Increased precipitation partially alleviates the carbon-water tradeoff under the Grain for Green program

Since the implementation of the Grain for Green program, the Loess Plateau has experienced substantial vegetation greening. However, the integrated impacts of largescale vegetation restoration on regional carbon sequestration and water resources under climate change remain insufficiently understood. In this study, a remote sensing-driven Coupled Carbon and Water (CCW) model was used to quantify the effects of climate change and vegetation cover change on gross primary productivity (GPP), evapotranspiration (ET), and water yield (WY) across the loess Plateau from 2001 to 2020. Results showed that GPP and ET increased significantly (P < 0.05) at rates of 15.41 g C m^-2 yr^-1 and 6.67 mm yr^-1, respectively, with vegetation cover change accounting for 89.38% and 90.55% of these increases. Although WY exhibited no significant long-term trend (-1.75 mm yr^-1, P > 0.05), the ratio of WY to precipitation declined substantially from 46.70% in 2001 to 28.26% in 2020, indicating reduced hydrological efficiency under vegetation restoration. Increased precipitation partially alleviated vegetation-induced water stress by compensating for rising ET demand. Overall, vegetation greening substantially enhanced ecosystem carbon sequestration while intensifying the tradeoff between carbon sequestration and water availability. These findings underscore the challenges of sustaining largescale ecological restoration under future drought conditions in semiarid regions.