A high-resolution temperature climatology over France using a spatialization of daily temperatures extremes from 1947 to present

Climate normals have been set up at Météo-France to characterize climate trends and to situate a day in its climatic context. First, these normals have been calculated for more than a thousand reference observations and have been recently updated with the 1991-2020 reference as stated by the World Meteorological Organization.

In order to assess more accurate temperature climatology of France, a high-resolution temperature climatology over France has been performed, based on a spatialization of extreme daily temperatures (called ANASTASIA) on a 1 km regular grid using a regression-kriging method. ANASTASIA data are available 1947 onwards.

Classic temperatures climatological indices are computed such as number of days above or below temperature thresholds, mean temperatures, etc. Less common indices are computed like the first/last date of temperature threshold or the climatological equivalent date of an observed temperature for a given day.

Those climatology variables are of great interest in daily climate monitoring in order to fully understand exceptional meteorological situations such as heatwaves. That is why real-time products are also produced, sometimes with an indication of the geographical area impacted as a percentage of France total area, and latter with the number of people impacted.

 

Records on extreme temperatures and the year of the record, earliest/latest date of temperature threshold are also computed in order to complete the climatological dataset.

ANASTASIA product is of great interest and allows climatologists to have a better spatial representation of temperature patterns. However, the method used in ANASTASIA does not reproduce well inversion temperatures for example and may lead to great errors in such situations in mountain areas as the product is highly dependent on the observation network.