Objective This study investigated the spatiotemporal evolution of sediment connectivity and quantified the influence of land use, climate, and topography. The objective is to provide a scientific basis for elucidating hydro-sedimentary processes and enhancing soil and water conservation strategies in the low-mountain and hilly regions of southern China.

Method Using the Index of Connectivity (IC), combined with the XGBoost-SHAP model and Geodetector, this study analysed the spatiotemporal dynamics and key drivers of sediment connectivity at different slope gradients within the Poyang Lake Basin for the period 2000–2020.

Result (1) From 2000 to 2020, the mean IC value in the Poyang Lake Basin was −9.24, exhibiting an overall trend of initial decline followed by subsequent increase. In total, 54.49% of the areas displayed an upward trend in IC, among which 12.92% showed significant increases, primarily distributed in flat regions such as river valleys and floodplains. In contrast, only 5.44% of the areas exhibited significant decreases. (2) During the study period, the areas of cropland and impervious surface in the basin increased by 1694.88 km² and 2633.40 km², respectively, while the area of forest decreased by 3866.52 km². Significant variations in the IC were discerned among different land use types (p < 0.01), with the IC values ordered as follows: water < forest < shrub < grassland < cropland < barren < construction land. (3) The importance ranking of factors affecting sediment connectivity was: slope (29.3%), elevation (23.8%), precipitation (15.7%), human activities (12.3%), temperature (7.7%), soil moisture (7.4%), and potential evapotranspiration (3.7%). The interaction among factors exhibited a bivariate or non-linear enhancement effect, meaning their combined explanatory power for IC was greater than that of individual factors. While this interaction effect was relatively weak in flatlands (explaining < 20% of the variance), interactions involving human activities became significantly stronger on gentle slopes. On moderate and steep slopes, the interaction between precipitation and elevation was the most dominant.

Conclusion Sediment connectivity exhibited a distinct distribution pattern, with elevated values concentrated in valleys and lower values on hillslopes. The continued expansion of cropland and impervious surface led to a significant increase in sediment connectivity in the mid- and downstream valleys and floodplains. The dominant factors and interactions between factors affecting sediment connectivity changes were significantly different under different slope gradients. The study emphasizes that under the dual influences of climate change and human activities, future watershed soil and water conservation efforts must implement precise management strategies tailored to different terrains to address the complex changes in regional sediment connectivity.