Beyond Atlas 14: Non-Stationary Extreme Rainfall Estimation for the 21st Century

Numerous studies indicate that rainfall worldwide has exhibited non-stationarity due to climate disruption over recent decades, and that change is likely to accelerate in the future (e.g. Kunkel et al., 1999; Groisman et al., 2005). While US EPA promulgates guidance for changes in "near" and "far" term (through 2049 and 2074 respectively) 24-hour rainfall depths through its CREAT and SWMM-CAT software, much urban infrastructure serves watersheds with times of concentration ranging from minutes to a few hours, and changes in 24-hour rainfall may not provide an adequate basis for forecasting changes in short-duration maxima. This paper examines trends observed in the location, scale, and shape parameters of the generalized extreme value (GEV) distribution across the US, and presents a readily applied and understandable methodology that can be used to project extreme rainfall depths for the next several decades.