Nine departments are currently placed on orange alert for the heat wave on Tuesday. They exceeded the departmental alert temperature thresholds for three consecutive days, including at night.
The northern hemisphere begins a new week of oppressive heat on Monday, with temperatures in Europe expected above 40° in Italy and heat wave alerts in Spain, and devastating fires which continue to rage in Canada and California. Up to 48°C are expected at the start of the week in Sardinia, a Mediterranean island west of the Italian Boot And Rome expects a heat peak of 40°C on Monday before reaching 42°C on Tuesday C, according to the Italian Air Force weather site. In France, we expect an equivalent heat stroke, especially in the southern part, with temperatures of 40 degrees in the shade on Tuesday.
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One question remains: when are the “heat wave” alerts triggered in France? And above all, why are there differences according to the regions although the temperatures remain particularly high everywhere?
Regional criteria and thresholds
The criteria, to be classified as a heat wave, actually depend on the departmental thresholds which are not the same everywhere. Example: around the Mediterranean, heatwave vigilance is triggered with 35°C during the day and 20°C to 22°C at night, whereas in Brittany, it is enough to have nights at 19°C and days at 32°C to switch to orange alert.
In fact, we go into heat wave vigilance when the risk of heat-related mortality is twice as high as the average. This alert system was set up by the health authorities in collaboration with Météo France after the 2003 heat wave.
If these alert levels are established locally, it is because in the sunniest regions, the organisms are better adapted to the heat and the ways of life, housing and town planning are also, in general, better designed to cope with high temperatures.
Temperatures are monitored 24 hours a day
Night temperatures are important in triggering these heat wave alerts because normally at night, during sleep, the body temperature must drop without expending too much energy, to guarantee good recovery. For this, the body normally releases heat to the outside, dilating the blood vessels. Obviously, it doesn’t work if the temperature is too high in the room. In this case, the bodies tire more quickly, especially after 65 years.
Figures released on Monday January 10 indicate that last summer’s heat led to nearly 61,000 additional deaths in Europe. Is the alert system sufficient? The problem is that heat records are falling year after year. Remember that we lived in 2022, the hottest summer ever observed in Europe and that ultimately there were 10,000 fewer deaths than in 2003 on the continent. This shows that health prevention is progressing.
But 61,000 additional deaths due to heat, including nearly 5,000 in France, according to figures published by I’Inserm and the Barcelona Global Health Institute: this shows that much remains to be done to protect populations. Especially since with global warming, the number of heat waves could double by 2050.