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Thunderstorms, hail and tornadoes

Localised but extremely destructive

Losses from thunderstorms are rising

Lightning is not the only peril thunderstorms bring. Hail, strong gusts of wind and tornadoes are common secondary hazards that can cause flooding, landslides and even flash floods. Losses can total billions of dollars. 
25
US$ bn
Losses from severe thunderstorms in North America in 2017 alone

After hurricanes, thunderstorms are the most significant severe weather risk for the insurance industry in the United States. A tornado or a violent hailstorm occurring in the centre of a major city can result in extremely high losses.

The situation in the areas to the east of the Rocky Mountains is unique in the world; these areas experience violent and frequent heavy storms, very often accompanied by multiple tornadoes.

Even when adjusted for the increase in value, aggregated losses point to an upward trend in recent decades. In 2017 alone, overall losses from severe convective storms in North America totalled more than US$ 25bn. Around three quarters of that total was covered by the insurance sector. In addition to property damage, a considerable amount was paid out for damage to vehicles.

Severe thunderstorms and climate change

Scientific studies are showing that the trend towards rising losses from severe thunderstorms in North America is related to changes in meteorological parameters, in particular to increased atmospheric temperatures and humidity.

It therefore seems highly probable that the increase in (value-adjusted) losses from severe thunderstorms is linked to climate change. 

Normalised losses from heavy thunderstorms in North America are increasing

Just as in North America, normalised losses from thunderstorms have also increased in Europe

The intensity of thunderstorms in certain regions of Europe has also increased in recent years.

Severe thunderstorms can occur virtually anywhere. However, it is possible to identify areas that have a particularly high probability of thunderstorms and, as a result, a high probability of loss. In these regions, the loss potential can often run into the billions. 

In Europe, as in North America, there are scientific studies to suggest that loss potential, in particular from thunderstorm-related hailstorms, is changing in parts of the region, and not only as a result of increasing assets and rising repair costs; the probabilities relating to the frequency and intensity of thunderstorms are also changing. As in America, climate change could also be a factor given that higher temperatures lead to a more humid atmosphere. 

Buildings and infrastructure are particularly prone to losses from violent hailstorms. Loss prevention measures are essential given the pattern of growing losses.

Flash floods, landslides and flooding — Severe thunderstorms bring a variety of perils

Thunderstorm cells can essentially occur anywhere, and this is precisely why loss prevention is so challenging. It is virtually impossible to predict exactly where a thunderstorm will discharge its rain. This also applies to the hazards that follow in the wake of thunderstorms: How quickly, where and to what extent heavy rainfall will result in flooding and flash flooding depends on the catchment area. If the ground becomes saturated as a result of repeated downpours, landslides can occur on hillsides. When rivers and culverts become blocked, water builds up behind the obstacle. If it gives way, a flood wave forms. Of all the factors relating to flash flooding, however, it is extreme precipitation over a very short period that is the biggest loss driver.

Tornadoes — Not just in the United States

Of all wind systems, it is tornadoes that produce the highest wind speeds. Tornadoes are formed whenever strong vertical air movements occur in the atmosphere and are therefore always linked to intensive thunderstorm cells. The average width of a tornado funnel is around 100 metres and the average path is a few kilometres, although widths of more than 1000 metres and paths of up to 300 km have been observed. The outer wall of the funnel can experience wind speeds of over 500 km/h. These storms occur across the world, mostly in the temperate regions at latitudes between 20 and 60 degrees north and south of the Equator. 
The animation illustrates the flow processes in and around a tornado
Tornadoes are so dangerous because they can form in a matter of minutes and, owing to their highly localised extreme wind speeds, can be even more destructive than a hurricane. Geographically, we often associate these events with the American Midwest, where they frequently occur up and down the infamous Tornado Alley. The region extends from Texas in the south through Oklahoma, Kansas and Nebraska to South Dakota and Iowa in the north, running more or less parallel to the Rocky Mountains. In recent years, an average of over 1000 of these whirlwinds have been recorded each year in the United States. According to the European Severe Weather Database (ESWD), between 300 and 400 confirmed tornadoes are recorded each year in Europe. 
Contact our experts
Eberhard Faust
Head of Research: Climate Risks and Natural Hazards
Mark Bove
Mark Bove
Senior Research Scientist at Munich Reinsurance America, Inc.
Anja Rädler
Meteorologist, storm expert
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