Competing Effects of Vegetation Greening-Induced Changes in Summer Evapotranspiration and Precipitation on Water Yield in the Yangtze River Basin Based on WRF Simulations

Remarkable vegetation greening has been observed in the Yangtze River Basin (YRB) during the past two decades, triggering noteworthy hydrological consequences. Previous studies have assessed the hydrological effect of vegetation greening but ignored the vegetation-precipitation feedbacks from land-atmosphere interactions. To address this knowledge gap, here we conduct coupled land-atmosphere model simulations prescribed with satellite vegetation observations to investigate how vegetation greening in the YRB affects regional hydrological cycles through vegetation physiological processes and biophysical feedbacks, with potentially competing effects on water yield (WY) by altering evapotranspiration (ET) and precipitation. Over the 2001–2020 period, the leaf area index in summer shows a significant increasing trend at a rate of 0.34 m² m⁻² decade⁻¹ (P < 0.01). This vegetation greening causes a substantial rise in ET, primarily due to increased plant transpiration and canopy evaporation, along with reduced soil evaporation attributed to enhanced root water uptake and shading of the soil surface. Moreover, the modeled results indicate that vegetation greening is the key driver for the observed ET enhancement. In addition, vegetation greening induces increases in precipitation by modulating moisture flux convergence, which although statistically insignificant, provides considerable water to compensate for the enhanced ET. For the cumulative effects of vegetation greening from 2001 to 2020 at the basin scale, the increased precipitation (approximately, 101 mm) outpaces the increased water consumption (approximately, 93 mm), resulting in an insignificant effect on WY. Our findings underscore the importance of considering vegetation-precipitation feedbacks in evaluations of the hydrological response to natural or deliberate vegetation changes.