Spatial and Temporal Changes in Suspended Sediment Load and Their Contributing Factors in the Upper Reaches of the Yangtze River

In recent decades, the suspended sediment load (SSL) of many rivers around the world has shown a significant decreasing trend, which is particularly prominent in large river basins such as the Yangtze River and the Yellow River. One of the key challenges currently faced is how to quantitatively determine the relative influence of the dominant factors on the basis of systematically assessing the changing trend of SSL. This study takes the upper reaches of the Yangtze River as the research object. Based on the observation data from representative hydrological stations during 1966–2024, it systematically analyzes the interannual variation trend of SSL in different sections of the study river reach, identifies several mutation points, and divides the SSL change process into a baseline period, change period I, and change period II. Using the SCRCQ (slope change ratio of cumulative quantity) method, the study finds that the contribution ratio of human activities to the reduction of SSL in different sections of the study river reach ranges from 87.5% to 111.9%, the contribution ratio of precipitation change ranges from −14.3% to 12.4%, and the contribution ratio of evapotranspiration change ranges from −0.1% to 0.6%. For the entire upper Yangtze River basin, the contribution ratios of human activities to the reduction of SSL during change period I and change period II are 87.5% and 95.1%, respectively, while those of climate change are 12.4% and 4.9%, respectively. Human activities play an absolutely dominant role in the reduction of SSL in the upper Yangtze River. The results of this study can provide guidance for the scientific management of river reaches with concentrated large-scale reservoirs in the upper Yangtze River and also offer references for the formulation of management measures for similar rivers worldwide.