INFOGRAPHICS. In France, heat waves are becoming more frequent, earlier, and more intense.

France is experiencing its first heatwave of the summer. It is also the fiftieth since the end of the Second World War, Météo-France pointed out. However, the meteorological institute recorded 17 such heatwaves between 1947 and 2000 and... 33 since 2000.

Climate change is making heatwaves more frequent due to rising global temperatures. According to experts, France has already warmed by 1.9°C compared to so-called pre-industrial levels, that is, before the massive combustion of coal, oil, and gas by human activities.

This Saturday, June 21, fourteen departments in the West, from Manche to Charente-Maritime and from Morbihan to Indre-et-Loire, are on orange "heatwave" alert, as are the Rhône and Isère, and almost the entire rest of the country is on yellow alert.

"Monthly maximum temperature records (often around 40°C and generally dating from 2019 or 2022) could be approached," Météo-France predicts. This Friday, the temperatures measured significantly exceeded seasonal norms, sometimes by more than 10°C.

As the graph below shows, since 2009, there has been at least one heatwave per year (with the exception of 2014 and 2021), a sign of the increasing frequency of their number in recent years.

A heat wave is defined as "an episode of temperatures significantly higher than normal for several days." This is therefore a national definition.

A heatwave corresponds to "an episode of high temperatures day and night" lasting at least three days "which is likely to constitute a health risk, particularly for vulnerable or overexposed people." In this case, a heatwave can be declared at the departmental level, as is currently the case.

Beyond their increased frequency, these heat waves are also occurring earlier. All heat waves that began before the summer solstice occurred in the 21st century. The June 2022 heat wave is the earliest on record nationwide.

They are therefore arriving earlier in the year, but are now also later. A heat wave was recorded in mainland France after August 15 for the first time in 2001. Since then, it has occurred eight more times, as shown in the graph above.

In short, such heatwaves are no longer confined to the two months of July and August as they once were. Summer is increasingly encroaching on spring and then autumn. With this lengthening of the hot period of the year, according to a study published in 2021 in the journal Geophysical Research Letters , summer has already increased by seventeen days between 1952 and 2011, going from 78 to 95 days in France.

Finally, heat waves are also becoming more intense. The June 2019 heat wave was the most intense. France recorded its hottest day on record, with temperatures reaching an unprecedented 46°C in Vérargues, Hérault.

In the graph above, we can see that heat waves recorded since 2018 are on average hotter than those of previous decades, despite exceptions.

As Météo-France states: "future summers will be hotter than any known to date."

Consequence: in a France at +4°C by 2100 (compared to pre-industrial levels), temperatures above 40°C could occur every year, and unprecedented heat peaks could reach up to 50°C locally. By the end of the century, we should expect ten times more heatwave days.