Storm damage at ten-year high

Although total losses in 2018 were well below the inflation-adjusted average of 306 million Swiss francs for the years 1972-2017, they were higher in 2018 than in any of the preceding ten years. 2007 was the last year with significantly above-average losses from natural hazards. At that time, the Swiss Federal Research Institute registered WSL damage amounting to 700 million Swiss francs. Since then, the annual damage amounts have ranged between CHF 20 and 200 million, according to WSL.

2018: Thunderstorms dominated

In terms of meteorological triggers, thunderstorms dominated in 2018 with 69%, followed by the combination of snowmelt and rain (15%) and continuous rain (13%). Floods, surface runoff, and debris flows accounted for the largest share of damage costs (79%), followed by landslides (19%) and fall processes (2%). Fortunately, there were no fatalities in 2018 from the natural hazard processes studied here, WSL points out.

Swiss precipitation record

From April until the end of 2018, it was very dry throughout Switzerland. Nevertheless, individual local thunderstorms caused high damage, for example in Lausanne VD late in the evening of June 11, where 41 mm of rain fell in just ten minutes. So much precipitation in such a short time has never been measured in Switzerland before. The sewage system and the soil were unable to absorb the masses of water, and the surface runoff flooded several streets and the cellars of numerous residential buildings, stores and schools. Shortly before, on May 30, heavy rain and hail caused flooding between Baden AG and Dielsdorf ZH. And in the late afternoon of May 31, the town of Yverdon-les-Bains VD was hit by heavy rain showers that flooded the basements and underground garages of several buildings. Finally, on June 8, 200 cellars had to be pumped out in Frauenfeld TG as a result of thunderstorms.

Valais strongly affected

Although 2018 as a whole was exceptionally dry, it began with very high precipitation. As early as January 4 and 22, prolonged rainfall, in some cases combined with melting snow, led to flooding and landslides in the cantons of Bern, Vaud and Valais. In Valais, this caused extensive damage to roads and other infrastructure. An evening stationary thunderstorm led to high discharges in Navisence in the rear part of Val d'Anniviers VS on July 2 and 3 (see photo). The torrential water and debris damaged the river bank over a length of 20 km, causing it to overflow its banks in several places. In the municipalities of Anniviers and Chippis, the damage was massive. On the afternoon of August 1, several thunderstorms occurred in eastern Switzerland. Then, in the early evening of August 6, a violent thunderstorm caused surface runoff in Sion VS, flooding streets and inundating more than a hundred cellars.

Source: WSL