Collapsed villages, torrents of mud sweeping away everything in their path, landslides: the toll of torrential rains and floods that hit Germany, Belgium and Luxembourg continues to worsen, with nearly 130 dead Friday, July 16 in the afternoon. Jean-Pascal van Ypersele, climatologist at the Catholic University of Louvain and former vice-president of the Intergovernmental Panel on Climate Change (IPCC), warns of the increase in such extreme events under the effect of climate change.
How do you react to these floods?
Like many of my colleagues, I am shocked. And also moved, because it is happening very close to home. People have lost everything in some places that I know, it touches me a lot. These are events that we, climatologists, announced thirty years ago, and which are becoming very concrete. As early as 1990, the first IPCC report indicated that the greenhouse effect will accentuate the two extremes of the hydrological cycle: there will be more episodes of extremely heavy rains and more severe droughts.
However, I was surprised by the scale and intensity of this event. The evacuation of the center of Liège is very significant. The last time there was flooding of this magnitude in the Meuse valley was in 1926. Almost 100 years ago.
Climate change is therefore responsible for these torrential rains?
We do not yet have the results of the attribution studies, which will define the responsibility for global warming, but in my opinion, we cannot explain what is happening at the moment without taking into account the disruption of the climate. There is a combination of two factors: on the one hand, global warming increases the intensity of precipitation. The higher temperature of the atmosphere causes on average more water vapor in the air, and therefore more rainfall.
On the other hand, this depression, the source of precipitation, remained in the same region for a long time because it moved very slowly. It is probably linked to climate change, but on this point there is no scientific consensus. Work shows that climate change, due to a decrease in the thermal contrast between equatorial and arctic regions, leads to larger oscillations of the jet stream [vents forts situés en altitude et qui tournent autour de la Terre]. However, when the jet stream twists and turns, it causes depressions from west to east less quickly. They therefore move more slowly.
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