Response of synergetic optimal operation of cascade reservoirs to drought in the main stream of the Yellow River

The scientific operation of cascade reservoirs is an important means of mitigating losses from drought. In this study, a multi-spatial-temporal scale synergetic optimal operation model of cascade reservoirs is established with the goal of decreasing the severity of water shortages in the basin and optimize the spatial and temporal distribution of those shortages. An interactive and improved nested particle swarm optimization (PSO) algorithm was used to produce the model. In the outer layer, the optimal control of drought limit water level for multi-year regulating storage reservoir was realized, and in the inner layer the water storage and discharge processes of cascade reservoirs were optimized to realize the inter-annual regulation, intra-annual optimization, synergy among cascade reservoirs, and spatial coordination. The model developed in this study was applied to the cascade reservoirs in the main stream of the Yellow River during 2012—2014 to optimize drought limit water levels of the Longyangxia Reservoir and water discharge processes of cascade reservoirs to cope with the serious drought in 2014. The results show that inter-annual water supply is realized through the use of the drought limit water level in the Longyangxia Reservoir, which kept the water shortage ratios of each year between 4.9% and 5.7%. The system also kept water shortages evenly distributed across different regions at different times by optimizing the water discharge processes of cascade reservoirs. The agricultural water shortage ratios were kept between 7.0% and 11.0%, mitigating drought loss significantly.