Evapotranspiration Characteristics of Different Oases and Effects of Human Activities on Evapotranspiration in Heihe River Basin

Evapotranspiration plays a decisive role in the whole oasis ecosystem and is an important factor to maintain the ecological stability of oases. To quantitatively analyze the evapotranspiration differences of oases at different scales and the expansion of urbanization, it is necessary to compare and discuss them at different time scales. In this study, the spatial and temporal characteristics of evapotranspiration of Zhangye Oasis, Jinta Oasis, and Ejina Oasis in the Heihe River basin were analyzed by using the remote sensing dataset of daily surface evapotranspiration of 100 m resolution from 2010 to 2016. The difference in evapotranspiration intensity in different oases was analyzed, and the influences of irrigation and urbanization expansion on evapotranspiration were discussed. The conclusion is as follows: Zhangye Oasis is the largest oasis in the area and, compared with other oases, due to the largest proportion of wetland and farmland in the underlying surface, the intensity of evapotranspiration is also the largest, reaching 650 mm/year on average. There is no obvious annual change; the range of evapotranspiration changes fluctuates between positive and negative 60 mm/year. Jinta Oasis began to decline after 2012; the evapotranspiration value dropped from 620 mm/tear to 560 mm/year, while Ejina Oasis showed a slight increase after 2014. In the irrigation stage, the evapotranspiration intensity increased significantly. Especially in the peak season of crop growth, the evapotranspiration after irrigation increased by 4 mm/day compared with that before irrigation. The evapotranspiration in urban and oasis areas is different in summer: compare that of 2010 with 2016—the evapotranspiration intensity of the expanding towns in the northeast direction decreased by about 50 mm/month, the northwest expanding towns decreased by about 110 mm/month. There was no obvious annual change in evapotranspiration in the urban area. With the expansion of urbanization, the evapotranspiration intensity in oases decreased. The results of this study provide some reference for the study of oasis irrigation activities and urbanization expansion.