Extreme offshore wave statistics in the North Sea

Abstract

As part of the flood risk assessment in The Netherlands, extreme hydraulic boundary conditions (HBC) at coastal water defenses are calculated to assess the safety and sufficiency of the defenses. For this purpose, extreme offshore values of wave height and wave period with a frequency of occurrence of 1/10,000 years need to be estimated. The estimation is carried out using measurements at nine offshore locations in the North Sea, with a record length of 30 years.To estimate extreme wave heights and wave periods, the Generalized Pareto Distribution (GPD), which follows from extreme value theory, was fitted to peaks-over-threshold (POT) at each of the nine measurement stations. The fitted GPD parameters and consequently the extrapolated extreme values are particularly sensitive to the choice of threshold. A reproducible method was employed for threshold selection based on the anticipated behavior of the GPD shape parameter as the threshold approaches the domain of attraction. A modified regional frequency analysis (MRFA) was subsequently carried out to spatially smooth the GPD shape parameters. Final GPD fits were made using the shape-parameter output of the MRFA to produce final extrapolated extreme value estimates. The extreme values were compared with those resulting from an operationally-used distribution function in The Netherlands known as the conditional Weibull distribution.

Determining local scale extreme sea level elevation at the open coast of Côte d’Ivoire: Case study of the Bay of Port-Bouët

“…𝑁 where, 𝑁 is the total number of time-steps, 𝑀 𝑖 is the modelled value at time-step 𝑖, and 𝑂 𝑖 is the observed value at time-step 𝑖. series have a Poisson distribution and are independent and identically distributed from the GPD (Caires, 2011;Cañellas et al 2007;Roscoe et al 2010). The method involves the following steps:  Defining a high threshold;  extracting the exceedances time-series i.e., selection of all values above the defined threshold;  definition of clusters of exceedances based on the maximum storm duration (in hours).…”

Análises estatísticas de alturas significativas de ondas de série temporal de curto prazo na costa do Rio Grande do Norte

“…Assim, compreender as condições extremas de onda é de interesse não só da comunidade científica, mas também para o interesse econômico (Teena et al, 2012). Muitos autores nas últimas décadas têm estudado e discutido a análise de valores extremos para ondas, entre eles: Mathiesen et al (1994), Ferreira & Guedes Soares (1998), Van Gelder et al 2000, Coles (2001), Singh (2006), Roscoe et al (2010), Martucci et al (2010), Izaguirre et al (2011), Caires (2011).…”