Floods in Libya: What is a “medicane”, this weather phenomenon at the origin of the disaster?

Storms and squalls With global warming, “medicans” will “gain in intensity and perhaps frequency”

According to scientists, Storm Daniel is the latest extreme weather event to bear some of the hallmarks of climate change. — Jamal Alkomaty/AP/SIPA

• A powerful storm hit Libya on Sunday, causing dams to break and destroying infrastructure. The toll from the floods is currently at least 5,000 dead, while 10,000 people are missing.
• This storm, which had already affected Greece, Bulgaria and Turkey, strengthened at sea, creating what weather experts call a “medican”, contraction of Mediterranean and “hurricane” (hurricane, in English). /li>
• “We are starting to approach the intensity of tropical cyclones” with medicans, which are powered by the heat of the Mediterranean, explains geosciences professor Sabrina Speich. However, with global warming, the Mediterranean continues to break heat records.

Covered in mud, rubbish and littered with lifeless bodies, the streets of Derna are unrecognizable. In this town of 100,000 inhabitants, on the north-eastern coast of Libya, it was not only storm Daniel which struck with violence, but also the waters of two dams which gave way. ; under excess rain. The meteorological phenomenon which affected Libya was no longer the storm that hit Libya. Greece and Turkey; As it crossed the Mediterranean, it became what weather experts call a medicane, a contraction of Mediterranean and “hurricane”. (hurricane, in English).

What is the difference between a medic and a storm? Does such an intensity? Is this phenomenon normal? Should we fear more violentmedicines at home? the time of climate change? 20 Minutes takes stock with Sabrina Speich, professor of geoscience at ENS de Paris.

What is the difference between a storm and a “medicine ”?< /h2>

“It all depends on the strength of the intensity’ of the winds,” says Sabrina Speich. Based on the Beaufort scale, a storm corresponds to a depression accompanied by winds of between 89 and 102 km/h, with gusts exceeding 110 km/h, according to Météo-France. But when this storm passes over a hot Mediterranean, “the air heats up, by convection and by evaporation,” deciphers the professor of geology. osciences, specializing in the study of meteorological phenomena linked to the oceans. However, the warmer the water in the Mediterranean, the greater the “quantity” it has. energy.

And when, once it rises into the atmosphere, “the water vapor becomes droplets, it releases energy,” she explains. “We end up with more energetic and more precipitating storms,” the idea of ​​a storm that would have “recharged” above the sea. « We start at approach the intensity of the tropical cyclones,” says Sabrina Speich, whose doctor has certain characteristics, observes Météo-France. « This year, the Mediterranean was very popular. five degrees warmer than usual for several months,” explains the ocean specialist. And in the case of Storm Daniel, “there was an influx of cold air from the Balkans which created a cyclonic situation » while pushing the depression towards the warm sea.

A storm of such intensity and who travels this much distance, is this normal?

First Greece, then a rise towards the north-east and the coast of the Black Sea in Bulgaria, to descend towards Turkey before crossing the Mediterranean towards the south. Storm Daniel traveled a long way before falling on Derna. “A storm, it moves,” Sabrina Speich immediately asks. But “what is not classic is this strong intensification of the disturbance,” which, after having been caused by “Fed by air from the Balkans”, was loaded with precipitating water during its journey over the Mediterranean.

“The precipitation regime is changing”, observes the ocean expert. “The Mediterranean is an evaporation basin,” which generally limits precipitation on its outer coasts, explains it, but if “precipitation is less significant over the year, extreme precipitation increases in frequency” over the years. A phenomenon clearly linked to to climate change for the geosciences professor.

Is there a risk of seeing more medicine with the effects of global warming?

< p>Among the cascade of temperature records broken throughout the summer, this one was passed almost unnoticed. The 28.71°C reached at the end of July in the waters of the Mediterranean, however, confirms a worrying underlying trend: the Middle Sea is warming rapidly. And “she’s going to get hotter again,” warns Sabrina Speich, making the medicines “even more intense and perhaps more frequent”. This trend “had been’ “It’s projected and we observe it,” she emphasizes. Worse, if the storms gain strength at a later date. “A gradual rhythm normally, in recent years we have seen an increase in the intensity of very fast » during certain episodes.

Problem: “Templates are having trouble updating ; follow » face to face this excitement, while “forecasts are the key” to put in place adaptation policies and effective responses in the event of disasters. One avenue for improvement would be to integrate more data from the oceans into the models, but these observations “are not financed by the State today” ». More broadly, “States must act intensely and quickly to reduce CO2 emissions and limit global warming. “We need to implement structural change,” insists the ocean specialist.