Heatwave: how to explain this “early and intense” heat wave?

Almost all regions of France will experience temperatures above 30°C this week, with peaks of 35°C in the north, and 40°C or more in the south. France seems increasingly affected by waves of heat early: June 2017, June 2019then June 2022.

For Alain Mazaudresearcher emeritus at the Laboratoire des Sciences du Climate and the Environment (LSCE), ” these events actually become earlier and above all more intense. As with the global warmingthe season summer spreads out more in the year, we can consider that there are more heat waves, because the conditions favorable to heat are present for longer”.

The meteorological seasons are not shifted, they are actually lengthened, and it happens in some years that the summer period lasts much longer than 3 months: “ The meteorological spring starts earlier, then the summer too because, with the warming, the air masses hot arrive sooner. L’fall also lasts longer and thewinter is more reduced, with fewer frosts and less intense cold snaps. »

The warming gives the warm tropical air the energy to rise

If the mechanism weather report of the heat pump is well known, with the presence of a depression that brings hot air from the Maghreb to France, the climatic mechanism that causes this also seems increasingly clear: ” With global warming, the rising air is already warmer at the base and arrives in greater quantity. This dry air comes from Hadley’s cell. Generally, at the equator, warm air rises. There is then condensation and precipitation, which releases additional heat that reinforces this ascent. This air, which has become dry, descends to the level of the tropics and this is what is happening to us. As the riser at the equator is warmer, it contains more moisture and therefore moreenergy condensation, so the motor is more powerful. In the end, the Hadley cell tends to get bigger and more warm air can reach our latitudes“.

A process of desertification in the southeast

the climate system rises in latitude and the concrete consequences on the vegetation are already visible, as the researcher points out: “ The typical southern vegetation rises a few kilometers a year. We grow vineyards at higher latitudes than before”. The situation is particularly worrying for the south-east of France, plagued by a drought sustainable : ” Climate forecast models almost all agree that the southeast will get hotter and drier. In Spain and around the Mediterranean, it is therefore a real process of desertification which is likely to take place, with the problems that this will pose for water resources. »

If nothing is done, 50°C will be possible in France in the future

While the absolute heat record in France was beaten during the early heat wave of 2019 (46°C in Verargues in the Hérault on June 28, 2019), can we imagine one day reaching the extreme value of 50°C which has been recorded in California and Pakistan This year ?

“The question of 50°C during a really extreme heat event in France is possible, probably not right away because it is still 4°C above the current record, but it will be possible in the future. . Warming is much faster than we thought 10 or 15 years ago, we will reach the threshold of 1.5°C of warming compared to pre-industrial levels much faster than we believed, in the next few years. But we must not be too pessimistic, there are still many actions to be taken to limit global warming”.