Hydrological implications of vegetation-associated precipitation recycling during peak growing season over the Loess Plateau

Abstract. Vegetation restoration on the Loess Plateau has led to continued debate over whether enhanced land–atmosphere coupling can meaningfully alleviate water scarcity in this water-limited region. In this study, we combined the WAM-2layers atmospheric moisture-tracking model with a random forest–enhanced Budyko framework and introduced a vegetation-weighted leaf area index (LAI_w) to examine vegetation-associated precipitation recycling and its hydrological implications during the peak growing season (July–August) from 2000 to 2022. Precipitation over the Loess Plateau is dominated by land-sourced moisture, which accounts for 86.5 % of total precipitation. Internal moisture recycling contributes 14.4 % of total precipitation and shows a declining trend of −0.073 mm yr⁻¹. Surface water availability also declines significantly, at a rate of −0.34 mm yr⁻¹, mainly because evapotranspiration increases by 0.31 mm yr⁻¹. At the regional mean scale, vegetation-associated recycled precipitation makes only a limited contribution to precipitation, evapotranspiration, and surface water availability, accounting for 0.059 %, 0.02 %, and 0.107 %, respectively. This low net contribution partly reflects the fact that internal moisture recycling itself represents only a limited fraction of total precipitation, and that positive and negative vegetation-associated effects partly offset each other. However, the hydrological effect varies clearly along the LAI_w gradient, with weak positive contributions under low vegetation density and increasingly negative contributions under high vegetation density. These findings suggest that under water-limited conditions, enhanced vegetation–atmosphere coupling does not necessarily lead to meaningful gains in surface water availability. This seasonal focus is intended to capture the period of strongest vegetation–atmosphere coupling rather than the full annual water balance.