Germany Hail Storm

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Posting Date: August 23, 2013, 6:38:00 AM

Event Summary

After a prolonged period of above average temperatures in Central Europe, several severe hail events were triggered on the 27th and 28th of July, ahead of a low pressure system named Andreas. On July 27 in northern Germany, a hail supercell was first reported northeast of Dortmund and propagated toward Wolfsburg. A second severe hail storm on July 28 was similarly triggered, but affected Reutlingen, Nürtingen, and Kirchheim unter Teck in southern Germany, which is a heavily populated region with high concentrations of exposure value.

 Location (green triangles) of reported hail events on July 27 (northern Germany) and July 28 (southern Germany) (Source: ESWD)

Reported losses for both events combined are estimated to exceed EUR 1.3 billion (USD 1.7 billion), with some estimates of up to EUR 1.5 billion (USD 2 billion), making this the second largest hail event after the devastating 1984 Munich hailstorm and one of the ten costliest natural disasters in Germany. As the recent events narrowly missed the cities of Stuttgart and Hannover, the already large losses serve as an impressive reminder of the significant loss potential of hail in Central Europe.

The final insured number is likely to be higher still because many residents were away on holiday and losses were not reported in time for the preliminary reports. It is interesting to note that although much larger in size, the northern event contributed less to the overall loss than did the very intense but smaller event in the south, mainly as a result of the higher concentration of exposure in the area.

Synoptic Description

During the month of July, a stationary high pressure system located over Central Europe was responsible for a prolonged period of warm and dry conditions, with clear skies.

At the end of July, an upper-level trough—advecting warm and dry air masses from North Africa—reached Central Europe and caused a short but intense heat wave. On July 27, several weather stations in Germany recorded temperatures above 38°C, representing the peak of the heat wave.

During the night of July 26, and ahead of the low pressure system Andreas, a large mesoscale convective system (hundreds of kilometers in area) developed over the Bay of Biscay and moved over France and Benelux toward Germany. The following afternoon, the convective system approached Germany, and the coincidence of the mesoscale convective system with the prevailing warm air masses initiated the development of a long-lived supercell.

This supercell moved from Bielefeld over Hannover to Wolfsburg and produced hailstones of extremely large diameter (the largest recorded was approximately 12 cm across). On the afternoon of July 28, a convergence line (also associated with the low pressure system Andreas) in combination with upper-level rotating winds contributed to the development of another supercell over the Black Forest mountain range in southern Germany. The second supercell also produced large hailstones, up to 10 cm in diameter. The southern supercell moved from Schramberg towards Stuttgart and crossed the heavily populated areas of Tübingen and Reutlingen.

                                  Supercell over Reutlingen (photo courtesy of Benjamin Wolf)

Reported Impacts

Based on the latest reports, approximately 100,000 buildings and 50,000 automobiles were damaged by hail from these two events. Building damage was mostly from broken windows and roller shutters, broken roofs tiles, and perforated siding.

The predominant roofing material in Germany is clay or concrete tile, or less commonly, aluminum or copper. While hail damage to copper and aluminum roofs is typically cosmetic, clay tiles can be severely damaged by large hailstones, leaving the building’s interior vulnerable to additional damage from precipitation.

Aerial photograph showing extent of roof damage. Damaged roofs are covered by tarps. (photo courtesy of Marco Kaschuba

For energy conservation, buildings in Germany are commonly insulated to some degree. Insulation using styrofoam or mineral wool, although typically covered in plaster, is fairly susceptible to large hailstones and in recent years the German government has instituted special financial programs to increase the number of well insulated houses. During the recent hailstorms, soft siding was commonly damaged and required repair.

Another significant source of loss was to solar equipment, which is often attached to the roof for maximum sun exposure and is thus very susceptible to the impact of hailstones. An increasing number of houses are equipped with solar panels and solar heat exchangers for utility water preparation. In the affected area, many solar elements have been damaged, requiring special repair efforts in addition to roof repairs.

Skylights are also susceptible to damage. In contrast, regular double-paned wall-windows are usually strong enough to withstand the impact of hailstones because of the typically shallow angle of impact. However, due to the prolonged heat wave, many roller shutters were lowered—not necessarily to protect the windows from hail, but to reduce incoming sunlight. Many lowered shutters have been damaged severely during this event.

Roofers in the area are completely overwhelmed by the high demand and expect that the completion of all repairs will take extraordinary long, increasing the likelihood of consequential damage from everyday weather conditions.

The reported number of damaged automobiles is already near 50,000 and this does not include an estimated 28,000 automobiles at a Volkswagen manufacturing lot in Wolfsburg. Observed car damage is in line with typical hail damage, including dented exteriors and broken windshields. Damage per automobile can easily surpass EUR 5,000 to EUR 10,000, resulting in a total loss in many cases.

Damages to house siding and cars (photo courtesy of Benjamin Wolf)

Impact on the Insurance Industry

Given the commonly applied 72 hours clause, these spatially distinct events will be considered as a single occurrence for reinsurance purposes. For some companies, this event represents the largest loss since winter storm Kyrill in 2007. Added to the losses from the July flood of this year, the industry is faced with a large loss burden from recent natural catastrophes.

The Outlook

AIR Worldwide is currently developing a pan-European severe thunderstorm model that will help the insurance industry manage this risk. The ability to realistically model the complexity of hail events will be an important component of the model, and this latest outbreak will be used as a benchmark event. The event also serves as a powerful reminder of the loss potential from hailstorms in Central Europe. It is important to also keep in mind that much larger losses could have materialized if a nearby large city like Stuttgart or Hannover was directly hit.

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Posting Date: August 23, 2013, 6:38:00 AM