• 22 degrees in Nice, +4 degrees between Corsica and the Balearic Islands….

    with the record heat in May, the surface water temperature of the Mediterranean is breaking records.

  • For scientists and weather forecasters, warmer seas earlier can lead to more severe weather events in the fall.

  • As a result, this year “will be interesting to observe” to refine future forecasts.

It seems that this year summer has taken the lead in the Mediterranean.

While many temperature records fell this month of May, the western Mediterranean, in a large area between Corsica and the Balearic Islands, recorded at the end of May "an anomaly" in the temperature of the upper surface waters of around 4 degrees for the season, according to observations by ECMWF, the European Center for Medium-Range Weather Forecasts.

On Monday, the water temperature in Nice was measured at 22 degrees, a level usually reached in July.

Data that can delight bathers, but also forecasters, if not the environment:

Storms with hurricane characteristics

"Because the heat arrived particularly early, this year will be interesting to study", estimates Mathieu Panizzon, forecaster in Paca of Météo-France.

Because the situation is, for the time being, conducive to the occurrence this autumn of Mediterranean episodes, particularly intense stormy phenomena.

“These episodes take place in the fall, when the sea temperature has risen throughout the summer and encounters colder continental air, due to the season and the shortening of the days. “says forecaster.

And in meteorology, the greater the temperature difference between the air masses, the more violent are the conflicts and the meteorological phenomena.

"These intense precipitation events are a subject of great concern to meteorologists", continues Florian Pantillon, researcher in aerology, the study of the properties of the lower regions of the atmosphere.

“A warmer sea gives more evaporation, therefore more intense precipitation.

And it's not linear.

A 1% rise in temperature does not, for example, increase precipitation by 1%.

A small rise in temperature greatly increases these capacities, and consequently a small difference can have big consequences”, summarizes the researcher at the CNRS.

A meeting in Athens on medicine

But Florian Pantillon's favorite subject of study are storms and depressions in the Mediterranean, in particular the phenomenon of medicanes.

“Medicane is a contraction of Mediterranean and hurricane.

These are fairly rare lows, occurring about once a year, in the fall, and exhibit some of the characteristics of hurricanes, i.e. rolling cloud, eye and winds that briskly exceed 100 km/h”.

Unlike the cyclones and hurricanes observed for several decades and several of which occur each year, the phenomenon of these "subtropical cyclones" is still poorly studied because of their rarity.

But the scientific community is mobilizing.

A first meeting of European researchers is planned on this subject for the end of June in Athens, in a country violently affected by a medicane on September 17 and 18, 2020.

“We can expect these phenomena to become more and more frequent”

“The formation of medicanes depends on very large-scale, near-continental air mass conditions and conflict.

But a warmer sea can allow these explosive storms to intensify, even if it does not reach 26.5 degrees, the surface temperature necessary for the formation of cyclones, ”continues Florian Pantillon.

“Afterwards, they will always take less power and momentum than in the Atlantic or the Pacific, where they have thousands of kilometers without obstacles to strengthen themselves”, he nuances.

While it remains difficult to predict the appearance of meteorological phenomena over the long term, the only certainty with an already high average temperature of 1.5 degrees, "we can expect these phenomena to become more and more frequent" , indicates the researcher at the CNRS.

Especially since according to the Medecc report on the climate future of the Mediterranean, the temperature of the water is expected to increase further by 3.8 to 6.8 degrees, with significant consequences for biodiversity and marine species. .

"Tropical species are already observed in the eastern Mediterranean, which is warming up faster, such as barracudas, rabbitfish or certain species of algae", explains Joël Guiot, CNRS researcher at the European Center for Research and teaching in environmental geosciences.

“What we are currently experiencing and observing is a taste of what lies ahead,” he concludes.

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