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Understanding and forecasting floods

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In Switzerland, flooding causes damages costing over CHF 300 million on average per year. To keep this damage (and the costs) to a minimum, we need hazard maps, forecasts, protective structures and optimally coordinated responses to emergencies. We have been developing the scientific basis for this for over a century.


In Switzerland, flooding is the natural hazard which causes the greatest material damage: following the floods of August 2005, the total costs to the repair the damage amounted to around CHF 3 billion – considerably more than for any previous natural event, all of which have been systematically recorded since 1972.

The aim of risk management is to avoid damage by not building in at-risk areas and providing more open space around waterways. If these measures are not sufficient, new protective structures are built. This requires hazard maps. The data and methodology for these maps are provided by our research.

For example, we have been studying steep mountain streams for more than 40 years. Using measuring systems which we developed in house, we can determine water flows, bedload volumes and snowpack in Alptal (Schwyz). Virtually no other mountain torrent in the world has been surveyed as thoroughly as this one.

Flood forecasting

Within the Hydrological Forecasts group, we develop computer models and operational alarm systems for flood warning purposes. One of our main tasks is to analyse current events. Another is to use years' worth of measurement data from our flood and landslide damage database to, for example, improve hydrological forecasts using simulations and statistics.

Snowmelt can play a significant role in causing flooding. At the WSL Institute for Snow and Avalanche Research SLF, we run an operational snow-hydrological service (OSHD). This analyses where and how much snow there is in Switzerland, and how much of it will melt. This enables to lower water levels in reservoirs in good time in order to prevent flooding.

Sihl flooding: early warning system for Zurich

If we enter data such as current discharge rates or satellite snow maps into our models, we are able to identify flooding in good time. We have been running this type of early warning flood detection system since September 2008 for the city of Zurich and the Sihl valley (IFKIS-Sihl). The system improves the safety of the city and of Zurich's main train station. This was especially crucial during the construction works at Löwenstrasse station from 2008 to April 2011.



Swiss flood and landslide damage database

Since 1972 we have been systematically collecting and analysing the damage caused by storms in a damage database on behalf of the FOEN.

WSL database for deaths due to natural hazards

The database encompasses deaths caused by naturally occurring natural hazard processes for the years since 1946.


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