Revegetation Does Not Decrease Water Yield in the Loess Plateau of China

Vegetation restoration over degraded drylands has considerable climate, carbon and ecosystem benefits, yet its water impacts remain contentious. Previous studies suggest that extra vegetation in drylands could lead to decreased soil moisture and runoff caused by enhanced evapotranspiration. However, these studies ignore important vegetation-climate feedbacks that can partially offset such negative consequences. Here, we examine how revegetation affects water budgets in China's Loess Plateau, where the world's largest revegetation occurs. Despite increased evapotranspiration, long-term observations exhibit robust increasing trends (2.76 mm yr(-2)) of surface water yield over a large swath (82.3%) of the Plateau since revegetation starts. This is mainly caused by increased regional precipitation that outweighs increases in evapotranspiration. Numerical experiments further reveal that the increased precipitation is largely driven by revegetation-induced enhancement in land-atmosphere interactions that greatly accelerate local moisture recycling. Our findings highlight the importance of considering vegetation-climate feedbacks in assessing hydrological responses to large-scale vegetation changes. Plain Language Summary Vegetation restoration is one of the most effective ecological engineering measures for ecosystem remediation and climate mitigation, and has been widely implemented across the globe over the past few decades. Previous studies suggest that revegetation could threaten long-term water sustainability of the Loess Plateau in China, a typical dryland region that has witnessed widespread vegetation restoration over the past two decades, as extra vegetation consumes more water through evapotranspiration, leading to decreased soil moisture and runoff. Here we challenge this conclusion by showing that a large swath of the Loess Plateau has experienced robust upward trends of surface water yield since the start of large-scale vegetation restoration. This is primarily caused by increased regional precipitation that outpaces the increased evapotranspiration induced by revegetation. Further, we demonstrate that the increase in precipitation is largely driven by enhanced land-atmosphere interactions that accelerate local moisture recycling following revegetation. Our results suggest that previous offline assessments, which ignore important vegetation-climate feedbacks, may overstate the threats of revegetation on dryland water resources. These findings provide an important scientific basis for guiding current and future revegetation activities toward sustainable ecosystem development and water resources management.

Automated summary

Revegetation in China's Loess Plateau has led to an increase in surface water yield, despite the enhanced evapotranspiration. This is mainly due to the increase in regional precipitation that outweighs the increase in evapotranspiration. Enhanced land-atmosphere interactions following revegetation have accelerated local moisture recycling and contributed to the increased precipitation. Previous assessments that ignore vegetation-climate feedbacks may have overestimated the threats of revegetation on dryland water resources.