Historic rainfall has prompted Météo-France to issue a red alert for flooding in Loire-Atlantique, Morbihan, and Ille-et-Vilaine, with Rennes experiencing its worst floods in over 40 years. January rainfall in Rennes has reached record levels, exacerbated by prior storms and urban development that limits water absorption. Experts note that climate change and seasonal temperature increases are intensifying these extreme weather events, leading to more frequent and severe flooding incidents in the region.
Historic Rainfall Triggers Red Alert in Three Departments
On January 28, Météo-France issued a red alert for floods in three departments: Loire-Atlantique, Morbihan, and Ille-et-Vilaine, due to the impact of the Herminia depression. Additionally, four other departments are under an orange alert for similar flooding concerns.
The red alert specifically highlights the rivers Seiche and Vilaine. Ille-et-Vilaine has been under this alert since Monday, with the city of Rennes experiencing its worst flooding in over 40 years, as the Ille and Vilaine rivers converge. These extreme weather patterns prompt a deeper exploration into the causes behind these unprecedented conditions.
Understanding the Causes of the Severe Flooding
Are the rainfall amounts truly record-breaking? In Rennes, January has seen the highest rainfall totals since meteorological records began in 1944. The recent deluge followed the Éowyn storm, saturating soils that were already damp from a particularly wet year in 2024. Since the start of 2025, the region has recorded 171 mm of rain, translating to 170 liters of water per square meter, a figure not seen in 30 years. This is three times the typical monthly average and surpasses the previous record set in 1995.
Experts point to vegetation’s role in this flooding crisis. During winter, when plants are dormant, the soil quickly becomes saturated, leading to immediate runoff into rivers. Jean-Luc Jégou, director of ‘Water & Vilaine’, emphasizes that the rainwater flows straight into already full river basins, causing overflow.
Human activity and climate change also contribute to the crisis. Since the 1960s, Rennes has undergone extensive urban development, which has exacerbated flooding by preventing water from naturally infiltrating the ground. Nadia Dupont, a geography lecturer, explains that urbanization near rivers has made areas more susceptible to flooding. In response, the town hall is actively developing a new flood prevention strategy aimed at enhancing water absorption across the municipality.
While the current weather patterns can be attributed to natural variability, climatologist Simon Mittelberger notes that higher seasonal temperatures are intensifying the situation. Warmer air can retain more water vapor, leading to increased rainfall from Atlantic depressions. Climate change is also resulting in more pronounced seasonal contrasts, causing less rainfall in summer and heavier precipitation in winter, especially in northern France. Consequently, the overflow from rivers is becoming more frequent due to the saturated soils and slow drainage following storms.