Impacts of inter-basin water transfer on reservoir storage and regional drought characteristics

The Middle Route Project of the South-to-North Water Diversion (SNWD-MRP) is an important measure for alleviating water scarcity in central and northern China. To clarify the regulatory effects of inter-basin water transfer on reservoir droughts in both water intake and receiving regions, this study reconstructs a daily reservoir storage dataset for 1990-2024 using multi-source remote sensing data. A Remote Sensing-based High-Resolution Reservoir Drought Index (RS-HRDI) is developed to identify drought events, and copula functions are applied to examine drought characteristics, spatial heterogeneity, and the evolution of joint drought probabilities before and after project commissioning across the water intake (Danjiangkou Reservoir) and receiving sub-regions (a, b, and c). The results show that, after project commissioning, drought responses in the receiving regions are weaker than those in the water intake, and the frequency of drought events lasting longer than 15 days decreases. In addition, the joint drought probability declines from 2.83%-6.12% to 0.18%-0.51%, while the regional drought dependence structure shifts from the Clayton copula to the Gumbel copula. These changes suggest that the spatial propagation of drought signals is weakened after project commissioning and are consistent with a reduced risk of drought events lasting longer than 15 days in the receiving regions. Overall, these findings provide scientific support for drought risk management and the coordinated operation of inter-basin water transfer systems.