Estimated increase in inundation probability with confidence intervals for Pensacola, Florida and Key West, Florida

One of the most frequent and costly natural disasters that affects societies around the world is flooding. The combination of sea level rise and population growth in coastal regions makes it essential to continue improving flood management strategies. The main objective of this research is to model and compare the impact of sea level rise on the frequency of inundation for two Florida locations, Pensacola and Key West. The research is based on data from these two stations that benefit from existing long term sea level records, have similar relative sea level rise trends, but different surge histories and bathymetry. Pensacola is a sea port on Pensacola Bay, which joins the Gulf of Mexico. Water level records measured hourly are available starting in January 1924 till present. The Key West station is located at the southernmost point of Florida. The station´s records are available starting in January 1913 till present and include water levels measured hourly. Both areas have been impacted by hurricanes. Hurricane Wilma in 2005 was the last major storm to impact Key West, while Hurricane Ivan in 2004 and Hurricane Katrina in 2005 were the last hurricanes to impact Pensacola. Previous work identified the General Extreme Value (GEV) distribution as an appropriate model for surges in the Gulf of Mexico. Ensembles of surge models are computed based on the 99-year record of Key West, Florida and the 88-year record of Pensacola, Florida. The extreme surge distributions are then combined with sea level rise projections to estimate future water level exceedance probabilities. Increases in inundation frequencies are computed based on two possible sea level rise scenarios, a conservative linear continuation of the past century´s trend and a scenario based on the upper limit of the sea level range in the IPCC AR4 report, i.e. the A1FI scenario. The uncertainty associated with surges´ climatic variability is investigated using a bootstrap technique. The bootstrap is used to e- timate 90% and 95% confidence intervals around the estimated proportional change in water level exceedance probabilities for varying surges for these two sea level rise scenarios. Vertical land motion, global sea level rise, and tidal and atmospheric forcings are considered separately. The research shows that the projections of the probabilities of inundation defer significantly. The relative increases in the estimated probabilities reach their maximum for different water levels: 0.43 m for the Key West station and at 0.64 m for the Pensacola station assuming a continuation of last century´s rate of sea level rise. By the end of the century the frequency of exceeding water levels of 0.43 m is projected to increase at least by 5 times for station Key West, but only by 2 for 0.64 m water level for station Pensacola, with very little difference between the 90% and 95% confidence intervals. The differences in water level exceedance probabilities are discussed and associated with the statistical parameters of the distributions, local coastal settings and surge histories. The probability of water levels exceeding the levels associated with Hurricane Wilma in 2005 (one of the most devastating hurricanes in the history of Florida Keys) may triple by the end of the century for the more conservative sea level rise scenario.