Evolution characteristics of urban flood disasters chain and approaches for disaster mitigation

China's urban flood disasters have been simultaneously occurring in multiple areas in both northern and southern regions and are superimposed by floods and typhoons. The complexity and uncertainty in disaster propagation have resulted in severe consequences. Disaster chains act as carriers of matter and energy during disaster propagation. Following the process of analyzing "disaster chain generation–evolutionary characteristics of disaster chains–approaches for disaster chain mitigation", research on the propagation, chain-like evolutionary characteristics, and mitigation methods of urban rainstorm and flood disaster chains has been conducted. The method of generation of urban flood disaster chains is jointly affected by external destructive behaviors, system structural forms, and the surrounding environment. On the basis of disaster characteristics, disaster chains can be categorized into serial, concurrent, and compound types. The propagation of disaster chains is characterized by homology and co-occurrence, accumulation and amplification, and variability and complexity. The methods for rupturing disaster chains involve disaster-causing factors, disaster-prone environments, disaster-bearing bodies, and emergency management measures. Taking the "7·20" rainstorm event in Zhengzhou and the "fatal incident on Metro Line 5" as examples, the generation of the disaster chain and strategies for breaking the chain and mitigating the disaster under the actual rainfall conditions were analyzed. Adopting measures such as predisaster prevention and control, disaster handling during an event, and postdisaster emergency response are highly important for breaking disaster chains and mitigating damage in disaster chains.