China’s response to the encroachment of its northern deserts on cities such as Beijing is a tree-planting exercise, the Three-North Shelterbelt. But while the so-called Green Great Wall is one of the world’s most ambitious environmental projects, it is just one of many attempts to protect cities against pollution, storms and temperature rises by tapping into a valuable resource: nature.
It has long been known greenery improves air quality, which is why large urban parks, such as the Maidan in Kolkata, India, or New York’s Central Park, are often referred to as the “lungs of the city”. But as pollution and increasingly intense storms threaten urban areas, planners are starting to recognise that nature has more than one purpose.
So-called “green infrastructure” can be used to soak up water that can otherwise inundate municipal areas. When superstorm Sandy hit New York and New Jersey late in 2012, for example, storm water flowed through subway tunnels and shut down ground-level power and communications networks.
“The frequency, unpredictability and intensity of storms is overwhelming a lot of conventional systems,” says Jason Scott, co-managing partner at Encourage Capital, an asset management firm specialising in investments that can help to resolve social and environmental problems.
Severe rainstorms are responsible for sending large amounts of untreated water — containing everything from motor oil and lawn fertiliser to raw sewage — into drinking water systems and open waterways.
“In places like Milwaukee and Chicago, storm water is combining with sewer overflow and going in people’s homes, so it’s not a theoretical problem — it’s very real,” says Mr Scott.
Green infrastructure — such as grass roofs, planters and permeable pavements that allow water to filter the soil below them and soak up storm water — can help prevent this. “The idea behind the green infrastructure approach is to mimic the way nature handles water,” says Larry Levine, senior attorney in the water programme at the Natural Resources Defence Council, a US environmental group.
Nature can improve cities’ air quality. In Ahmedabad, the Indian state of Gujarat’s largest city, where summer temperatures can be above 40C, a development plan includes linking the city’s Sabarmati River with lakes, building a series of parks and planting trees.
Such schemes can help to control summer temperatures, says Ian Mell, lecturer in planning and civic design at Liverpool university. “They’re using trees and better management of the lakes and river to moderate the extremities of the climate,” he says.
Other natural assets can be tapped, too. “In some parts of the world, mangroves are tremendous at flood protection and preventing soil erosion,” says Mr Levine. “Green infrastructure of that sort is very much part of the toolkit for climate change adaptation.”
But while green infrastructure does much to tackle flooding, air pollution and inhospitable city temperatures, it can be hard to persuade developers and investors it is worth the extra money.
“It’s about learning how to understand the upfront costs and how they translate to benefits over time,” says Eric Mackres, building efficiency manager at the World Resources Institute’s Ross Center for Sustainable Cities.
This is a particular difficulty in growing economies, where the race to develop means that urban centres are being built at terrific speed, often without sufficient planning. “The scale of development means climate change gets addressed later,” says Mr Mell.
Some older cities are creating financial incentives for developers to go green. In Washington DC, for example, regulations have been introduced that make it mandatory for buildings in certain areas to include green infrastructure. The city has introduced a stormwater retention credits trading scheme for developments where this is not technically feasible.
Credits, which are traded in an open market, can be bought from developers operating in parts of the city not covered by the regulations but who have nonetheless invested in sustainable projects.
Mr Scott believes that more of these kinds of innovative financial arrangements will be needed to increase the adoption of urban green infrastructure. “A lot of the solutions are financing solutions because the capital markets don’t know how to value these projects,” he says.