Roland Müller in conversation with Julius Stucke

An element of the sponge city is also implemented at the Institute of Physics of the HU Berlin: the green facades. (picture alliance / dpa-Zentralbild / Britta Pedersen)

Cities that temporarily store rainwater for dry periods: The sponge city concept aims to mitigate the effects of climate change, especially through green roofs. But measures are not enough against the water masses of extreme storms.

A city that absorbs water like a sponge: The concept of the sponge city is an idea for adapting cities to climate change. Roland Müller from the Helmholtz Center for Environmental Research heads the Leipziger BlauGrün research project, in which the Sponge City is carried out in a district of Leipzig.

The concept is to make cities able to store water when there is plenty of water so that water is available when it is urgent, Müller explains: for example, to irrigate urban greenery or trees in the middle of summer. In some areas this is associated with drought conditions in which water is urgently needed.

Wuppertal, which was hit by flooding in West Germany, is now on its way to becoming a sponge town. This is a welcome initiative, says Müller, but stresses that a sponge city cannot sufficiently limit the consequences of extreme storms like the ones we have experienced in Germany in recent days: “A sponge city cannot handle this amount of water to save. ”In order to process such amounts, considerable structural engineering measures are required.

Green roofs, better microclimate

However, cities can be better prepared for the consequences of climate change and its negative effects can be weakened, explains the expert. As an example, he cites an element of the sponge city that is now being implemented in Leipzig: green roofs. These are available in different designs and, in addition to better water management, also have other positive effects:

“These green roofs can store water, for example, and also divert it specifically to other storage basins. They have an aesthetic function, evaporate water and contribute to the microclimate and insulate houses”, explains Müller.

In addition to the green roof, there is also a range of technologies to turn cities into sponges, for example by unsealing existing seals. The interior courtyard of a building can also be designed in such a way that rainwater can enter the water table.

More safety, more quality of life

It is easier to implement the concept of a sponge city in new neighborhoods. But it is also possible to create sponge cities in existing buildings. In existing neighborhoods, you must communicate directly with residents and explain to them why a measure is positive for them:

“Ultimately, the measures should serve to ensure safety, but also to improve the quality of life. A green city is much more attractive to its inhabitants.