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Download Present Situation Challenges for Adaptation A Local Example
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Challenges for Adaptation to Sea Level Rise in the Coastal Areas of Germany Ralf Weisse, Jens Kappenberg, Janina Sothmann, Insa Meinke Present Situation Germany’s coastal areas are exposed to extra-tropical storms and related marine hazards such as wind waves and storm surges. Rising mean sea levels provide a substantial threat as they shift the baseline for storm surges and wind waves towards higher values. As a consequence extreme sea levels have increased in the area over the past about 150 years at a rate roughly comparable to global mean sea level rise. Other effects, in particular from engineering in estuaries, further contribute and exacerbate the situation and increasing tidal ranges or storm surge heights have been observed over the past decades at some places. About 50% of the coast is below 5 m NN (Figure 1). As a consequence these areas are nowadays protected from the impacts of tides and storm surges by an almost continuous dike line. Increasing mean sea levels will raise the flooding risk for these areas, but hardly expand the area at risk. Figure 1: Protected areas and areas at risk at the German North coast. Yellow indicates land with elevations below the average twice daily tidal high water levels. Light green indicates additional regions with elevations below the height of the devastating storm surge in February 1962. Dark green areas additionally account for a 1.1 m increase in mean sea level. Taken from and more information at www.kuestenschutzbedarf.de. Challenges for Adaptation Because a considerable part of Germany’s coastal areas is already nowadays threatened by the impacts from extreme sea levels (Figure 1), retreat hardly represents an option for most regions. This is explicitly formulated, for example, in the climate change adaptation strategy of the federal state of Lower Saxony to which much of the coastal area illustrated in Figure 1 belongs to. The situation is further complicated as climate change often represents only one of the drivers contributing to the observed changes (Figure 2). Moreover, future (climate) changes for which adaptation is envisaged are often highly uncertain. Because of the long time scales associated with planning, adaptation options are needed that are robust and flexible; that is, options working for broad range of expected future developments and that may be adapted in the course of time when more information becomes available. Figure 2: Change in annual mean high (MHW) and low (MLW) water levels at the tide gauge Hamburg, St. Pauli located about 140 km inside the Elbe Estuary. Timing of major waterworks in the estuary is indicated by the black horizontal bars. Within the period shown, the mean tidal range in Hamburg increased from about 2 to 3.5 m. (Courtesy: Hamburg Port Authority) A Local Example Conclusions Concept for a sustainable development of the Elbe Estuary Germany’s coastal areas are at threat from rising mean sea levels and related marine hazards such as storm surges. Expected future changes remain highly uncertain and climate change represents only one of the drivers contributing to the observed changes. The tidal system of the Elbe Estuary has changed significantly in the past. Due to anthropogenic interventions and natural changes flood plains were reduced and the friction of the Elbe Estuary decreased. As a result tidal range and sediment transport increased upstream. Furthermore the tidal wave propagates faster through the estuary, resulting in increased tidal ranges in Hamburg (Figure 2). This leads to a heightening of the flood risk along the estuary. In the framework of the European Project THESEUS the efficiency of five different artificial sandbank scenarios in the mouth of the estuary for attenuating the incoming tidal energy either by reflection or by increasing friction is investigated using numerical modelling. Results show that the effects on currents and storm surge height is only local and relevant only during flood-tide. Re-activating former flood plains might be more efficient. Figure 3: Location of the modelled artificial sandbanks in the Elbe estuary (Sothmann et al. 2011) Therefore development of robust and flexible adaptation options and concepts is needed taking the different drivers into account, encompassing the needs and perceptions from stakeholders and society. For this purpose and apart from specific solutions as illustrated in the example on the left, three important issues need to be addressed: The development of homogeneous data bases allowing for assessments of past and the full range of possible future changes. For an example we refer to our coastDat data base (www.coastdat.de). Regional assessments. For an example see the Baltic Sea Climate Change assessment (www.baltex-research.eu/BACC/). Research into science stakeholder interaction & development of climate services. For an example see products from our North German Climate Office (www.norddeutsches-klimabuero.de/). Helmholtz-Zentrum Geesthacht • Max-Planck-Straße 1 • 21502 Geesthacht / Germany • Phone +49 (0)4152 87-0 • Fax +49 (0)4152 87-1403 • [email protected] • www.hzg.de Contact: Dr. Ralf Weisse • Phone +49 (0)4152 87-2819 • Fax +49 (0)4152 87-42819 • [email protected]@hzg.de