Black Swans and Risk - Assessing Consequences of Extreme Events for the German Bight

Abstract

Westerly and north-westerly storms regularly hit the German North Sea coast causing surges of several meters at the dikes. But extreme events like cyclone Xaver in 2013 are not the largest physically possible events on record. Dangendorf et al. (2016) show that the individual components of the total water level (i.e. mean sea level, surge, and tide) were not at their observed maximum during Xaver. The research project “EXTREMENESS” was initiated to examine the meteorological potential of storms in the German Bight and to assess the consequences of extremely large and rare but physically possible storm surge events, so called “black swans”. Our project partners, the German Meteorological Office, the German Federal Waterways Engineering and Research Institute, and Helmholtz-Zentrum Geesthacht, evaluate possible meteorological and resulting hydraulic boundary conditions including regionally projected sea level rise scenarios which we use to simulate inundations in the study area around Emden (Lower Saxony, Germany) using a two-dimensional hydrodynamic numerical (2D-HN) model. Large parts of the region are situated below mean sea level and drained using tide gates and pumping stations. Therefore the area is highly vulnerable to dike failures and loads exceeding the design levels of defense structures. Combining inundation scenarios with exceeding probabilities and dike failure probabilities will yield risk maps, showing the most vulnerable dike sections and pointing out areas that need particular attention in maintenance.

Storm Tilo over Europe in November 2007: storm surge and impacts on societal and energy infrastructure

“…For Storm Tilo, the trough-to-peak height of these features was smaller than range of the tides and storm surge at most North Sea stations, so that they were of second order importance for coastal flooding risk. On the other hand, storm flood levels during Storm Britta exceeded the numerical model predictions that encapsulate the understanding of storm surge dynamics (RWS, 2006a(RWS, , b, 2007a, and certain reports indicate there may have been a high risk of coastal dyke breaches and flooding (Ulm et al, 2018). As well, the highest of the short period oscillations during Storm Tilo appeared to show correspondence in time and location with some of the reported infrastructure events.…”

Storm Xaver over Europe in December 2013: Overview of energy impacts and North Sea events

“…There were floods six years ago (Lowestoft Journal, 2014)". Questions were also raised about the worst case surge flood that might hit the North Sea coasts -the so-called Black Swan event that no one has ever seen before -and model studies suggest that this might be >1 m higher than any event in the measurement record (Ulm et al, 2018).…”