Increased evapotranspiration from land cover changes intensified water crisis in an arid river basin in northwest China

Evapotranspiration (ET) plays an important role in determining the available water resources of a basin. In past decades, the Heihe River basin (HRB) in Northwest China has suffered severe water crisis and ecological problems due to large land cover changes (LCCs), especially oases expansion for irrigation agriculture. This study quantifies the ET variations due to LCCs in the HRB from 2000 to 2015 using the Ecological Assimilation of Land and Climate Observations (EALCO) model and detailed LCC measurements. Large variations in ET with land cover type is seen in the HRB. In the past fifteen years, crop expansion from bare soil or desert grass caused most of the increase in ET, while the conversion of alpine grass to desert grass caused most of the decrease in ET. As a result, a net 1.03 billion m3 of increased water consumption per year resulted from the overall LCCs in the HRB. This increased water use for ET largely intensified the water crisis in the HRB and deteriorated the health of the downstream ecosystems. Our results show that the water consumed in crop expansion can be used to recover almost ten times the area of the degraded desert grass ecosystem. A stricter policy that limits agriculture expansion is recommended in land use planning for a sustainable ecosystem development in the basin. This study also helps to better understand ET changes from LCCs and manage the limited water resources for sustainable ecosystem development in other arid regions of the world.