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Green cities for climate resilience, not air quality

Many cities are taking steps to go green. London has an ambition to plant 3m more trees by 2050, and Vancouver has a target to ensure that all of its residents live within a five-minute walk of a park, greenway or other green space by 2020.

 

Cities with greenery are nicer places to live in. It’s much more pleasant to look out on green than grey.  They can be calming and beneficial for our health.  And, of course, they support biodiversity.  Our own research shows that fewer than half of Londoners think it’s a green city, so there’s still much to do at home.

As well as wellbeing there’s other strong reasons to build green into cities.

Most importantly, green cities are better suited for future climates than bare concrete surfaces.  For example, Central London was 10oC hotter than rural areas in the hot summer of 2003.  Due to climate change cities will become even hotter in the future.  Green measures including planting urban trees have been shown to reduce this effect, both through shading streets and also in cooling the air through transpiration. 

Climate change will also lead to more heavy downpours, causing local flooding and disrupting transport networks. Installing plants and vegetation on roofs and fitting gravel drainage systems can all help to slow the flow in a much more cost effective way than traditional solutions.

The right green spaces, trees and shrubs can also help improve air quality. Academics from the Swedish National Road and Transport Research Institute recently suggested that hedges are good for dealing with poor air quality. However, the level of this issue is too big for just creating green spaces alone. In reality it is much more cost effective to address air quality at its source rather than taking the pollution down.  That means changing how we travel and heat our buildings, by moving to electric vehicles and promoting heat pumps rather than gas boilers. 

At a national level, we need to design infrastructure projects that improve, rather than damage nature (read our paper on the topic and our work here). Back in the city, the largest challenge, which we’re researching over the summer, is to figure out how to retrofit green at scale into cities today; taking lessons from schemes like the RHS’ Barbican project and London’s Pocket parks to scale in every city, in every community and in a cost-effective way. Stay tuned for more on this throughout the summer.

Tom Butterworth is WSP associate director for biodiversity