Tag Archives: Flood risk

Friday 13th and the Long-Term Cost of False Alarms

If the prospect of flooding along the East Coast of England earlier this month was hard to forecast, the newspaper headlines the next day were predictable enough:

Floods? What floods? Families’ fury at evacuation order over storm surge … that never happened (Daily Mail)

East coast residents have derided the severe storm warnings as a ‘load of rubbish’ (The Guardian)

Villagers shrug off storm danger (The Times)

The police had attempted an evacuation of some communities and the army was on standby. This was because of warnings of a ‘catastrophic’ North Sea storm surge on January 13 for which the UK Environment Agency applied the highest level flood warnings along parts of the East Coast: ‘severe’ which represents a danger to life. And yet the flooding did not materialize.

Environment Agency flood warnings: January 13 2017

Water levels were 1.2m lower along the Lincolnshire coast than those experienced in the last big storm surge flood in December 2013, and 0.9m lower around the Norfolk towns of Great Yarmouth and Lowestoft. Predicting the future in such complex situations, even very near-term, always has the potential to make fools of the experts. But there’s a pressure on public agencies, knowing the political fallout of missing a catastrophe, to adopt the precautionary principle and take action. Imagine the set of headlines, and ministerial responses, if there had been no warnings followed by loss of life.

Interestingly, most of those who had been told to evacuate as this storm approached chose to stay in their homes. One police force in Essex, knocked on 2,000 doors yet only 140 of those people registered at an evacuation centre. Why did the others ignore the warnings and stay put? Media reports suggest that many felt this was another false alarm.

The precautionary principal might seem prudent, but a false alarm forecast can encourage people to ignore future warnings. Recent years offer numerous examples of the consequences.

The Lessons of History

Following a 2006 Mw8.3 earthquake offshore from the Kurile Islands, tsunami evacuation warnings were issued all along the Pacific coast of northern Japan, where the tsunami that did arrive was harmless. For many people that experience weakened the imperative to evacuate after feeling the three-minute shaking of the March 2011 Mw9 earthquake, following which 20,000 people were drowned by the tsunami. Based on the fear of what happened in 2004 and 2011, today tsunami warnings are being ‘over-issued’ in many countries around the Pacific and Indian Oceans.

For the inhabitants of New Orleans, the evacuation order issued in advance of Hurricane Ivan in December 2004 (when one third of the city’s population moved out, while the storm veered away), left many sceptical about the mandatory evacuation issued in advance of Hurricane Katrina in August 2005 (after which around 1500 drowned).

Agencies whose job it is to forecast disaster know only too well what happens if they don’t issue a warning as any risk looms. However, the long-term consequences from false alarms are perhaps not made explicit enough. While risk models to calculate the consequence are not yet available, a simple hypothetical calculation illustrates the basic principles of how such a model might work:

  • the chance of a dangerous storm surge in the next 20 years is 10 percent, for a given community;
  • if this happens, then let’s say 5,000 people would be at grave risk;
  • because of a recent ‘false’ alarm, one percent of those residents will ignore evacuation orders;
  • thus the potential loss of life attributed to the false alarm is five people.

Now repeat with real data.

Forecasting agencies need a false alarm forecast risk model to be able to help balance their decisions about when to issue severe warnings. There is an understandable instinct to be over cautious in the short-term, but when measured in terms of future lives lost, disaster warnings need to be carefully rationed. And that rationing requires political support, as well as public education.

[Note: RMS models storm surge in the U.K. where the risk is highest along England’s East Coast – the area affected by flood warnings on January 13. Surge risk is complex, and the RMS Europe Windstorm Model™ calculates surge losses caused by extra-tropical cyclones considering factors such as tidal state, coastal defenses, and saltwater contamination.]

How U.S. inland flood became a “peak” peril

This article by Jeff Waters, meteorologist and product manager at RMS, first appeared in Carrier Management.

As the journey towards a private flood insurance market progresses, (re)insurers can learn a lot from the recent U.S. flood events to help develop profitable flood risk management strategies.

Flood is the most pervasive and frequent peril in the U.S. Yet, despite having the world’s highest non-life premium volume and one of the highest insurance penetration rates, a significant protection gap still exists in the U.S. for this peril.

It is well-known that U.S. flood risk is primarily driven by tropical cyclone-related events, with storm surge being the main cause. In the last decade alone, flooding from tropical cyclones have caused more than $40 billion (2015 USD) in insured losses and contributed to today’s massive $23 billion National Flood Insurance Program (NFIP) deficit: 13 out of the top 15 flood events, determined by total NFIP payouts, were related to storm surge-driven coastal flooding from tropical cyclones.

Inland flooding, however, should not be overlooked. It too can contribute to a material portion of overall U.S. flood risk, as seen recently in the Southern Gulf, South Carolina, and in West Virginia, two areas impacted by major loss-causing events. These catastrophes caused billions in economic and insured losses while demonstrating the widespread impact caused by precipitation-driven fluvial (riverine) or pluvial (surface water) flooding. It is these types of flooding events that should be accounted for and well understood by (re)insurers looking to enter the private flood insurance market.

It hasn’t just rained; it has poured

In the past 15 months the U.S. has suffered several record-breaking or significant rainfall-induced inland flood events ….

To read the article in full, please click here.

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.

Just How Unlucky Was Britain to Suffer Desmond, Eva, and Frank in a Single December?

Usually, it’s natural disasters occurring elsewhere in the world that make headlines in Britain, not the other way around. But you’d have to have been hiding under a rock to have missed the devastation wrought by flooding in the U.K. last month, thanks to the triple-whammy of storms Desmond, Eva, and Frank. Initial analysis from the Association of British Insurers suggests that the damage done could run to the region of £1.3bn.

But just how unlucky was the U.K.to suffer not just one, or two, but three big storms in one December, and for these three storms to interact in such a way as to produce the chaos that followed?

First it’s worth pointing out that floods in the U.K. are—as is usually the case elsewhere—subject to important seasonal variation (see chart below). The winter months bring the highest number of events, and December does in fact come out (slightly) on top, especially for flooding events of the sort seen last month, which tend to follow heavy rainfall leading to soil saturation (November 2015 received about twice the average climatological rainfall for November in the U.K.).

Source: RMS

The reason this matters is that, when soil is sodden following an extended period of heavy rains, further rains can more easily run off the surface, exacerbating the risk of pluvial flooding. The water will then follow natural and artificial drains until it reaches the closest river network, in which it can accumulate, potentially triggering river or “fluvial” flooding. The runaway effect of the masses of water can also cause what is known as ground-water flooding. This cumulative phenomenon means that—as we saw in December—flooding can persist for a significant amount of time, leading to several flood events in close succession.

A flood CAT model that properly captures these sorts of interactions between rainfall events and hydrological systems will allow not just for an assessment of the likelihood of a single severe event, but also a better understanding of the compounding factors that can lead to the sort of flooding seen in the U.K. last month. And based on our latest RMS pan-Europe flood model, the chances of having three rainstorms lead to major inland flooding over a single December are far from negligible.

Source: RMS Europe Flood Model

The chart above shows the probability of one, two, three, and four flood events for the month of December. What it means is that, on average, every second December in the U.K. has at least one flood event, and every third December has only one flood event. Around every eight years there are two flood events, and a cluster of three flood events happens once every quarter-century.

Now, this does not mean that flooding on the scale just witnessed happens on average every 25 years—just that this is the average period for seeing three flood events in one December. Even if it did, it wouldn’t mean that the U.K. can rest on its laurels until 2041… this is just a statistical average. It is quite possible for clusters to hit several years in a row—a so-called “flood-rich period”.

This gets to the real nub of the issue. The question of how often this sort of flooding takes place in the U.K. is almost by-the-by. The point is that it isn’t rare as hen’s teeth, and so the U.K. needs to be prepared. And what was most shocking about December wasn’t the flooding itself, so much as the sheer lack of resilience on display. A media storm has understandably been whipped up regarding the level of investment into flood walls and so on, but protective infrastructure is only part of the equation. What is needed is not just flood walls (which can actually be counterproductive on their own), but a wider culture of resilience. This includes things such as flood warning systems, regular evacuation drills, citizens having personal plans in place (such as being ready to move furniture to upper levels in the case of an alert) and, critically, the ability to respond and recover should the defences fail and the worst happen (which is always a possibility). The U.K. is the world’s sixth richest country—it has the resources to cope with flood events of this magnitude… whether they happen every five, ten or 25 years.

Can Flood Walls Reduce Resilience?

In early December 2015 Storm Desmond hit, bringing an “atmospheric river” to the northwest of England with its headwaters snaking back to the Caribbean. It broke the U.K.’s 24 hour rainfall record, with 341.1mm of rain recorded in Cumbria.

Just three weeks later, while a great anticyclone remained locked in place over central Europe and the atmospheric flows had only shifted south by 150km, Storm Eva arrived. The English counties of Lancashire and Yorkshire were drenched during December 26th, and the media was once more overwhelmed with flood scenes—streets of Victorian-era houses inundated by 30-40cm of slow-moving water.

Journalists soon turned their attention to the failure of flood protections in the affected regions. In one interview in Carlisle, a beleaguered Environment Agency representative commended their defenses for not having failed—even when they had been overtopped. If the defenses had failed, maybe the water would not have ponded for so long.

 The call for “resilience”?

The call has gone out worldwide for improved “resilience” against disasters. As outlined by the UN Secretary General’s Climate Resilience Initiative, resilience is defined as the ability to “Anticipate, Absorb and Reshape” or “A2R”.

How did the U.K.’s flood defenses match up to these criteria in December? Well, as for the two “A”s in A2R, the residents of Carlisle did not anticipate any danger, thanks to the £38 million spent on flood defenses since the last time Carlisle had a “1 in 200 year” flood in January 2005 (which hit 1,900 properties). And the only thing the houses of Carlisle were absorbing on the first weekend in December was the flood water seeping deep into their plaster, electricals, and furnishings. As for “reshaping”, beyond the political recriminations, now is the time for some serious thinking about what constitutes resilience in the face of floods.

A flood wall is not the same as resilience. Resilience is about the capacity to recover quickly from difficulties, to bounce back from adversity. Organizations such as the UK’s Environment Agency may be good at building flood defenses, but not so proficient at cultivating resilience.

A flood wall can certainly be part of a culture of resilience—but only when accompanied by regular evacuation drills, a flood warning system, and recognition that despite the flood wall, people still live in a flood zone. Because flood walls effectively remove the lesser more frequent floods, the small risk reminders go away.

A growing reliance on the protection provided by flood walls may even cause people to stop believing that they live in a flood plain at all, and think that the risk has gone to zero, whether this is in New Orleans, Central London or Carlisle.

Even when protected by a flood wall, residents of river flood plains should be incentivized, through grants and reduced insurance rates, to make their houses resistant to water: tiling walls and floors and raising electrical fittings. They should have plans in place—such as being ready to carry their furniture to an upper floor in the event of an alert—as one day, in all probability, their houses will flood.

Given the U.K.’s recent experience we should be asking are people becoming more resilient about their flood risks? It sometimes seems that the more we build flood walls, the less resilient we become.

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.

South Carolina Floods: The Science Behind the Event and What It Means for the Industry

South Carolina recently experienced one of the most widespread and intense multi-day rain events in the history of the Southeast, leaving the industry with plenty to ponder.

Parts of the state received upwards of 27 inches (686 mm) of rain in just a four day period, breaking many all-time records, particularly near Charleston and Columbia (Figure 1). According to the National Oceanic and Atmospheric Administration, rainfall totals surpassed those for a 1000-year return period event (15-20 inches (381-508 cm)) for parts of the region. As a reminder, a 1000-year return period means there is a 1 in 1000 chance (0.1%) of this type of event occurring in any year, as opposed to once every thousand years.


Figure 1: Preliminary radar-derived rainfall totals (inches), September 29-October 4. Source: National Weather Service Capital Hill Weather Gang.

The meteorology behind the event

As Hurricane Joaquin tracked north through the Atlantic, remaining well offshore, a separate non-tropical low pressure system positioned itself over the Southeast U.S. and essentially remained there for several days. A ridge of high pressure to the north acted to initiate strong onshore windflow and helped keep the low-pressure system in place. During this time, it drew in a continuous plume of tropical moisture from the tropical Atlantic Ocean, causing a conveyor belt of torrential rains and flooding throughout the state, from the coast to the southern Appalachians.

Given the fact that Joaquin was in the area, the system funneled moist outflow from it as well, enhancing the onshore moisture profile and compounding its effects. It also didn’t help that the region had experienced significant rainfall just a few days prior, creating near-saturated soil conditions, and thus, minimal absorption options for the impending rains.

It’s important to note that this rain event would have taken place regardless of Hurricane Joaquin. The storm simply amplified the amount of moisture being pushed onshore, as well as the corresponding impacts. For a more detailed breakdown of the event, please check out this Washington Post article.

Notable impacts and what it means for the industry

Given the scope and magnitude of the impacts thus far, it will likely be one of the most damaging U.S. natural catastrophes of 2015. Ultimately, this could be one of the most significant inland flooding events in recent U.S. history.

This event will undoubtedly trigger residential and commercial flood policies throughout the state. However, South Carolina has just 200,000 National Flood Insurance Program (NFIP) policies in place, most of which are concentrated along the coast, meaning that much of the residential losses are unlikely to be covered by insurance.


Figure 2: Aerial footage of damage from South Carolina floods. Source: NPR, SCETV.

Where do we go from here?

Similar to how Tropical Storm Bill reiterated the importance of capturing risk from tropical cyclone-induced rainfall, there is a lot to take away from the South Carolina floods.

First, this event underscores the need to capture interactions between non-tropical and tropical systems when determining the frequency, severity, and correlation of extreme precipitation events. This  combined with high resolution terrain data, high resolution rainfall runoff models, and sufficient model runtimes will optimize the accuracy and quality of both coastal and inland flood solutions.

Next, nearly 20 dams have been breached or failed thus far, stressing the importance of developing both defended and undefended views of inland flood risk. Understanding where and to what extent a flood-retention system, such as a dam or levee, might fail is just as imperative as knowing the likelihood of it remaining intact. It also highlights the need to monitor antecedent conditions in order to properly assess the full risk profile of a potential flood event.

The high economic-to-insured loss ratio that is likely to result from this event only serves to stress the need for more involvement by private (re)insurers in the flood insurance market. NFIP reform combined with the availability of more advanced flood analytics may help bridge that gap, but only time will tell.

Lastly, although individual events cannot be directly attributed to climate change, these floods will certainly fuel discussions about the role it has in shaping similar catastrophic occurrences. Did climate change amplify the effects of the flooding? If so, to what extent? Will tail flood events become more frequent and/or more intense in the future due to a rising sea levels, warming sea surface temperatures, and a more rapid hydrologic cycle? How will flood risk evolve with coastal population growth and the development of more water impermeable surfaces?

This event may leave the industry with more questions than answers, but one stands out above the rest: Are you asking the right questions to keep your head above water?

Coastal Flood: Rising Risk in New Orleans and Beyond

As we come up on the tenth anniversary of Hurricane Katrina, a lot of the focus is on New Orleans. But while New Orleans is far from being able to ignore its risk, it’s not the most vulnerable to coastal flood. RMS took a look at six coastal cities in the United States to evaluate how losses from storm surge are expected to change from the present day until 2100 and found that cities such as Miami, New York, and Tampa face greater risk of economic loss from storm surge.

To evaluate risk, we compared the likelihood of each city sustaining at least $15 billion in economic losses from storm surge – the amount of loss that would occur if the same area of Orleans Parish was flooded today as was flooded in 2005. What we found is that while New Orleans still faces significant risk, with a 1-in-440 chance of at least $15 billion in storm surge losses this year, the risk is 1-in-200 in New York, 1-in-125 in Miami, and 1-in-80 in Tampa.

Looking ahead to 2100, those chances increase dramatically. The chance of sustaining at least $15 billion in storm surge losses in 2100 rises to 1-in-315 in New Orleans, 1-in-45 in New York, and 1-in-30 in both Miami and Tampa.

Due to flood defences implemented since 2005, the risk in New Orleans is not as dramatic as you might think compared to other coastal cities evaluated. However, the Big Easy is faced with another problem in addition to rising sea levels – the city itself is sinking. In fact, it’s sinking faster than sea levels are rising, meaning flood heights are rising faster than any other city along the U.S. coast.

Our calculations regarding the risk in New Orleans were made on the assumption that flood defences are raised in step with water levels. If mitigation efforts aren’t made, the risk will be considerably higher.

And, there is considerable debate within the scientific community over changing hurricane frequency. As risk modelers, we take a measured, moderate approach, so we have not factored in potential changes in frequency into our calculations as there is not yet scientific consensus. However, some take the view that frequency is changing, which would also affect the expected future risk.

What’s clear is it’s important to understand changing risk as storm surge continues to contribute a larger part of hurricane losses.

New Storms, New Insights: Two Years After Hurricane Sandy

When people think about the power of hurricanes, they imagine strong winds and flying debris. Wind damage will always result from hurricanes, but Hurricane Sandy highlighted the growing threat of storm surge as sea levels rise.

While Sandy’s hurricane-force winds were not unusual, the storm delivered an unprecedented storm surge to parts of the Mid-Atlantic and Northeast U.S. In total, Sandy caused insured losses of nearly $20 billion in the U.S., 65 percent of which resulted from surge-driven coastal flooding.

Considering the hazard and severity of the event, we used Sandy as the first real opportunity to validate our hydrodynamic storm surge model, which we released in 2011 and embedded in the RMS U.S. Hurricane Model. We verified the model against more than 300 independent wind and flood observations, the Federal Emergency Management Agency’s (FEMA) 100-year flood zones, and the FEMA best surge inundation footprint for New York City. The model captured the extent and severity of Sandy’s coastal flooding exceptionally well.

We also conducted extensive analysis of claims data from Sandy, which involved reviewing nearly $3 billion in location-level claims and exposure data across seven lines of business, provided by several companies. The purpose of the study was to deepen our understanding of the impacts of flooding on coastal exposures, particularly for commercial and industrial structures.

What struck us was how vulnerable buildings are to below-ground flooding. In many cases, damage to ground- and basement-level property and contents contributed a much higher proportion of the overall losses than expected, particularly for commercial structures in New York’s central business districts.

This insight has prompted us to improve the flexibility of how losses are modeled for contents and business interruption, specifically for basements. Early next year, we will release an update to our flagship North Atlantic Hurricane Models to provide the most-up-to-date view of hurricane risk with new vulnerability modeling capabilities based on insights gained from Sandy.

The model update includes new location-specific content triggers to enable users to make business interruption loss projections dependent on either contents or building damage, rather than on building damage alone. The model also allows users to assess the impact of multiple basement levels in a building, as well as the total value of contents stored within.

The claims data analysis also highlighted the importance of using high-resolution data to model high-gradient perils, such as coastal flooding. Flood losses are extremely sensitive to the locations of coastal exposures, as well as the surrounding topographical and bathymetrical features. Using high quality data with location-level specificity across a variety of building characteristics, as well as a high-resolution storm surge model that can accurately capture the flow of water around complex coastlines and local terrain, minimizes uncertainty.

At this time, RMS remains the only catastrophe modeling firm to integrate a hydrodynamic, time-stepping storm surge model into its hurricane models to represent the complex interactions of wind and water throughout a hurricane’s life-cycle, and we continue to implement lessons learned from new storms.

Understanding the Potential Impact of the Next Catastrophic European Flood

Over the past year, Europe has intermittently but consistently suffered from significant flooding.

Most recently, the Balkans experienced widespread devastation in May due to some of the region’s heaviest precipitation on record. Three months worth of rain fell in just three days. The subsequent flooding was so severe that entire towns were submerged. While it is too soon to estimate the full impact, the economic and humanitarian costs will be high.

This event follows one of the stormiest and wettest winters on record for the U.K. Remote locations bore the worst of it, and for now, the U.K. government and insurance industry appear to have largely escaped a sizeable bill, at least on the scale of previous flood events.

The events come just one year after the costliest natural catastrophe of 2013 for the insurance industry, when flooding inundated Central and Eastern Europe in late May and early June. The event caused around $20 billion (€12 billion) in economic losses, of which it is estimated that approximately 20 percent was insured.

As with the more recent Balkans and U.K. events, the May 2013 flooding followed a period of extreme rainfall; consequently, groundwater and soil moisture levels were saturated. As more rain fell in late May and early June, the precipitation had nowhere to go except to flow through catchments into the river network as runoff. The Danube, Elbe, and other rivers overflowed, resulting in significant flooding across Germany and the Czech Republic, and, to lesser extents, Austria, Switzerland, Poland, Slovakia, Hungary, Croatia, and Serbia.

Each of these events highlighted the importance of understanding the impact of precipitation, whether from a short, intense period of rainfall, prolonged wet conditions, or a combination of these characteristics. In each case, to evaluate flood risk, it is vital to understand how antecedent wetness conditions influences subsequent flooding.

In 2002, Central Europe was similarly inundated by severe flooding, producing economic losses of over $28 billion (€17 billion). Both events were triggered by similar meteorological phenomena, Genoa type-lows. However, the antecedent conditions in 2002 were comparatively dry compared to those in 2013, and the precipitation that triggered the eventual flooding was more severe in 2002 compared to 2013.

Both events had significant impacts, but what would happen if we combined the worst features of both to create a “perfect storm” type of flood event?

Combining the antecedent wetness of spring 2013 with the extreme precipitation of the August 2002 event, RMS researchers estimated how severe this “perfect flood” could be. Results of this study show a substantial increase in peak flow (more than 50 percent on average) for both the Elbe and Danube rivers.

Elbe River flood hazard map for a "perfect flood event," Riesa, Germany

Elbe River flood hazard map for a “perfect flood event,” Riesa, Germany

In certain locations, this scenario would be characterized by a flood extent (shown above for the area surrounding Riesa, Germany) of about 2.5 times that observed in 2002. But given the remarkable non-linearity between hazard and damage, RMS research estimates that the increased losses could aggregate to a total economic loss of approximately four times the 2002 losses. While this is a theoretical scenario, it is also an entirely realistic one.

The events that have occurred since May 2013 are a stark reminder that flood is a peril from which much can be lost.

After the 2002 flooding, flood defenses were improved in some locations, such as Prague, resulting in less severe flooding. However, because both the flood hazard itself and the physical environment change over time, Europe’s flood risk must be continually and holistically assessed to ensure that we are prepared for when, not if, a similar event occurs again.