What does the historical data show us about the frequency of 40°C days in France.
As France and in particular the south west of the country recovers after another heatwave lasting 11 days with temperatures above 40°C, it is interesting to consider the historical data for the frequency of 40°C days in the country. The latest heatwave produced a total of 214 monthly heat records, bringing the total to 646 in 2025.
At least 52 weather stations across France set new all-time high temperature records on 11 August. Carcassonne where records have been maintained since 1948 had never experienced two consecutive days at 42°C or higher but on the 11 and 12 August this was the case. Another significant feature of the latest heatwave was the high night time temperatures close to 30°C being experienced in to the early hours.
The graph below shows the number of days that the 40°C threshold was crossed from 1951 through to the 2025 based on information from the 120 stations of the Météo-France main network.
As can be seen before 1980, occurrences of exceeding the 40°C threshold on the network are extremely rare with only 5 occurrences between 1951 and 1980. By 2000, a total of 30 with 292 days in the last 25 years. Obviously the significant heat events in 2003 (87 times in August 2003 by 28 stations – 40°C exceeded) and 2019 contributed significantly to the frequency of such days.
Météo-France report that during the heatwave from August 8 to 18, the 40°C threshold was crossed 32 times across 20 stations.
In comparison with the heatwave of 2003, the geographical distribution of heat in 2025 shows lower temperatures in the north of the country with comparable and even higher temperatures in the south.
