Scenario-Based Projection of Extreme Sea Levels

ABSTRACT Obeysekera, J. and Park, J., 2013. Scenario-based projection of extreme sea levels. Heavily populated urban centers and natural areas located in low-lying coastal regions are highly vulnerable to sea-level extremes. Historical data at many tide gages suggest that changes over time in extremes generally follow the rise in mean sea level. Assuming this observation to hold in the future, a relationship between mean sea-level rise and its associated extremes with a generalized extreme value distribution can provide future return levels of extreme sea levels. Current projections of future sea level, which include varying degrees of acceleration, may result in large increases in extremes that need to be accounted for in the evaluation of existing coastal projects or in the planning of new ones. Because precise quantitative estimates of the uncertainties in sea-level rise projections are not available, scenario-based approaches have been suggested for project evaluation and design. Here, we propose a general method based on the synthesis of extreme value statistics with sea-level rise scenarios that allows any combination of linear or nonlinear local and global sea-level rise components and can accommodate the nonstationary evolution of sea-level extremes. The temporal variation of the design level of protection for coastal projects, expressed as the return period of extreme events, and the future behavior of the risk are explored. The concepts are demonstrated through application to tide gage data at several locations in the United States.