Crucial drivers and interaction mechanisms of ecosystem water use efficiency in the Yellow River Basin, China

Study region: The Yellow River Basin (YRB), China. Study focus: This study investigates the spatiotemporal trends of water use efficiency (WUE) in the YRB from 2001 to 2020 using ordinary least squares (OLS) regression and Sen's slope estimator. It integrates multi-source spatial data, random forest, and partial least square-structural equation modeling to identify key drivers and quantify the direct and indirect effects of the main driving forces on WUE, including an analysis of the antagonistic or synergistic relationships between these effects. New hydrological insights for the region: Results showed an overall increase in WUE in the YRB, with OLS and Sen's slopes of 0.02 and 0.128 gC·m−2·mm−1·yr−1, respectively. Key drivers included leaf area index, night lights, soil water, elevation, landform relief, temperature, precipitation, and solar radiation. The five-year average effect intensities ranked as: water conditions (0.646) > leaf area index (0.506) > human actvities (0.235) > radiation–temperature (0.115) > geographic environment (0.070). The direct effect of radiation–temperature on WUE was positive; however, negative indirect effects antagonized this contribution, resulting in a net negative total effect. Water conditions and human activities showed synergistic effects that reinforced their positive impacts, whereas the geographic environment exhibited mainly negative direct effects partially offset by positive indirect consequences. These findings demonstrate that strategically leveraging mediating effects can effectively enhance the sustainability of ecosystem WUE in the basin.