In the future, it will rain more heavily and more frequently due to climate change. What this means for Switzerland.
In recent days, heavy thunderstorms have led to flooding and inundation in many places. It is not possible to say exactly what influence climate change had on the individual events. But one thing is clear: with climate change, heavy rainfall has increased. And it will become more frequent and more intense in the future.
This is a law of nature, says hydrologist Manuela Brunner. She researches extreme events at ETH Zurich and the WSL Institute for Snow and Avalanche Research in Davos. This is because the warmer the air, the more water the atmosphere can store. And: “The more moisture is stored, the more water can rain down on the land surface in a short period of time.”
The more moisture is stored, the more water can rain down onto the land surface in a short period of time.
This is a law of nature, says Manuela Brunner. The warmer the air, the more water the atmosphere can store. And: “The more moisture is stored, the more water can rain down on the land surface in a short period of time.”
Surface runoff is increasing
And because these heavy rainfall events are increasing, it is also clear that surface runoff is becoming more frequent and more intense, says Manuela Brunner. This refers to rainwater that cannot seep into the ground. It flows off the surface, flooding streets or garages, as is currently the case in Pratteln or Liestal.
Overall, surface runoff now accounts for around half of the damage events, says Josef Eberli. He heads the Hazard Prevention Department at the Federal Office for the Environment (FOEN) and is responsible for natural hazards in Switzerland. He says: “Surface runoff was an issue that we paid little attention to in Switzerland for a long time. We have a lot of catching up to do there.”
It was not until 2018 that the Federal Office for the Environment, together with insurers, created the first Hazard map for the whole of SwitzerlandThis map is now being revised, says Eberli. Climate change will also be taken into account.
Where to put the water?
Then two things actually need to be done: firstly, new buildings need to be built in such a way that no water can penetrate. Secondly, drainage systems need to be adapted, as they are unable to cope with the more intense rainfall. In the future, the extra water could be channeled into troughs or retained in basins, for example. And attempts are being made to allow more water to seep away.
Flood protection is an ongoing task that will never be finished.
There is still a lot to do, says Josef Eberli. Even if we are already well prepared in principle today. “Flood protection is an ongoing task that will never be finished.” The existing protection systems on lakes and rivers must also be adapted to climate change, says Eberli. Because when it rains a lot, river levels can rise locally and that can also lead to flooding.
“When it comes to future scenarios for river floods, the situation is even more uncertain compared to surface runoff,” says hydrologist Manuela Brunner. The reason: flooding on a river or lake does not only depend on precipitation. Soil moisture and snow melt also play a role. Both are also changing with climate change, and this varies from region to region.
Clear statements on the likelihood of flooding in various regions of Switzerland are therefore still lacking. Manuela Brunner says she is currently researching this. Like flood protection itself, this too remains an ongoing task.