No wind, a blazing sun and the impression of living in an open oven. Saturday, June 21, the first heat wave of 2025, particularly early, will reach a hot peak in France: 37 ° C in Lyon, 38 ° C from Bordeaux to Tours, and even 39 ° C in Rennes. For several days already, temperatures exceptionally high for the season warm the cities. This weekend again, the thermometer will not descend within 20 ° C in the heart of the night, qualified as “tropical” in many areas. In their bulletins, Météo France forecasters take into account this particularly harmful night overheating phenomenon: the urban heat island.

Thus, in the capital during a heat wave, it can be up to 10 ° C more at night than in the periphery; During the day, the difference is only 1 to 2 ° C. “As soon as the sun sets, the countryside cools, but not the city, because the buildings and the streets have stored heat and restore it. During the first two or three hours of the night, we observe the most important differential. This increases health risks: the APs