Tag Archives: European Windstorm

When Did Windstorms Become So Wet?

Looking back to the start of the European windstorm season, my colleague Brian Owens pondered whether the insurance industry would experience a windfall or windy fall? Well, a week into February, I think all observers would agree that this has been a very active season.

As the industry continues to count the cost of the succession of systems that have assaulted our shores, it is apparent that the accumulated losses over the season will make this a year from which much can be learned.

The storms impacting northern Europe have frequently brought damaging winds to coastal areas, occasionally exceeding 90mph in the most exposed areas.

However, the driving jet stream has typically been very strong to the west but tapered off in the northeast Atlantic. This has caused systems to explosively deepen and mature before they reached the U.K. and Ireland, but then decay as they approached these shores. Consequently, the long storm paths have prompted higher waves and storm surges, but the latter decay, even for extremely deep cyclones, has meant less damaging winds. This has thus far spared Atlantic-facing countries from extreme wind losses.

But as the season has developed, the main story hasn’t been storm gusts. Anyone living in or visiting the U.K. this winter can testify that it has been exceedingly wet. Not just from excessive rainfall, but from repeated coastal inundations from storm surges combined with high tides as well. Consequently inland and coastal flooding has been significant, dominating our attention.

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The persistent rainfall since December has caused river catchments such as the River Severn and Somerset Levels to swell, particularly across southern England and Wales. Groundwater reservoirs and soils are also saturated, leading to pluvial and groundwater flooding.

However, perhaps most interesting this season has been the surge-driven coastal flooding. Storm surges occur when strong winds force the underlying water toward the coast. As the surge develops, water levels are influenced by the shape of the coastline and tidal interactions, both of which can act to amplify surge heights and resulting coastal flooding.

While property damage has not yet reached the scale of prior major flood incidents in the U.K., this series of events highlights the importance of evaluating the complete flood cycle, from the initiating precipitation and antecedent conditions to the final mode of flooding, as seen during the 2012 U.K. flooding.

With tidal ranges as large as 15 m in the U.K., the timing of the surge is vital for determining the scale of the hazard. Surges that impact a region at high (spring) tide pose the most risk for flooding. The storms impacting northern Europe this winter have consistently coincided with some of the highest tides of the year.

Level of surge (green), relative to actual (blue) and predicted (red) storm-tide

Level of surge (green), relative to actual (blue) and predicted (red) storm-tide

Beginning with Windstorm Xaver in December, the U.K. east coast and coastal locations in Germany were given their sternest test since the devastating 1953 and 1962 events. Fortunately coastal defenses have been improved since those historical floods and the subsequent flooding was not significant.

Numerous systems have continued to arrive through January, with southeast England and Wales, Ireland and northern France particularly affected. As recently as last week, Windstorms Petra and Ruth brought yet more coastal damage and flooding, and the risk of more flooding remains high this week.

As with the wind and inland flood impacts of each individual storm, the coastal damage may not be viewed significant in isolation. Consequently specific storms from this season may not stick in the memory, like 87J has. But the accumulating damage and cost of this continuous series of events has made this a season to remember.

It has also posed a question around how we as an industry evaluate our wind and flood risk. Do we evaluate these perils in isolation or do we consider the correlation these perils have in winter months. A question that may become more prominent as the future of flood insurance in the U.K. evolves.

A Tale of Two Storms

“Horror and confusion seized upon all, whether on shore or at sea: no pen can describe it; no tongue can express it; no thought conceive it…”

Those were the words of Daniel Defoe in “The Storm”, which he published the year following the great 1703 windstorm, an event that saw it’s 310th anniversary on December 7. This event truly was a great storm, estimated to be one of the strongest windstorms to impact the UK.

RMS performed an innovative footprint reconstruction and estimates that wind speeds up to 110 mph were experienced across an area the size of greater London. These speeds are 30-40 mph stronger than those brought to the UK recently by windstorm Christian and are comparable to a category 2 hurricane. Such speeds can cause considerable damage, particularly to inadequately designed and constructed properties.

January also sees the 175th anniversary of the Irish “Oiche na Gaoithe Moire”; which is “The Night of the Big Wind” for those who don’t speak Gaelic.

Reports of the precise meteorological characteristics of this storm are unclear, but analyses of the event estimate that wind gusts in excess of 115 mph occurred and maximum mean wind speeds could have reached 80 mph. At the time it was considered the greatest storm in living memory to hit Ireland and its intensity may not have been rivaled since.

However, other than an interesting history lesson, is there anything valuable to note from these events from an insurance industry perspective?

Both events were severe European windstorms, causing significant widespread damage, but both would also be significant today.

Hubert Lamb’s unique study analyzing historic European windstorms over a period of 500 years places these events in the top grade of severity, at number 4 and 6 in his severity index and RMS estimates that a reoccurrence of the 1703 storm would cause an insured loss in excess of £10B ($16B).

A feature of both events at the time was the extensive and widespread damage to roofs. The 1703 event left tiles and slates littering the streets of London and the 1839 event caused parts of Dublin to look like a “sacked city”.

Roof damage was in part due to poor construction, lack of maintenance and inadequate design for the wind speeds experienced. This is a significant consideration today. Across Europe, design codes in relation to wind damage vary significantly and are a key source of uncertainty when modeling wind vulnerability.

Similar risks and construction types can perform quite differently comparing the north and south of the UK or Ireland. Properties further north experience higher wind speeds more frequently and are generally better prepared. Historically adopted construction practices and older buildings that pre-date many of the building codes and design guidance existing today further complicate the issue.

Another feature of both events were the extents of severe damage, which led to inflated repair costs due to the demand for materials and labor. These were early examples of what we now refer to as post-event loss amplification (PLA). From an insurance perspective we consider inflated “economic” costs (i.e. temporary shortage of material and labor) and also inflation of claims due to relaxed claims processing procedures after an event.

While events today exhibit different forms of PLA compared to historical events, it is clear that PLA has potentially always been an issue after large events, so we need to continue studying this phenomenon, to understand possible future costs. For example, many companies now establish mitigating measures, such as pre-event contracts, guaranteeing services, should an event occur.

For 300 years we have observed common factors across windstorms in Europe and there are lessons to learn from each event. However, the key to being prepared in the future is to:

  • Monitor changing trends
  • Maintain an accurate and up-to-date representation of exposure at risk
  • Understand how losses behave when events occur