SUSTAINABILITY

The threat of flood damage is underestimated

To date, the possible risk of flooding in Switzerland has been underestimated. Areas in which there is only a low risk of flooding are often heavily built-up, so the potential damage to buildings in the event of flooding is much greater overall than previously assumed. This is demonstrated by a new online tool developed at the Mobiliar Lab for Natural Risks at the University of Bern.

Four out of five Swiss municipalities have been affected by flooding in the past 40 years. This resulted not only in inconvenience for the affected population, but also in high costs. Many floodplains are now overbuilt with buildings and infrastructure of all kinds, so adequate protection is needed to prevent major damage.

Holistic view in risk management

This is why detailed hazard maps have been drawn up for the entire settlement area of Switzerland. But these maps only show how often flooding can take place and how intensive it can be. They do not provide information about what exactly is at risk and how high the level of damage would be in a flood. “But this information is central to a holistic view in risk management,” says Margreth Keiler, who until February 2021 was Professor of Geomorphology, Natural Hazards and Risk Research at the University of Bern and co-head of the Mobiliar Lab for Natural Risks at the University of Bern and is now Professor at the University of Innsbruck as well as Director of the Institute for Interdisciplinary Mountain Research (IGF) of the Austrian Academy of Sciences. Because as Keiler says: “A low danger level does not automatically mean low damage.” The cantons and the federal government are also taking this into account and are therefore increasingly drawing up risk overviews.

This video uses municipalities as an example of how the damage simulator can be put into practice.

Damage simulator shows possible extent of damage for each municipality

The Mobiliar Lab for Natural Risks at the University of Bern is supporting these efforts to achieve a holistic view in risk management with the damage simulator launched in June 2020 (www.schadensimulator.ch). For each municipality in Switzerland, this new web tool shows how great the potential extent of damage is in the event of a flood. It can also be used to simulate how the potential extent of damage could change in the future, for example if the existing building zones are built over. The damage simulator is thus an important decision-making aid for public authorities, planners and engineers.

Extensive damage in spite of low danger level

Research by the Mobiliar Lab for Natural Risks based on the damage simulator shows that possible damage in areas in which there is only a low risk of flooding (yellow zones on the hazard map) has been massively underestimated. The reason: Although the damage to an individual building is small, the total amount of damage here is also very high compared to the more vulnerable blue and red zones because the yellow zones are often heavily overbuilt. The yellow danger zone in particular is still often neglected today when it comes to risk reduction. In most cantons no specific anti-flooding measures are required here – unlike in the blue zone – when it comes to conversions or new build.

This video shows the benefits of the damage simulator using the Canton of Graubünden as an example.

Reducing damage with protective measures on buildings

The research carried out with the damage simulator also highlights the impact of the densification of built-up areas on the value of objects exposed to a flood hazard. If we assume that one-third of the available building zone reserves are developed across Switzerland by 2040, the value of buildings at risk could increase by CHF 5.3 billion. If the available building zone reserves across Switzerland were developed in entirety, the value of buildings at risk could increase by CHF 16.6 billion.

This video shows how the damage simulator can help to optimize the protection of existing buildings and new builds.

However, the higher damage caused by an increase in the value of buildings at risk can be limited with appropriate measures. “In view of the possibly high extent of damage, measures would also be important in the case of a low flood risk,” explains Margreth Keiler. What are referred to as property protection measures, for example, could have a great impact at low cost. Such small structural adjustments include raised door thresholds or light wells that prevent water from entering the building. If the possible extent of damage is to be reduced decisively, it will not, however, be sufficient to prescribe property protection measures for new buildings only, Keiler stresses: “Then it is imperative that they are also implemented on existing buildings.”