In this report, some results are presented on the research on the impact of changing meteorological conditions on the extreme wind speed, significant wave height and storm surges at the Belgian coast. Seven results of regional atmospheric models were obtained in the framework of the CORDEX.be Brain.be project or were downloaded from the CORDEX website. All models cover the North-west European Continental Shelf with a resolution of about 12.5 km and a time resolution of at least 6h. A 30-year period covering the current climate (historical run) and a 30-year period, covering the last 30 years of the 21th century, assuming the IPCC RCP8.5 scenario, were studied. A two-dimensional hydrodynamic model COHERENS, was used to calculate the storm surges, while a third-generation WAM model, was used to calculate the waves. The study focuses on the extreme events and used a Weibull distribution to parametrise the probability distribution functions and to calculate the return periods for a certain level (of wave height, wind speed or storm surge). A bias-correction method, based on quantile mapping, is used to correct the model results for the bias, and to map the historical runs results with the measurements that were available. The research shows that for the extreme wind speeds, some increase could be expected due to climate change. Although a large variability exists in the model results, most models indicate an increase in high wind speeds. This is however not the case for the extreme wave heights and the extreme storm surges. Here not significant changes are to be expected. One must however take into account also here the large variability in the model results. A first attempt is made to explain why the wind speeds are expected to increase, while this is not the case for the waves and the storm surges. One of the main reasons that can be found is the fact that for the higher wind speeds, an anti-clockwise change in direction from north to north-east could be expected in the models. |
