30 May 2022
30 May 2022
Status: this preprint is currently under review for the journal NHESS.

The role of preconditioning for extreme storm surges in the western Baltic Sea

Elin Andrée1,2,a, Jian Su1, Morten Andreas Dahl Larsen2, Martin Drews2, Martin Stendel1, and Kristine Skovgaard Madsen1 Elin Andrée et al.
  • 1Danish Meteorological Institute, Lyngbyvej 100, 2100 Copenhagen, Denmark
  • 2Technical University of Denmark, Dept. of Technology, Management and Economics, Produktionstorvet, Building 424, 2800 Kgs. Lyngby, Denmark
  • apresent address: SMHI Göteborg, Sven Källfelts gata 15, 426 71 Västra Frölunda, Göteborg, Sweden

Abstract. When natural hazards interact in compound events, they may reinforce each other. This is a concern today and in the light of climate change. In the case of coastal flooding, sea-level variability due to tides, seasonal to inter-annual salinity and temperature variations or larger--scale wind conditions modify the development and ramifications of extreme sea levels. Here, we explore how prior conditions influence peak water levels for the devastating coastal flooding event in the western Baltic Sea in 1872. By imposing a range of antecedent conditions in numerical ocean model simulations, we quantify the change in peak water levels that arise due to alternative preconditioning of the sea level before the storm surge. Our results show that different preconditioning could have generated even more catastrophic impacts. As an example, a simulated increase of 36 cm compared to the 1872 event was seen in Køge just south of the Danish capital region – a region that was already severely impacted. The increased water levels caused by the alternative water mass distributions propagate until encountering shallow and narrow straits, thereafter the effect vastly decreases. Adding artificial increases in wind speeds to each study point location reveals a near-linear relationship with peak water levels for all Western Baltic locations highlighting the need for good assessments of future wind extremes. Our research indicates that a more hybrid approach to analysing compound events, and readjusting our present warning system to a more contextualised framework, might provide a firmer foundation for climate adaptation and disaster risk management.

Elin Andrée et al.

Status: open (until 11 Jul 2022)

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Elin Andrée et al.

Elin Andrée et al.


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Short summary
When natural hazards interact in compound events, they may reinforce each other. The combined effect can amplify extreme sea levels when storms occur when the water level is already higher than usual. We used numerical modelling of a record-breaking storm surge and showed that other prior sea-level conditions could have further worsened the outcome. Our research highlights the need to consider the physical context of extreme sea levels in measures to reduce coastal flood risk.