Changes in North Sea storm surge conditions for four transient future climate realizations

Storm surges in the North Sea are one of the threats for coastal infrastructure and human safety. Under an anthropogenic climate change, the threat of extreme storm surges may be enlarged due to changes in the wind climate. Possible future storm surge climates based on transient simulations (1961-2100) are investigated with a hydrodynamical model for the North Sea. The climate change scenarios are based on regionalized meteorological conditions with the regional climate model CCLM which is forced by AR4 climate simulations with the general circulation model ECHAM5/MPIOM under two IPCC emission scenarios (SRES A1B and B1) and two initial conditions. Possible sea level rise in the North Sea is not taken into account. The analysis of future wind-induced changes of the water levels is focused on extreme values. Special emphasis is given to the southeastern North Sea (German Bight). Comparing the 30-year averages of the annual 99 percentiles of the wind-induced water levels between the four climate realizations and the respective control climates, a small tendency toward an increase is inferred for all climate change realizations toward the end of the twenty-first century. Concerning the German Bight, the climate change signals are higher for the North Frisian coastal areas than for the East Frisian ones. This is consistent with an increase in frequency of strong westerly winds. Considering the whole time series (1961-2100) for selected areas, this tendency is superimposed with strong decadal fluctuations. It is found that uncertainties are related not only to the used models and emission scenarios but also to the initial conditions pointing to the internal natural variability.