Valais is the canton where residents face the highest flood risk, with 24% of the population living in a hazard zone.
The University of Neuchâtel study compared six cantons across the plateau, the Alps and the Jura.
Jura came second, at 17.4%, with much of its population strung along fast-flooding streams.
In Valais, most people and infrastructure sit in the Rhône valley, where secondary rivers converge and water levels rise quickly in heavy rain.
Communities along the big plateau lakes are largely protected, thanks to dams like the Seujet on Lake Geneva and the Platzspitz on Lake Zurich.
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More killed in Valais this year than the whole of 2025
