Are we heading for a drought in Brittany this summer 2022? Measurements of the quantity of water in the water tables of the region can make fear it. In March 2022, the level is particularly low compared to the last fifteen years. In some areas, such as Pontivy, the situation is even critical right now.
Interview with Bruno Mougin, hydrogeologist engineer at the Bureau of Geological and Mining Research (BRGM), an organization that measures the evolution of the groundwater level Breton.
What is the level of groundwater in Brittany at the end of March, and which sectors are more worrying?
We measured a moderately low groundwater level in Brittany, compared to the months of March of the last fifteen years, in half of our 52 drilling points. We even have lower levels still in central Brittany, particularly in Morbihan, where it has rained the least during the last six months, compared to what usually falls. The situation is critical in Pontivy, where rainfall was 58% below normal, but also in Rennes, with a 25% deficit.
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State of groundwater levels in Brittany, at the end of March 2022. © BRGM
Why is the situation at the end of March a key indicator for the summer?
Because the so-called “effective rains” fall between October and March. Afterwards, the vegetation regains its rights and captures a large part of the rainwater, which no longer reaches the groundwater. It is therefore essential to have a lot of rain during this strategic period. However, if it rained well in October 2021, this period was followed by four months of rain deficit. Until March, a month with a 30% deficit in the region. We are therefore starting to be vigilant, to anticipate a possible summer drought.
Could the rainy weather at the beginning of April change the situation?
There are concerns, but we noted, in mid-March, the filling of several water tables around Quimper, thanks to a short period of effective rains. Beyond the theory, if the month of April is very rainy, over several consecutive days, the ground can still become waterlogged and feed the groundwater. Which are not, as we imagine, underground caverns: the water lodges in the cracks of the rocks or sometimes in the sand, a few meters from the ground (hence the close link with the level of the rivers) up to several tens of meters below ground.
Even if this is not good news for vacationers, next week is forecast to be rainy, and we are not immune to a good surprise at the end of the month, during our next survey.
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