1. Built environment
September 27, 2017updated 02 Aug 2021 2:02pm

Berlin offers a model for how cities can cope with increasingly regular extreme floods

By Jack May

We’ve become accustomed to quasi-apocalyptic images of cities swapping streets for rivers.

Typhoon Hato led to deluges in Hong Kong and Macau, causing £757m and £1.1bn worth of damage, respectively. Hurricanes Irma, Maria, and Jose battered the Carribbean and the south-easternmost states of the United States, while Hurricane Harvey was devastating to coastal areas of Texas.

Houston, Havana, Roseau, Miami, San Juan, St John’s – the list of cities overcome by water and wind this year is a long one.

Even aside from such dramatic events, abnormal rainfalls have caused extraordinary floods in several cities across the world.

Mumbai and Dhaka were just two cities caught up in the vast flooding across India, Nepal, and Bangladesh, which killed at least 1,200 people and put one-third of Bangladesh underwater.

Cities across central and southern China – from Chongqing to Changsha, down into Duyun and Jiangxi province – saw serious flooding, with more than 18,000 homes destroyed.

Content from our partners
The key role of heat network integration in creating one of London’s most sustainable buildings
The role of green bonds in financing the urban energy transition
The need to grow London's EV infrastructure at speed and scale

Flooding in Mumbai in August 2017. Image: News Measurements Network Live.

In Quebec in Canada, nearly 2,500 homes were flooded across Montreal and Laval, while Paris, Berlin, and parts of Switzerland have all spent time partially underwater recently. Images from the French capital, where water gushed and danced down the steps into metro stations, were particularly striking.

One neighbourhood in Berlin is trying to ensure that cities can become better-adapted to the increasing likelihood of extraordinary wet weather events.

The theory rests on the logical foundation that cities are inherently unnatural. By smothering the earth in concrete and tarmac and loading it up with vast structures of brick, steel, and glass, cities interfere with the way nature regulates itself.

The concentration of buildings, people, and activity increases temperatures – while tarmac and concrete surfaces naturally absorb, retain, and emit heat, only pushing the mercury higher.

On the aquatic side of the equation, unnatural, man-built road and pavement surfaces stop any falling water absorbing into the ground and then naturally providing moisture for soil and vegetation during dryer periods, while also evaporating to provide a kind of natural air conditioning.

The area of Rummelsburg in the city’s east, was built 20 years ago and serves as an exemplary model of the ‘Sponge City’ concept – ‘Stadtschwamm’ in German.

Rummelsberg, from ground level. Image: Lotse.

Buildings are wrapped in green walls, roofs, and garden terraces, with thick tranches of soil up to 80cm deep, while roadside trenches between pavements and streets create a miniature urban wetland, which can retain water and both feed it into the water table and evaporate it to keep the city cool.

During heavy rainfall, the thick layers of greenery handle the water better than the conventional concrete-and-drainage system. There’s less likelihood of drains overflowing because they’re blocked or merely overwhelmed, and pavements are less likely to be transformed into temporary white water rafting courses.

The system is also better for water quality in lakes and rivers. During extreme weather events, the grit and grime of urban living can be swept straight into these bodies of water, where unnatural substances can harm animals and plants, and natural materials like pollen and leaves can overwhelm marine life by giving them too many nutrients in one go.

While it’s a great idea, of course, it can be hard to put into practice. While many cities – London included – are on a splurge of building new developments that often conform to higher eco-friendly standards (and could be encouraged, or mandated, to conform to ‘Sponge City’ design benchmarks), the vast bulk of prohibitive surfaces have already been built.

The cities of the UK, for example, already have their streets, pavements, tiled and concrete roofs – so retrofitting is the order of the day. This can be more expensive, more difficult, and can be tricky to incentivise. And while there could be profiteering enticements – a building with an accessible green roof is likely to be more interesting and appealing to buyers and renters, and public or commercial buildings could grow produce in these spaces – it’s unclear whether that will be a significant enough boon.

Nonetheless, as extreme weather events become less out of the ordinary, adapting our greatest centres of population to better accommodate the demands of nature seems like common sense – even if it does mean boggy pavements.

Jack May is a regular contributor to CityMetric and tweets as @JackO_May.

Want more of this stuff? Follow CityMetric on Twitter or Facebook.

This article is from the CityMetric archive: some formatting and images may not be present.
Topics in this article :
Websites in our network