Changes in the eco-flow metrics of the Upper Yangtze River from 1961 to 2008

► A framework of analyzing changes in the Yangtze River streamflow using eco-flow metrics. ► Precipitation decrease caused recent increasing of autumn ecodeficit. ► The Three Gorges Reservoir (TGR) intensified increase of autumn ecodeficit. ► TGR should start water storing from early autumn for mitigating negative effects. Flow regime changes in the Upper Yangtze River were investigated using the eco-flow metrics (ecosurplus and ecodeficit) and the “Indicators of Hydrologic Alteration” (IHA) parameters. Results showed that annual streamflow decreased in the period from 1961 to 2008. Autumn streamflow evidently decreased after the 1980s, which resulted from the decrease in precipitation and water storing by reservoirs. Summer flow decreased after the 1980s which was also primarily attributed to the decrease in precipitation. Winter streamflow increased in the two most recent decades, which resulted from the reservoir release. Results also showed that the Three Gorges Reservoir (TGR) elevated low flow in the dry season and reduced peak flow in summer since 2003. The decrease in autumn precipitation since 1990s, suggests that TGR is facing a serious challenge in maintaining water storage in the reservoir and releasing the water to the downstream ecosystem. Therefore, to mitigate the negative effects on the river ecosystem in the downstream and to maintain its water storage capacity, TGR should start storing water earlier than its designed schedule to meet the requirements for both power generation and ecosystem protection. A comparison between the eco-flow metrics and the IHA metrics demonstrated that combination of the two groups of metrics provided a sufficient measure of the changes in the flow regime.