Impact of a wind climate change on the surge in the southern North Sea

The aim of this paper is to gain quantitative insights into the surge-impact of a possible change of the wind climate in the southern part of the North Sea. The approach taken is based upon an initial review of the results of General Circulation Model scenarios for climate change under greenhouse forcing and of their likely effects upon wind climate. Two scenarios of possible wind climate change are formulated. Scenario 1 assumes a northward shift of the entire wind climate system in the southern part of the North Sea; scenario 2 describes an increase of the intensity of storms in this area. To model these scenarios, the concept of 'parametric storms' is presented, which considers the characteristics of a storm to be conditional upon a limited number of parameters. Applying this concept to the well-known 1953 storm yields promising results. On the basis of this parametric 1953 storm, a large set of storms which are assumed to be consistent with the present (surge generating) wind climate in the southern part of the North Sea is generated. Because these storms do not all have equal chances of occurrence, this set is supplemented by a probability distribution. The future wind climate, which might develop as a result of the 2 wind climate change scenarios, is then modelled by changing this probability distribution and/or some parameters of the storm set. The surge-impact of the 2 modelled scenarios of wind climate change is determined using the Dutch Continental Shelf Model, which describes the depth-averaged tidal flow and storm surges in the North Sea and surrounding areas. For several locations in the southern part of the North Sea, the model output is analyzed and presented in terms of a frequency distribution of storm surge levels. With respect to scenario 1, these simulation results show that a relatively large northward shift of the entire wind climate system in the southern part of the North Sea will only have a small impact on the storm surges in this area. In the case of scenario 2, however, the results show that a relatively small increase of the intensity of depressions in the southern North Sea will result in a relatively large impact on the storm surges in this area.