RMS’ Juergen Grieser reflects on this year’s unusually large hail losses in France…

France – hail storm

Through mid-August 2022, France Assureurs registered nearly one million individual claims due to severe convective storms, with the industry expected to pay out around €4bn.

Record-breaking hailstorms in France have driven the risk. Over 20 years, France Assureurs calculates the average annual hail loss at just above €200mn. 2022 losses are about €2bn, a factor of 10 higher than average. Add in high business interruption and post-loss amplification, and reinsurers expect total insured hail losses in France to be above €6bn.

What happened? Up to the end of August 2022, the number of hailstorms in France reported by the European Severe Weather Database (ESWD) exceeded the maximum of previous years by a factor of seven, and it was not a single event that caused the losses. Figure 1 shows days during May to August 2022 where reported hailstones were larger than a given diameter threshold (red line), and the same period for previous years since 2009 (blue lines). None of the previous years had as many days with observed exceedances as in 2022.

Large-hailstone-frequency-in-France

How unlikely were these hail losses?

What return period does this represent? Using an exceedance probability (EP) curve of observed annual hail losses in recent decades and our model EP curve, both are very well in line with each other. The observations suggest an exponential EP curve, so we fit an exponential distribution to the observed annual hail losses in France as well.

This allows for estimating the return period for 2022 using observed hail losses based purely on observations over the last two decades and alternatively from our models.

This leads to a heavy-tailed distribution of annual hail losses in France and a return period for the 2022 annual hail loss in the order of 425 years, based on an event set covering 50,000 years. The pure statistical fit of an exponential distribution to the observations, although a good fit, leads to estimated return periods in the range of 82,000 years, which is more than 190 times higher than the RMS estimate.

While the return period from our models is large, it is realistic, indicating that the French hail losses seen in 2022 happen very rarely – based on a hail model that assumes a stationary climate.

Is it due to climate change?

While no trend is visible in ordinary hail loss years over the last two decades, we cannot exclude that climate change has increased the likelihood of the large losses experienced this year. Summer was exceptionally hot in the region, and very high sea surface temperatures in the Mediterranean contributed to providing the necessary humidity for hail-producing severe convective storms to develop. While this is conceptual evidence that the 2022 high hail losses in France may be at least somewhat attributable to climate change, it is not proof.

Due to the uncertain and potentially competing impact of climate change on numerous factors critical to severe convective storm formation, there is no consensus as yet on how climate change may affect the frequency and severity of damaging convective weather events, including hail. An assumption of stationarity remains reasonable for now. If several exceptional years like 2022 occur in short succession, that opinion may well change.

Juergen Grieser is Senior Director at RMS