Study on the Variation Law of Runoff at Key Cross-Sections of the Yangtze River Mainstream

The Yangtze River runs through China from east to west, and its coastal areas serve as a crucial economic belt in the country. In recent years, amid intensifying climate change, the evolution of runoff in the Yangtze River Basin has shown complex spatiotemporal heterogeneity. This study focuses on the CTS, HKS, and DTS along the main stem of the Yangtze River, and conducts a detailed analysis of the intra-annual distribution and inter-annual variation patterns based on long-term runoff data. The results indicate that the intra-annual runoff distribution at the three stations is uneven, with peak values in summer and the lowest in winter, suggesting a high-flow concentration pattern. The inter-annual unevenness and concentration degree gradually decrease from the upper reaches to the lower reaches. No significant trend is observed in interannual runoff; CTS has long been characterized by abundant water but the largest extreme low-flow depth, while the HKS and DTS are mostly normal-water years, with the DTS experiencing more low-water years and facing the risk of consecutive droughts. The long-term, medium-term, and short-term fluctuation periods are 30.5 years, 8 years, and 3 years, respectively, and the runoff at the DTS also exhibits a 20-year cycle. This study provides a reference for the rational formulation of water resources management planning schemes for the upper, middle, and lower reaches of the Yangtze River Basin.