Comparison of Predicted Increases in Inundation Frequencies due to Relative Sea Level Rise in the Gulf of Mexico

Rates of relative sea level rise around the Gulf of Mexico vary substantially due to different rates of vertical land motion. As the century progresses, the rate of global sea level rise is generally predicted to increase progressively and become a larger component of local relative sea level rise. As sea levels increase, flood events will threaten more lives, and damage higher numbers of public and private properties, a problem compounded by the growth of coastal populations. Developing coastal adaptation strategies will become essential for the continued economic viability of coastal regions. The effectiveness of such planning will depend in large part on the accuracy of flooding predictions. In this work, we calibrate General Extreme Value (GEV) distributions to quantify present and future water level exceedance probabilities at eight locations around the northern Gulf of Mexico from Key West, Florida, to Port Isabel, Texas. Vertical land motion, global sea level rise, and tidal and atmospheric forcings are considered separately in this approach. Individual local extreme surge distributions are combined with relative sea level rise projections to estimate future water level exceedance probabilities. The uncertainty associated with the surges' climatic variability is also estimated using a non-parametric bootstrap technique and computing 90% and 95% confidence intervals. The studied locations' respective vulnerability to sea level rise are compared by computing the ratios of future to present water level exceedance probabilities for a range of water levels above present mean sea level. By the end of the century, for a conservative continued linear relative sea level rise, maximum inundation frequencies are predicted to increase by factors of 3 to 17 times for water levels ranging from 0.4m to 1.3m above present mean sea levels. For an accelerating global sea level rise based on the A1FI scenario, increases in maximum inundation frequencies of 12 to 112 times are predicted for water levels ranging from 0.8m to 1.6m above present mean sea levels. The differences in increases in water level exceedance probabilities are discussed and related to the respective rates of local vertical land motion and ranges of historical surges. The research shows that while rates of relative sea level rise will likely increase progressively as the century unfolds, changes in inundation frequencies can increase at a much faster rate depending on water level. For example, the frequency of inundation can increase from below 20% to a yearly occurrence in just 20 to 30 years for water levels that have caused considerable damage in the recent past. This nonlinear increase in inundation frequency must be accounted for when devising coastal adaptation strategies and should be considered when assessing and comparing the vulnerability of coastal locations to higher future relative sea levels.modified by 72.48.192.104 on 8-15-2013-->