Water balance evaluation of downstream areas before and after the construction of the Three Gorges Reservoir and adaptive regulation

This study aims to analyze the impacts of Three Gorges Reservoir (TGR) operation on the regional water balance in the downstream area and provide a basis for adaptive regulation that coordinates engineering scheduling with regional demands. To address the data linkage challenge in accounting for socio-economic water use (agricultural, domestic, industrial) and natural system components (precipitation, evaporation, and runoff), we integrated meteorological/hydrological observations, water resources bulletins, and multi-source data products, deriving water balance indices that account for both component via spatiotemporal interpolation. The results show that before the reservoir construction, the water balance indices exhibited a non-significant decline, but increased significantly afterward, accompanied by a decrease in the mean intra-annual concentration index, reflecting the impact of the TGR’s scheduling of decreasing flood discharge and increasing low flow. A three-level regulation scheme was proposed based on index thresholds: medium and low-flow schemes better align with the synergized objectives of flood control and water supply, whereas high-flow schemes prioritize ecological baseflow at the cost of potential trade-offs in stored energy loss. The proposed scheme considers the interaction mechanism between hydraulic engineering operation and the regional water resources system, offering a scientific reference for optimizing reservoir operation strategies and coordinating regional development demands.