Abstract
This study proposes a method for improving the estimation of surface turbulent fluxes in surface energy balance system (SEBS) model under water stress conditions using MODIS data. The normalized difference water index (NDWI) as an indicator of water stress is integrated into SEBS. To investigate the feasibility of the new approach, the desert-oasis region in the middle reaches of the Heihe River Basin (HRB) is selected as the study area. The proposed model is calibrated with meteorological and flux data over 2008–2011 at the Yingke station and is verified with data from 16 stations of the Heihe Watershed Allied Telemetry Experimental Research (HiWATER) project in 2012. The results show that soil moisture significantly affects evapotranspiration (ET) under water stress conditions in the study area. Adding the NDWI in SEBS can significantly improve the estimations of surface turbulent fluxes in water-limited regions, especially for spare vegetation cover area. The daily ET maps generated by the new model also show improvements in drylands with low ET values. This study demonstrates that integrating the NDWI into SEBS as an indicator of water stress is an effective way to improve the assessment of the regional ET in semi-arid and arid regions.
Highlights
Evapotranspiration (ET), which is the sum of soil surface evaporation and plant tissue transpiration, is an important energy exchange process of the soil-vegetation-atmosphere system that affects the redistribution of terrestrial surface radiation and precipitation [1]
When the soil water availability is sufficiently high (i.e., SM is greater than 0.3 m3/m3), ET is controlled by the available radiant energy, and the effect of soil moisture on ET is not siRgenmiofitecSaenns.t.2015, 7 page–page
Surface Energy Balance System (SEBS), which estimates evapotranspiration from the energy balance, does not explicitly consider soil moisture when calculating land surface fluxes and ET, but it assumes that the soil moisture information is incorporated into the land surface temperature state variable
Summary
Evapotranspiration (ET), which is the sum of soil surface evaporation and plant tissue transpiration, is an important energy exchange process of the soil-vegetation-atmosphere system that affects the redistribution of terrestrial surface radiation and precipitation [1]. Examples of these models include the Surface Energy Balance Algorithm for Land (SEBAL) [15], the Simplified Surface Energy Balance Index (S-SEBI) [16], the Surface Energy Balance System (SEBS) [17], the satellite-based energy balance for Mapping Evapotranspiration with Internalized Calibration (METRIC) [18], and the Two-Source Energy Balance Model (TSEB) [19], which have been thoroughly discussed in a previous study [20] Data assimilation is such a methods that can be used to combine land surface models and observations to accurately estimate ET on a continuous spatial and temporal scale [21,22,23]. Comparisons of different methods for estimating land surface fluxes at the local and global scales have demonstrated that the models have different degrees of success [24,25]
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