Switzerland must adapt to changing flood risks, warns Swiss hydrologist

Monitoring the way temperatures fluctuate during the year should help experts reduce the risk of flooding and other weather-related disasters. Keystone / Jean-Christophe Bott

Heavy rains and melting snow have triggered spectacular floods and deadly landslides in parts of the Swiss Alps. Unusually warm temperatures, most probably linked to the climate crisis, suggest the situation is changing and Switzerland needs to better adapt, says a Swiss expert.

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In the past, the greatest risks of flooding used to be at the end of summer after the hot season, Frédéric Jordan, a Swiss hydrologist told Swiss public radio, RTS, on Monday.

“In the last hundred years or so, heavy floods have typically occurred between August and October. However, if we look at the last 12 months, we had a major flood on the Rhône River on November 14, 2023 and one on June 21, 2024, which is quite new,” he explained.

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This change is “very probably” linked to climate change, he noted, and high temperatures are a factor that increases the risks.

“In Zermatt, it was 14°C during the rainstorm on Friday. That’s warmer than in August 1987 or October 2000, when the Rhone floods were at their worst”, he pointed out.

In mountainous regions, with steep slopes and large catchment areas, the risk is much greater because “the phenomena can arrive quickly and be more violent than on the plains”, said Jordan.

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“We’ve known for several days that precipitation was expected in the form of thunderstorms moving up from the south, but at this stage we never know where the thunderstorm cells will arrive nor how big they will be,” he said.

The presence of large quantities of snow at high altitude this year further increased the risk, he noted.

New information

The situation “may be changing” and Switzerland must “take account of this new information and adapt”, according to the hydrologist. The system in place over the past 30 years is based on land-use management and the creation of hazard maps, some of which were drawn up recently but others, 20 or 30 years ago, he said.

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“This process is ongoing and really needs to continue” in order to regularly monitor these aspects and “revise” what needs to be revised, he told RTS. “Obviously, every time an event like this happens, it stimulates the desire to reassess and study these phenomena to reduce the risks to particular locations,” he said.

Adapted from German by DeepL/dkk/sb

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