Weather: Will three months of rain save us from drought in 2023?
Rainfall since November has been exceptional, albeit unevenly distributed, in the Hauts-de-France. A large western section is in the process of adequately replenishing groundwater, while the eastern is at risk of more tongues sticking out next summer…
Here’s a little phrase that’s starting to get around: ” With so much rain, won’t we be talking about a drought anyway? “. Legal reasoning. We would like to say common sense. Especially in recent days, floods due to bad weather conditions have increased. But when it comes to water resources, everything is not so simple.
Heavy rainfall here…
The first observation is obvious: it has rained, and a lot of rain has fallen in the region in recent weeks… Lille-Lesquin meteorological station recorded 83.7 mm (i.e. 19% above normal) and 93.4 cumulative precipitation in November. mm cumulative in December (i.e. 38% more!). November and December 2022 rank here as the 16th and 14th wettest November and December since 1978, respectively. On the coast, the weather station Le Touquet does even better, recording 243 mm of total rainfall in November (+133% of normal). !) and 112.5 mm (+ 20%) in December. We have the 2nd and 8th wettest November and December since 1978.. Since September, DREAL Hauts-de-France has thus recorded a significant excess of precipitation in Calais (83%), Dunkirk (64%), Lille (32%)… And January is more like a rainy month: 15 we had 40.9mm in Lille (60.5mm normal for the whole month) and 58.4mm in Le Touquet (73.9mm normal for the month).
But what’s missing there…
However, not all of the Artois-Picardie basin is in the same boat. To the west of the Lille-Amiens line, the rains since September have been abundant and above normal, to the east it is quite a different matter. Rainfall deficit is 14% in Arras, 10% in Troisvilles, near Cowdry., 4% in Thiérache. DREAL clearly differentiates between areas of effective rainfall (i.e. groundwater recharge), maximum from the Kalezis to the Authie valley, and areas that do not fare much better.
Tables are always worth it!
This is the second observation to remember: if groundwater levels have started to recharge for most of them thanks to the recent rains, there are some that continue to decline until December. . The Bureau of Geological and Mining Research (BRGM) thus distinguishes 8 measurement points (piezometers) out of 15 in the Artois-Picardie basin.
But being on the rise doesn’t mean reaching normal levels… In Pas-de-Calais, it’s no surprise, given the heavy accumulation of rain Buire-le-Sec (Ternois), Preures (Montreuillois) and Audrehem (Audomarois) are on the rise and show “medium” levels. compared to seasonal norms. Measurement point Wirwignes in Boulonnais is the only one in the region classified as “moderately high”.
If we shift to the east, the groundwater level is in phase with the total precipitation: classified. “Moderately low” in Tincques, Oppy, Havrincourt in Artois, Baisieux in Lille metropolitan area, Rombies in Valenciennes and Marchipont. Although this level has increased, it is equal It ranks “low” in Grand-Fayette, in Avesnois. Far from reassuring in the event of a new episode of summer drought. We will still need plenty of rain in the coming months to protect us.
Better for waterways
If there’s one point where the impact of the rain over the past few weeks has been immediately measured, it’s in the course of rivers. The latter are experiencing a general increase, even with several rivers in recent weeks cautioned against flooding, especially those of Boulogne (such as Liane and Hem). In fact, the rains almost everywhere allowed us to find near-normal values for the season after the summer and early autumn marked by many dry streams. It can be said that the rivers Valenciennes and Avesnois remained at the level considered on December 31 “Lower” or “too low” than normal. Overall, except for the Boulonnais rivers, all measured average flows in the region ” It is much lower than what was observed in 2021 “.
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