A collective reminder for forgetful Switzerland

28 May 2018

At the OCCR, the Mobiliar Lab for Natural Risks aims to better inform authorities and the public about the risks associated with flooding. For this reason, it’s creating an interactive online database of images illustrating floods: the “Collective Flood Memory”.

Every seventh building in Switzerland is at risk of flooding, and four out of five Swiss communities have been affected by floods within the past 40 years. Although floods can cause serious damage to those directly affected, most people tend to forget them rather quickly. Within a few years, they fade from the population’s consciousness.

This is set to change with the recent launch of the Collective Flood Memory project at the OCCR’s Mobiliar Lab for Natural Risks. The project website publishes flood photos from all over Switzerland. The collection should continue to grow with the help of the general public, which is called upon to submit its own pictures on the interactive website.

“This project has several goals,” explains OCCR member Rolf Weingartner, Professor of Hydrology and Co-Director of the Mobiliar Lab. “On the one hand we want to remind people of flood risks, and on the other, flood patterns are an important source of information for experts and authorities when assessing dangers.” Existing hazard assessment tools, such as risk maps, are too abstract and hard to understand for non-specialists, according to Weingartner. Photos are much more helpful for people trying to imagine the effects of flooding.

Major damage, poor memory

On the web platform www.ueberschwemmungsgedaechtnis.ch, visitors can search locations and dates for images of flooding. Currently, it dates back to the year 1529. One of the oldest pictures in the flood memory bank so far is an engraving that shows how the Arve overflowed its bank in Carouge near Geneva in the night between September 14th and 15th in 1733. Among other things, the river tore down a bridge and washed it away. From a historical point of view, two depictions of Küsnacht on Lake Zurich are also interesting. Both show the devastating damage the village stream caused on July 8, 1778 – and again exactly 100 years to the day later. Much more recent are the photos from September 1, 2005, of Lütschental in the Bernese Oberland. Among other things, they show how the railway line to Grindelwald was destroyed by the Lütschine, which had overflowed its banks. The heavy precipitation at the end of August 2005 led to large floods in many parts of Switzerland. That year’s flooding resulted in the largest total financial loss caused by a single natural disaster in Switzerland in recent decades: around three billion Swiss francs. But in the public consciousness, this major event is gradually being forgotten.

In addition to reminding the population of the hazards posed by flooding, the Collective Flood Memory is also meant to provide a basis for decision-making when it comes to flood prevention. “Flood photos can help make local decision-makers aware of protective measures – like at a town meeting where people need to vote on a protection project,” says hydrology professor Rolf Weingartner. Science can also benefit from the database. For example, flood patterns can be used to validate hydrological models, ultimately leading to better simulations of flood events and more accurate risk assessments.

Collecting scientific data with the public’s help

The images already available at www.ueberschwemmungsgedaechtnis.ch came from historical archives and administrative offices. But this photo collection can only reach its full potential if it includes a large number of pictures from all over Switzerland. Therefore the Mobiliar Lab for Natural Risks is relying on the support of the general public, and heartily invites everyone to upload their own flood photos onto the new web platform.

The Mobiliar Lab already has some experience with crowdsourcing data. Thanks to its cooperation with the Federal Office of Meteorology and Climatology, MeteoSwiss, the public can report hail via the MeteoSwiss app. Since its launch in 2015, more than 50,000 observations have been recorded, and they are now being evaluated scientifically. Among other things, this research is about improving hail warnings.