Abstract
In this study, the projected future long-term changes of the local wave conditions at the German Baltic Sea coast over the course of the 21st century are analyzed and assessed with special focus on model agreement, statistical significance and ranges/spread of the results. An ensemble of new regional climate model (RCM) simulations with the RCM REMO for three RCP forcing scenarios was used as input data. The outstanding feature of the simulations is that the data are available with a high horizontal resolution and at hourly timesteps which is a high temporal resolution and beneficial for the wind–wave modelling. A new data interface between RCM output data and wind–wave modelling has been developed. Suitable spatial aggregation methods of the RCM wind data have been tested and used to generate input for the calculation of waves at quasi deep-water conditions and at a mean water level with a hybrid approach that enables the fast compilation of future long-term time series of significant wave height, mean wave period and direction for an ensemble of RCM data. Changes of the average wind and wave conditions have been found, with a majority of the changes occurring for the RCP8.5 forcing scenario and at the end of the 21st century. At westerly wind-exposed locations mainly increasing values of the wind speed, significant wave height and mean wave period have been noted. In contrast, at easterly wind-exposed locations, decreasing values are predominant. Regarding the changes of the mean wind and wave directions, westerly directions becoming more frequent. Additional research is needed regarding the long-term changes of extreme wave events, e.g., the choice of a best-fit extreme value distribution function and the spatial aggregation method of the wind data.
Highlights
Human-made emissions of greenhouse gases have caused warming of the global climate system and the mean global temperatures are expected to increase further and cause long-term changes in all climate system compartments including the oceans [1,2,3].the changes in global temperatures are expected to affect the wind conditions on different regional and temporal scales and the mean and extreme sea levels
The REMO simulation can contain a significant bias for both near surface wind speed and mean wind direction; within the range of −1.9% to +4.8% for the wind speed, respectively, −28◦ to +3◦ for the wind direction for the 30-year annual averages
The main goal of this study was the assessment of the future changes of the wave conditions at the German Baltic Sea Coast, based on a multi-model- and multi-member ensemble of climate projections of the regional climate model (RCM) REMO
Summary
The changes in global temperatures are expected to affect the wind conditions on different regional and temporal scales and the mean and extreme (storm surge) sea levels. The changes of the wind conditions and water levels will affect the local wave climate and the wave-induced loads on coastal protection structures as well, e.g., on the wave-induced sediment transport. These processes include the long-shore sediment transport, that influences the long-term morphology of the coast (including coastal erosion) [4]. The future changes of the wind and wave conditions along semi-enclosed basins, e.g., the Baltic Sea, which are investigated within this study, depend on the (i) forcing global climate model/GCM (model uncertainty) [9], (ii) future forcing scenario (scenario uncertainty), (iii) realization of the climate projection (internal variability), (iv) future time period (temporal variability) and (v) location (spatial variability) [10,11]
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