EGU General Assembly edition:2012 location:Vienna, Austria date:22-27 April 2012
To improve on the efficacy of flood risk mitigation measures, it is essential to investigate the relative importance
of the future impact pressures. This is more so in areas which are found to be hot spots for flooding.
One such area was identified in the Scheldt region located in Belgium. The Dendermonde area is a place where
both the downstream coastal and the upstream river flow boundary conditions interact and jointly control the flood
risk. Downstream of this area, the coastal level changes include both the sea level rise and storm surge changes
due to climate change impacts on the wind climate over the North Atlantic and North Sea region. Upstream of the
Dendermonde area lies the Dender river which introduces an extra pressure on the Dendermonde area. Against
this back drop, impact analysis was performed using a hydrodynamic model that accounts for such changes. The
climate data for future scenarios were extracted from the climate databases PRUDENCE (http://prudence.dmi.dk),
ENSEMBLES (http://www.ensembles-eu.org/), IPCC AR4 (www-pcmdi.llnl.gov/ipcc/about_ipcc.php) and
CERA (CLM from MPI-M/MaD).
Future changes were derived from the large ensemble set of climate model runs and their effects simulated
in the hydrodynamic model based on statistically processed climate change scenarios of sea level rise, SLP change
and related storm surge changes and upstream runoff due to changes in rainfall and potential evapotranspiration.
Changes in SLP were transferred to changes in storm surges at the Scheldt mouth (at Vlissingen) based on a correlation
model between the SLP at the Baltic Sea and the storm surge level. This model was derived after analysis of
SLP composite maps and SLP-surge correlation maps for days where the surge exceeds given thresholds (for different
return periods). Correlations between the inland (rainfall, runoff) and coastal climatic changes were considered.
The impact analysis to analyze the importance of the pressures for the Dendermonde area was based on
hydrodynamic impact model results. From the water level impact results, it was deduced that the sea level rise and
surges are by far the most important factors when evaluating the flood risk in the Dendermonde region. When the
extreme changes for the three main boundary conditions (mean sea level, surge and upstream runoff) coincide, the
impact is disastrous. For example, water levels at Dendermonde were simulated to change around +1.8m for return
periods in the range between 100 and 10000 years and the scenario with +0.6m mean scenario for sea level rise
,+21% high scenario change in surge levels, and +30% high scenario change in upstream flow. For the high mean
sea level rise scenario of +2m, the changes are even much higher. Water management plans, which are currently
under way such as the Sigma Plan, can be informed from such studies so as to test the robustness of the proposed
flood mitigation measures.