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A new study published in Natural Hazards and Earth System Sciences (NHESS) by Laura Hasbini, a PhD researcher at the Laboratory for Climate and Environmental Sciences (LSCE) and the Generali Climate Lab, together with Pascal Yiou, Senior Research Scientist at CEA, highlights the dominant role of storm clusters in insured losses in France.
Winter windstorms are Europe’s costliest natural hazard for the insurance industry. However, these storms do not always arrive alone. Several storms can strike the same region within a few days, creating what researchers refer to as storm clusters. One of the best-known examples is the winter of 1999-2000, when storms Lothar and Martin crossed France on 25 and 26 December 1999, causing widespread destruction.
The study introduces an innovative method that systematically attributes each insurance claim to the storm responsible for the damage. Applied to Generali France’s claims portfolio, the approach enabled the creation of an event-based catalogue linking insured losses to specific storms. This provides valuable new tools for risk assessment, loss modelling and reinsurance applications.
For the case of storm clusters, defined as sequences of storms affecting the same region within a 96-hour period, the analysis shows that clustered storms are generally more intense than isolated events, exhibiting lower minimum sea-level pressure and higher vorticity.
The study also finds that, within a storm cluster, a single storm accounts on average for nearly 70% of the total insured losses, while the remaining storms contribute to the residual damage. Overall, 85% of insured storm losses in France between 1998 and 2024 are associated with storm clusters.
These findings demonstrate the importance of explicitly accounting for storm clustering in insurance and reinsurance risk models, leading to more accurate loss estimates and improved risk management.
Hasbini, L., Yiou, P., Hénaff, Q., Boissier, L., and Perringaux, A.: Unravelling wind-driven impact of storm clusters, a case study for the insurer Generali France, Nat. Hazards Earth Syst. Sci., 26, 2817–2839, https://doi.org/10.5194/nhess-26-2817-2026, 2026.