This Monday, June 26, 2023, an extremely rare meteorological phenomenon hit Languedoc and Provence. This event is called “the hair dryer effect”, or the “Heat Burst” in English (“heat stroke”). Its particularity: it makes the thermometer rise dazzlingly and violently. “This Monday, the temperatures reached 35 to 37°C. […] These high temperatures are still maintained on Tuesday and Wednesday before gradually dropping from Thursday”, announces La Chaîne Météo. What causes such a heat episode?

As its name suggests, the “hair dryer effect” is linked to the presence of a very sudden hot wind. “It’s a bit like opening the doors of an oven”, explains Serge Zaka, agrometeorologist and weather popularizer, to France 3.

According to Futura Science, this hot wind responsible for the hair dryer effect is usually caused by the end of life of a thunderstorm. Indeed, when the last stormy rains fall, they evaporate before touching the ground, cooling the air. As the cooled air mass falls, it compresses the air below. This compression causes a sudden increase in temperature and generates a strong gust of hot wind. The resulting heatstroke is very short-lived: temperatures drop as quickly as they rise, sometimes in less than an hour.

A dry, hot wind coupled with low humidity can cause the soil to dry out suddenly and significantly. What are the consequences of such drastic and rapid temperature changes? Is the hair dryer effect dangerous?

The hair-drying effect can lead to massive and sudden drying of the floors. It is therefore a source of danger for vegetation and biodiversity. Indeed, unlike a classic dryness, extending over a few weeks or a few months, the hair-drying effect only lasts a few hours, or even overnight. Then, it is all the more violent for the plants, unable to acclimatize to sudden changes in temperature. This was the case, for example, on June 28, 2019: a hair dryer effect had charred the Languedoc vines.

In these extreme heat conditions, animals can also be in danger. Is France regularly exposed to such heat episodes?

According to agrometeorologist Serge Zaka, France experienced one of its first hair dryer effects in June 2019. Normally, the hair dryer effect is a rather common phenomenon in the great American plains. However, last year, he was back in France. In June 2022, in Cap Béar (Pyrénées-Orientales), the temperature soared by almost an additional 15°C in just two hours. This year again, it hit in the south. Monday, June 26, 2023, temperatures rose sharply in Montpellier, Nîmes and Marseille, peaking at over 37°C locally, reports Le Midi Libre.

However, according to Serge Zaka, climate change is not the cause of the multiplication of these weather events, reports France 3. It would be the multiplication of measurement points and the densification of weather stations which would, in reality, make it possible to better observe the hair dryer effect and therefore discover more occurrences of it in France.