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United States Department of Agriculture

Agricultural Research Service

Research Project: Ecohydrological Processes, Scale, Climate Variability, and Watershed Management

Location: Southwest Watershed Research

Title: Modeling evapotranspiration and its partitioning over a semiarid shrub ecosystem from satellite imagery: a multiple validation

Authors
item Yang, Y. -
item SCOTT, RUSSELL
item Shang, S -

Submitted to: Journal of Applied Remote Sensing (JARS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 1, 2013
Publication Date: October 25, 2013
Citation: Yang, Y., Scott, R.L., Shang, S. 2013. Modeling evapotranspiration and its partitioning over a semiarid shrub ecosystem from satellite imagery: a multiple validation. Journal of Applied Remote Sensing (JARS). 7:1-16. DOI: 10.1117/1.JRS.7.073495.

Interpretive Summary: Evapotranspiration (ET) is a major component of the global water cycle, but it is difficult to measure. Furthermore, even when such sophisticated measurements are available, information about how much ET is from bare soil evaporation (E) and how much is from plant transpiration (T) is often desired to better understand the water use of ecosystems. In this paper, an algorithm that combines routine satellite measurements with ground-based ET measurements to partition ET into its respective components was tested with measurements of E and T made in a desert shrubland environment in Arizona where it was relatively easier to measure E and T separately. The algorithm capably produced accurate estimates of E and T at the time of the satellite measurements, though challenges about how to interpolate the estimates between satellite measurements which are available once every few days to weeks remain.

Technical Abstract: Numerous modeling approaches have been proposed to estimate evapotranspiration (ET) and its partitioning between evaporation from soil (E) and transpiration from vegetation (T) over the last several decades. Although these ET models claimed to give reasonable E and T partitioning, few studies have compared their modeling results with direct E and T observations. In this study, a hybrid dual source scheme and trapezoid framework based evapotranspiration model (HTEM) fed with MODIS data was applied in a Chihuahuan Desert shrubland during the growing season of 2003 and validated with direct ET measurement using the Bowen-ratio technique and T measurement using scaled-up sap-flow measurements. Results show that the HTEM is capable of decomposing the remotely sensed land surface temperature into temperature components (soil and canopy temperatures) and providing accurate E and T estimates. At satellite overpass time, the root-mean-square error (RMSE) of estimated latent heat flux (LE) is 47.7 W/m2. The agreement between estimated and simulated LE was largely improved when observed net radiation and ground heat flux were used (35.1 W/m2). At daily scale, the RMSE of estimated daily ET, E, and T are 0.52, 0.36, and 0.41 mm/day, respectively.umerous modeling approaches have been proposed to estimate ET and its partitioning between evaporation from soil (E) and transpiration from vegetation (T) over the last several decades. Although these ET models claimed to give reasonable E and T partitioning, few studies have compared their modeling results with direct E and T observations. In this study, a Hybrid dual source scheme and Trapezoid framework based Evapotranspiration Model (HTEM) fed with MODIS data was applied in a Chihuahuan Desert shrubland during the growing season of 2003, and validated with direct ET measurement using Bowen-ratio technique and T measurement using scaled-up sap-flow measurements. Results show that the HTEM is capable of decomposing the remotely sensed land surface temperature into component temperatures (soil and canopy temperatures) and providing accurate E and T estimates. At satellite overpass time, the root-mean-square error (RMSE) of estimated latent heat flux (LE) is 47.7 W/m2. The agreement between estimated and simulated LE was largely improved when observed net radiation and ground heat flux were used (35.137 W/m2). At daily scale, the RMSE of estimated daily ET, E and T are 0.52, 0.36, 0.41 mm/day, respectively.

Last Modified: 7/25/2014
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