The objective of this study is to achieve the dynamic optimization of the flood limited water level (FLWL) in parallel reservoirs, using Luhun Reservoir and Guxian Reservoir as case studies. The innovation lies in establishing a dynamic control optimization model for the FLWL of parallel reservoirs, considering the uncertainty in the forecasting period of the flood forecast due to the varying locations of the rainstorm center from upstream to downstream. To commence, the Fisher optimal segmentation method is employed for flood season staging to determine the staged FLWL of each reservoir. Subsequently, considering the uncertainty in the foresight period, the upper range of the dynamic FLWL is determined through the improved pre-discharge capacity constraint method and Monte Carlo simulation. Finally, a multi-objective optimization model is established to determine the optimal dynamic FLWL control operation scheme for parallel reservoirs, utilizing the Non-Dominated Sorting Genetic Algorithm II (NSGA-II). This model takes into account both downstream flood control requirements and the water supply benefits of the parallel reservoirs. Through the optimization of the scheme, the water supply of the parallel reservoirs can be augmented by 15,347.6 m³ during the flood season. This optimization effectively achieves a harmonious balance between flood control and water supply, holding significant implications for mitigating drought risks amid changing conditions.

Setting the staged flood limit water level (FLWL) through flood season staging is an important means of fully utilizing reservoir flood resources. The widely-used Fisher optimal partition method requires a certain time domain as the basic unit in determining the optimal staging of a flood season. Currently, 5 and 10 days matching the month and solar terms are usually used as the time unit. This study aimed to analyze the influence of other time-domain units (7 and 15 days) that meet the relevant requirements on the staging results and to provide a scientific basis for the selection of time-domain units in flood season staging. The rationality of the staging scheme was tested using the improved Cunderlik method, and the influence of specific basic units in the Fisher optimal partition method on the staging results was evaluated. The highest relative superiority of 0.9876 was found for 5 d, indicating that this is a suitable time-domain unit. The optimal staging result was determined as 20 June for the first segmentation point and 20 August for the second. A comparison of the staged FLWL with a single fixed FLWL showed that the water level was raised by 1.56 m in the pre-flood season, 0.65 m in the main flood season, and 1.37 m in the post-flood season. Water storage increased by 12.79 million m³ during the flood season, effectively alleviating the mismatch between water supply and storage.

In recent years, the increasing frequency of extreme rainfall has exacerbated urban waterlogging, which has seriously constrained the sustainable development of cities. Given the problem that the impact of social information on waterlogging risk is easy to ignore in the urban risk waterlogging assessment process, it is of great significance to carry out a comprehensive waterlogging risk assessment and identify the waterlogging risk for urban waterlogging prevention and control. Based on the hazard–vulnerability assessment framework, this study comprehensively considers the flood disaster hazard and socio-economic vulnerability to carry out a multi-scenario urban waterlogging risk assessment in the central urban area of Zhoukou. The results show that, in comprehensive risk assessment, the area proportions are expressed as medium risk > low risk > higher risk > high risk. For a single waterlogging hazard assessment, the area proportions are shown as low risk > medium risk > higher risk > high risk. The difference ranges in area proportions of low, medium, higher, and high risk are (−61.00%, −54.00%), (49.00%, 56.00%), (1.30%, 2.70%), and (1.80%, 4.00%), respectively. It can be seen that compared with the single waterlogging hazard assessment, in the comprehensive waterlogging risk assessment with the introduction of the vulnerability factor, the waterlogging risk in the area with highly waterlogging vulnerability increases correspondingly, while the waterlogging risk in the area with low waterlogging vulnerability decreases relatively, and the waterlogging risk assessment results are more in line with the actual situation.

Setting the staged flood limit water level (FLWL) through flood season staging is an important means of fully utilizing reservoir flood resources. The Fisher optimal partition method has been widely used to determine the optimal staging of a flood season. It requires a certain time-domain as the basic unit. This study aimed to analyze the influence of various selected time-domain units on the staging results and to provide a scientific time-domain selection basis for the application of the method in flood season staging. Flood season staging was conducted by taking four specific time-domains: 5, 7, 10, and 15 days as the basic units. The rationality of the flood season staging scheme was tested using the improved Cunderlik method, and the influence of specific time-domains as the basic units in the Fisher optimal partition method on the staging results was evaluated. The results showed the highest relative superiority of 0.9681 for the time-domain unit of 5 d. Therefore, it is recommended that 5 d be used as the time-domain unit. The optimal staging result was determined as June 20 for the first segmentation point and August 20 for the second. According to the results of the staged FLWL compared with a single fixed FLWL, the water level was raised by 5.2 m in the pre-flood season, 0.3 m in the main-flood season, and 3.7 m in the post-flood season. Water storage increased by 24.628 million m³ during the flood season, effectively alleviating the contradiction between water supply and storage.