Joint Probability Analysis of Extreme Precipitation and Water Level for Chicago, Illinois

A compound flooding event occurs when there is a combination of two or more extreme factors that happen simultaneously or in quick succession and can lead to flooding. In the Great Lakes region, it is common for a compound flooding event to occur with a high lake water level and heavy rainfall. With the potential of increasing water levels and an increase in precipitation under climate change, the Great Lakes coastal regions could be at risk for more frequent and severe flooding. The City of Chicago which is located on Lake Michigan has a high population and dense infrastructure and is very vulnerable to a compound flooding event, even with the implementation of its water control structures. For this case study, annual maximum precipitation and corresponding lake water level data were analyzed to examine the bivariate return period of a compound flood event using a copula function. The results show that under climate change if the water level were to rise by 0.2, 0.45, or 0.8 m, compound flooding events due to heavy precipitation and high water level will be more likely in the future. By documenting the joint risk of potential compound flooding in this area, preventative measures and planning can be implemented