The Sponge City: A city which can deal with rainwater and heat
Cities are concrete, glass and steel – they look and act unnaturally – absorbing heat and repelling water. The urban areas are at odds with nature though. But, in parts of the German capital things are different. To deal with rainwater and heat, Berlin is being transformed into what is called The Sponge City. The basic idea of ‘Sponge City’ is to keep the rainwater in the city. When water evaporates, the city is cooled accordingly. Carlo Becker is the architect of Berlin’s Sponge City Strategy which harnesses rainwater and manages heat. For us, the rainwater is a resource which shouldn’t be carried away anymore but has to remain in the city.
In a natural ecosystem, rainwater is soaked up by soil and vegetation, the majority then evaporates and the rest filters deeper into the ground. The evaporating waters then cool the surroundings. Cities disrupt this system. Water gets piped away as it can’t be soaked through the concrete. The Sponge City Strategy aims to keep rainwater where it lands, to imitate the natural water cycle. Buildings are covered in green roofs and facades. And down on street-level, urban wetlands and road-side trenches – known as Swales – filter run-offs and hold water, keeping the city cool by imitating nature.
In East Berlin, a city named Rummelsburg built 20 years ago is a large scale example of the Sponge City Concept. On the top, there is the extensive green roof of approximately 6-8 centimetres and from there the water flows into these courtyards here in the middle, and underneath there is a garage. On top of the underground garage, there is a soil layer of almost 80 cm. It is like a sponge and it soaks the water during heavy rainfall and then, it is used by the plants. Thus, they take all the water and finally evaporate it.
Heiko Sieker is the brains behind the neighbourhood’s innovative management of stormwater. In the neighbourhood area, there is no storm sewer system, so no conventional pipe system has been made. The water flows from the road surface into the swales and from here it is infiltrating into the round. On summer days, you can really feel the coolness here, it is much cooler compared to other parts of the city because of the evaporation. Rummelsburg is just one example of the Sponge City. Neighbourhoods across Berlin have implemented similar initiatives. But Berlin isn’t a perfect Sponge City. In the middle of summer 2017, the heaviest rain in the century hit the city, submerging parts under water and warning how much work there is still to do. The climate adaptation measures are essentially known, they just have to be implemented. In fact, the city council has recently decided all new developments should manage stormwater on site, in the spirit of Sponge City. Climate change is forcing Berlin and many other cities around the world to adapt to urban environments transforming them to work with nature, not against it.