High connectivity region dominates the critical source area of sediment yield in the Loess Plateau watershed

In recent decades, soil erosion on the Loess Plateau has markedly declined, leading to a significant reduction in sediment entering river systems. However, the relationships among sediment connectivity, soil erosion, and critical source areas (CSAs) of sediment yield remain inadequately understood. This study addresses this gap by developing a coupled erosion and sediment yield model that integrates the Revised Universal Soil Loss Equation (RUSLE), the modified Index of Sediment Connectivity (IC_R), and sediment retention estimates from check dams. The Geodetector model is employed to identify the dominant factors influencing soil erosion, while statistical analyses based on land use and land cover (LULC) data are used to identify CSAs. The results demonstrate that the coupled erosion-sediment yield model is both applicable and robust for the Yanhe watershed over the study period from 2000 to 2020. Vegetation cover, slope, and slope length are identified as the primary driving factors of soil erosion. The contribution of sediment reduction by check dams significantly declined from 60.7 % during 2000–2003 to 14.7 % during 2016–2020. The remaining 39.3 %–85.3 % of sediment reduction is attributed to changes in sediment connectivity driven by vegetation restoration and rainfall variability. The contribution from vegetation-induced sediment reduction is expected to increase over time. Areas characterized by both high sediment connectivity and high erosion intensity are identified as key zones for erosion control. Spatial analysis reveals that 76.82 % of CSAs are located in regions with high connectivity. Receiver Operating Characteristic (ROC) curve analysis identified CSAs thresholds of 10.74 % for forest cover and 27.84 % for source land types (cropland and bare ground). Based on these thresholds, CSAs occupy only 36.54 % of the watershed area but contribute 52.16 % of the total sediment yield, indicating their disproportionate impact on sediment production.