Estimated Increase in Inundation Probability with Confidence Intervals for Galveston, Texas

This study uses bootstrap methods to estimate confidence intervals for increases in inundation probability at the Pier 21 tide gauge in Galveston, Texas. The local surge is modeled using the generalized extreme value (GEV) distribution. Resamples of the historical record are created, and a GEV model is fitted to each resample. This ensemble of models is then used to estimate future water level exceedance probabilities under 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 distribution of future exceedance probabilities is trimmed to estimate 90% and 95% confidence intervals around the estimated proportional change in annual water level exceedance probabilities by 2100. The study shows that even under the conservative scenario and using the wider 95% intervals, the frequency of surges of 1.1 m (current return period of 16 years) becomes at least 4 times as common by the end of the century.