Scale dependent effects and threshold identification of key influencing factors on runoff and sediment in the Wei River Basin

Study region Wei River Basin, a typical erosion prone basin on the Chinese Loess Plateau, northwestern China. Study focus Based on eight watersheds within Wei River Basin, the separate and joint contributions of climate, land surface composition (e.g. vegetation coverage, land use and land cover change) and landscape configuration were quantified across different spatial scales. Subsequently, their sensitivity were evaluated and threshold behaviors were identified. New hydrological insights for the region Runoff and sediment reductions since the early 21st century were mainly associated with human activities. Across spatial scales, landscape configuration exhibited stronger independent contributions (approximately 15∼21%) than precipitation (3%∼7%) and land surface composition (3%∼5%). Clear scale dependence was observed, with the highest explanatory power at the 500 m buffer scale, where combined factors explained up to 84.8% of runoff and sediment. Furthermore, sediment load showed stronger sensitivities than runoff to key factors. Among the tested factors, LSI was identified as the most sensitive factor, with a 1% increase being associated with relative increases of 1.60% in runoff and 2.46% in sediment load, respectively. Moreover, runoff and sediment load may undergo sudden changes once key landscape metrics exceed critical values. These findings reveal the importance of spatial structure and scale effects in regulating runoff and sediment processes in erosion dominated watersheds.