The famous “seasonal normals” are getting a little hot.

Météo-France will use, from Tuesday, "normal" updated from a new reference period, the decades 1991-2010.

Every ten years, Météo-France updates the reference period to align with the recommendations of the World Meteorological Organization (WMO).

The new reference period will be 1991-2020.

And the shift highlights some changes compared to the previous period, 1981-2010.

Over the period 1991-2020, the new average annual temperature normal in France is nearly 12.97°C, up by just over 0.4°C compared to the reference period 1981-2000 ( 12.55°C), according to Météo-France.

The climatic normals, statistical products, make it possible to "characterize the climate" over a given period, by convention a period of thirty years, and "serve as a reference for analyzing climatic events in real time", explain the French weather services.

The most affected

It is in spring and summer that the increase in the new normal temperature is the strongest.

It is also slightly more marked on the continental east (Grand-Est and Bourgogne-Franche-Comté) and a little less on the coastal areas (Brittany and Corsica), notes Météo-France.

Compared to the previous period, the number of days of high heat (maximum temperature greater than or equal to 30°C) increased in particular in Nîmes (+8), Figari (Corsica, +9) or Marignane (+10).

It can be noted that changes in climatic normals do not call into question the heat wave vigilance thresholds, which "are calculated in relation to bio-meteorological indices", in collaboration with Public Health France and other agencies, explains Matthieu Sorel, climatologist at Météo-France.

The number of frost days (temperature below 0°C) is down, from 8 days in Troyes, Poitiers, Langres or Chambéry, to 10 days in Lyon.

For its part, the average cumulative precipitation changes little (a range between 911 and 935 mm over the updates), except in the North-East where this average cumulative decreases more significantly.

Conversely, in PACA and Corsica, average precipitation increases, particularly during the groundwater recharge period (September to March).

Seasonal normals are used in different sectors, such as agriculture or energy, and also allow you to compare the climatic conditions between different places.


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