Assessing the Impact of Multi-Reservoir Rationing on Downstream Drought Occurrence: A Case Study of Dez and Gotvand Reservoirs

Water resource management in multi-reservoir systems is critical for meeting diverse demands while ensuring sustainability. In this study, we delve into optimizing the operating rule curve for such systems by integrating the Particle Swarm Optimization algorithm. Our overarching goal is to minimize relative deficiencies in water supply, considering both standard operating policies (SOP) and discrete two-level hedging policies. Our case study focuses on the Great Karun basin, a real-world scenario where water scarcity poses significant challenges. By coupling the PSO algorithm with a system simulation model, we search for optimal hedging levels across all reservoirs and months. Additionally, we rigorously compare the output results of our combined simulation-optimization model with those obtained from a SOP-based simulator. Furthermore, we analyze the flow drought index at key points throughout the basin under both rationing and SOP policies. Notably, while rationing generally reduces average drought severity, it may inadvertently exacerbate conditions in severely water-stressed areas like the Dez basin. The novelty of this study lies in coupling PSO-based optimization with detailed system simulation to develop dynamic hedging policies for multi-reservoir drought management. Our research contributes valuable insights into multi-reservoir system operation, shedding light on effective strategies for meeting water demands while mitigating the impact of droughts.