Raising dikes and the large-scale implementation of managed realignment are not sufficient to mitigate increasing flood risk along the German Baltic Sea coast

Abstract

Across Europe, the North- and the Baltic Sea coasts are expected to experience the highest increase in extreme sea levels until the end of the century, mostly due to rising sea levels. This increase will have serious implications for coastal flooding and adaptation planning, which is particularly true for Germany. Without adjusted and/or upgraded adaptation, Germany is projected to be among those European countries that suffer largest absolute flood damages in 2100.Here we use a fully validated modelling framework to explore the effectiveness of raised dike crest elevations and managed realignment as a nature-based adaptation option in reducing flood extent and exposed population during a 200-year surge event, also accounting for two sea-level rise scenarios (1 m and 1.5 m). We explore the potential for managed realignment in the study region by introducing a fully automated modelling approach that considers elevation, land use and infrastructure.We find that managed realignment is more effective in reducing the population exposed to coastal flooding compared to increasing dike crest elevations. However, maximum reduction in population exposure amounts to 26 %, suggesting that redesigning existing dikes by managed realignment is not enough for maintaining flood risk at today´s levels. Our results show that the greatest potential for protecting people and property from coastal flooding in the future lies in developing adaptation strategies for those coastal sections, where currently no dikes are present. Here we argue that more landward dike lines, as created by managed realignment, allow for a wider buffer zone between land and sea, and constitute a promising option to complement conventional coastal defense schemes.