Abstract: The aim of this study is to assess the changes in eco-hydrological regime and its ecological effect in the headwaters of the Yangtze River.According to the daily flow data of Zhimenda Hydrological Station from 1957 to 2021,we obtained the time of abrupt change in annual average flow of Zhimenda hydrological station via Bayesian change-point test,evaluated the abrupt change degree by using IHA-RVA (Indicators of Hydrologic Alteration and Range of Variability Approach),and then assessed the time-series changes of monthly average flow and annual extreme flow by using trend slope,Kendall trend test and detrended fluctuation analysis.We found that 1) the average annual flow of Zhimenda hydrological station changed abruptly in 2004.2) The comprehensive hydrologic change degree reached 37.2%,implying a moderate change.3) The average monthly flow was moderately changed,and the average monthly flow increased in different degrees,which added to the available water for aquatic life in the river.4) The extreme values of flow were slightly changed,indicating that extreme flow events remained in a stable range,which maintained the stability of the ecosystem in the headwaters.The increase of minimum flow better guaranteed the ecological flow of the watershed.5) The occurrence time of extreme values was slightly changed,posing little impact on aquatic habitats and fish migration.6) The pulse frequency of high and low flows both changed to low degrees,which reflected that the frequency of drought and flood decreased in the headwaters of the Yangtze River,sustaining the water reception of the river and riverbanks.The high and low flow pulse duration also brought about uncertain influence to the ecological environment of river and riverbanks in the source region.7) The rising rate,declining rate and reversal rate of flow all changed to low degrees,which indicated that the change degree of flow in the headwaters of the Yangtze River was low and maintained in a relatively stable state of the ecosystem.In general,the ecological environment in the headwaters of the Yangtze River showed a trend of improvement,and the increased ecological flow was conducive to maintaining the biodiversity and the healthy and sustainable development of the ecosystem in the source region.

Key words: headwaters of the Yangtze River, ecological flow, IHA indicators, hydrological regime, hydrologic change degree, detrended fluctuation analysis