Download Present Situation Challenges for Adaptation A Local Example

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