The water and mud swept away everything in their path. Cars, electric poles, furniture, human lives, etc. While part of the Valencia region is still on red alert, the death toll from the floods affecting southern Spain since Tuesday is now 158. In the rain which continues to fall, emergency services are still searching for dozens of missing people.
The government has declared a three-day national mourning, while images of dozens of cars carried by muddy water in the streets continue to loop on the news channels. How can we explain the scale of the disaster? Several factors come into play and have combined: global warming, regional geography, massive concreting and failing alert service.
A typical global warming disaster
To understand the very violence of the rains which affected the Valencia region, it is necessary to specify the nature of the meteorological phenomenon at work. “We are in the presence of a cold drop, that is to say a pocket of cold air at altitude which meets warm air which rises”, explains to 20 Minutes Freddy Bouchet, climatologist, research director at CNRS and professor attached to ENS PSL. “Hot air arrives from the South and picks up moisture as it crosses the Mediterranean, which remains particularly hot,” explains Marie-Antoinette Mélières, physicist and climatologist. This warm air “rises as it arrives at the mountain foothills” and collides with a “cold ceiling”. It is the famous cold drop, which detached itself earlier from the “polar jet current”, and forms a “dense pocket which descends”, adds Célia Fontaine, trainer for the Fresque du Climat association.
The encounter of this influx of warm, humid air with the stable “cold ceiling” leads to “intense and renewed rains”, concludes Marie-Antoinette Mélières. A phenomenon identical to the Cevennes episodes, and which is not unusual in Spain, our three experts agree. But “with climate change, these events will occur more frequently and more violently, this is only the beginning,” warns Célia Fontaine. “We will have an increase in these extreme events anyway,” agrees Marie-Antoinette Mélières. The episode experienced in Ardèche two weeks ago is a perfect example. “Today, precipitation is 10 to 15% more intense compared to a climate without warming,” supports Freddy Bouchet. And around a Mediterranean which is warming faster than the global average, it hasn’t stopped raining.
Mountain and concrete, matrices of mudslides
The topology of the Valencia region cannot be ignored to take into account the extent of the flooding. As Marie-Antoinette Mélières points out, the presence of mountain foothills is an element of the meeting between air masses, and therefore of the appearance of rain. “This kind of relief is found almost everywhere around the Mediterranean, it could just as easily have taken place in Perpignan or Nice,” raises Freddy Bouchet. However, geography is not in itself a “determining factor” in explaining floods, if we do not take into account the urbanization of the Valencia region.
“There are small villages perched in the mountains, surrounded by lots of small rivers and with strong urbanization,” underlines Célia Fontaine. “In fifty-five years, the agglomeration of Valence has destroyed 9,000 hectares of orchards due to the action of urbanization”, i.e. the surface area of Paris intramural, emphasizes on X the doctor in urban planning Clément Gaillard. Between concrete, drought and exposed clay soils, in addition to increasingly reduced vegetation, the impermeable soils were unable to withstand “a year of rain falling in a few hours”. “The small streams overflowed and the rain washed away the mud that was at the bottom,” continues Célia Fontaine, carrying it to flow into the tarmac streets of the agglomeration of Valence, the third most populous city in Spain.
A very late alert message
To these factors which have become structural, we must add a grain of sand in the machine. Although the Spanish meteorological agency (Aemet) issued a “red alert” at 7 a.m., the region’s services were slow to react. The Integrated Operational Coordination Center (Cecopi), responsible for coordinating the rescue action, only got into working order around 5 p.m., when the rain was already falling. Worse, the Civil Protection alert message, equivalent to the FR-Alert system, was only sent to the inhabitants of Valencia at 8 p.m., and even 9 p.m. in certain villages, notes The Country.
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Far too late to tell people not to leave their homes. All day long, despite the danger, residents went to work, took their cars, and many of them were in traffic jams when the rivers overflowed. “Of course we need good prevention, good forecasts and a good alert system. But the risk is to look for a scapegoat,” notes Freddy Bouchet. After the Cannes floods in September, Mayor David Lisnard thus “attacked Météo-France in an unjustified manner”, protests the climatologist, but “the responsibility lies well upstream, in the denial of global warming and adaptation needs”. Because more floods will come.