More than 200 people and billions of euros in damage: the heavy toll of the floods that ravaged Germany and Belgium mid-July must be blamed on climate change. According to a study released Tuesday, August 24, this extreme episode was made up to 9 times more likely by human-induced warming, with at least 20% more probability. Climate change has also “Increases the amount of rain over a day by between 3% and 19%”, according to scientists from World Weather Attribution (WWA), which brings together experts from various research institutes around the world.
On July 14 and 15, heavy flooding caused by torrential rains had killed at least 190 people in Germany and 38 in Belgium. Germany will have to devote 30 billion euros to the reconstruction of disaster areas and the disaster has placed the issue of the climate emergency at the center of public debate a few weeks of decisive elections at the end of September for the succession of the Chancellor Angela Merkel.
Increased probability and intensity
For the 39 international scientists gathered under the WWA banner, there is no doubt: “Climate change has increased the probability, but also the intensity” July events, said Frank Kreienkamp, of the German weather service, who piloted the study, in an online presentation. The episode has “Largely beaten historically recorded precipitation records” on affected areas, say the researchers.
The increase in precipitation is an expected consequence of warming, since a physical phenomenon increases the humidity of the atmosphere by about 7% for each additional degree.
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This is the second study to clearly point to warming in the natural disasters that have multiplied this summer. The WWA had previously calculated that the “Heat dome” that suffocated Canada and the American West at the end of June would have been “Almost impossible” without the effects of climate change.
Warming up faster than expected
In early August, the UN climate experts (IPCC) had also sounded the alarm in a shock report, pointing to a global warming even faster and stronger than feared, threatening mankind with disasters ” unprecedented “. The +1.5 ° C threshold – an ideal target not to be exceeded according to the Paris agreement – could thus be reached around 2030, ten years earlier than estimated. The devastating effects – droughts, fires or floods – are already being felt around the world.
The authors ran different models to estimate how warming affected the maximum amount of precipitation over a period of one or two days in the most affected regions, the Ahr and Erft river basins in Germany and the Meuse valley. in Belgium. But also over a larger region covering these two countries, as well as the neighboring Netherlands, affected to a lesser extent.
They observed a “Tendency to reinforce”, even if there remains a “Great variability” from one year to the next. And evaluated the probability of occurrence in Western Europe of an episode like that of July at once every 400 years. In other words, a one in 400 chance each year that such a disaster will occur. And they “Will become even more common” if warming continues, the study points out.
It is accordingly “Important to know how we reduce the vulnerability to these episodes and their impacts”, said one of the authors, Maarten van Aalst, director of the Red Cross and Red Crescent Climate Center. Because “Unfortunately, people are often ready … but for the previous disaster”.