Quantifying the Impacts of Climate Change and Human Activities on Runoff in the Upper Yongding River Basin

Due to the impact of climate change and human activities, part of the Yongding River has stopped flowing, and the hydrological environment is damaged. The hydrological condition can be used to assess the ecological environment of the watershed, and analyzing the driving factors affecting the hydrological condition is essential for the environmental restoration of the watershed, but it is particularly challenging on a daily scale. This paper used the Indicators of Hydrologic Alteration and the Range of Variability Approach (IHA-RVA) method to screen out the sensitive indicators in different periods that are representative of each river; determined the hydrological variation periods of the upper Yongding River and the two subbasins, the Yang River and the Sanggan River; and quantitatively identified the contribution of climate change and different human activities (water withdrawals and reservoir storage) to the basin's runoff by constructing a daily-scale model named the Water and Energy Transfer between Soil, Plants, and Atmosphere (WetSpa) model. The results showed that the upper Yongding River, the Yang River, and the Sanggan River had a high degree of variation (87.2%), a low degree of variation (20%), and a moderate degree of variation (37.5%) in 1975-1988, 1980-1986, and 1978-1993, respectively. Human activities were the main driving factors, but their contributions varied across different basins. The Yang River is mostly affected by water withdrawals, with a contribution rate of 125.90%. The Sanggan River was affected mostly by reservoir storage, with a contribution rate of 153.47%. The upper Yongding River was affected mostly by climate change. A stricter management system can reduce the impact of human activities on runoff changes and provide a guarantee for the restoration of the ecological environment of the upper Yongding River.