Influence of water conservancy project on runoff in the source region of the Yellow River and wetland changes in the Lakeside Zone, China

The source area of the Yellow River (SAYR), located above the Huangheyan hydrological station, is important for ecological preservation and water source conservation in the Yellow River Basin. In this area, the impact of water conservation projects on the hydrology and the ecological environment is pivotal in protecting water resources and alpine vegetation ecosystems. This study investigates the impact of the Yellow River Source Hydropower Station on the runoff and ecological evolution of the SAYR, along with the underlying mechanism, using extensive datasets encompassing long-term meteorological, hydrological and remote sensing data from various time periods. Results show that, over the long term, precipitation is the primary factor driving runoff variations in the SAYR. Nevertheless, from 1990 to 2020, there is a notably inconsistent relationship between precipitation and runoff. After the completion of the Yellow River Source Hydropower Station in 2001, the water level of Eling Lake experienced and elevation of 2–3 m, leading to a gradual recovery of runoff. In addition, the basin's water balance shifted from a negative to a positive equilibrium, oscillating with changes in lake water levels. Consequently, the overflow zone of the Tangchama alluvial–proluvial fan in the upper reaches of the lakeshore shifted by 500 m, and marsh wetlands expanded by 20.78 km². The increased storage of lakes and groundwater in the SAYR is the key controlling factor for the runoff recovery, changes in the basin's water balance, and enhancements in lakeshore vegetation ecology. Under the geological background of the Qinghai–Tibet Plateau's upliftment and intensified upstream river erosion, the basin experienced a substantial water imbalance due to declining discharge base levels, which is the most critical factor behind runoff attenuation in the SAYR towards the end of the 20^th century. The construction of the hydropower station objectively raised the drainage base level of the basin, thereby positively contributing to the preservation of water balance, runoff stability, and the enhancement of swamps and wetlands along the lakeshore.