A heat peak, a heat wave, a heat wave… These terms come up in the news, while an exceptional rise in temperatures is expected this week in France. But what is their exact definition? We take stock.
Peak or heat wave: temperatures and duration as references
A heat spike is defined as intense but short-lived episode of heat, which can last one to two days
explains Samuel Morin, researcher at Météo France and director of the national meteorological research center (Météo France – CNRS). It is distinguished from the heat wave, and it is also somehow too short to be called a heatwave
.
For a heat wave to be established, two variables must be observed: the average temperatures, and the duration of the period considered. Thus, Météo France indicates that for a heat wave, in the meteorological sense of the term, to be observed, the temperature must be equal to or exceed the threshold of 25.3° C for three consecutive days. In addition, the temperature should not fall below 22.4° C, and not fall below 23.4° C more than once.
We have blocked the display of this content to respect your cookie choices.
By clicking on “Consult”, you accept the deposit of cookies by social network services such as Twitter.
–
–
–
?? Term “heat wave”
??In France, last heat wave (in the climatological sense) recorded: 08/2020.
For 8 days (6-13/08), national thermal indicator fulfilled all the conditions.
??=25.3°C for 3 days
??Not once and more than once https://t.co/dxPUvk2FJM pic.twitter.com/HPLhfA0vy2— Meteo-France (@meteofrance) May 13, 2022
Heat wave: night temperatures and territories for benchmarks
There remains the definition of a heat wave. Are we going to experience one this week? Well, everything will depend on the temperature it will be at night. The minimum temperature value obtained at night is taken into account. We can have heat waves during which the night cooling is relatively active, the human body can recover.
However, in the event of a heat wave, temperatures remain high, even after dark.
What is the minimum temperature to reach? It differs according to the departments, explains to West France Samuel Morin. Because for the same meteorological event “warm day and night”, “The buildings and the habits of the populations are not the same in the north and the south of France. The thresholds strongly depend on the department and the health context “. To sum up briefly, the inhabitants of Brest are less accustomed to high temperatures and could suffer from high temperatures more quickly than the inhabitants of Provence who are more accustomed to it.
“These thresholds are developed jointly between Météo France and public health actors, Santé Publique France and the Regional Health Agencies”explains Samuel Morin. “This information is processed directly at the level of the public authorities”. They are used to establish the level of heatwave vigilance, as this is one of the phenomena covered by meteorological vigilance, which is produced in four levels: green, yellow, orange and red.
Could these criteria change?
The definition of a heat wave is therefore not the same everywhere in France, and even less for all countries, recalls Françoise Vimeux, Director of Research at the Research Institute for Development (IRD): The same criteria do not apply for France or for India or Africa
.
And these could change, in France. We observe that these phenomena are repeated and intensified due to global warming. We speak of a heat wave when the temperatures are very high and remain above a certain threshold for at least three days and three nights. This threshold depends on the territories and may change in the future. However, even if the exceptional becomes the norm, these heat waves will be no less dangerous.
–
:quality(80)/cdn-kiosk-api.telegraaf.nl/ad73531c-eba9-11ec-9c60-0255c322e81b.jpg?resize=150%2C150&ssl=1)