Erosive rainfall effects on runoff-sediment dynamics across climatic zones in Southwest China

Four typical small watersheds in different climatic zones in Southwest China. Based on fixed-point monitoring data collected, 204 erosive rainfall events were classified into three distinct types using K-means clustering. Significant differences in total runoff and sediment yield were observed among the rainfall types. Moreover, this study marks the first application of partial least squares structural equation modelling (PLS-SEM) under multiple climatic conditions in the Southwest China, enabling a comprehensive analysis of the influence of various factors on runoff and sediment. (1) Significant differences in total runoff and sediment yield were observed among the rainfall types, with the sequence ranked as Type III > Type II > Type I. (2) Linear regression analysis revealed a stable runoff-sediment relationship in the Yizhe Small Watershed (YSW), with coefficients of determination exceeding 0.995. In contrast, a weaker fit was observed in the Taqing River Small Watershed (TSW), indicating limited consistency between runoff and sediment. (3) The results of the multi-climate PLS-SEM analysis indicated that climatic variation directly altered hydrological responses and indirectly influenced sediment transport by modifying vegetation cover and drainage network structure. Runoff and sediment exhibited clear spatial heterogeneity shaped by differences in climatic zones. (4) The highest runoff depth ( H ) and sediment yield ( S ) occurred in the southern subtropical watershed, followed by the central subtropical region, with the lowest values in the northern subtropical zone. This study revealed unique runoff-sediment response patterns across climate zones, providing scientific basis for regional soil and water conservation and ecological environmental protection. • Systematic multi-climatic rainfall-runoff-sediment analysis in southwestern China. • PLS-SEM reveals climate-hydrographic surface interactions. • Quantify runoff-sediment thresholds by erosive rainfall type.