What are the differences between a heat wave, a peak and a heat wave?

Peak, heat wave and heat wave correspond to precise climatic criteria, with the heat wave vigilance also taking into account the possible health consequences, explains Météo-France.

What do heat peaks and waves mean?

“A heat peak indicates a short period of 24 to 48 hours when temperatures are higher than normal for the season”explains Météo-France on its website, adding: “A heat wave indicates a period of temperatures that are significantly higher than normal for the season for several consecutive days.”

The definition of a heat wave varies by region, depending on temperatures and duration, as populations do not have the same adaptability. “A heat wave episode is detected once the national thermal indicator reaches or exceeds 25.3°C and remains high for at least 3 days”adds the public service of meteorology and climatology in France.

And a heat wave?

The heat wave indicates: “an episode of high temperature, day or night, over an extended period of time (at least three days)”, explains Météo-France. the meteorologists “have defined thresholds that vary according to the departments. For example, in Toulouse, Météo-France will speak of a heat wave when, during the three days and three nights, the maximum temperatures will be above 36°C and the minimum temperatures will be above 21°C”gives the Meteorological Institute as an example.

Temperatures can be lower in northern France. Heat wave vigilance can be yellow, orange or red, the latter threshold corresponding both to an exceptional meteorological event and to a health warning justifying maximum mobilization, with risk of excess mortality.

Episode Multiplication

These heat episodes usually affect mainland France between the beginning of July and mid-August, but they can also occur outside this period, such as in 2016, 2019 or 2020. Since 1947, 45 heat waves have been recorded in France, the last dating back to July 2022.

these waves “have been considerably more numerous in recent decades. In the past 35 years they have been three times as numerous as in the past 35 years. Number of days of heat waves increased tenfold”indicates Météo-France.


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