CMIP6 Multi-model Assessment of Northeast Atlantic and German Bight Storm Activity

Abstract. We assess the evolution of Northeast Atlantic and German Bight storm activity in the CMIP6 multi-model ensemble, as well as the Max Plack Institute Grand Ensemble with CMIP6 forcing (MPI-GE), using historical forcing and three emission scenarios. We define storm activity as upper percentiles of geostrophic wind speeds, obtained from horizontal gradients of mean sea-level pressure. We detect robust downward trends for Northeast Atlantic storm activity in all scenarios, and weaker but still downward trends for German Bight storm activity. In both the multi-model ensemble and the MPI-GE,we find a projected increase in the frequency of westerly winds over the Northeast Atlantic and northwesterly winds over the German Bight, and a decrease in the frequency of easterly and southerly winds over the respective regions. We also show that despite the projected increase in the frequency of wind directions associated with increased cyclonic activity, the upper percentiles of wind speeds from these directions decrease, leading to lower overall storm activity. Lastly, we detect that the change in wind speeds strongly depends on the region and percentile considered, and that the most extreme storms may become stronger or more likely in the German Bight in a future climate despite reduced overall storm activity.