Raising dikes and managed realignment may be insufficient for maintaining current flood risk along the German Baltic Sea coast

Abstract

Without upgrading existing adaptation, Germany is projected to be among those European countries that will suffer severe flood damages in 2100. Here we use a validated modeling framework to explore the effectiveness of two hypothetical upgrades to existing dike lines in reducing flood extent and population exposure along the German Baltic Sea coast. We perform a number of model runs where we increase the heights of existing dikes by 1.5 m, implement managed realignment as a nature-based solution, where physically plausible, and run a 200-year surge under two sea-level rise scenarios (1 and 1.5 m). We show that managed realignment is more effective in reducing future population exposure to coastal flooding compared to increasing dike heights. However, the maximum reduction in population exposure compared to a do-nothing approach amounts to only 26%, suggesting that even managed realignment is insufficient to maintain flood risk at today´s levels. The greatest potential for protecting people and property from future flooding lies in developing adaptation strategies for currently unprotected coastal sections.

Brief Communication: From modeling to reality – Insights from a recent severe storm surge event along the German Baltic Sea coast

“…During that surge, dikes that were located further inland behind beach ridges were not damaged, while dikes directly behind the beach experienced strong damages (Hofstede, 2024). The availability of potential areas for implementing such buffer zones by means of managed realignment and their potential to mitigate the impacts of storm surges has recently been assessed by Kiesel et al (2023a) along the German Baltic Sea coast. The potential effectiveness of a natural buffer zone is further demonstrated by the example of the dike breach north of Falshoeft (Geltinger Birk, Flensburg Fjord), where a ~600 m dike breach led to extensive flooding.…”