In 2011, the current record year, severe thunderstorms caused US$ 47bn in economic losses in the USA, i.e. about as much as a medium hurricane. From the long-term perspective also, on average severe US thunderstorm losses increased significantly from the end of the 1980s in particular, and the fluctuations between the years were more extreme.
In this respect, this peer-reviewed study examines hail, tornado, thundersquall and heavy rainfall losses in the USA. The result of the study is that, after adjusting the losses to take account of socio-economic changes, increases still remain which cannot therefore be explained by changes in exposed values. They are, however, correlated with the increase in meteorological potential for severe thunderstorms and its variability revealed by the study. It has thus been possible for the first time to scientifically prove that climatic changes have already influenced US thunderstorm losses.
Eberhard Faust from Munich Re's Geo Risks Research and a co-author of the study: "It is therefore clear that the change in losses during the period in question is largely driven by changes in climatological boundary conditions. "In particular, the potential energy required in the atmosphere for the formation of severe thunderstorms has increased in the course of time".
The study was not able to conclusively differentiate in the climatological forcing of loss changes between the natural and the man-made components of climate change. But the results are consistent with the anticipated effects of anthropogenic climate change.
Dr. Peter Röder, member of Munich Re's Board of Management: "This scientific study shows, on the one hand, that some regions already need to adapt to changing weather risks. This concerns the insurance industry as risk carrier, first and foremost, but also those in the private and public spheres responsible for deciding on prevention measures".
The study examines events with losses exceeding US$ 250m in the period 1970-2009, past losses being extrapolated to current socio-economic conditions using a normalisation technique. These losses account for some 80% of all severe thunderstorm losses in the USA to the east of the Rocky Mountains. Using this technique, the distorting effect of small losses, the reporting of which is improving in the course of time, is eliminated.