Unraveling future hydrological and sediment dynamics through an integrated GCMs-PLUS-SWAT coupling framework

Under the combined stresses of global climate change and anthropogenic activities, the watershed hydrological cycle is undergoing multidimensional complex evolution. This study constructs a comprehensive SWAT hydrological model database for the Yangtze River Basin, integrating multi-resolution data to delineate sub-basins and hydrologic response units (HRUs). We coupled CMIP6 climate projections with the PLUS land-use change model to generate scenario data, establishing an integrated "GCMs-PLUS-SWAT" framework. This framework quantified projected hydrological element evolution under SSP245 and SSP585 scenarios. Model validation demonstrated high accuracy in streamflow simulation (R² = 0.83-0.95) and credible upstream sediment load simulation (R² = 0.82-0.85). Results indicate a 4.43% higher precipitation increase and maximum temperature rises up to 10.29 °C during the latter SSP585 period compared to SSP245. This intensifies seasonal heterogeneity in erosional processes, combining summer sediment load declines with slight autumn/winter increases. Projected annual streamflow increases under SSP585 later in the century are 28.6% higher than under SSP245, exhibiting distinct intra-annual redistribution: increases in winter/spring, decreases in summer, and compensatory increases (over 50% contribution) in autumn. Sediment transport exhibits significant spatiotemporal divergence. Near-term SSP585 projections show a dramatic 93.88% sediment load surge at Cuntan Station (upper basin), shifting to long-term decline due to synergistic climate-substrate interactions. Mid-lower basin sediment loads stabilize, driven by hydraulic engineering regulations. The study reveals asymmetrical responses of water-sediment processes under high-emission scenarios, providing a scientific basis for integrated watershed water resource management and ecological conservation.