Tag Archives: inland flood modeling

Euro 2016: France inundated by fans and floods

This week the final knockout rounds of Euro 2016 take place in France. Sadly, England has long since left the country and the tournament, largely due to some inept displays. But more miserable than England’s performance, was the weather at the start of the tournament, which caused concern in the capital as intense precipitation on top of an already saturated France, led to severe flooding.

Some areas of the country experienced the worst flooding they have seen in a century, with the floods across eastern and central France declared a natural disaster by French President François Hollande. River levels in the Seine were at their highest in nearly 35 years, impacting Paris, and leading to three of the capital’s best-known museums — the Louvre, the Grand Palais, and Orsay —closing their doors to the public, as staff moved priceless works of art to the safety of higher floors.

Source: The Guardian

There were also concerns surrounding how the flooding could impact the tournament. However, as you can see in the below image, which represents the RMS 1,000 year inland flood hazard extent, neither of the two stadia located in France’s capital (yellow markers) were really at any risk of flooding. The same can’t be said for the fan zone adjacent to the Eiffel Tower though (red marker). Continued intense rainfall, would have led to increased flood severity, meaning that 90,000 or so fans would have been in need of their waders.

Stade de France and Parc des Princes (yellow markers); Paris Fan Zone (red marker)

Paris wasn’t the only location in France to be impacted by the floods though; further south the town of Nemours observed severe flooding as the River Loing burst its banks. While devastating to the local community, this severity of flooding can be expected in the town. The RMS Europe Inland Flood maps demonstrate such flooding for events in excess of the 50 year return period, but as the below image of the 200 year flood extent demonstrates, the flooding could have been even more severe.

Rue de Paris, Nemours (yellow marker) and Château-Musée de Nemours (red marker)

The flooding in Nemours is a good example of why it is so important to understand the standard of protection offered by local flood defenses, in order to fully understand flood risk. The RMS Europe Inland Flood models and maps explicitly represent the impact of flood defenses and provide some noteworthy insights into the potential exposure at risk, if the standard of protection is not maintained or local flood defenses are overtopped.

Rue de Paris, Nemours. Source: The Guardian

If we removed all flood defenses and consider a 100 year return period level of flood hazard across France, the RMS analyses estimate that over €600 billion of insured exposure is at risk to flood damage. However, approximately 40 percent of this exposure at risk is protected against such levels of hazard by local flood defenses.

Source: Château-Musée de Nemours

And in the largest exposure concentrations, such as Paris and its surrounding area, the importance of local defenses is even more prominent. Looking at a similar 100 year return period level of flood hazard in this region, almost €60 billion of insured exposure would be at risk of flooding, but approximately 90 percent of that exposure is protected against this level of hazard.

Flood can be thought of as a polar peril; if you’re in the extent of a flood event, the costs are high but if you’re on the edge then you’re safe. And for this reason, an understanding of the impact of flood defenses is vital, because if they breach or become overtopped, the losses can be high. Knowing where exposure is protected allows you to write business smartly in higher risk zones. But understanding the hazard, should defenses fail, is also vital, enabling a more informed understanding of severe flood risk and its associated uncertainties.

This post was co-authored by Rachael Whitford and Adrian Mark.

Are (Re)insurers Really Able To Plan For That Rainy Day?

Many (re)insurers may be taken aback by the level of claims arising from floods in the French Riviera on October 3, 2015. The reason? A large proportion of the affected homes and businesses they insure in the area are nowhere near a river or floodplain, so many models failed to identify the possibility of their inundation by rainfall and flash floods.

Effective flood modeling must begin with precipitation (rain/snowfall), since river-gauge-based modeling of inland flood risk lacks the ability to cope with extreme peaks of precipitation intensity. Further, a credible flood model must incorporate risk factors as well as the hazard: the nature of the ground, such as its saturation level due to antecedent conditions, and the extent of flood defenses. Failing to provide such critical factor can cause risk to be dramatically miscalculated.

A not so sunny Côte d’Azur

This was clearly apparent to the RMS event reconnaissance team who visited the affected areas of southern France immediately after the floods.

“High-water marks for fluvial flooding from the rivers Brague and Riou de l’Argentiere were at levels over two meters, but flash floodwaters reached heights in excess of one meter in areas well away from the rivers and their floodplains,” reported the team.

This caused significant damage to many more ground-floor properties than would have been expected, including structural damage to foundations and scouring caused by fast-floating debris. Damage to vehicles parked in underground carparks was extensive, as many filled with rainwater. Vehicles struck by more than 0.5 meters of water were written off, all as a result of an event that was not modeled by many insurers.

The Nice floods show clearly how European flood modeling must be taken to a new level. It is essential that modelers capture the entire temporal precipitation process that leads to floods. Antecedent conditions—primarily the capacity of the soil to absorb water must be considered, since a little additional rainfall may trigger saturation, causing “saturation excess overland flow” (or runoff). This in turn can lead to losses such as those assessed by our event reconnaissance team in Nice.

Our modeling team believes that to achieve this new level of understanding, models must be based on continuous hydrological simulations, with a fine time-step discretization; the models must simulate the intensity of rainfall over time and place, at a high level of granularity. We’ve been able to see that models that are not based on continuous precipitation modeling could miss up to 50% of losses that would occur off flood plains, leading to serious underestimation of technical pricing for primary and reinsurance contracts.

What’s in a model?

When building a flood model, starting from precipitation is fundamental to the reproduction, and therefore the modeling, of realistic spatial correlation patterns between river basins, cities, and other areas of concentrated risks, which are driven by positive relationships between precipitation fields. Such modeling of rainfall may also identify the potential for damage from fluvial events.

But credible defenses must also be included in the model. The small, poorly defended river Brague burst its banks due to rainfall, demolishing small structures in the town of Biot. Only a rainfall-based model that considers established defenses can capture this type of damage.

Simulated precipitation forms the foundation of RMS inland flood models, which enables representation of both fluvial and pluvial flood risk. Since flood losses are often driven by events outside major river flood plains, such an approach, coupled with an advanced defense model, is the only way to garner a satisfactory view of risk. Visits by our event reconnaissance teams further allow RMS to integrate the latest flood data into models, for example as point validation for hazard and vulnerability.

Sluggish growth in European insurance markets presents a challenge for many (re)insurers. Broad underwriting of flood risk presents an opportunity, but demands appropriate modeling solutions. RMS flood products provide just that, by ensuring that the potential for significant loss is well understood, and managed appropriately.