LONG-TERM HINDCASTS OF GLOBAL EXTREME SEA LEVELS USING UNSTRUCTURED GRID MODELS

Abstract

 Global estimation of extreme sea levels is required for coast protection. First, 62-year-long historical total sea levels were calculated using an unstructured grid storm surge model and validated against tide gauge data all across the coastlines. Total sea levels were calculated by summing up astronomical tide and storm surge, which were derived separately. JRA-55 global reanalysis data, which is precise, especially for tropical cyclones, was used as input for calculating accurate storm surges. Next, hourly modeled sea levels and hourly tide gauge sea levels were compared at each tide gauge point. Adding storm surge to tide level makes these sea-level data more accurate than just using the astronomical tide model. Likewise, modeled monthly maxima show great agreement with observed monthly maxima. The results show that this model reproduces episodic sea level rise correctly. Finally, extreme sea levels which occur once per 10, 50, or 100 years were evaluated by fitting generalized extreme value distributions to monthly maxima. As a result, the model shows extreme sea levels, which can be observed once in 100 years, exceed 3.5 m at the coasts of western and central Europe, Mainland China along the east china sea, northwestern Australia, southern Alaska, and northeastern America.