Enhanced evapotranspiration induced by vegetation restoration may pose water resource risks under climate change in the Yellow River Basin

Quantifying the impacts of climate change, vegetation greening and human activities (CVH) on evapotranspiration (ET), surface drought intensity (ET divided by precipitation, SDI), and vegetation available water (precipitation minus ET, VAW) would improve our understanding of water cycle processes. The Yellow River Basin (YRB) is a significant climate-sensitive region in China, resulting in an obvious spatiotemporal heterogeneity of ET, SDI, and VAW in response to driving variables. In this study, we analysed the spatiotemporal variation characteristics of ET, SDI, and VAW in the YRB from 1984 to 2018. We also quantified the direct and indirect contributions of the CVH to the changes in ET, SDI, and VAW, and revealed the influence mechanism of each link. Finally, water resource risks were assessed from a probabilistic perspective. The results indicated that vegetation greening was the primary driver of ET with an increase rate of 1.60 mm/a, which was also the most important influencing factor of SDI increase and VAW decrease. Leaf area index (LAI) and relative humidity (RH) jointly dominated the ET changes in 66 % of the YRB, temperature (Temp) dominated the SDI changes in nearly half of the basin, precipitation (Pre) and LAI jointly dominated the VAW changes in 66 % of the YRB. Temp indirectly influenced ET primarily through LAI, whereas LAI primarily influenced ET directly. Temp had a significant direct impact on SDI, while LAI mainly influenced SDI through RH and wind speed (WS). Temp exhibited the most substantial negative influence on VAW. LAI was identified as the primary factor contributing to water resource risks, with a probability reaching 0.8, while the probabilities associated with other factors inducing such risks were similar at the basin level, but disparities existed among different land use types. The findings of the study significantly enhanced our understanding of the role that the CVH played in hydrological processes, serving as a crucial foundation for achieving a balance between ecological restoration and socio-economic development in the YRB.