Technical Approach

Analysis of Pacific Island tide gauge records show that extreme water levels primarily result from a combination of global and regional changes in mean sea level, El Niño Southern Oscillation (ENSO) and other modes of natural variability, tropical and extratropical storms, and unusually high tides. This suggests that in response to a changing climate, and in addition to increasing global sea level, alterations to natural patterns of sea level variability and storminess may contribute to the more frequent occurrence of extreme water level events. The tide gauge analyses also show that the relative importance of the various contributors to extreme water levels differs from location to location. This suggests that changes in the frequency of occurrence of extreme water level events due to a changing climate may be highly localized. Potential limitations related to the sparseness of data (e.g., sea level station records may be of limited duration or no station occurs near a location of interest) represent another set of issues that need to be accounted for. In this project, a phased sequence of analysis will be conducted to address these and other concerns. Specifically, nonstationary models of the Generalized Extreme Value (GEV) distribution and the Generalized Pareto Distribution (GPD) will be used to compute extreme value statistics of tide gauge records as a means to account for variability in water level patterns as well as trends. Other statistical methods also will be employed to assess the sensitivity of result to record length.