Abstract
Abstract. A new procedure for the identification of storm surge situations for the German Bight is developed and applied to reanalysis and global climate model data. This method is based on the empirical approach for estimating storm surge heights using information about wind speed and wind direction. Here, we hypothesize that storm surge events are caused by high wind speeds from north-westerly direction in combination with a large-scale wind storm event affecting the North Sea region. The method is calibrated for ERA-40 data, using the data from the storm surge atlas for Cuxhaven. It is shown that using information of both wind speed and direction as well as large-scale wind storm events improves the identification of storm surge events. To estimate possible future changes of potential storm surge events, we apply the new identification approach to an ensemble of three transient climate change simulations performed with the ECHAM5/MPIOM model under A1B greenhouse gas scenario forcing. We find an increase in the total number of potential storm surge events of about 12 % [(2001–2100)–(1901–2000)], mainly based on changes of moderate events. Yearly numbers of storm surge relevant events show high interannual and decadal variability and only one of three simulations shows a statistical significant increase in the yearly number of potential storm surge events between 1900 and 2100. However, no changes in the maximum intensity and duration of all potential events is determined. Extreme value statistic analysis confirms no frequency change of the most severe events.
Highlights
Storm surges at the German coast have a high socioeconomic impact, as they are the most dangerous hazard for the coastal areas, even affecting the densely populated urban region of Hamburg.The factors influencing storm surges are summarized in Weisse et al (2012) and the knowledge about past and possible future changing storm-surge statistics is reviewed in von Storch and Woth (2008)
We detect storm surge relevant situations using effective wind components calculated from ERA-40 reanalysis data (Uppala et al, 2005) solely over the German Bight
Detection of potential storm surge events under recent and future climate conditions gives an estimate of the possible changes in storm surge activity over the German Bight region
Summary
Storm surges at the German coast have a high socioeconomic impact, as they are the most dangerous hazard for the coastal areas, even affecting the densely populated urban region of Hamburg.The factors influencing storm surges are summarized in Weisse et al (2012) and the knowledge about past and possible future changing storm-surge statistics is reviewed in von Storch and Woth (2008). Other factors influencing the rise of the water level during a storm are local water depth and external surges (Tomczak, 1960; Gönnert and Sossidi, 2011a, b). The height of a storm surge is defined by the rise of the water level above the mean high water level (MHW). Following the definition used by the German Maritime and Hydrographic Agency (BSH) a storm surge event at the German North Sea coast with water levels exceeding the MHW by 1.5 to 2.5 m is called a “storm surge”, an excess of 2.5 to 3.5 m is defined as a “heavy storm surge”, and an event exceeding 3.5 m above MHW is called a “very heavy storm surge” (Müller-Navarra et al, 2012). The shape of the German Bight coastline and its estuaries intensifies the water rise as water that is pushed by north-western winds into the southern North Sea is impounded
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