Damage caused by floods, debris flows, landslides and fall processes
Floods, debris flows, landslides and fall processes can cause significant damage. The extent of the damage is influenced by the use of built-up area and the intensity and spatial extent of the natural hazard events. Hence it also depends on the measures taken to protect human life, the environment and material assets. The amount of losses associated with such events is an indicator of, first, the success of the preventive measures implemented to protect against natural hazards and, second, the vulnerability of buildings and infrastructure.
Between 1972 and 2022, floods and debris flows caused damage to the tune of around CHF 14.3 billion. The damage caused by landslides and fall processes totalled at 1.2 billion. Hence, the total cost of damage arising from these natural events was CHF 15.5; this corresponds to an average annual cost of CHF 304 million.
The amount of losses is primarily dictated by individual hazard events. For example, the floods of August 2005 alone generated damage totalling around CHF 3.2 billion (adjusted for inflation). Half of the damage is accounted for by the five biggest individual hazard events.
According to nationally available data, approximately 1.8 million people, that is around 20 percent of the Swiss population, live in areas at risk from flooding. Approximately 1.7 million or 30 percent of the country’s jobs are also located in such areas and around 25 percent of material assets (total approximately CHF 840 billion) can be found in potential flood areas. A large proportion of economic value creation also takes place there. The existing protective infrastructure protects these areas against frequent flood events. Without this protective infrastructure, losses would be significantly higher.
Damage can be prevented or limited if the the hazards are known. Therefore the compilation of hazard maps, their continuous updating and their consistent implementation are matters of extreme urgency. Hazard potential can be limited through hazard-appropriate land-use. Buildings and infrastructure must be designed in a way that avoids major damage. Preventive measures (e.g. hazard prevention structures) must be designed in a robust way which ensures that they withstand excess loads and are able to be adapted to new conditions (climate change). The residual risks must be limited through comprehensive emergency planning and optimised warning and alerting systems.
Absolute safety in dealing with natural hazards is impossible to achieve. The analysis of major flood events, in particular the OWARNA project, have shown that consistent implementation of modern flood protection strategies and improved alerting and alarm systems would enable the avoidance of up to 20% of the damage. For this reason the indicator state is evaluated as medium. The development is not evaluated as the strong annual fluctuations and relatively short monitoring period do not allow clear conclusions to be drawn.
As mandated by the Federal Office for the Environment, the Swiss Federal Institute of Forest, Snow and Landscape Research WSL has been collecting data systematically on storm damage in Switzerland since 1972. The hazard processes floods, debris flows, landslides and rockfall (since 2002) are surveyed. The surveys are mainly based on reports from approximately 3,000 Swiss newspapers and magazines and – in the case of extensive hazard events – the information provided by the cantons and insurance companies.
 According to the study “Die volkswirtschaftliche Bedeutung der Immobilienwirtschaft der Schweiz “ (“The economic significance of the property market in Switzerland”) (Staub P., Rütter H., 2014), the construction value of Switzerland’s buildings is CHF 3,355 billion.