Assessment of Wet-Season Water Storage Variations in Dongting Lake During 1990–2022 Using a Hydrodynamic-Simulation-Based Estimation Framework

Dongting Lake is one of the most important floodplain lakes in China and plays a critical role in regional flood regulation, ecological conservation, and water-resource management. Understanding long-term variations in lake water storage is therefore essential for evaluating hydrological responses to climate change and human activities. In this study, a hydrodynamic-simulation-based storage estimation framework was developed to quantify wet-season water storage variations in Dongting Lake during 1990–2022. The proposed estimation equation showed strong agreement with hydrodynamic-simulation-derived water storage, with a coefficient of determination (R2) of 0.972 and a root mean square error (RMSE) of 0.86 billion m3. Results indicate that both annual peak water storage and mean wet-season water storage exhibited significant declining trends over the study period. Mann–Kendall analysis revealed an evident decrease in peak storage after 2008 and a major hydrological transition around 2003, corresponding to the initial operation of the Three Gorges Dam (TGD). Comparative analysis showed that the average annual peak storage decreased from 17.27 billion m3 during 1990–2002 to 14.41 billion m3 during 2003–2022, while mean wet-season storage decreased from 8.16 billion m3 to 7.23 billion m3. Reduced inflow from both the Yangtze River and the Four Rivers was identified as the dominant factor controlling the decline in water storage. Although lakebed erosion increased the potential storage volume associated with bathymetric evolution by approximately 0.95 billion m3, its contribution was substantially smaller than the reduction in inflow runoff. Although long-term storage decreased, Dongting Lake retained substantial flood-regulation capacity, with only limited changes observed in flood-retention performance during major flood events. The findings contribute to a better understanding of long-term hydrological changes in Dongting Lake and provide useful information for flood control and water-resource management in the middle Yangtze River basin.