Runoff response to hydroclimate and human influence in China's Danjiangkou Reservoir, South-to-North Water Diversion

The South-to-North Water Diversion Project in China aims to address the imbalanced distribution of water resources between the northern and southern regions, a critical safeguard for sustainable socio- economic and ecological development. In this study, we investigated the hydroclimatic evolution of the water source area and its driving mechanisms using the inflow runoff data at Danjiangkou Reservoir from 1954 to 2013, along with multiple gridded hydroclimatic datasets. Based on the correlations between instrumental runoff data and gridded hydroclimatic variables, we used linear regression to extend the long-term runoff record to the period of 1902-2019. Our results indicate that climate changes, dominated by regional wet-dry cycles, have significant impacts on runoff variations, while the influence of human activities remains comparatively limited. Danjiangkou Reservoir can maintain a balanced base flow, even during the operation of the water diversion project. Preliminary synoptic climatology analyses reveal that runoff variations are mainly driven by the El Niño-Southern Oscillation (ENSO) and the Pacific Walker Circulation (PWC), which affect runoff by altering large-scale ocean-to-continent water vapor processes. This study advances the field by integrating multi-source data with analytical techniques, which enhances understanding of long-term runoff changes in the Danjiangkou Reservoir and their climatic drivers, ultimately supporting sustainable water resource management.