Scenario-dependent responses of soil conservation service flow to climate change across karst development gradients in the Pearl River Basin

Climate change profoundly alters basin-scale soil–water processes and ecosystem service flows. Conventional soil conservation assessments, which primarily emphasize local erosion control within a supply–demand framework, are insufficient to reveal the spatial transfer and downstream realization of soil conservation benefits. As an indicator that explicitly characterizes the hydrological transmission and actual use of soil conservation benefits, the response of soil conservation service flow (SCSF) to climate change across different karst development degrees (KDD S ) remains poorly understood. Focusing on the Pearl River Basin (PRB), one of the largest karst basins in the Northern Hemisphere, this study establishes a coupled Global Climate Model (GCM)-Soil and Water Assessment Tool (SWAT) modeling framework to quantify SCSF dynamics under three Coupled Model Intercomparison Project Phase 6 (CMIP6) scenarios and four KDD S (Full coverage (FC), High coverage (HC), Low coverage (LC), and Non-karst coverage (NC)), aiming to reveal climate-driven scenario-dependent and geomorphological controls on service flow responses. The results reveal scenario-dependent responses of SCSF to climate change. Under SSP126, basin-scale SCSF exhibits a continuous increasing trend, rising from 7.96 × 10 6 t to 8.97 × 10 6 t, while a gradual increase is observed under SSP245. In contrast, SCSF under SSP585 shows a rise-then-decline pattern, decreasing from 1.01 × 10 7 t to 9.56 × 10 6 t. KDD S exert a significant regulatory effect on SCSF, with FC and HC sub-basins maintaining consistently higher and more stable service flow levels, whereas LC and NC sub-basins are more prone to fluctuations and declines under SSP585. The highest mean SCSF occurs in FC areas under SSP126 (49.3 t), while the lowest mean value is observed in LC areas under SSP585 (9.87 t). This study systematically elucidates the regulatory mechanisms of climate change on SCSF, fills the research gap regarding differential responses among KDD S , and enhances the understanding of coupled soil–water processes and ecosystem service flows, providing scientific support for soil erosion (SE) control and adaptive basin management in karst regions. • Karst development degrees to reveal geomorphological controls on soil conservation service flow. • The KDD exerts a significant influence on SCSF. • SCSF increases under SSP126, grows moderately under SSP245, and rise-then-decline under SSP585. • The supply of SCS is highest under the SSP126 scenario, while the demand reaches its maximum under the SSP585 scenario. • Future high SCSF areas remain concentrated in western karst mountains, underscoring terrain's vital role.