Resilience benefit assessment for multi-scale urban flood control programs

Urban flood frequencies have increased and will continuously increase due to global climate change and rapid urbanization, causing enormous economic problems and social impact. Resistant strategies are no longer the best option for disaster mitigation. Improving cities' resilience to external disruptions is becoming a more important method for mitigating the impact of urban flooding. However, there are relatively little research has been conducted on the resilience of urban flood control systems. The introduction of the concept of resilience can provide a new way of thinking for urban flood control research, which can help to understand the coping process of the system during heavy rainfall, emphasizing the absorption, resistance, and recovery stages to improve the system's adaptability to the changing environment and effectively alleviate the pressure of urban flooding. This study discusses the impact of the design and configuration of urban flood control programs on the resilience of the system under heavy rainfall. Moreover, the resilience benefit is presented to quantify the phased process of system resilience capacity for measuring the quantitative relationship between programs and system resilience. Finally, the unit annual average cost of the program is combined with the resilience benefit to make decisions and ensure that cities are effectively reducing the risk of urban flooding with the optimal alternatives. The proposed framework was applied to Zhangjiagang City, a highly urbanized and densely populated city in China. The results showed that (1) during the same rainfall event, the hydrological indicators characterizing the system's resilience process (absorption, resistance, and recovery) have distinct weights; (2) rainfall has an effect on the index weight, and the weight fluctuates when the system responds to rainfall in distinct return periods; (3) rainfall return periods can have an impact on a program's effectiveness in improving the system's resilience at various stages, and the extent to which different programs are affected by the return period varies; and (4) combining large-scale and micro-scale programs improve the resilience of the system more effectively, whereas concentrating on expanding storage volume without raising the water surface rate improves the resilience of the system less effective. This framework can be used to assess the improvements in resilience acquired from various urban flood control program configurations and to assist city planners in selecting the optimal configuration, so assisting in the decision-making process for urban planning and disaster mitigation.