Incorporating the RUSLE model into the sediment connectivity index to explore the relationship between soil erosion and sediment transport

• The four-quadrant method for erosion-connectivity maps requires determining thresholds based on local erosion conditions. • Comprehensive consideration of soil erosion and sediment connectivity is helpful to identify erosion hotspots. • The high erosion-low connectivity area was the sediment storage area. • The low erosion-high connectivity area was mainly distributed in the gully. Clarifying the source and transport difficulty of eroded sediment is key to the watershed management. However, assessments of soil erosion and sediment connectivity in watersheds are usually independently, and differences in their spatial distributions are rarely integrated to identify erosion hotspots. In this study, the revised Universal Soil Loss Equation (RUSLE) was used to assess the spatiotemporal variations in soil erosion within a typical watershed on the Loess Plateau under changes in the underlying surface. Additionally, factors derived from RUSLE were integrated into the connectivity index (IC) to evaluate the spatiotemporal changes in sediment connectivity. More importantly, by identifying threshold values of soil erosion intensity and sediment connectivity, we accurately detected the matching and mismatched areas of their spatial distributions. The results showed that, driven by a significant increase in vegetation cover and terrace area, both soil erosion and IC exhibited significant decreasing trend from 1986 to 2018 (P < 0.01). Specifically, the proportion of low erosion–low connectivity areas increased from 2.37 % to 48.03 %. In contrast, the proportion of high erosion–high connectivity areas, which are critical for erosion control, decreased from 33.26 % to 1.74 %, mainly distributed on steep slopes without forest cover. The proportion of low erosion-high connectivity areas (5.52 ± 0.76 %) were mainly distributed in the gullies and channels, and were potential areas for triggering shallow landslides. The proportion of high erosion-low connectivity areas (0.47 ± 0.30 %) were the sediment storage area, and also the area where soil erosion and sediment transport are decoupled. Overall, changes in vegetation cover were the dominant factor reducing sediment connectivity, accounting for 77.25 % of the total contribution, while terraces contributed 22.75 %. The research results improve the understanding of soil erosion and sediment transport in watershed, and the generated spatial distribution provide key information for watershed management.