Abstract
Abstract. With access to claims, insurers have a long tradition of being knowledge leaders on damages caused by windstorms. However, new opportunities have arisen to better assess the risks of winter windstorms in Europe through the availability of historic footprints provided by the Windstorm Information Service (Copernicus WISC). In this study, we compare how modelling of building damages complements claims-based risk assessment. We describe and use two windstorm risk models: an insurer's proprietary model and the open source CLIMADA platform. Both use the historic WISC dataset and a purposefully built, probabilistic hazard event set of winter windstorms across Europe to model building damages in the canton of Zurich, Switzerland. These approaches project a considerably lower estimate for the annual average damage (CHF 1.4 million), compared to claims (CHF 2.3 million), which originates mainly from a different assessment of the return period of the most damaging historic event Lothar–Martin. Additionally, the probabilistic modelling approach allows assessment of rare events, such as a 250-year-return-period windstorm causing CHF 75 million in damages, including an evaluation of the uncertainties. Our study emphasizes the importance of complementing a claims-based perspective with a probabilistic risk modelling approach to better understand windstorm risks. The presented open-source model provides a straightforward entry point for small insurance companies.
Highlights
Severe windstorms are responsible for widespread socioeconomic impacts such as damage to buildings, structures, transport networks, forests, and even loss of lives
This study shows how GVZ uses both the Windstorm Information Service (WISC) dataset and the new probabilistic hazard event set for assessing the potential building damage and risk due to extreme windstorm events, including an evaluation of the uncertainties of such assessments
After a description of the insurance claims data (Sect. 2.1) and the windstorm hazard event sets used (Sect. 2.2), we introduce the GVZ and the CLIMADA risk assessment models applied for damage modelling (Sect. 2.3) and conclude this section with a brief recapitulation of the risk assessment metrics employed in this study (Sect. 2.4)
Summary
Severe windstorms are responsible for widespread socioeconomic impacts such as damage to buildings, structures, transport networks, forests, and even loss of lives. The impact of a windstorm in terms of building damages depends on the severity of associated surface winds and gusts as well as on the exposed values and the respective vulnerability (i.e. damage susceptibility) of the buildings being subject to the hazard – with both building stock and vulnerability changing over time. High wind speeds cause large pressure and suction effects, which in turn are responsible for damage to the roof and the building facade. Damaging winds and violent gusts in the canton of Zurich are mainly due to the passage of large-scale extratropical cyclones and their associated fronts during autumn and winter as well as due to mostly local convective storms during summer. Winter windstorms typically cause widespread minor building damages summing up to large amounts, whereas it is not unusual
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