Joint Impact of Rainfall and River Water Level on Urban Flooding: A Case Study of Wuhan City

Rainfall and river water level are the main factors to affect urban flood disaster.In order to assess flood risk better, the joint impact of rainfall and river water level on urban flooding should be considered.Taking the Wuhan City as a study area, the Copula functions were used to quantitatively evaluate the joint distribution characteristics of rainfall and river water level during different periods.The SWMM model for the Qingshan district of Wuhan City has been validated using the typical rainfall processes in 2016, and the validated model was used to simulate the effects of different rainfall and river water level processes on urban flooding.The results show that the waterlogging rate increased by 0.5%~2.2%, with the river water level increasing from 21.7m to 28.0m.With the rainfall return period increasing from 5-yr to 100-yr, the waterlogging rate increased by 28.5%~29.1%, and the reduction value of the waterlogging rate causing by the pump operation decreased from 20.6%~21.0% to 4.1%~4.9%.Apparently, urban inundation was mainly caused by heavy rainfall, and the increasing river water level could lead to more significant adverse effects on the regional waterlogging.Meanwhile, the effect of pump station on drainage became smaller with an increase in rainfall return period.The joint risk probability of rainfall in Wuhan and water level at Hankou of the Middle Yangtze River during flood seasons was greater than that of a single factor, implying that ignoring the correlation between rainfall and river water level could lead to the underestimation of flood risk.The comparison of the joint risk probability and encounter risk probability of heavy rainfall and high-water level during different periods of 2010~2020 and 2000~2009 show increasing trends, with the increasing rate more than 70%, indicating that the extreme events of intense rainfall and higher water level events have occurred frequently in recent years.Therefore, the results can provide technical reference for flood control and drainage planning and design in the cities along the Middle Yangtze River.