Estimating and validating basin-scale actual evapotranspiration using MODIS images and hydrologic models

An algorithm for estimating daily spatial actual evapotranspiration (ET) from remotely sensed MODIS data is presented. It is based on the surface energy balance scheme and the modified Priestley–Taylor equation, and has been applied to the MODIS data acquired during growing seasons over the Laohahe River basin, northeastern China. Spatial distributed mapping of daily ET for 22 clear sky days in the year of 2000 from MODIS images over the study area were obtained. In order to validate ET values estimated from MODIS data, regional daily ET values were calculated using the lumped modified Xinanjiang hydrologic model and distributed SWAT model based on the water balance scheme, respectively. The relationship between actual daily ET estimated from MODIS images and basin-scale ET calculated from the hydrologic model were in good agreement with acceptable correlation coefficient. The results suggested that the algorithm is applicable and operational for estimating and mapping basin-scale distributed daily actual ET over the study area. In order to use the algorithm proposed by this paper for water resource management and agricultural decision making, the algorithm should be validated using more data and be tested under different environment and different land use scenario conditions in future work.