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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, tornadoes and heavy precipitation are also regularly involved. Flash floods, river flooding and landslides may follow. Losses can total billions of dollars. 
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

Science has shown that the frequency of meteorological conditions causing the formation of extreme thunderstorms has increased, while substantial loss events have also been on the rise. Climate-model-based studies have identified increasing levels of moisture due to rising ocean temperatures and evaporation rates as the most important driver.

These are substantial indications that climate change is a contributing factor to the increase in (value-adjusted) losses from severe thunderstorms. 

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, it has been demonstrated that severe thunderstorm hazards — in this case large hailstones and strong gusts — have increased in frequency in some regions, thereby contributing to rising loss potential. This is in addition to increased losses as a result of higher asset values and repair costs.

As increasing moisture levels have been demonstrated to be the main driver, the fact that higher ocean temperatures and evaporation rates lead to a more humid atmosphere indicates that climate change is a contributing factor.

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 up to approximately  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
Eberhard Faust
Head of Research: Climate Risks and Natural Hazards
Mark Bove
Mark Bove
Senior Research Scientist
Munich Re US
Anja Rädler
Anja Rädler
Meteorologist, storm expert
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