Attribution of Runoff Decrease at the Guanyintang Station in the Yongding River Considering the Impact of Coal Mining

The Yongding River basin has greatly changed in recent years; its runoff has decreased sharply and has even been cut off. In this study, the Guanyintang station in the upstream Yongding River basin was selected to quantify the impacts of climate change, water use, and coal mining on its runoff. The Mann-Kendall analysis method was used to analyze the climate change trend of the Guanyintang basin from 1956 to 2018. Then, the water and energy transfer processes in large river basins (WEP-L) model was improved to consider the impact of coal mining and applied to quantitatively analyze the impact of meteorological elements and human activities on runoff. The results show that, from 1956 to 2018, the precipitation in the Guanyintang basin decreased slightly, whereas the temperature obviously increased, the potential evapotranspiration changed marginally, and the runoff significantly decreased with a mutation point around 1998. The study period was divided into a calibration period (1956-1976), validation period 1 (1977-1997), and validation period 2 (1998-2018). Compared with the calibration period, the runoff in the validation periods decreased a lot and could not meet the water balance without considering the coal mining impact. After considering coal mining, the simulation accuracy of the model was satisfied. Generally speaking, climate change and coal mining were the main factors for runoff attenuation in validation period 1. In validation period 2, coal mining became the dominant factor, whereas land use change also made certain contributions.