Assessing the Dominant Impact of Climate and Land Use Change on Runoff Through Multi-Model Simulation in the Karst Headwater Region of the Wujiang River

Assessing the runoff response to land use and climate change in karst basins is essential for sustainable water resources management and for advancing the understanding of basin-scale hydrometeorological processes. This study applied the SWAT model integrated with CA-Markov–based land use projections and CMIP6 climate data under the SSP245 (medium emissions) and SSP585 (high emissions) scenarios to conduct multi-scenario simulations, evaluating the impacts of these changes and projecting future runoff in the Wujiang River source region. The results indicate that (1) the SWAT model performed satisfactorily in simulating hydrological processes in this karst basin, with R2 and NSE values during calibration and validation reaching at least 0.75 and 0.7, respectively—furthermore, the PBIAS absolute values were below 10% during both calibration and validation; (2) runoff variations under four land use scenarios from 2000 to 2015 showed limited deviation from the baseline; (3) more pronounced runoff alterations were observed under extreme land use scenarios when compared to grassland-dominated conditions; (4) future climate scenarios SSP245 (medium emissions) and SSP585 (high emissions) consistently project a decreasing trend in runoff; and (5) combined scenario analyses reveal that climate change acts as the dominant factor driving runoff reduction in karst basins. These findings improve the mechanistic understanding of karst hydrological processes under global change, and the methodology established here holds potential for extension to other karst regions, thereby supporting strategic water resources planning.