Abstract: With the development of society and economy under global warming, extreme drought events occur frequently in the Yangtze River Basin (YRB), and the Three Gorges reservoir is faced with a severe challenge in guaranteeing water security in the middle and lower reaches of the Yangtze. Drought-limited water level (DLWL) is a crucial parameter for reservoir drought relief operation to enhance this basin’s drought mitigation capability. This paper defines the reservoir’s staged grading DLWL, and construct a multi-objective optimization DLWL model based on a parameterization-simulation-optimization framework that is solved by an intelligent optimization algorithm. The results show that the reservoir’s DLWL is more significant in flood season than non-flood seasons, and DLWL at the first grade is 154 m, 156.9 m, and 164.8 m in the stages of 6/10-7/31, 8/1-9/9, and 9/10-30 respectively. By implementing DLWL operation, the reservoir can improve all the benefits－in terms of impoundment, power generation, water supply, and navigation－each to a different degree. The increases in power generation will be 1.29% and 6.54% for multi-year average and typical dry year, respectively. This study would be useful for reservoir DLWL operation and drought-relief operation.

Key words: reservoir operation, Three Gorges Reservoir, drought-limited water level, staged and grading, simulation-optimization