The month of October was not half-measured in France from a meteorological point of view. It is marked by sometimes pronounced deviations from the seasonal averages, whether in terms of precipitation, temperatures or sunshine, according to the report drawn up Thursday by Météo France.
The most striking figure is that of rain. On average throughout the country, 40% more water fell compared to normal, which is based on the period 1991-2020. October “follows a month of September which was also very rainy (+60%)”. “It was marked by a succession of intense episodes, leading locally to significant flooding,” recalls the meteorological organization.
Twice as much water as normal in the Paris Basin
Many geographic areas were particularly wet. At the top of the list are the Var and Nice hinterlands as well as the Ardèche Cévennes. “The rainfall there is more than three times normal.” Then come the foot of the Pyrenees and the Paris Basin, watered twice as much as the norm. The rainfall “also reaches twice normal from the South-West to Limousin, from the Center to Picardy, from the south of the Alps to the Mediterranean and in the lands of the Pyrénées-Orientales”.
This map shows the amounts of rain that fell in mainland France over the period. The darker the color turns to green, the greater the quantities compared to standards. Conversely, the more it tends towards brown, the less it rained. Météo France thus estimates that the rainfall is “more in line with normal in the west of Brittany, the North-East and the middle and lower Rhône valley”. “It is slightly in deficit on the Channel coasts, as well as on the coast of Languedoc and Roussillon. »
Three periods have been noticeably rainy in recent weeks. The first, on October 9, with the passage of the remains of Hurricane Kirk. Precipitation totals at this time often met or exceeded the monthly average in just one day. The soils being already very humid after a rainy month of September and the water tables being already well filled, absorption was almost impossible and significant flooding took place, in Île-de-France in particular.
In mid-October, a record Cévennes episode took place in the center-east of the country and in Ardèche. In this department, it has never rained so much in two days. Several red alerts were triggered with, again, serious flooding. The Cévennes episode is the local variation of a more global phenomenon that is the Mediterranean episode. This is a strong, even very strong, concentration of rain, over a small area, in a short time, around the Mediterranean.
Return of rain in the Pyrénées-Orientales
Finally, last week, between October 24 and 27, a new Mediterranean episode occurred in the South-East. In Vidauban, in the Var, the equivalent of 119 liters per square meter fell in just one hour during the night from Thursday to Friday, an accumulation never seen in such a short period of time in this department, reports Météo France. This episode is linked to the cold drop which caused the dramatic floods in Spain. A cold drop is an isolated upper-altitude depression in the middle of a warmer air mass, which can cause severe weather.
These numerous, sometimes dangerous, rainy episodes were nevertheless accompanied by good news: the return of rain in the Pyrénées-Orientales. It fell “at the very end of the month, particularly inland”, notes Météo France. “132 mm were measured in 24 hours in Perpignan on October 28. In 24 hours, half of the total for the year 2023 fell on the Catalan city (245 mm).”
Low sunshine, except in Brittany and on the Normandy coasts
Going hand in hand with the numerous disturbances, the sun was logically often absent in October in France. The deficit reaches 20% compared to normal across the country.
It was “particularly shy from the Pyrenees to the Pays de la Loire (-20%) or from Alsace to the Alps and as far as Corsica. Brittany and the Normandy coasts, on the other hand, benefited from excess sunshine of 10%, locally 20% on the Côtes-d'Armor,” explains Météo France.
This map from the meteorological organization summarizes the situation. The more the color turns gray, the less sunny a region has been; the more it yellows, the more the sun has been present. “Since the start of the year, only the months of January and August have benefited from more generous sunshine than the 1991-2020 normal”, underlines Météo France.
Finally, despite the lack of sunshine, temperatures were well above average. The start of October was certainly marked by several days below seasonal norms. But this was more than largely offset by the surplus the rest of the month, which ended up +1.6°C above standards. With an average temperature of 15.27°C over the entire period, October 2024 enters the top 10 hottest Octobers since measurements have existed. He ranks ninth.
One element in particular brought the average up: minimum temperatures. They were much higher than usual with a “particularly marked warm anomaly in the center-east and south-east of the country”, according to Météo France. “October follows two abnormally warm Octobers: +3.5°C in October 2022, the hottest October since measurements began in 1900, and +2.7°C in October 2023, second hottest month of October. »
This graph allows you to visualize the deviation from the average on a day-to-day basis. In blue appear the days when the temperature is below normal and in red those where they exceed it. Without going into the details of the figures, the observation is easily visible: hot periods are longer and more pronounced than cooler periods. More generally, this situation is one of the characteristic elements of climate change.
Apart from perhaps an exception in the middle of next week, the first two weeks of November should be marked by stable weather. The sun should generally be present, despite the regular presence of fog in the northernmost regions. It would rain little, if at all, in several regions. Temperatures would be several degrees above average.
