Estimation of potential evapotranspiration and its variability in the upper and middle reaches of the Heihe River basin

On the basis of the MODIS LAI remote sensing products, China Meteorological Forcing Dataset and other multi-source datasets, the Shuttleworth-Wallace (S-W) model, which considers the temporal variation of leaf area index (LAI), was applied to estimate potential evapotranspiration (ETP) during the period of 2000-2010 in the upstream and midstream areas of the Heihe River basin. To investigate the temporal and spatial variability of ETP, sensitivity of ETP to meteorological parameters and LAI was calculated for each land cover type. To compare ETP and ET0 values for runoff simulation, a conceptual hydrologic model with precipitation and ETP or ET0 was developed in the upstream area of the Heihe River basin. Results showed that: (1) S-W model, based on high-resolution remote sensing datasets, was able to accurately estimate annual and seasonal ETP in large river basins with complex underlying surfaces as well as in ungauged basins. The values of ETP in summer contributed more to the annual value than those of other seasons. ETP in areas with different land cover types varied greatly. Generally speaking, ETP decreased with the development of vegetation. (2) In the study area, ETP was most sensitive to relative humidity. The sensitivity of ETP to LAI was as great as that to net solar radiation. The sensitivity of ETP to meteorological parameters and LAI became greater with the decline of vegetation. (3) Compared with hydrologic model with ET0 calculated by P-M model, the model with ETP better simulated the depth of runoff at Yingluoxia hydrologic station. Hence, ETP calculated by S-W model was more suitable for the simulation of runoff in the present study. ©, 2015, Science Press. All right reserved.