Our cities are getting hotter, more crowded and noisier. Climate change is bringing more heatwaves, placing pressure on human health, urban amenity, productivity and infrastructure. Urban residents naturally want to stay cool. Air conditioning is the usual choice, but it can be expensive to run. Air conditioning also adds carbon pollution, creates noise and can make outdoor spaces hotter. So what else can we do to manage increasing urban heat? And who has the ability to act? Urban planners are increasingly involved in developing and delivering urban greening strategies. While it seems like a “no brainer” to green cities, our international researchshows that planners are not always comfortable with this idea. However, green infrastructure – including street trees, green roofs, vegetated surfaces and green walls – is emerging as a viable way to help cities adapt to increased heat. Uptake of these technologies is slowly increasing in many cities around the world.
Green walls cooling a building in Singapore. Image: Tony Matthews.The Australian government has recognised this trend. An agenda to green Australia’s citiesis now in place. Stated aims include managing climate change impacts, reducing urban heat, improving urban well-being and increasing environmental performance. This urban greening agenda is part of the Clean Air &Urban Landscapes hub, under the National Environmental Science Program.
Benefits of urban greeningThe broadening appeal of green infrastructure is helped by the fact it offers multiple benefits. For example, shading from strategically placed street trees can lower surrounding temperatures by up to 6℃, or up to 20℃ over roads. Green roofs and walls can naturally cool buildings, substantially lowering demand for air conditioning. Green infrastructure can also provide habitat for wildlife, recreational opportunities for people, better management of stormwater runoff and improved urban aesthetics.
Street trees and green walls helping to reduce urban temperatures. Image: Tony Matthews.Hard surfacing, including concrete, asphalt and stone, is common in cities. It can increase urban temperatures by absorbing heat and radiating it back into the air. Green infrastructure can minimise this difficulty, as it better regulates ambient air temperatures. Foliage allows local cooling through evapotranspiration, where plants release water vapour into the surrounding atmosphere.