Rennes Flood Risk: Are Floods a Threat?

While the memory of the floods of January 2025 is still fresh in our minds, in Ille-et-Vilaine, many watch with concern the days of rain that follow one another. Should we be worried? We are monitoring the situation very closelywarns Météo France climatologist Franck Baraer. After Monday and Tuesday, a third episode of rain is forecast for Wednesday, February 11. It will surely be the heaviest of the week with 15.3 millimeters of water expected. 15 millimeters? The equivalent of 15 liters of water per m².

Twice as much rain in January as usual

In January, the rains were very generous in Rennes and its surrounding region. 120 millimeters fell according to Météo France, almost double that of a normal January. And in February? For the moment we can add 35 mm more. This precipitation falls on soils that are already completely saturated and are no longer able to absorb them.

However, Ille-et-Vilaine is doing rather well compared to Finistère or Morbihan, where the rains are even more abundant. Anne Morantin also wants to be reassuring: Ille-et-Vilaine is rather in a preserved situation compared to the rest of Brittany.

Read also: The rule changes in Rennes: is your home now in a flood zone?

She heads the department of the Regional Directorate for the Environment, Development and Housing (Dreal), which, from Rennes, scans Breton waterways 24 hours a day to prevent the risks of flooding. Its teams of forecasters have been particularly mobilized since the beginning of January. To the two bulletins normally published all year round on the Vigicrues websiteat 10 a.m. and 4 p.m., they offer two additional ones at 10 p.m. and 6 a.m.

No worsening expected

La Vilaine has nevertheless been placed on yellow alert, the first level of vigilance. The Meu also which we monitor a little more closely because it reacts more quickly to precipitation. Yellow vigilance is triggered when the first overflows are noted. You just need to drive around Rennes to see it. But we are not at all in the situation of January 2025. Rennes then recorded its historic rainfall record with 202 millimeters and suffered significant flooding.

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Based on the information currently available, we should remain at this level of river overflow at least until the end of the week. But what is also certain is that we do not see a clear improvement in the weather forecast, which would allow for a good decline.

On the ground, elected officials from municipalities hit hard last year also want to be confident. As in Noyal-Châtillon-sur-Seiche where the level of the Seiche, precisely, has fallen very sharply, it’s very reassuring”, recognizes Mayor Sébastien Guéret. For the mayor of Bruz, Philippe Salmon, where the municipal protection plan is still active, even if the levels are still high, we are very far from what we observed at the end of January 2025.