When talking Nat Cat, let's hope for the best but prepare for the worst

Severe natural catastrophes tarnished our recollection of 2021 in our region, particularly the severe convective storm "Volker" in June and the flood caused by the low-pressure system "Bernd" in July.

In June 2021, a special weather situation in Europe caused an extraordinary number of thunderstorms. The storms caused by the low "Volker" (download report), which swept over southern Germany and Austria from 20 to 24 June 2021, were particularly devastating. Strong gusty winds and hailstones of up to 7 cm in diameter caused considerable damage to vehicles and buildings.

Hail frequently occurs in conjunction with thunderstorms. Thunderstorms occur when there is enough warm, moist air that is quickly forced to rise (convection). Basically, there are three processes that cause the air to rise and the associated cloud formation: warming of the earth's surface by solar radiation, orographic uplift due to obstacles such as mountains and dynamic ascent at air mass limits. In June 2021, all three factors played a role.

Generally, we make a distinction between two different types of thunderstorms: single cell or supercell thunderstorms. The former is common but usually short-lived and weak. However, if several single cells combine, they give birth to a supercell with more destructive power that can cause large damage. Supercells are long-lived, have a larger spatial extent and are often accompanied by heavy precipitation, extreme hail, severe downbursts and tornadoes. In Europe, supercells are rare, but important from an insurance perspective. During the storms in June 2021, such supercells appeared and caused considerable damage.

The flood event "Bernd" (download report) was the most momentous inland flood event in Europe, and globally it is considered one of the most cost-intensive flood events of recent decades.

After causing some wetness, the low-pressure area "Bernd" that lasted from 12 to 19 July, caused additional heavy rainfall. These led to pronounced flooding, especially in North Rhine-Westphalia and Rhineland-Palatinate, with considerable damage to infrastructure and, regrettably, a high number of fatalities.

Warm and very humid air masses reached Germany from the Mediterranean. A forced uplift and slight congestion effects on the western low mountain ranges (Sauerland, Westerwald and Eifel) occurred regionally at first, spreading later at large scale in the form of recurring or persistent heavy rain.¹ Precipitation intensities exceeded 100 mm between 13 and 15 July and hydrological return periods were locally over 100 years.² The subsequent flood event was a complex interplay of many factors and drastic from both a meteorological and insurance point of view.

What was striking in 2021 was the exceptionally long period with increased storm potential. This was due to a weak jet stream, which enabled the steady behaviour of the lows. Due to different warming trends between the polar region and the equator, weather phenomena such as low-pressure areas and thunderstorms could remain stationary more frequently for a certain period of time in the future.³ However, a final scientific consensus about these phenomena has not yet been reached, but for our industry it means we should be prepared. We must learn from the past to better predict the future. For an optimum outcome, data transparency and collaboration among industry players is essential to enable the production of analysis such as "Volker" and "Bernd" that can help us prepare for the headwinds nature sends our way.