Comprehensive evaluation of the ecohydrological response of watersheds under changing environments

Human activities and climate change pose a continuous threat to the ecological stability of natural rivers in many ways. Understanding and analyzing changes in flow regimes from a multidimensional perspective is essential for water resources management. In this research, a comprehensive evaluation framework was developed to quantitatively assess the hydrological condition of the basin in four aspects: river flow regime, ecological water demand, multiple time scales, and drivers. The health status of the Yuanjiang River was assessed using a combination of Indicators of Hydrologic Alteration (IHA) and eco-flow metrics, and differences in different drivers at different time scales were quantified based on the Choudhury-Yang equation and the ABCD model. The results show that after the abrupt change of the Yuanjiang River in 2004, the runoff decreased by up to 72.97 mm, three of the five groups of IHA reached moderate alteration or above, and its ecological flow was in a tight state for a long time. In addition, the reduction of runoff by precipitation and potential evapotranspiration is not negligible (contribution 40.56%, 6.91%), and the drastic changes in land use and the construction and operation of cascade reservoirs highlight the human impact (contribution 52.53%). Anthropogenic contributions to runoff changes deepen in the order of spring, summer, fall, and winter (6%, 51%, 83%, 95%), and on a monthly scale, human activities were the dominant factor in runoff variability in nine months (61–98%), with climatic factors driving runoff increases of 0.24–6.07 mm only in March, June, September, November, and December.