration crop coefficients for Common reed, Cottonwood and Peach-leaf willow in the Platte River Basin, Nebraska-USA

    NASA Astrophysics Data System (ADS)

    Irmak, S.; Kabenge, I.; Rudnick, D.; Knezevic, S.; Woodward, D.; Moravek, M.

    2013-02-01

    SummaryApplication of two-step approach of evapotranspiration (ET) crop coefficients (Kc) to "approximate" a very complex process of actual evapotranspiration (ETa) for field crops