Sensitivity of Potential Evapotranspiration to Climate and Vegetation in a Water-Limited Basin at the Northern Edge of Tibetan Plateau

Potential evapotranspiration (PET) is important for both hydrological studies and water resources management, especially in arid regions. To better understand how PET varies due to the changing environment, analysis of the sensitivity of PET to climate and underlying surface characteristics is an important necessity. Based on gridded multi-source data sets, the present study estimated PET by using the Shuttleworth-Wallace model from 2000 to 2010 in the upstream and midstream areas of the Heihe River basin. Sensitivity coefficient and contribution coefficient of each parameter were calculated by the sensitivity coefficient method to quantitatively detect and compare the effect of changes in vegetation and climate exerted on the variation of PET. Results showed that: (1) PET varied greatly in the study area. Both climate and vegetation exert effects on the variation of PET; (2) PET is most sensitive to relative humidity in the study area. The sensitivity of PET to vegetation was also great and it increased with the decline of vegetation; (3) relative humidity contributed more to the intra-annual variation than other selected parameters. Vegetation indicated by LAI contribute more than net solar radiation. With this study, our understanding of variations of PET and its driving factors could be expanded from meteorological aspects to vegetation or ecological aspects, which is quite important for eco-hydrology and agricultural water resources management.