Modelling the spatial distribution of daily evapotranspiration based on GIS in the middle Heihe River Basin, China

Understanding reference crop evapotranspiration (ET0) is essential in planning economic uses of water resource in the and northwest China. The major purpose in this work is to estimate areal distribution of reference crop evapotranspiration using meteorological data based GIS-assisted methods in the middle Heibe River basin. The spatially-modeled results of ET0 were tested by the station-observed ET0 on 15(th) of each month at the six representative stations. The modeled ET(0)s are good agreement with those measured in situ, assuring our confidence on the spatially-modeled results of ET0. From the approach, conclusion can be drawn that FAO-Pemnan model may be the best way to estimate ET0 in the study area. ET0 has temporal and spatial variation. Spatially, the higher ET0 values are registered in the western part of Heihe River and lower ET0 value appears in the middle-eastern part. Temporally, the daily differences in ET0 rates are mainly due to daily differences in irradiance (R-n) and to daily differences in vapor pressure deficit (D).