Small changes to the season’s most severe storm could have meant a major loss event like 87J
The most severe storm of the 2023-2024 European windstorm season was Storm Ciarán (Emir), which broke meteorological records by obtaining the lowest mean sea level pressure recorded in both England and Wales. Ciarán was meteorologically similar to The Great Storm of 1987 (87J).
Despite these feats, losses were relatively low from a historical perspective. CoreLogic estimated that Ciarán generated an industry gross loss exceeding €1.8 billion[1].
In the recently published white paper, CoreLogic used the Eurowind™ model perturbation scheme to produce “what-if” scenarios for key historical storms.
The same “what-if” analysis was applied to storm Ciarán to explore the questions:
- Was there a high chance that conditions could have differed enough to produce a much larger loss?
- How close was this storm to being another 87J? In other words, was Ciarán another near-miss event?
About the Storms: Ciarán and 87J
As Storm Ciarán approached the European continent, the central low-pressure center skirted eastwards along the English Channel before moving overland into Hampshire, England. The storm travelled in a northeast direction across southeastern England.
European windstorm risk impacts enterprise risk management strategies
As shown on the left side of Figure 1, this movement led to the highest overland gusts from the storm occurring along the northern coast of France. Despite the record-breaking meteorological observation data in the UK, strong gusts were limited to a narrow strip of the southern coast.
Ciarán was reminiscent of 87J in terms of location and intensity. Both storms underwent explosive intensification as they reached the UK. However, 87J’s storm track differed enough from Ciarán to create a much more damaging footprint in both the UK and France, as shown on the right side of Figure 1.
When 87J was over the UK, it tracked further north than Ciarán, leading to the most damaging wind speeds manifesting in the highly populated area of southeast England. At the time, this caused record-breaking levels of economic and insured loss [1].
The CoreLogic Eurowind model, which contains the damage and financial modules necessary to quantify loss, read each footprint to generate gross loss estimates from both storms[2].
The 87J footprint results in a loss dominated by roughly equal contributions from southern UK and northern France. The Ciarán loss in France is ~60% of the 87J loss under today’s exposure. By contrast, the Ciarán loss in the UK is a small fraction of the “as-now” 87J loss. This is to be expected given that Ciarán was a near-miss event for the UK, and the high winds were limited to coastal areas.
What Could Have Been? A Counterfactual Analysis of Ciarán
To answer the question of how damaging Ciarán could have been if meteorological conditions had been different, CoreLogic produced a family of alternative or counterfactual storms.
These simulations addressed uncertainties by altering the storm’s physical characteristics including the location, orientation, spatial extent, intensity, and duration.
The CoreLogic Eurowind model was applied to each alternative footprint to generate a probability distribution of counterfactual losses. The Storm Ciarán loss probability distribution for all of Europe is shown in Figure 2. Loss values were normalized to the mean Ciarán loss (€1.8 billion) as shown by the vertical red line.
- What were the chances of Ciarán causing greater loss than 87J?
According to this distribution, there was a 40% chance of Ciarán having caused a greater loss than €1.8 billion.
- But what were the chances of Ciarán causing a loss on the scale of 87J?
The right-most green vertical line in Figure 2 shows the loss due to the 87J footprint. There is only a 2% chance that Ciarán could have reached this level, but there is a modest 14% chance of reaching half (left-most green, vertical line) the 87J loss.
- What changes in the Ciarán footprint would have led to losses approaching the level of 87J?
The combined effect of moving the Ciarán footprint southwards and increasing gust intensities leads to a larger footprint over northern France and an 8% chance of attaining the same loss as 87J in France.
By contrast, moving the strong winds located in the English Channel and over France in the Ciarán footprint northwards would have increased the UK loss. There was only a very small (4%) chance of reaching 87J’s loss, but there was a 13% chance of reaching half that value.
Future European Windstorm Risk Remains High
While it is unlikely that storm Ciarán could have produced insured losses like those created by 87J, it could nonetheless have led to significantly higher losses given relatively small perturbations in position and intensity. This highlights the fact that European windstorm risk remains high even though losses in recent years have been low with respect to the historical time series.
©2024 CoreLogic, Inc. All rights reserved. While all of the content and information is believed to be accurate, CoreLogic makes no guarantee, representation, or warranty, express or implied, including but not limited to as to the completeness, accuracy, applicability, or fitness, in connection with the content or information or the products or the regulations referenced herein and assumes no responsibility or liability whatsoever for the content or information or products or regulations referenced herein or any reliance thereon. CoreLogic® and Eurowind™ are the trademarks of CoreLogic, Inc. or its affiliates or subsidiaries.
[1] Gross losses are calculated after the application of limits and deductibles and include damage buildings and contents, as well as business interruption costs to residential, commercial, industrial, and agricultural properties.
[2] Storm Ciarán and 87J losses were generated using 2023 vintage of the CoreLogic Insured Exposure Database (IED).
