Drivers of Runoff–Sediment Load Nexus Evolution in the Liujiaxia–Heishanxia Reach of the Upper Yellow River: Natural Variability Versus Anthropogenic Interventions

The Liujiaxia–Heishanxia reach is critical for water and sediment regulation in the upper Yellow River, where changes in runoff–sediment relationships greatly affect downstream channel stability and flood safety. Climate change and intensive human activities have substantially altered local hydrological regimes in recent decades. Using long-term hydrological records from five stations during 1956–2020, this study applied the Mann–Kendall test, moving t-test, wavelet analysis and XGBoost algorithms to analyze the trends, abrupt changes and periodic features of runoff and sediment load, and quantify the contributions of natural and human drivers. The results show that both runoff and sediment load decreased significantly, with a sharper decline in sediment load. Major abrupt changes occurred in 1969, 1986, 1996 and 2008, and both variables presented a dominant 40-year interdecadal cycle. Human-induced landscape changes became the leading factor driving hydrological variations after 1996. Our findings suggest that future watershed management should combine landscape optimization and climate adaptation to maintain stable runoff-sediment conditions. This work provides scientific references for water resource management and the construction of the Heishanxia Water Conservancy Project.