Runoff Evolution and Its Attribution to Climatic Variability and Anthropogenic Influences in the Source Region of the Yellow River, China

This study investigated the long-term evolution and driving mechanisms of runoff in the Source Region of the Yellow River (SRYR) using runoff records from 1960 to 2020. An integrated framework combining the Soil and Water Assessment Tool (SWAT) model, statistical analyses, and scenario simulations was developed to identify runoff evolution patterns, quantify the contributions of climatic variability and anthropogenic influences mainly represented by land-use change within the attribution framework, and evaluate runoff responses to environmental changes. The results showed that runoff exhibited distinct stage-wise characteristics, with an initial decline followed by gradual recovery, and 1987 was identified as the primary change point. Mean annual runoff during the impact period decreased by 10.07% compared with the baseline period, while the updated runoff record through 2020 revealed a gradual recovery trend during the most recent decade. The SWAT model showed satisfactory performance during calibration and validation, supporting runoff attribution analysis. Climatic variability was the dominant contributor to runoff variation, accounting for 66.73% of the observed runoff change, whereas anthropogenic influences mainly represented by land-use change accounted for 33.27%. This climatic contribution represents the combined effects of observed climatic conditions, including long-term trends and internal variability, rather than the isolated effect of anthropogenic climate change. Scenario simulations indicated that runoff was more sensitive to precipitation than temperature changes. A 10% increase and decrease in precipitation resulted in runoff changes of 20.47% and −16.54%, respectively, while a 1 °C increase and decrease in temperature caused changes of −3.28% and 3.04%, respectively. Land-use change affected runoff mainly by modifying runoff generation and routing processes, but its influence was weaker than that of climatic variability. These findings improve understanding of runoff evolution and controlling mechanisms in alpine headwater basins.