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River floods

River floods cause major economic losses, being the most common natural disaster in Europe. Climate change could increase the magnitude and frequency of these events, leading to higher costs. The objective of the river flood impact assessment is to quantify changes in river flood hazard, followed by computing the expected people affected and expected economic damages, in view of specific climate and socio-economic developments.

Methodology

The methodology implemented for the impact assessment follows closely that of the PESETA study (Feyen et al., 2012), and that of the FP7 ClimateCost project ((Feyen and Watkiss, 2011). The assessment uses high-resolution climate model projections to force the hydrological model LISFLOOD (van der Knijff, 2010) at pan-European scale to assess changes in future flood hazard with respect to a control period (1961-1990). Socio-economic impacts are estimated by combining flood inundation maps with information on exposure (land use and population density) and vulnerability (depth-damage functions). The impacts reported here only include physical losses due to direct contact with water and could, therefore, be conservative.

There is a lot of uncertainty regarding developments of climate variables (e.g., extreme precipitation) important for flood generation. The river flood assessment has therefore been made using a large ensemble of twelve A1B climate runs (including the Reference) and three E1 climate runs (including the 2°C run). The results presented here are conditional on the emission scenario and climate model chain (combination of GCM and RCM) used.

Main results and findings

Under the Reference run, climate change is expected to increase the number of people affected by flooding annually from the current level of around 167 000 to 290 000. Under the same run, annual direct flood damages are estimated to increase from around €5 billion to around €11 billion. This assumes current protection levels and does not take into account socioeconomic changes that affect the number of people and value of assets at risk. Once these socioeconomic changes are taken into account, estimated damages increase to €98 billion (€68 bn in a 2°C scenario), though adaptation (maintaining protection against a 1 in 100 year flood event) can reduce this to €53 billion.

It is important to note that there is a large variability in the impact estimates of river floods derived from the alternative climate runs used. With twelve different climate runs for the A1B and only three runs for the E1 scenario, the E1 results presented in the report account for much less uncertainty in climate developments.


Figure. EU27 Expected Annual Damages from floods in billion € for baseline period (1961-1990), 2000s (1981-2010), 2020s (2011-2040), 2050s (2041-2070) and 2080s (2071-2100) for the A1B scenario. Ensemble average results based on LISFLOOD simulations driven by 12 regional climate models (all numbers in constant prices of 2006).

References

Van der Knijff, J., Younis, J., and de Roo, A., 2010. LISFLOOD: a GIS-based distributed model for river basin scale water balance and flood simulation, Int. J. Geogr. Inf. Sci., 24, 189–212, doi:10.1080/13658810802549154.
Feyen, L., R. Dankers, K. Bódis, P. Salamon, J.I. Barredo (2012).
Fluvial flood risk in Europe in present and future climates.
Climatic Change, Climatic Change, May 2012, Volume 112, Issue 1, pp 47-62.
Feyen, L. and Watkiss, P. (2011).
Technical Policy Briefing Note 3. The Impacts and Economic Costs of River Floods in Europe, and the Costs and Benefits of Adaptation. Results from the EC RTD ClimateCost Project. In Watkiss, P (Editor), 2011. The ClimateCost Project. Final Report.
Published by the Stockholm Environment Institute, Sweden, 2011. ISBN. 978-91-86125-35-6.
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