Ecological Instream Flow in the Yangtze River Basin under the Hydrological Change: Changes, Impacts, and Attributions

Climate change and human activities may cause change points in hydrological processes, which have serious impacts on the stability of watershed hydrological ecosystems. The Pettitt test method was used to identify the change point of discharge in the Yangtze River basin, and ecological water demand was estimated based on generalized extreme value distribution. The results show that: (1) the ecological water demand guarantee rate of the Yangtze River basin increased from a viewpoint of the whole basin during the past decades, especially in dry seasons. Due to the regulation of reservoirs and dams in the Yangtze River Basin, the ecological surplus (ecological deficit) tends to increase (decrease) in the dry season of the Yangtze River Basin, while it tends to reverse in the wet season. (2) The degree of hydrological alterations in the trunk stream of the Yangtze River Basin is the highest (D0 reaches 50% or more), and the river hydrological situation and ecosystem are under high risks (the total DHRAM score is more than 10 points), and the biodiversity shows a significant downward trend. (3) Climate change and human activities have the opposite impact on ecological streamflow of the Yangtze River Basin, that is, climate change increases ecological surplus and decreases ecological surplus. Overall, climate change is the leading factor affecting ecological surplus (the contribution is more than 50%).