Flood risk map in France: one in four French people live in an exposed area

The map of France is adorned with a mosaic of blue. From lightest to darkest, the color indicates for the first time the risk of flooding in each group of municipalities, whether on the coasts, along major rivers, or overseas . This map was unveiled this Tuesday, September 9, by the National Institute of Geographic and Forest Information (IGN), as the risk of flooding—the main natural disaster in France—continues to increase in the country, aggravated by global warming.

If we refer to this map and the dark blue territories, the Mediterranean rim is particularly exposed, as are the Loire Valley and Réunion Island, in terms of population numbers. The municipalities bordering the Seine and its tributaries, such as the Rouen metropolitan area or the Greater Paris metropolitan area, are also tinted blue. A map of the Pointe de Penmarch, in Finistère, highlights the significant risk of marine submersion by 2100.

The elected officials concerned have been saying this for many years: it has become urgent to anticipate and adapt . Currently, one in four French people is exposed to flooding due to overflowing rivers or marine submersion. "We must prevent tragedies through knowledge and awareness," writes the Minister for Ecological Transition, Agnès Pannier-Runacher, in the introduction to the IGN report. "Because scientists are unequivocal: extreme rainfall will become more and more frequent and more and more intense in the decades to come . " "We wanted to show the extent of this flood risk, what it has become over time with climate change and how we can combat it," Sébastien Soriano, director general of the institute, told AFP.

In the eye of Libé

Compiled through fieldwork, aerial and satellite images, and artificial intelligence tools, this data allows us to better "identify the risk of flooding, inform watercourse management" and "rethink spaces and the role of natural solutions," the public operator emphasizes in a press release. The IGN is relying in particular on a new 3D map of the entire territory, which allows for highly detailed modeling of the path of rainfall that falls across almost all of France. "This 3D map will be entered into various models such as Vigicrues to predict flows and floods, and therefore develop the territory accordingly," explains Swann Lamarche, partnership relations officer at the IGN.

Flood risk is the leading "natural" risk in France due to the extent of the damage it causes and the number of municipalities affected by ground movements. There are several types: overflowing rivers, marine submersion, rainwater runoff and rising water tables. Some of these, such as flash floods and mudslides , are constantly increasing. According to Météo-France, 2024 will be one of the wettest years of the century .

With rising temperatures, clouds tend to store more moisture, and their precipitation capacity increases by 7% every 1°C rise in atmospheric temperature, the Institute points out. "Across France, global warming has already resulted in a 12% increase in the intensity of extreme rainfall compared to the 1960s, and our climate models predict a further 10% to 15% increase in these same intense rainfall events by 2050," emphasizes Benoît Thomé, Director of Institutional Relations at Météo-France.