Quantitative evaluation of the evolution of the ecohydrological regime and its drivers in the Han River Basin

The hydrological regime of the Han River Basin has changed significantly under the double pressure of climate change and human activities, and the ecosystem's health is facing severe challenges. In this study, the ecohydrological regime of the basin was comprehensively assessed through various statistical methods and ecohydrological indicators. The results showed that the runoff volume of the Han River Basin decreased significantly, with an abrupt change in 1990, and the overall hydrological variability of the basin reached 42%. The ecological surplus decreased, the ecological deficit increased, and the ecological flow was strained for a long time. The optimal ecological flow thresholds for annual, spring, summer, autumn, and winter were 89, 97, 85, 83, and 98%, respectively. Quantitative separation of the effects of climate change and human activities on runoff reduction based on Budyko's hypothesis revealed that human activities were the main factor with a contribution of 59.73%, while precipitation and potential evapotranspiration contributed 31.08 and 9.19%, respectively. The study results can provide a scientific basis for water resource management and ecosystem restoration in the Han River Basin.