This study used the ERA-Interim dataset produced by ECMWF,
spanning over 33years from January 1979 to December 2011 ,to
investigate different methods of estimating extreme wave conditions, and produced a 100-yr return level map for the North Atlantic region and North Sea.
The different approaches to estimating 100-yr return values were reviewed and data analyses
were conducted. The results of the study are summarized below.
The block maxima approach ,by dividing clusters based on storms ,and the POT method ,treating all excesses above a threshold, were compared.
Using a Generalized Pareto Distribution to fit all excesses above a high threshold yielded more reliable estimates of return values than the approach of fitting a GEV model to the storm maxima.
Among the extreme value distributions ,the FT-II type of distribution best fit storm maxima.
This raises doubts about the suitability of the traditional method of fitting a Gumbel or Weibull
distribution to the sample of maxima, especially for the region studied.
This also suggests that the parent distribution of wave
height data from the region might not be either Weibull or lognormal.
The effect of the duration of data on the return value estimates was investigated and the results suggest that using short periods of data(e.g.lessthan7years)may yield inaccurate results.
Using data with a duration of more than 10 years is likely to produce
more reliable return value estimates.
100-yr return values were estimated by fitting a GPD to all excesses above a high threshold, selected as the 95% quantile.
These values were compared with previously published estimates