Regional assessment of extreme significant wave heights in the Bohai Sea and northern Yellow Sea

Abstract

The regional assessment of extreme significant wave heights (SWHs) is crucial for the design of coastal and offshore structures. In this study, the Bohai Sea and northern Yellow Sea are selected as the study region, and a 40-year (1979-2018) time series hindcast of SWHs is selected as the initial database. To extract the independent and identically distributed sample from this database, an automated method is employed. Since the winter storm dominates the extreme wave and winter storm samples are similar to independent non-tropical cyclone samples, especially for large samples, the extreme sample is extracted from the independent non-tropical cyclone sample. In most of the study region, large independent non-tropical cyclone samples occur evenly every year. The N-largest maxima (NLM) method is used for extraction, and the reasonable N values are determined by analysing the fitting result and extrapolation uncertainty and validated by the reasonable threshold range of the POT method. At a few locations, the large independent non-tropical cyclone sample rarely or never occurs in particular years. The diagnostic NLM method is proposed to exclude the small values. Benefitting from this method, a regional assessment of extreme SWHs is performed.