Sponges, urban forests & air corridors How nature can cool cities


Thirty pilot cities in China are trying to trap and hold more water to deal with problems from flooding and drought to extreme heat and pollution.

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LONDON: As China battles the twin challenges of rapid city growth and extreme weather, it is adopting a new tactic: Turning its cities into giant sponges. Thirty pilot cities in the country are trying to trap and hold more water to deal with problems from flooding and drought to extreme heat and pollution. The effort, launched by Chinese President Xi Jinping, relies on a range of innovations, from green roofs on buildings to more urban wetlands. It is already being hailed as a bold step to solve some of the environmental problems plaguing the world’s most populous country.” It’s a timely reminder that dealing with urban climate challenges requires a holistic approach,” said Sunandan Tiwari, a sustainable urban development expert at ICLEI – Local Governments for Sustainability, a global network of 1,500 cities, towns and regions.

People and water

Rapid urbanisationand extreme weather, such as severe floods, water shortages and heatwaves problems can leave more people at risk – but the sponge city effort, launched in 2015, aims to reduce the threats.The pilot cities have been charged with finding ways to absorb, store, filter and purify rainwater, retain it within their boundaries, and release it for reuse when needed instead of channelling it away through sewers and tunnels. The cities, including the capital Beijing, Shenzhen and Shanghai, receive funds and practical help to redesign their urban areas in a water-sensitive way, with the aim of turning 80 percent of China’s urban areas into sponges by 2030. Flood control and water conservation, among other issues, are at the heart of the ambitious push.

“Cooling is largely seen as a co-benefit of sponge cities. But with record temperatures in China and many parts of the world, it is becoming a key element in planning for climate-resilient cities,” said Boping Chen, China director at the Hamburg-based World Future Council, a think tank.

Getting hotter

Shanghai, China’s most populous city with 24 million people, baked under a record high temperature of 40.9 degrees Celsius last July even as southern China was hit by torrential rain and floods.

The govt has allocated each pilot city between 400 million yuan and 600 million yuan ($60 million to $90 million) each year for three consecutive years, and cities are encouraged to raise matching funds through public-private partnerships and other financial ventures, according to a 2017 study in the journal Water.

Forest cities

Boeri, who made headlines when he covered two residential tower blocks in Milan with 800 trees, 4,500 shrubs and 15,000 other plants, has won planning approval to build a forest city in Liuzhou in southern China. Conceived as a green metropolis, the city will house 30,000 people and all its buildings will be covered entirely with plants and trees, said Boeri, who declined to give a cost estimate for the project.

In total, Liuzhou’s forest city aims to host 40,000 trees and almost one million plants from more than 100 species, planted over buildings to improve air quality, decrease temperatures and contribute to biodiversity, Boeri said.

The city is expected to absorb almost 10,000 tons of carbon dioxide – the equivalent emissions of 2,000 passenger cars driven for a year – and 57 tons of pollutants per year. The greenery will also produce some 900 tons of o2 every year, Boeri said.

(With inputs from Thomson Reuters Foundation)