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Deciphering Floods: Event analysis

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We develop models to predict floods. It is difficult, however, to predict such events with high accuracy. Analysis of past storms points to necessary improvements in our models and thus helps to make predictions more precise.


The flood event in August 2005 cost 6 people their lives in Switzerland. Flooding, erosion, overbank deposition, landslides and debris flows caused damages amounting to a total of 3 billion CHF – a sum unparalleled in the past three decades.

Another extreme situation was the avalanche winter 1999 (Link SLF). Switzerland experienced about 1200 avalanches causing damages. In the alps, many roads were blocked and entire valley cut off. Hundred thousand of tourists were affected. The direct and indirect damages amounted to over 600 million CHF.

Turning catastrophes into opportunities

Such extreme events offer a good opportunity to thoroughly investigate extraordinary natural disasters. For many years, we at WSL and SLF have been creating event analyses after floods or avalanches, usually on behalf of and in cooperation with the FOEN. This not only serves to understand natural processes but also review how well the hazard data and documentationserved and how they were put into action. How well did preventive measures work, how efficient were predictions, warnings and alerts of the crisis management?

This type of analysis we call integral risk management. It follows several steps: Risks are monitored, their acceptability is evaluated  and then precautions are taken against risks considered inacceptable (risk management – Link SLF). Event analysis’ lead to a better understanding of the processes and the effectiveness of various measures and thus forms a central basis for future protective measures in Switzerland.