Nice, France
The forecast of a tsunami in the Mediterranean Sea in the coming decades is accelerating the need to have evacuation plans, especially on the French Riviera.
The Mediterranean Sea is considered to have a low tsunami risk. History and recent modeling technologies have demonstrated that destructive waves have already reached the French coast and could do so again.
The results of a project carried out in Nice and along the French Riviera show why early and preventative evacuation measures remain the only truly effective means of saving lives.
Tsunamis are among the most destructive natural phenomena. Triggered by earthquakes, submarine landslides or volcanic eruptions, spread quickly over long distances before releasing their energy close to shore in the form of sudden submersion and extremely powerful currents.
From a few centimeters to several meters, this flooding is usually characterized by several waves, and the first waves are not necessarily the largest. The speed of the current is such that the pressure exerted on coastal infrastructure can reach several tons per square meter.
Since 1970, tsunamis have caused more than 250,000 deaths worldwidenamely the 2004 Boxing Day tsunami in the Indian Ocean and the March 11, 2011 tsunami in Japan, for example.
A risk that, after all, is not so unlikely
In the collective imagination, tsunamis are traditionally associated with the Pacific and the Indian Ocean. The risk of a high-sea tsunami in the Mediterranean has often been considered marginal, and This in itself can be misleading. In June 2022, UNESCO, which is dedicated to increasing global awareness of the risk of tsunamis among coastal communities, stated:
“Statistics show that there is a 100% probability of a tsunami at least one meter high in the Mediterranean Sea in the next 30 years.”
After the Pacific, the Mediterranean basin concentrates the largest number of historical tsunamis recordedseveral of which made landfall on the Côte d’Azur in France.
According to available data, around twenty occurrences in the maritime area of the French Riviera between the 16th century and the beginning of the 2000s, with waves that frequently exceeded two meters.
Evacuation times generally very short
The origins of tsunamis in the Mediterranean can be local or distant. In some cases, the flooding time of the first waves may be less than ten minutesparticularly in the event of a submarine landslide or earthquake close to the coast, as in the Ligurian Sea between Corsica and the Italian coast.
On the other hand, tsunamis generated further away from France, for example off the north coast of Africa, can reach the French Riviera in less than 90 minutes.
The Boumerdès earthquake (Algeria), on May 21, 2003, caused devastation across the French Mediterranean coast. A field investigation revealed that eight marinas on the French Riviera experienced significant drops in sea level (from 50 cm to 1.5 m), basin blowdowns, strong eddies and currents, as well as damage to vessels, consistent with port resonance phenomena. The effects were observed on the coast of the French Riviera one hour and fifteen minutes after the earthquake.
Of more local origin, the Nice tsunamion October 16, 1979, triggered by the underwater collapse of part of the construction site of the new commercial port of Nice (Alpes-Maritimes), adjacent to the airport, caused the death of eight people and significant damage in Antibes, Cannes and Nice. The phenomenon was observed in Antibes for about thirty minutes.
Another scenario that could occur closer to the coast is the seismic tsunami that hit the Ligurian Sea on February 23, 1887, following an underwater earthquake with a magnitude between 6.5 and 6.8 on the Richter scale.
Contemporary accounts describe a sudden retreat of the sea by around one meter in Antibes and Cannes, leaving fishing boats stranded, before the arrival of a wave of almost two meters that covered the beaches.
These events remind us of who we are caught by surprise and how such short time frames demonstrate the limitations of traditional warning systems. The ability to quickly evacuate coastal communities becomes crucial.
An operational alert system for France
France has a national tsunami warning system, integrated into the Tsunami Warning Center (Cenalt) since July 2012, together with the international system coordinated by UNESCO in the Mediterranean.
This system allows rapid earthquake detection with the potential to generate tsunamis and the transmission of an alert in less than fifteen minutes to the Interdepartmental Crisis Management Center (COGIC) and international warning centers.
It is then up to the authorities to disseminate warning messages to the population, mainly through the FR-Alert platform, which allows sending notifications to cell phones of people located in the danger zone.
However, this global system only covers tsunamis caused by distant earthquakes and is ineffective in the case of local tsunamis or those caused by submarine landslides, where the tsunami can reach the coast in less time than the advance warning time.
It is for this reason that it is essential to raise awareness among coastal populations about the warning signs: felt earthquakes, abnormal sea movements and, in most cases, a drop in sea level before the tsunami arrives, although not always.
The Nice – Côte d’Azur coast is at high risk
Along the entire French Mediterranean coast, an evacuation zone was defined by government agencies and the University of Montpellier, based on altitude, distance to the sea and historical data.
Corresponds to coastal areas with altitude inferior a 5 metros and less than 200 meters from the sea. At the mouths of rivers, this distance is increased to 500 meters in relation to the estuary.
Including Corsica, 1700 km of coastline, 187 towns along the French Mediterranean coast and at least 164,000 residents would be affected. At the height of summer, an estimated 835,000 swimmers would also need to be considered in the event of a tsunami.
The Nice – Côte d’Azur metropolitan area is vulnerable for several reasons: dense urbanization, strong tourist interest and very busy beaches.
A photographic analysis and modeling made it possible to estimate that tens of thousands of people are present in the area to be evacuated during periods of high visitor flow (between 10,000 and 87,000 people on the beaches, depending on the season and time).
Evacuation before a tsunami: the plan for Nice and adjacent coastal areas
In the face of a tsunami, evacuation is the only effective means of ensuring the safety of the population. International experience shows that rapid and well-planned evacuation procedures can save the vast majority of people exposed.
Reactive evacuation measures, for example, saved 96% of Japanese residents when the great tsunami hit the coast of Tohoku on March 11, 2011.
In Nice – Côte d’Azur, a comprehensive evacuation strategy was developed supported by scientific research led by the Laboratory of Geography and Territorial Planning at the University of Montpellier. It is based on optimized walking routestaking into account slopes, obstacles, travel speeds and congestion points.
Refuge sites located outside the reach of waves were identified and validated by local authorities, and evacuation routes were drawn up using algorithms to find the quickest routes.
In total, almost one hundred places of refuge were mapped and incorporated into operational evacuation plans, designed to quickly guide people to safe locations.
From science to action: preparing the population
Tsunami awareness should go beyond evacuation mapping: Safety simulations, such as evacuation drills, particularly in schools, or the gradual introduction of public warning signs, help to encourage responsible behavior.
Several initiatives like these were implemented in Nice through a project with students from Montpellier.
In Nice, a publicly accessible information platform with interactive maps also allows users to find evacuation areas, routes and instructions to follow in case of an alert. These tools contribute to the development of a true tsunami risk culture.
Becoming a “Tsunami Ready” territory
In addition to the coastal region of the Côte d’Azur, in France, the information portal can be applied to other coastlines in France and Europe, both in the Mediterranean and on other continents, where the flooding time of a tsunami can be equally short.
The initiatives being implemented in Nice are in line with UNESCO’s “Tsunami Preparedness” (TRRP) international recognition program. This 12 point program aims to certify territories capable of anticipating the risk of tsunamis, preparing their populations and coordinating an appropriate response.
The first cities to receive the seal and to benefit from scientific and technical support were Deshaies, in Guadeloupe, and Cannes, and Nice is expected to join the program soon.
When you’re facing a wave that can arrive in a matter of minutes, being prepared to evacuate makes all the difference.
