179 - Updating Intensity-Duration-Frequency (IDF) Curves for Short-duration Precipitations under Climate Change: The Case of Pensacola and Perdido Bays Watershed

Updating design storms is an essential step to prepare for future floods under various climate pathways. However, future projections of such storms at a regional scale have been rarely done for short-duration events ( < 24 hours), mainly due to the unavailability of long-range sub-daily data for historical observations. In this study, precipitation intensity–duration–frequency (IDF) curves are developed under future climate for the Pensacola and Perdido Bays Watershed, located on the border of Florida and Alabama. Historical precipitation data are derived from NOAA’s weather stations. Future climate is determined by downscaling the outputs of global climate models (GCMs) for Coupled Model Intercomparison Project Phase 6 (CMIP6) scenarios—shared socioeconomic pathways (SSPs). The IDF curves are developed for storm events with 3-, 6-, 12- and 24-hour durations and for return periods ranging from 1 to 1,000 years. Clustering techniques are applied to group historical and future rainfall events based on their duration. Extreme cumulative distribution functions like Generalized Extreme Value (GEV) and Gumbel are fitted for derivation of the IDFs. Maximum likelihood estimations are used to select the best distribution. Our preliminary analyses showed that sub-daily extreme precipitation events tend to intensify over longer durations. These results point out the vulnerability of the existing water resource system and civil infrastructure to control precipitation-induced events like flooding. State and local agencies can adapt pertinent policies and decisions by using the updated IDFs to lessen this vulnerability.