A Multi-Method Approach to Develop Extreme Storm Surge Events to Strengthen the Resilience of Highly Vulnerable Coastal Areas

Abstract

The North Sea coast is seriously threatened by storm surges. Climate change and its consequences, such as rising sea level, will have a serious impact on the safety of people and economic assets in coastal areas. The uncertainties resulting from these consequences necessitate new concepts for coastal protection, together with new extreme storm surge scenarios under current and future climate conditions. Extensive knowledge about extreme storm surge events is essential to strengthen the resilience of highly vulnerable coastal areas. Based on the knowledge about extreme events safety standards for coastal regions could be newly defined, improved or re-defined. This helps to strengthen the resilience by taking into account the natural extreme events as well as the costs for measures of coastal defense. This paper focuses on the results of subproject la of the XtremRisK project with the aim to determine the relevant extreme events under today's conditions. Within the process in the XtremRisK project, these events were taken as a basis to assess extreme events under conditions reflecting the climate change scenarios. Within the scope of this project, methodical alternatives for the calculation of extreme events were evaluated. It turns out that empirical and numerical, as well as statistical approaches have different strengths as each possesses various restraints. In order to utilize the advantages and minimize the limitations, a multi-method approach was developed in which existing methods were exercised and brought together. The multi-method approach facilitates consideration of all storm surge components at their maximum value. Based on validation of the meteorology and consideration of the hydrodynamics, nonlinear effects between the storm surge components can be included. Examination of the storm surge curve is a special characteristic of the approach that enables consideration of the whole storm surge run. The basic concept was to regard results as ascertained only if they were proven by multiple currently valid methods. The extreme storm surges calculated in this way are statistically classified by subproject lb [see Wahl et al., 2015 in this journal] and used within the analysis of the failure mechanism of the existing flood defence structures by subproject 2 [see Naulin et al., 2015 in this journal].