Rising extreme sea levels in the German Bight under enhanced $${{\mathrm {CO}}_2}$$ CO 2 levels: a regionalized large
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Rising extreme sea levels in the German Bight under enhanced CO2 levels: a regionalized large ensemble approach for the North Sea Andreas Lang1 · Uwe Mikolajewicz1 Received: 4 March 2020 / Accepted: 3 July 2020 © The Author(s) 2020
Abstract We quantify the change in extreme high sea level (ESL) statistics in the German Bight under rising CO2 concentrations by downscaling a large ensemble of global climate model simulations using the regionally coupled climate system model REMO-MPIOM. While the model setup combines a regionally high resolution with the benefits of a global ocean model, the large ensemble size of 32 members allows the estimation of high return levels with much lower uncertainty. We find that ESLs increase with atmospheric CO2 levels, even without considering a rise in the background sea level (BSL). Local increases of up to 0.5 m are found along the western shorelines of Germany and Denmark for ESLs of 20–50 years return periods, while higher return levels remain subject to sampling uncertainty. This ESL response is related to a cascade of an enhanced large-scale activity along the North Atlantic storm belt to a subsequent local increase in predominantly westerly wind speed extremes, while storms of the major West-Northwest track type gain importance. The response is seasonally opposite: summer ESLs and the strength of its drivers decrease in magnitude, contrasting the response of the higher winter ESLs, which governs the annual response. These results have important implications for coastal protection. ESLs do not only scale with the expected BSL rise, but become even more frequent, as preindustrial 50-year return levels could be expected to occur almost every year by the end of the century. The magnitude of the relative change in ESL statistics is hereby up to half of the expected rise in BSL, depending on the location. Changes in the highest extremes are subject to large multidecadal variations and remain uncertain, thus potentially demanding even further safety measures. Keywords Extreme sea level · Storm flood · Climate change · Grand ensemble · German Bight
1 Introduction Extreme high sea levels caused by storm floods constitute a major geophysical hazard for low-lying coastal regions such as the southeastern North Sea, known as the German Bight. Strong tidal oscillations due to the shallow shelf sea and the basin’s geometry (Fig. 1), combined with its situation along the major northern hemispheric storm-track path can lead to particularly high storm floods. While these conditions have lead to several severe disasters such as the flood of 1962,
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00382-020-05357-5) contains supplementary material, which is available to authorized users. * Andreas Lang [email protected] 1
Max Planck Institute for Meteorology, Bundesstr. 53, 20146 Hamburg, Germany
they have also triggered various counteractions and regulations in coastal protection (MELUR 2012). Anthropogenic climate change, howeve
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