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Hazard · Natural hazard

Flooding

Do not enter cellars, underground car parks and underpasses any more and switch off the power in endangered rooms. Avoid flowing water – just a few decimetres can sweep you off your feet – and follow the instructions of the emergency services. On the natural hazards portal, warning level 3 and above indicates elevated danger; monitor the water levels on FOEN.

In Switzerland, flooding is usually caused by prolonged rain, local thunderstorm cells or snowmelt — often in combination. Large lakes (Lake Biel, Lake Thun, Lake Lucerne) can overflow with a delay, while streams and small rivers swell within minutes.

Cellars, underground car parks and underpasses are particularly dangerous: there the water rises several metres within minutes, and as little as 20 cm of moving water can sweep a person off their feet. In steep areas, debris flows and landslides are added.

Flooding is Switzerland's most expensive natural hazard: the 2005 event caused around 3 billion francs in damage. The municipalities' hazard maps show whether your own address lies in an exposed zone — the most important first step of preparedness.

Risk rating

Risk · High (level 4 of 5)

Likelihood: High · Impact: Medium → Overall risk: High.

Risk matrix: likelihood runs vertically (top = high), impact runs horizontally (right = high). The highlighted cell shows this hazard's rating.
Impact
Low Medium High
Likelihood High This hazard's rating
Medium
Low

Legend: Low (green) · Medium (yellow) · High (red). Overall risk is likelihood multiplied by impact.

Heavy rain and snowmelt make rivers and lakes burst their banks. Cellars and underground car parks often fill within minutes.

Immediate measures

  • Clear the cellar, secure the drains
  • Avoid underground car parks and underpasses
  • Switch off the power in flooded areas

Warning signs

  • Natural hazards portal / MeteoSwiss: flood warning level 3 and higher (max. level 5)
  • Rising levels on the FOEN's live hydrological data (hydrodaten.admin.ch)
  • Persistent heavy rain over hours, saturated soils, already full streams
  • Turbid, fast-flowing water, carried debris, gurgling sewers / backflow
  • Official warnings or road closures

Before · During · After

Before

  • Know your municipality's hazard map
  • Move valuables and electronics out of the cellar
  • Check backflow valves and drains
  • Keep sandbags / sealing material ready

During

  • Do NOT enter cellars and underground car parks any more
  • Switch off the power in exposed rooms
  • Avoid moving water – 20 cm is enough to sweep you off your feet
  • Follow the instructions of the emergency services

After

  • Only return once the authorities give clearance
  • Document the damage before clearing up
  • Heed the municipality's notices on drinking water

This really happened

  1. 2024 Maggia Valley severe weather

    On the night of 30 June 2024 around 200 mm of rain fell in 24 hours in the upper Maggia Valley (TI); floods and debris flows destroyed buildings in Cevio and the Lavizzara and claimed several lives.

    Source

  2. 2024 Misox severe weather

    On 21 June 2024 a debris flow swept away houses and a stretch of the A13 motorway in Lostallo (GR) and claimed several lives.

    Source

  3. 2021 Summer of storms

    Weeks of thunderstorms in July 2021 brought Lake Biel, Lake Thun and Lake Lucerne to the highest danger level; Lake Biel reached a record level, with total damage of around 450 million francs.

    Source

  4. 2005 Once-in-a-century flood

    On 21/22 August 2005 the most expensive natural event in Swiss history claimed 6 lives and caused around 3 billion francs in damage; Bern, Lucerne, Uri, Obwalden and Nidwalden were the worst affected.

    Source

Frequently asked questions

How do I prepare for flooding?

Check your municipality's hazard map to see if your address is in a endangered zone. Move valuables and electronics out of the cellar, check backflow valves and drains and keep sandbags ready.

Why are cellars and underground car parks so dangerous during flooding?

Water rises several metres within minutes. Just a few decimetres of fast-flowing water can sweep a person off their feet. Do not enter cellars, underground car parks and underpasses during flooding.

What should I do after flooding?

Only return when the authorities give clearance. Document the damage before you start clearing up and heed your municipality's notices on drinking water.

Official sources