Characteristics of changes in the hydrological regime in the Zi River Basin and analysis of their attribution

ABSTRACT The river hydrological regime is a key indicator to ensure the ecological function of rivers. We evaluated the changes in the hydrological regime of the Zi River by combining two methods for assessing the degree of change. Furthermore, we screened the most ecologically relevant hydraulic indicators (ERHIs) using principal component analysis (PCA) and quantified the independent impacts of human activities and climate change using the Whale Optimization Algorithm and Random Forest model (WOA-RF). The results showed that (1) 1987 was the year of the Zi River flow mutation, the overall average annual runoff in the Zi River Basin showed a decreasing trend, and the flow had four cyclic change time scales. (2) The overall hydrological variability in the Zi River Basin was 42%, and after the preferential selection of hydrological indicators, eight indicators were identified as the ERHIs of the basin, and the hydrological variability was 48.5%. The hydrological change in the basin was determined to be moderate. (3) The contribution of climate change is 28.8%, and the contribution of human activities is 71.2%. The construction of reservoirs was the most significant factor contributing to the impact of human activities, with a 65.6% contribution.