The waters will rise slowly when the next great flood comes to Paris. There will be no flash flood that sweeps away infrastructure in an instant. Instead, the River Seine will creep up at a rate of about 2cm per hour.
It will take 10-15 days for water to reach the same levels as the capital’s last centennial flood in 1910, during which the river reached a depth of 8.62 metres.
Forecasts show a flood of this scale submerging vast swathes of the city underwater. Hundreds of streets in proximity to the riverbanks will be deluged, but flooding could also extend as far north as Saint Lazare station in the 8th arrondissement (district). The Eiffel Tower, the Louvre and Notre-Dame Cathedral will all be inundated, as will thousands of homes.
When this happened in 1910, the city ground to a halt as tens of thousands of buildings flooded and infrastructure collapsed. As the streets filled with icy waters, polluted by the city’s sewage system and drains, police, firemen and soldiers used boats to distribute emergency supplies to stranded residents, while evacuees were housed in emergency shelters in churches, schools, and government buildings.
Could the same thing happen in modern-day Paris? “We use the 1910 flood as a reference in terms of the height the river reached and the speed at which it flowed,” says Ludovic Faytre, risk specialist in the Environment department at research institute L’Institut Paris Region. “But the region has been modified so much that we can’t compare the events of 1910 to what could happen today.”
The ‘flood of the century’
For one thing, Paris now has emergency flood plans in place. By the time the authorities are sure enough to warn the public that the great flood is coming – and urge those who can to leave the city – preparations will be under way.
Every day, Paris authorities monitor river levels using a measure fixed to the Austerlitz bridge. When the water hits the critical threshold of 6.18 metres – more than double its normal depth – the city’s emergency plans will go into action.
The Louvre museum will start moving valuable artworks to safe storage outside of the city. The more modern François Mitterand library, built in the 1990s, will shut the watertight doors in its subterranean carparks. The police will call in thousands of soldiers to reinforce their security operation, and evacuations will begun in municipal buildings including hospitals and homes for the elderly.
At this level the river will be visibly overfull, having risen so high it is impossible for most boats to safely pass underneath its bridges.
But simulations for the “flood of the century” are based on the river rising more than two metres higher, to the same height as in 1910.
Each year, there is just a 1% chance that a flood of this magnitude will hit Paris. But experts are “certain that it will happen” at some point, says Faytre. “Statistically we know that this phenomenon will occur in Ile-de-France, but we don’t know when,” he says.
An underground crisis
In some ways, Paris is now more vulnerable to a large-scale flood. As climate deregulation accelerates, the risk of severe weather throughout France has increased and become less predictable. Traditionally, the risk period for a major flood in Paris would be from November to March, but now one could just as easily happen in June.
Paris has also become the most densely populated city in Europe with the lowest percentage of green space.
The police prefecture says it will be able to alert the public 2-4 days before the floodwaters reach their peak – time enough for those who can to leave the city. But hundreds of thousands of people will still be stranded living in old apartment buildings that are poorly prepared to withstand natural disasters.
Official estimates are that nearly 350,000 homes could be deluged and more than 700,000 could be subject to electricity cuts. Schools, libraries, hospitals, parks and small businesses in the flood zone will also be impacted.
And as conditions deteriorate above ground, a crisis will be unfolding underneath the city.
Below street level sits centuries worth of underground excavations from historical limestone quarries and war bunkers to modern carparks and shopping malls, not to mention the city sewers, telephone and electricity cables, and the underground metro system.
All of this will be inundated, partly due to the lack of green space in the city. “There is no natural floor that can absorb the water,” says Boris Weliachew, an architect and civil engineer specialising in natural disaster mitigation. “So the floodwater will basically go underground, get into the subway and damage everything.”
Paris’s public transport network, the RATP, has a flood emergency plan which includes mobilising 1000 employees to build emergency protective structures throughout its network in the days before the flood hits. Even with these in place, it estimates repair costs of up to €5 billion due to an accumulation of mud and debris in tunnels and destruction of tracks and facilities.
An ‘expensive disaster’
As the floodwaters will be slow to rise they will also take time, possibly weeks, to disperse; the great flood of 1910 took 45 days to recede.
During this time, residents will be surrounded by stagnant, possibly polluted pools of water and streets and buildings will be weakened by prolonged exposure to damp. Interconnected infrastructure throughout the entire Ile-de-France region will be impacted, potentially affecting more than 12 million people.
One of the biggest challenges of the flood will be “getting things up and running again quickly”, in the aftermath says Faytre.
Doing so will also be expensive, with the OECD estimating direct damage could total up to €30 billion in repair costs.
“Paris flooding is perhaps the most expensive disaster that could occur in France,” Weliachew says.
But much of the damage could be preventable with more of the right kind of protections in place, he says. “The disaster is not the flood itself. A disaster is caused by a hazard hitting an area a lot of people are living in, and it’s the vulnerabilities of the area that cause damage.”
Preparation plans
In the past 20 years Paris has “made a lot of progress” towards flood preparation, says Faytre, “but the region is so complex that there remains a lot of work to do”.
While the city has made emergency flood plans and has encouraged institutions and infrastructure networks to do the same, not all of them have.
In 2022 France’s supreme court, the Cour de Comptes, found that Paris was insufficiently prepared for another major flood, and “much less protected against major floods than other international cities”.
This, the court said, was largely due to a lack of co-ordination between local authorities in the Seine River basin, the drainage basin for the river and its tributaries which stretches from north of Dijon in eastern France to Le Havre on the Atlantic coast.
A combined effort could enable flood protections along the length of the Seine that would better protect the capital – as in the southeastern city of Grenoble where efforts to create controlled flooding fields and alluvial forests outside the city have successfully reduced the impact of flooding.
One such project is under way in Ile de France. Public river management organisation L’Etablissement Public Territorial de Bassin in January carried out a flood test on the fifth giant reservoir it has constructed on the outskirts of Paris, designed to help manage river flows.
The new giant basin in Seine-et-Marne has a capacity of 10 million cubic metres and could reduce flood levels in Paris by 15 cm, “considerably” cutting down damage in the event of smaller floods said Baptiste Blanchard, General Manager of Seine Grands Lacs.
But in the case of major flooding, the reservoir “won’t offer total protection”, Blanchard said.
Read moreGiant anti-flooding device built upstream of Paris
In the meantime, other efforts to prepare for floods continue. In 2025, Paris city hall is planning a crisis simulation exercise based around a river flood with the police prefecture.
It will also run training sessions open to all residents providing information on what each home should keep in its emergency kit, and how to keep safe during a flood.
Raising public awareness about flood preparations and safety is now a key concern.
“There is still a lot of knowledge that needs to be shared,” says Faytre. “[People need to know] yes, we live in an area prone to flooding and it’s not just because you live on the second floor that you won’t be exposed to the risks – you’ll be directly impacted by the flood, when it happens, and it’s going to be very difficult to live through for a few weeks.”
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