September 29th, 2009

Impact and Implications of Swiss Hailstorms in July 2009: Overview

Posted at 11:59 AM ET

Executive Summary

Severe hailstorms caused widespread property, motor and crop damage in Switzerland on July, 23 2009. Although hail losses only make up an average of 9 percent of all claims in Switzerland every year, the peril has the potential to cause severe localised damage in the country. Hailstorms can trigger insurance claims totaling hundreds of millions of euros if they hit Swiss urban areas, and this scenario was realized on July 23 when hail measuring up to 50 mm in diameter badly battered central and northern cantons and caused the biggest Swiss hail loss in recent memory.

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In Switzerland, obligatory cover for natural hazards, including hail, is provided by a two-tier system of cantonal and private insurers. For the purposes of this report, Guy Carpenter spoke to representatives of both, and the responses we received suggest cantonal and private insurers are likely to payout more than 150,000 claims totaling more than CHF733 million (EUR485 million).

This is a significant loss for the Swiss insurance market and the hailstorms are expected to have a substantial influence on the (re)insurance renewal process in the country for 2010. The event illustrates the need for good quality tools and data to help (re)insurance companies quantify their exposure to the hail peril, and Guy Carpenter intends to play a leading role in developing these solutions.

Meteorological Summary

The evening of July 22 was characterized by a particularly strong foehn wind1 in the alpine valleys which was the product of pressure gradient extremes across the Alps. The foehn wind was particularly strong for the time of year and resulted in local temperature gradient extremes.

Storms of July 23

The severe storms that hit Switzerland on July 23 were fuelled by a warm and humid air mass that moved up from the Mediterranean Sea. The storm-inducing potential of this air mass was increased by the presence of strong winds at high altitude.

The Swiss Plateau and the Prealps were in the path of some of the most powerful and fast-moving storm cells. As these storm cells were moving at speeds of greater than 60 kmph, the worst hit areas were subjected to total precipitation accumulations equivalent to more than 100 mm per hour. Additionally, maximum wind gusts recorded by MeteoSwiss weather stations during the passage of the storm were in excess of 90 kmph and it is likely that wind speeds of over 100 kmph were experienced in localized areas during the passage of the most active storm cells.

Damage Potential of Hail

Most of the precipitation produced by the storm cells fell as large hailstones that resulted in severe damage. Some of these hailstones were larger than 50 mm in diameter and commonly of at least 20 mm in diameter.

Some of the hailstones produced on July 23 were the size of golf balls and billiard balls. Such hailstones have the capacity to severely damage fruit and other agricultural crops, in addition to vehicle windscreens and bodywork, and property windows and glass roofs. Damage evidence gathered from the July hailstorms seems to confirm this classification.


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  1. A foehn wind is a type of dry, down-slope wind that occurs in the lee of a mountain range. Foehn winds can raise temperatures by as much as 30°C in a matter of hours.

Guy Carpenter’s Instrat® department provides CAT-i reports for major natural catastrophes worldwide. These reports cover catastrophes including worldwide tropical cyclones, earthquakes, major UK and European floods and any other natural event that is likely to incur a significant loss to the (re)insurance industry. Please email if you wish to be added to the free email distribution list.

Instrat also provides RISK-i reports for major technological or man-made events worldwide. These reports cover risks to property, transport and life including explosions, fires, crashes, engineering disasters and terrorist attacks that are likely to incur a significant loss to the (re)insurance industry. Please email if you wish to be added to the free email distribution list.

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