Joint Probability Extremal Analysis of Combined Storm Surge and Precipitation

Most coastal infrastructure is designed according to an acceptable risk of a specific event (e.g., the 100-year flood). However, there are challenges with establishing risk-based design conditions for problems that depend on multiple forcing conditions, such as compound flooding. For compound flooding, the flood extent will depend on both storm surge and precipitation, and there may be multiple combinations of these variables that result in the same flood extent. Traditionally, this problem might be addressed by making a conservative assumption in one of these variables and performing an extremal analysis on the other; however, this process is fraught with uncertainty, and the results of this method do not offer any true statistical representation of risk. This paper explores a simple methodology for establishing joint extremal probabilities between environmental variables that may be correlated, such as precipitation and storm surge, which are both associated with tropical storms.