Who will be the French most exposed to heat anomalies in summer?

Climate simulations confirm that over the next three decades, the number of abnormally hot days and nights will increase significantly in France. INSEE and Météo-France have sought to find out who will be the most exposed French people

By abnormally hot, we mean a day or a night for which the maximum temperature (or minimum for one night) will exceed the maximum temperature (or minimum) by 5°C over the reference period, between 1976 and 2005.
In a study published on Tuesday, INSEE and Météo-France looked at the territories that should experience the most hot anomalies in summer over the next three decades, and the share of the populations living there.
Currently, one metropolitan in seven lives in territories where there will be more than 20 abnormally hot days in summer.
The Auvergne-Rhône-Alpes, Bourgogne Franche-Comté and Occitanie regions are the most exposed.

Exceptional series during hot days (more than 25°), for 113 days in Marseille or 50 days in Strasbourg.

A thermometer that has repeatedly reached records, such as in Brest (39.3 ° C) or in the port of Dieppe (40.4 ° C) in July.

The summer of 2022, with its three episodes of heat waves which suffocated almost the entire country, is the hottest since 2003, Météo France points out on Tuesday.

This assessment is in line with those that preceded it and which rank these last few years among the hottest on record.

Just a start?

"The most recent climate simulations confirm that during the summers of the next three decades, the number of abnormally hot days and nights will increase significantly throughout the metropolitan territory", note in the preamble the National Institute of Statistics and economic studies (Insee) and Météo France in a study which is also published this Tuesday.

Abnormally hot?

This Insee Première did not stop at these climate projections, but sought to determine the French people who will be the most exposed to heat anomalies.

"We consider as such a day or a night for which the maximum temperature (or minimum for a night) is at least 5°C higher than the maximum (or minimum) reference temperature", explains Caroline Jamet, director general of the Insee Occitanie and responsible for the study.

These reference temperatures are calculated at the local level over the period 1976-2005.

They were on average 23°C during the day and 16°C at night for Paris between June and August;

23°C and 14°C for Nantes;

26° and 17°C for Toulouse…

In other words, the study does not say where it will be the hottest in France in the next three decades, but where the differences with the maximum temperatures of the summers from 1997 to 2005 should be the most frequent.

An indicator that matters.

“There are territories more used to heat than others, so that a 39°C will not be experienced in the same way, nor will it have the same health consequences in Marseille as in Brest”, underlines Jean-Michel Soubeyroux, climatologist at Météo-France and co-author of the study.

9.3 million French people in the most exposed areas

Be that as it may, this Insee Première begins by putting the whole metropolis on an equal footing: over the next thirty years, the whole of the territory will be exposed to an increase in the number of abnormally hot days and nights in June, July and August.

A large part even, comprising nearly 80% of the population, will experience 16 to 29 abnormally hot days in summer, compared to less than 16 over the period 1976-2005.

The trend is the same for nights.

"Some territories will experience up to 19 abnormally hot nights, while the maximum was 7 during the years 1976-2005", continues the study.

Some territories are expected to experience more than 20 abnormally hot days.

“That is the equivalent of 3 weeks out of the 12 that make up the summer”, illustrates Caroline Jamet.

9.3 million French people currently live in these regions.

Or one in seven metropolitans.

Auvergne-Rhone-Alpes, Occitanie and Bourgogne-Franche-Comté on the podium

Among these most exposed regions, we find in particular the many low mountain areas (less than 1,000 meters above sea level) in mainland France.

"Which is explained by their continental climate, which is a little more contrasting," says Jean-Michel Soubeyroux.

The Auvergne-Rhône-Alpes, Bourgogne-Franche-Comté and Occitanie regions are in the front line: 68% of the inhabitants of the first region, 47% of the second and 20% of the third (mainly Lot, Aveyron, Tarn, Tarn- et-Garonne) live in territories that should experience more than 20 abnormally hot days per summer, details the study.

It adds part of the Grand-Est (14% of the population - especially Vosges and Aube) and New Aquitaine (13% - Creuse, Correze and Haute-Vienne).

Coastlines a little less exposed?

Nearly two-thirds of the metropolitan population (65%) live, for their part, in territories where there will be between 16 and 20 abnormally hot days per summer.

These are mostly plains.

“Nearly all the inhabitants of Ile-de-France and Centre-Val de Loire, a large majority of those from Pays de la Loire (89%) and Grand-Est (86%) and three quarters of those from Hauts-de-France (77%) and Nouvelle-Aquitaine (77%) reside in one of these territories”, details the study.

Only then Brittany, Corsica, Normandy and Provence-Alpes-Côtes-d'Azur seem less exposed.

“Heat anomalies will affect the coastline slightly less than the interior,” explain the authors.

Thus, in Brittany and Corsica, only 13% of the population live in areas that will experience fifteen abnormally hot days in the next three decades.

The ratio climbs to 26% in Paca and 27% in Normandy.

880,000 people aged 75 and over in the most exposed regions

The repetition of abnormally hot days, associated with nights where temperatures remain high, increases health risks (dehydration, aggravation of certain chronic diseases, heat stroke, etc.), recalls the study.

Among the most exposed categories: the elderly.

Currently, 880,000 people aged 75 and over – or 16% of them – live in the territories that will be most exposed during the day.

Young children, who have little autonomy to hydrate themselves, are also among the most vulnerable populations, point out Insee and Météo-France.

400,000 children under the age of 6, or 13% of them, live in the areas that will be most exposed.

The standard of living is another criterion to be taken into account.

Because of their housing conditions – often with lower energy performance – the most modest people are more vulnerable to high temperatures, the study points out.

1,180,000 poor people (13% of them) live in an area that is among the most exposed to daytime heat anomalies.

Finally, INSEE Première looked at certain professions working outdoors and they too are more exposed to heat.

These include agricultural workers and construction workers.

“In the three most exposed regions (Auvergne-Rhones-Alpes, Occitanie, Bourgogne-Franche-Comté), nearly 462,000 jobs were in construction in 2020, and 193,000 people worked in agriculture.

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