Evaluation of hydrological regime alteration and ecological effects in the upper reaches of the Yangtze River, China

Abstract The state of water flow is recognized as a key driver of the structure and function of river ecosystems. We selected streamflow data (1960–2020) from three key hydrological stations in the upper Yangtze River: Pingshan, Cuntan, and Yichang. We analyzed the characteristics and changes of the hydrologic regimes of the Yangtze River using the Mann–Kendall method, wavelet analysis, and the IHA-RVA method, and explored the response mechanisms of fish to changes in the hydrological regimes. The results show that (1) the average annual discharge of the upper reaches of the Yangtze River is decreasing, and the abrupt changes in Pingshan, Cuntan, and Yichang stations occurred in 1985, 1998, and 2002, respectively, with the main period of 24–32 years. (2) The overall degree of hydrological changes at Pingshan, Cuntan, and Yichang stations is 45%, 50%, and 61%, respectively, all of which are moderate changes. (3) Dams in the upper reaches of the Yangtze River have caused changes in the flow regime of the Yangtze River. Among them, the changes in the alternating frequency of flow and the annual extreme flow have affected the habitat of aquatic organisms and seriously affected the reproduction of important fishes in the Yangtze River.