Nearly 40,000 people evacuated and displaced, 14 dead, more than 305 landslides engulfed thousands of homes and half a thousand roads cut off. The toll of the deadly floods that have hit the Emilia-Romagna region in northwestern Italy for several days is heavy.
This Sunday, May 21, while the red alert was maintained until the end of the day, the head of the Italian government Giorgia Meloni returned to her country, shortening her participation in the G7 summit in Hiroshima, Japan, to deal with the crisis.
The very sudden rise in water in the afternoon of Friday after canals overflowed, submerged by the waters of swollen rivers, is the direct consequence of an increasingly frequent weather phenomenon, the cold drop.
"It's a pocket of very cold air located at an altitude of more than 5,000 m," explains Météo France. When the polar jet stream deforms, it happens that a pocket detaches to go down to our latitudes, which is nicknamed a cold drop. It often causes disturbed weather, with showers, sometimes composed of sleet to the ground, associated with strong gusts of wind. »
A rare phenomenon in spring
This is exactly what has caused the very intense rainfall over Italy in recent days. "After crossing France and Switzerland, the cold drop deepened when arriving on the Emilia-Romagna region and meeting the warm Mediterranean air, causing very heavy rain showers, up to 300 mm in just two days," explains Guillaume Séchet, meteorologist and founder of the meteo-villes.com site.
This type of phenomenon occurs more in the fall, and much more rarely at this time of year when thunderstorms can be numerous, but not in this extreme form. »
As violent as it is unexpected in Italy, this phenomenon is no stranger to France. In June 2010, the Var department paid a very heavy price for what is called a Mediterranean episode, mainly in the Nartuby watershed and the lower Argens valley in the coastal area. Result: 27 dead and considerable material damage.
What are the risks today of seeing, in the coming days or weeks, a cold drop dump such a quantity of rain with, as a result, floods with dramatic consequences? "Not in the coming days and it is always difficult to predict in the long term, but yes, global warming and the so-called tropicalization of the Mediterranean climate increase the risk of seeing this type of event occur more often and more intensely," anticipates Guillaume Séchet.
First in France and Spain, two countries that directly face the rise of hot air from the Sahara. Mediterranean waters have remained exceptionally warm this winter and the "cauldron" effect is already present. »
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The possibility of very heavy rains is causing very strong concern for the south-eastern region or Occitania. Unlike northern Italy, where soils are normally wet for the season, those in these two regions are facing a historic drought. In case of rains, they would be unable to absorb huge quantities of water and a disaster as deadly as that of the Var in June 2010 would then be highly likely.