Presenter: Jadranka Sepic (Faculty of Science, University of Split)

Description:
Destructive flooding events related to extreme sea levels may generate substantial material damage on buildings and infrastructure, cause traffic disruption and endanger human lives. Well-known examples along the European coasts include strong surges along the southern and eastern coasts of the Baltic Sea, destructive flooding events along the low-lying coasts of the North Sea, surge events along the Atlantic coasts of western Europe, and the acqua alta (It. "high water") events at the Adriatic Sea. Traditionally, only the low-frequency component of these events has been studied in detail. However, analyses of higher resolution tide gauge and buoy data reveal that – like documented for hurricanes – the surge is often accompanied by intense sea level oscillations occurring at periods shorter than 2 hours, which can substantially add to the destructive height and effect. Sea level data – measured with a less than 20 min temporal resolution at more than 250 tide gauge stations spread along the European coasts – were analyzed for the period of availability (longest series start at the beginning of the 2000s). Basic statistical analyses were made to estimate the contribution of high-frequency components to the total extreme height. Several of the strongest events were extracted and analyzed in more detail from both oceanographic and meteorological perspectives. The events were chosen to cover various parts of the European coasts (the Baltic Sea, the North Sea, the Atlantic, the Mediterranean) to account for differences in the bathymetric and topographic characteristics. It is shown that depending on the site, event, and background atmospheric processes, the dominant contribution to flooding comes from storm surges, long ocean waves, seiches, infragravity, and/or wind waves.  The research is done within the framework of the ERC-StG SHExtreme project, which aims at estimating the contribution of high-frequency sea level oscillations to the European sea level extremes.