More than one million people exposed to the risk of major flooding in Ile-de-France

Nearly 555.000 homes in the region, mostly multi-family dwellings, are exposed to the risk of flooding from overflowing rivers, mainly along the Seine and Marne rivers, whose floods are characterized by a slow rise in water levels.

Major once-in-a-century floods – which have a one in 100 chance of occurring each year – are not predictable, "but they give us time to monitor the rising waters and prevent significant material damage," urban geographer Ludovic Faytre, author of the study, told AFP.

Hence the importance of locating vulnerable populations, in order to raise their awareness of the risk of a major flood like that of the Seine in January 1910, where the water level exceeded one meter. Many towns and neighborhoods remained underwater for several weeks, the study notes.

The last Seine flood, in 2016, mainly impacted the Loing valley, one of the river's main tributaries.

Paris and its inner suburbs concentrate more than 70% of the population potentially exposed to major floods.

The 15th arrondissement of the capital, where the Beaugrenelle district includes several large buildings on the banks of the Seine, has the highest number of exposed people (nearly 70.000). Alfortville (Val-de-Marne) is proportionally the most exposed municipality (approximately 45.000) in the region, followed by Asnières-sur-Seine, Gennevilliers and Colombes (Hauts-de-Seine), then Créteil.

Since the implementation, in the early 2000s, of the first flood risk prevention plans (PPRi) in Ile-de-France, more than 100.000 homes have been built in flood zones.

"These plans have been extremely effective in preventing the expansion of urbanization in at-risk areas. They have been somewhat less successful in controlling densification," notes Ludovic Faytre.

In a context of high demand for housing and scarcity of available space, the redevelopment of many areas involves, in particular, the transformation of former industrial sites built along the waterway, the study points out.

Ground-floor apartments are the most exposed to rising water, being on the front line for evacuation. But residents of higher floors should "also feel concerned, because even if their belongings are not directly impacted, they will suffer other consequences," such as a power outage, the expert points out.

According to projections from the Paris Urban Planning Workshop (Apur) presented in the Atlas of the Greater Paris Metropolis, the return of a flood similar to that of 1910 within the metropolitan area (130 municipalities) would flood 600.000 people, leave five million people without drinking water and one million without electricity.

Illustrative image of the article via Depositphotos.com.