Differentiating the Impacts of Natural Growth and Artificial Restoration of Vegetation on Water Use Efficiency in the Yellow River Basin

Abstract Vegetation change is closely linked to fluctuations in ecosystem water use efficiency (WUE). Although vegetation change (VC) involves the natural growth (NG) and the artificial restoration (AR), the individual impacts of these two processes on WUE remain poorly understood. This study used a recently developed ecohydrological model, integrating observed streamflow and multiple remote sensing data sets, to quantify the effects of NG and AR on WUE through three distinct vegetation scenarios in the Yellow River Basin (YRB) of China from 1998 to 2020. This region has experienced remarkable vegetation changes due to both natural and anthropogenic factors. The results show that, on average, VC led to a 13.3% increase in WUE in the YRB. However, NG and AR had contrasting impacts: the former contributed to a 7.4% decrease in WUE, whereas the latter caused a 22.4% increase in WUE. Spatially, NG reduced WUE in the southeastern YRB and the marginal areas of the Tibetan Plateau with somewhat higher precipitation but increased WUE in certain northern and northwestern regions of the YRB with lower precipitation. In contrast, AR generally reduced WUE in arid regions but increased WUE in wetter ones, showing effects opposite to those of NG. However, in specific areas like the Mu Us Sandy Land, a typical dry region, both NG and AR enlarged WUE. In all scenarios, the primary driver of WUE changes appeared to be net primary productivity rather than evapotranspiration. This study provides practical insights for sustainable water resource and ecological management.