Urban flood resilience assessment under compounding risk: joint impacts of precipitation and river level

Flood resilience assessment has become increasingly important for effective stormwater management in the context of frequent and severe urban flooding disasters. The severity of flooding in riverine cities is influenced by various factors, such as rainfall and river levels, but resilience assessments usually only consider the impact of heavy rainfall. Given the lack of urban flood resilience assessment under compounding risks, this study proposes a performance-based resilience assessment method considering the joint impacts of precipitation and river level, using a lake basin in Wuhan City as an example. Based on urban water system theory, the resilience assessment framework considered three subsystems’ resilience, i.e. the performance of the pipe network, the residual storage capacity of lakes, and the available discharge capacity of pumps. The Copula function was used to quantitatively assess the joint distribution characteristics of daily rainfall and the Yangtze River water level in Wuhan. A SWMM model was developed for hydrological simulation and resilience assessment under composite scenarios. Considering only the impact of precipitation would underestimate flooding risk relative to the joint effects of precipitation and river water level. The resilience index of the pipe network was the highest among the three subsystems, whereas that of the lake system was the most variable. For the same return period rainfall, the decrease in resilience of the pump system was the most pronounced as the river water level rose from 22.06 m to 29.25 m. In addition, the higher the rainfall magnitude, the more important it is to consider the jacking effects of the Yangtze River level on urban flooding. The proposed method evaluated the resilience-enhancing capacity of grey-green-blue infrastructures, and their combined effects were found to be non-linear. This research proposed a resilience assessment method founded upon joint risk and provided valuable feedback for developing effective flood resilient management strategies in riverine cities.