Evaluating Methods of Estimation and Modelling Spatial Distribution of Evapotranspiration in the Middle Heihe River Basin, China

Seven models commonly used to estimate the daily reference evapotranspiration (ET₀) were evaluated in the middle Heihe River Basin of the arid northwestern part of China. The objectives of the study are to choose the appropriate model for estimating the areal distribution of ET₀ and to explain the spatial-temporal distribution of the same through GIS in the study area. The results indicated that the FAO-Penman model is the best way to estimate ET₀; its RMSE ranged from 1.11 to 1.70 mm, and r² from 0.59 to 0.93. The spatial variations of ET₀ are higher in the western part than in the middle-eastern part of the study area. The temporal variations of daily differences in ET₀ rates are mainly due to the differences in irradiance (R_n) and to daily differences in the vapor pressure deficit (D). The spatially modeled ET₀ results (r² = 0.88) are in agreement with the corresponding data in situ on the 15th of each month.