Europe鈥檚 politicians should bulk-buy waterproof boots. By 2050 extreme floods will swamp Europe twice as often as they do now, and the annual costs of flood damage could increase fivefold.
A new analysis of peak river flows provides some of the best evidence yet that climate change will make floods worse. However, other factors such as building in flood zones have a bigger effect on costs, because more buildings are in harm鈥檚 way.
Unlike earlier studies, this study incorporates patterns of flooding that consistently affect several river basins at once, rather than working out the flood risk for each river basin in isolation.
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鈥淲e鈥檙e the first to look at correlations between peak discharges in different river basins, and the chance that if there鈥檚 flooding in one, it will spread to others,鈥� says of the VU University in Amsterdam, the Netherlands.
His team analysed data, collected since 1990, on the peak flows of water in rivers. They found clear patterns. For instance, peak flows in the Danube often coincide with peak flows in the Elbe, as happened in last summer鈥檚 devastating floods in central Europe.
The correlations make sense, says Jongman, because several river basins can simultaneously be affected by common periodic weather patterns, such as cyclones moving north from the Mediterranean.
Once they鈥檇 worked out the correlations between basins, the team fed them into climate models that predict patterns of rainfall and temperature between now and 2050, to evaluate how often floods would occur. 鈥淎ll the models we used assume rainfall will increase,鈥� says Jongman.
Spilling over
The models predict that major floods will occur every 10 years by 2050, instead of the current frequency of once every 16 years.
So far the evidence that climate change will make floods worse is surprisingly weak. The most recent report of the Intergovernmental Panel on Climate Change, released last year, says there is 鈥溾�� about whether global flooding has been increasing or decreasing over the last century. 鈥淲e can鈥檛 say on a global scale that flooding will increase as there鈥檚 not enough data yet to say one way or the other,鈥� says Jongman. But rainfall will increase, suggesting floods will too.
Jongman鈥檚 models also suggest that average annual losses in Europe from flood damage will increase to 鈧�23 billion by 2050, from the 鈧�4.9 billion seen from 2000 to 2012. Two-thirds of the extra damage is caused by economic growth and expanding populations, which mean more people living in flood-prone areas, says Jongman. Climate change accounts for the other third.
The best solution is to manage floods on a European scale, says Jongman, instead of relying on isolated national or local responses.
鈥淔lood hazard is certainly interdependent across regions,鈥� says of the University of Reading, UK. Governments must consider these links between rivers when they protect against floods. 鈥淭his approach provides an important basis for a new way of carrying out continental-scale risk management.鈥�
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