Contributions of climate change and vegetation greening to evapotranspiration trend in a typical hilly-gully basin on the Loess Plateau, China

Significant increases in vegetation cover on the Loess Plateau since the early 2000s have been well documented. However, the relevant hydrological effects are still unclear. Here, we investigated the changes in actual evapotranspiration (ETa) from 2000 to 2016 and related them to climate change and vegetation greening in Yanhe River basin (YRB), a typical hilly-gully basin on the Loess Plateau, by using the remote-sensing based VIP model. Results showed that the annual ETa in the YRB increased significantly with a trend of 3.45mmyr-1 (p<0.01) and changes of ETa in summer months dominated the annual trend. Partial correlation analysis suggested that vegetation greening was the dominant driving factor of ETa inter-annual variations in 56% area of YRB. Model simulation experiments illustrated that relative contributions of NDVI, precipitation, and potential evapotranspiration (ETp) to the ETa trend were 93.0%, 18.1%, and -7.4%, respectively. Vegetation greening, which is closely related to the Grain for Green (GFG) afforestation, was the main driver to the long-term tendency of water consumption in the YRB. This study highlights potential water demanding conflicts between the socio-economic system and the natural ecosystem on the Loess Plateau due to the rapid vegetation expansion in this water-limited area.