December 2020The rainy episodes were very rare and generally not very active except during two Mediterranean episodes on the 7th in the Cévennes and Provence and from the 27th to the 28th in Roussillon and Corsica. Rainfall was 50 to 80% deficit over most of the country. The deficit even exceeded 80% in places. The rainfall amounts were closer to normal over eastern Corsica and Roussillon, even occasionally exceeding 30% over the Pyrénées-Orientales and Bouches-du-Rhône. On average over the country and over the month, the deficit * was over 60%.
This month of November, without reaching the record of 1978 when the deficit had exceeded 80%, was comparable to November 1981 and thus ranks among the three driest months of November from 1959 to 2020.
As of November 16, 2020, 4 departments have implemented measures to restrict water use. By way of comparison, over the same period last year, 10 departments were affected by a prefectural order limiting uses. This figure was 12 in 2018.
January 2021The rainy episodes were very frequent and active except around the Gulf of Lion, on the eastern flank of the country and the east of Corsica. Rainfall amounts have often reached one and a half to two times normal over the western half of France as well as Auvergne and western Rhône-Alpes in the Cévennes and over western Corsica. Monthly records have been broken. The surplus reached two and a half to three and a half times the normal of the south of the Gironde in the Gers and in the Basque Country, even nearly four times in the Landes. Precipitation was closer to normal on the eastern flank and often lacking in Alsace, Savoie, Roussillon to Provence and on the east of the Isle of Beauty. The deficit exceeded 50% in the Pyrénées-Orientales, even locally more than 70%. On average over the country and over the month, the rainfall was in excess of more than 50%. This month of December ranks among the 10 rainiest months of December over the period 1900-2020.
Regarding groundwater, groundwater levels are mostly on the rise. Recharging began between the end of September and December on all the groundwater in the territory. Only the sectors with a rainfall deficit are still declining or stable: southern Alsace, Provence and southern Alps.
The situation in December is satisfactory over a large western part of the territory. In this sector, the benefit of the abundant recharge in winter 2019-2020 is still being felt, to which must be added the rainfall in October and December. Groundwater levels are therefore particularly high in the Adour-Garonne basin. The situation is less favorable, with low levels, for the groundwater in the Grand-Est, Bourgogne-Franche-Comté and Auvergne-Rhône-Alpes regions. However, the re-charge has started and the situation is slowly improving. Finally, the rainfall deficit this fall is felt on the Alsace water table south of Colmar and on the Provence and southern Alps water tables. The levels there are declining or stable and the state of the groundwater is deteriorating with moderately low to low levels.
In December, river flows decreased across the country with an increase in stations with values below the median and the dry decadal.
On January 1, the filling rate of reservoirs increased compared to the previous month on the whole of the territory.
As of January 20, 2021, 1 department has implemented measures to restrict water use. By way of comparison, over the same period last year, 5 departments were affected by a prefectural order limiting uses. This figure was 2 in 2019.
February 2021Precipitation, very abundant in the second part of the month, was above normal over a large part of the territory. The surplus has often reached one and a half to two times normal, or even locally more over a large north-eastern quarter, the eastern flank, the south-west and Corsica. Monthly records have been broken in the north of France and Corsica. Precipitation, closer to normal in the interior of Brittany and from Normandy to Poitou, was over 50% in deficit from Roussillon to the middle and lower Rhône valley. On average over the country and over the month, rainfall was in excess of nearly 40%.
The cumulative rains of December and January, excess on average in France by 50% over the two months, rank this early winter 2020-2021 among the wettest over the period 1959-2021.
On February 1, the soils were close to saturation, even locally saturated over almost the entire country. On average in France, the moisture index of surface soils reached a record value.
Regarding watercourses, flows have generally increased throughout the territory. However, a few stations with low hydraulicity persist on the Mediterranean rim.
The filling of the reservoirs continued overall in January.
As of February 10, 2021, a department has implemented measures to restrict water use. By way of comparison, over the same period last year, 5 departments were affected by a prefectural order limiting uses, while one department was in 2019.
March 2021Following on from the month of January, disturbances were frequent in the first part of the month, generating floods and flooding, particularly in the south-western quarter as well as to the north of the Seine. Snowfall occurred in the plains from the 7th to the 15th over the northern half of the country and freezing rains from Brittany to Poitou and Center-Val de Loire on the 11th and 12. The disturbed passages were then rarer and generally not very active except 22 on Haut-Languedoc and Montagne Noire. Rainfall amounts were below normal over most of the country. The deficit has often exceeded 30% in the regions bordering the English Channel, the eastern flank of the country, south of the Garonne as well as on the Mediterranean coast and north-eastern Corsica. Rainfall, more in line with normal over the rest of the country, was 10 to 40% in excess over northern New Aquitaine and western Corsica. On the Tarn and the Hérault, the surplus locally reached one and a half to two times normal. On average over the country and over the month, rainfall was nearly 20% short.
At the end of January and beginning of February, numerous floods and floods occurred in Nouvelle-Aquitaine and in the regions located north of the Seine, which recorded records for the saturation of surface soils. The average moisture index of surface soils also reached record values in France from February 1 to 3 (measurements since 1959).
In February 2021, the groundwater levels were mostly up. Recharge continues on the inertial aquifers in the center of the Paris Basin but slows down on the other aquifers. Only the aquifers of Roussillon, Provence and the Southern Alps have stable levels.
The situation in February is very satisfactory over a large part of the territory, the recharge has been substantial and the groundwater levels are above the monthly averages. The situation is less favorable, with moderately low to low levels, for the deep aquifers of the Rhone and Saône corridors, for the Sundgau aquifer and for the southern edge of the alluvial aquifer of the Alsace plain. The levels of these aquifers are on the rise in February but the rainfall inputs of recent months are insufficient to make up for the deficits of the recharge of previous years.
Regarding watercourses, flows have generally increased throughout the territory. However, a few stations with low hydraulicity persist mainly on the Mediterranean rim.
The filling of reservoirs continued overall in February.
As of March 10, 2021, a department has implemented measures to restrict water use. By way of comparison, over the same period last year, 3 departments were affected by a prefectural order limiting uses, while one department was in 2019.
April 2021From the 13th to the 19th, the disturbed passages were accompanied by abundant snowfall on the relief of the East and the Massif Central with sometimes a few flakes as far as the plain on the north-eastern quarter as well as in Provence on the 18th and 19th. .
Rainfall was in deficit by more than 25% over almost the entire country. The deficit has most often been between 40 and 80% over the western half of France and Corsica. It exceeded 80% on the Roussillon plain as well as from the east of the Hérault to the Ardèche and the PACA region with often less than 20mm. Following a very localized Mediterranean episode, the accumulations of rain were very locally in excess of more than 50% in the west of the Hérault. Over a large northeastern quarter, the rainfall was in places more consistent with normal. On average over the country and over the month, the deficit was close to 50%. March 2021 is therefore the driest March since 2012.
On April 1, the surface soil moisture index showed a deficit of more than 10% over most of the country. On the Mediterranean arc where the rains were almost absent, the drought continues.
During March 2021, the trends in groundwater levels reflect the gradual end of the winter recharge period. The reactive aquifers, sensitive to the absence of rains, observe downward trends while the recharge continues on the inertial aquifers.
From the end of February, the aquifers benefited from most of their 2020-2021 recharge. This was generally well above average, due to the consequent effective rains. The situation in March is satisfactory over a large part of the territory, with moderately low to high levels. The reactive slicks, however, observe a rapid degradation due to the absence of significant precipitation in recent weeks. The situation is less favorable, with moderately low to low levels, for the alluvial and karstic aquifers of the Montpellier, Nîmes, Provence and southern Alps regions as well as for the deep aquifers of the Rhone, Saône and Sundgau corridors.
Regarding the waterways, the flows have sharply decreased throughout the territory. The percentage of stations with high hydraulicity (greater than 120%) fell compared to the previous month, dropping from 77% to 1%.
Reservoir filling stagnated in March.
As of April 12, 2021, 2 departments have implemented measures to restrict water use. By way of comparison, over the same period last year, 3 departments were affected by a prefectural order limiting uses, while 4 departments were in 2019.
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https://www.brgm.fr/fr/actualite/communique-presse/nappes-eau-souterraine-au-1er-janvier-2021
