Examination of the evolution and influencing factors of flow and sediment processes in an inland river basin of agro-pastoral ecotone amidst environmental changes

Elucidating the spatiotemporal dynamics and primary controls of flow and sediment processes (FSP) is essential for sustainable water-soil resource management in inland river basins within agro-pastoral ecotones (IRB-APE). This study refined the Soil and Water Assessment Tool with a time-segmented dynamic parameter adjustment strategy to simulate runoff and sediment dynamics under varying radiative forcing scenarios in the Tabu River basin, northern China. The model achieved robust performance (R 2 > 0.83, NSE > 0.83, |Re| < 16%) across baseline (1982–2000) and changing (2001−2023) periods. During 2001–2023, runoff and sediment transport rates declined by 0.19 m 3 /s and 0.26 kg/s, respectively, attributable to intensified soil drought and vegetation recovery. Under future scenarios (2030−2100), runoff exhibited differential responses: insignificant trends under SSP126/SSP245 but significant increases under SSP370/SSP585 ( P < 0.01), with annual runoff consistently highest under SSP585 across all time horizons. This divergence arises from compound effects of pronounced warming and intensified precipitation under high radiative forcing, accelerating soil saturation and reducing infiltration. Spatially, runoff depth showed a decreasing-then-increasing pattern along the upstream-downstream gradient, with lowest values (≤ 0.84 mm) in middle-reach subbasins with thick permeable soils and highest values (≥ 9.34 mm) in upstream subbasins with steep topography and low-permeability soils. A strong nonlinear runoff-sediment relationship emerged under future scenarios, driven by intensifying extreme precipitation and heightened soil erodibility. Temperature dominated runoff variation across all scenarios, while sediment discharge showed a transition from anthropogenic dominance (SSP126/SSP245) to thermal forcing dominance (SSP370/SSP585), with a critical threshold between SSP245 and SSP370 marking the shift from vegetation protection to climate forcing control. These findings necessitate differentiated strategies: vegetation restoration and water retention infrastructure under low forcing scenarios versus high-efficiency irrigation and climate-responsive land use planning under high forcing conditions.