Abstract

This study investigates the wind gusts and associated economic loss patterns of high-impact winter windstorms in Switzerland between 1871 and 2011. A novel approach for simulating windstorm-related gusts and losses at regional to local scales is applied to a sample of 84 windstorms. The approach involves the dynamical downscaling of the Twentieth Century Reanalysis (20CR) ensemble mean to 3-km horizontal grid size using the Weather Research and Forecasting (WRF) model. Economic losses are simulated at municipal level for present-day asset distribution based on the downscaled (parameterised) wind gusts at high spatiotemporal resolution using the open-source impact model climada. A comparison with insurance loss data for two recent windstorms (“Lothar” in 1999, “Joachim” in 2011) indicates that the loss simulation allows to realistically simulate the spatial patterns of windstorm losses. The loss amplitude is strongly underestimated for ‘Lothar’, while it is in reasonable agreement for ‘Joachim’. Possible reasons are discussed. Uncertainties concerning the loss simulation arise from the wind gust estimation method applied; estimates can differ considerably among the different methods, in particular over high orography. Furthermore, the quality of the loss simulation is affected by the underlying simplified assumptions regarding the distribution of assets and their susceptibilities to damage. For the whole windstorm sample, composite averages of simulated wind gust speed and loss are computed. Both composites reveal high values for the densely populated Swiss Plateau and lower values for south-eastern Switzerland; metropolitan areas stand out in the loss composite. Eight of the top 10 events concerning the losses simulated for present-day asset distribution and summed over all Swiss municipalities occurred after 1950. It remains uncertain whether this is due to decadal-scale changes of winter windstorms in Switzerland or merely due to a possible bias of the 20CR ensemble mean towards lower wind speeds in the period before around 1950.

Highlights

  • Extreme windstorms are among the most destructive meteorological hazards affecting Switzerland (Imhof, 2011)

  • The approach involves the dynamical downscaling of the Twentieth Century Reanalysis (20CR) ensemble mean to 3-km horizontal grid size using the Weather Research and Forecasting (WRF) model

  • This loss modelling technique involves the dynamical downscaling of the 20CR ensemble mean to a 3 km by 3 km horizontal grid over Switzerland using the WRF model

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Summary

Introduction

Extreme windstorms are among the most destructive meteorological hazards affecting Switzerland (Imhof, 2011). Their socio-economic impacts depend on the severity of the windstorms and on the exposure and vulnerability of the values at risk (IPCC, 2012). Natural hazard risks always involve the combination of the hazard and socio-economic factors, and both are subject to changes over time The assessment of windstorm-related risks is important for insurance and reinsurance companies and for local governments, which are responsible for identifying measures to minimise the impact from natural hazards at the lowest cost to society (e.g. ECAWG, 2009). Good estimates of the probability of occurrence are indispensable for assessing windstorm risks. To study the regional impacts of windstorms, a large sample of events is needed for (http://creativecommons.org/licenses/by/4.0/), allowing third parties to copy and redistribute the material in any medium or format and to remix, transform, and build upon the material for any purpose, even commercially, provided the original work is properly cited and states its license

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