Fact check on storm myths Is climate change to blame for the deaths in southern Switzerland?

The devastating storms of recent weeks in southern Switzerland raise questions. Are such disasters becoming more frequent? Are villages in the Alps still safe? The WSL research institute has answers.

Within a week, nature strikes twice: first in Upper Valais and Misox and the following weekend in Saas Grund and the upper Maggia Valley. In addition, Chablais, where the Rhone flows into Lake Geneva, is flooded.

Some conclusions are obvious: such extreme events are becoming more frequent, they claim more victims and they particularly often affect the southern side of the Alps. People on the Central Plateau, on the other hand, have little to fear apart from material damage. But is this true? The Swiss Federal Institute for Forest, Landscape and Snow Research WSL explains.

Are extreme events becoming more frequent?

WSL has been keeping a database of storm damage for 50 years. The year 2024 is not yet included. But it shows that the last 15 years were no more damaging than those before, at least in financial terms. By far the most damaging year was 2005, with flooding in Graubünden, Central Switzerland and Bern.

Is climate change to blame?

The WSL writes in a new online publication: "According to current knowledge, major precipitation events are becoming more frequent as a result of climate change." However, it is not clear how often these lead to landslides or debris flows. The relationships between "runoff, debris transport, possible debris flows, protective measures and ultimately the damaging effect" are too complex. The only thing that is certain is that heavy rain falls more often. The coming years will show whether this leads to more landslides and debris flows.

Christoph Hegg, interim head of the WSL, explains the connection between heavy rainfall and landslides on SRF radio: "There was already a lot of moisture in the system. The steep slopes and streams in Ticino could then carry a lot of debris with them. Where the terrain becomes flatter, this is deposited, the stream is dammed and then a debris flow beyond the stream bed can destroy houses or even lead to fatalities.

What is the connection between global warming and debris flows in the Alps?

Warmer air stores more moisture than cooler air. This additional water leads to more precipitation. The WSL explains: "The warming of the Earth's atmosphere due to climate change therefore increases the potential for heavy precipitation."

The rising temperatures in the Alps are also causing permafrost soils to thaw, which can lead to additional rockfall and landslides. "If the material accumulates in channels, it can be transported downhill in the form of debris flows during heavy rainfall," explains WSL researcher Käthi Liechti. The mountain streams have more ammunition, so to speak, which they push down into the valley when a thunderstorm gives them the power to do so.

What influence does the snowy winter have?

The winter of 2023/24 was particularly snowy. "At high altitudes, there is still an above-average amount of snow for the time of year, which contributes to increased runoff due to the melting snow," explains WSL researcher Käthi Liechti at the request of blue news.

Is the south side of the Alps affected more frequently than the north?

Over the past two weekends, various places on the southern side of the Alps were affected, including the Misox and Maggia valleys as well as the Upper Valais and the Chablais where the Rhone flows into Lake Geneva. But the impression is deceptive, writes the WSL: "The south is not generally more susceptible. The conditions are simply different overall. On the southern side of the Alps, streams etc. are used to the heavier rainfall that carries away debris."

On the two storm weekends, however, this was no longer enough to prevent the devastating debris flows.

The WSL graphic also shows that it is by no means only in mountainous areas that people die in storms. Floods also repeatedly claim lives on the Central Plateau.

Why are houses built in landslide zones?

When houses built decades ago or even earlier are hit by landslides, the question arises as to whether they should have been built in these locations at all. Comprehensive hazard maps have only been available in Switzerland for ten years, and in some municipalities only for five. "These must always be checked for validity after a certain period of time or after particularly severe storms and updated if necessary," writes the WSL.

The destruction in the Maggia Valley, in Saas-Grund or in the Misox could therefore change the assessment of the dangers and mean that no one is allowed to live in certain areas.

Is there no danger on the Central Plateau?

Of course, there is only a risk of landslides where the terrain is steep enough. But even small elevations can cause a slope to slide. However, the WSL map shows that people are more likely to die in squalls on the Central Plateau.

The WSL map shows that there is no region of Switzerland where no one has ever died as a result of a natural event. In the flat Central Plateau, however, it is windstorms, lightning and floods that are more likely to claim lives.

Rockfalls, landslides and avalanches occur where the terrain is steep enough. However, people on the Central Plateau should not feel absolutely safe. Landslides occur time and again, even on inconspicuous hills in the Central Plateau.