| The Yangtze River is the largest in China,with abundant water resources and rich biodiversity.In the context of global warming,natural rivers in the basin are constantly evolving to meet various needs,such as urban and rural water supply,power generation,shipping,and flood control,leading to significant changes in the ecological environment of rivers,riparian zones,and flooded areas.In particular,the operation of the Three Gorges Dam has significantly changed the relationship between the rivers and lakes and has profoundly impacted the river ecosystem.This article evaluates the ecological and hydrological situation in the middle and lower reaches of the Yangtze River caused by climate change and human activities through statistical analysis,modeling,and other methods.The main research results include the following:(1)Characteristics of changes in hydrological and meteorological factors in the middle and lower reaches of the Yangtze River.The annual average runoff at Yichang Station decreased,while the average runoff at Hankou and Datong Stations increased.Under the coupling effect of human activities and climate factors,the watershed’s hydrological process gradually becomes complex.The complexity of precipitation in the Yangtze River basin is smaller than in the two lake basin.Various factors limit the spatial and temporal distribution pattern of precipitation,and different weather systems also impact precipitation characteristics.After the completion of the Three Gorges Reservoir,the hydrological environment in the middle and lower reaches of the Yangtze River has undergone significant changes.In this study,2003 was selected as the year of abrupt changes in runoff at hydrological stations in the middle and lower reaches of the Yangtze River.(2)Changes in ecological runoff characteristics and ecological effects in the middle and lower reaches of the Yangtze River.For the mainstream of the Yangtze River,the changes in ecological surplus and ecological deficit in spring and winter are relatively stable during the introductory period.The ecological surplus showed a significant and continuous increasing trend during the short change period,with the most significant change at Yichang Station.The range of change along the route decreased.The flow patterns at Yichang Station,Hankou Station,Chenglingji Station,and Hukou Station have changed moderately.In contrast,the flow patterns at Datong Station and Huangzhuang Station have undergone low changes.The degree of change in the flow regime decreases as it is farther away from the Three Gorges Dam site.(3)Attribution analysis of runoff changes in the middle and lower reaches of the Yangtze River.Human activities are the main driving factor for the change of annual runoff in the middle and lower reaches of the Yangtze River,with an impact weight ranging from 45.7% to 72.6%.The closer,the lower reaches of the Yangtze River to the estuary,the lower the impact of human activities on runoff changes,and the more significant the impact of climate change factors on runoff changes.Climate factors that affect the change of the hydrological regime mainly include precipitation,potential evapotranspiration,temperature,etc.Human activity factors include water conservancy project construction,land use,and habitat quality changes.(4)Analysis of the impact of hydrological regime changes on fish in the middle reaches of the Yangtze River.Yichang Station controls the basic water regime of the four famous domestic fish spawning grounds downstream of the Three Gorges Dam.The principal component analysis(PCA)method is used to extract the critical hydrological indicators of the station from the 32 IHA indicators of the Yichang Hydrological Station.Genetic programming(GP)and BP neural network select the hydrological variables most relevant to the "four famous domestic fishes" fry abundance from the extracted hydrological indicators.The research shows that the changes in monthly average flow in June and July,minimum daily flow,maximum daily flow,average flow in October,and flow rise rate in hydrological indicators will affect the changes of "the four famous domestic fishes" fry abundance. |
