Water level identification through the trade-off between the standards of drought defense and flood control for a reservoir in flood season

Abstract

Study Region: Songhuaba Reservoir, Yunnan Province, China Study Focus: As extreme droughts become increasingly frequent and widespread, the inherent conflict between drought defense and flood control presents a critical challenge for reservoir management, particularly during the flood season. To determine an optimal water level that balances the conflict for a reservoir in its flood season, a trade-off framework is developed to quantify drought defense and flood control standards and then the Technique for Order Preference by Similarity to Ideal Solution (i.e., TOPSIS) is applied to select the optimal water level. New hydrological insights for the region: Taking Songhuaba Reservoir in Yunnan, China, as a case study, the framework reveals a pronounced nonlinear trade-off relationship between drought defense and flood control standards. The flood control standard exhibits a steeper gradient when the drought defense standard is more stringent, indicating higher sensitivity under severe drought conditions. The optimal water level is identified as 1970.0 m, corresponding to a drought defense standard of 6.39% and a flood control standard of 0.87%, and indicates a compromise between the flood control and drought defense two objectives in the flood season. A weight analysis further reveals that the optimal water level adjusts stepwise with the varying criterion weights. The proposed framework for identifying an optimal water level can balance the conflicting drought defense and flood control and will help reservoir management in flood season.