Vegetation restoration weakens climatic control on sediment connectivity in ecologically fragile regions

Sediment connectivity regulates sediment transfer and landscape evolution, and is important for soil erosion mitigation and sediment yield reduction. Climate change and vegetation dynamics can alter sediment connectivity via ecohydrological processes, yet their long-term regulatory mechanisms remain unclear. This uncertainty is particularly important in ecologically fragile regions such as the 1.30 × 10 5 km 2 coarse sandy hilly catchment (CSHC) of the Loess Plateau. This study investigated the annual dynamics of the index of sediment connectivity (IC) in response to changing climate and vegetation, and identified its dominant controlling factors in the CSHC. IC was calculated for each grid cell along the downslope flow path to the nearest channel/gully network. The results showed a sustained and substantial decline in IC of the CSHC from 1991 to 2023, with a significant trend of −0.027 units per year ( p < 0.01). IC peaked in the early 1990s and declined steadily thereafter, coinciding with widespread vegetation restoration and suggesting a shift from climatic driving toward ecological regulation. The Bayesian-optimized XGBoost model showed good statistical performance (R 2 = 0.90, RMSE = 0.21) and identified precipitation, NDVI, soil moisture, evapotranspiration, humidity index, and natural restoration transformation as the primary factors affecting sediment connectivity. Convergent cross mapping showed that vegetation-related factors had stronger effects on IC than precipitation, suggesting that vegetation restoration has increasingly buffered the influence of climate on sediment connectivity. Structural equation modeling further supported this indirect regulation pathway. The spatial distribution of check dams and terraces largely overlaps with areas of significant IC decline, suggesting that these anthropogenic measures may have contributed to reduced sediment connectivity. These findings improve understanding of sediment connectivity dynamics under interacting climate, vegetation, and human influences, and can inform sustainable restoration and sediment management in ecologically fragile regions.