How can nature help tackle the Urban Heat Island Effect?

Trees help lower ambient temperatures in cities, and provide other benefits besides. Photo by Jessica Sysnegrath on Unsplash.

Extreme heat events in Australia have caused more fatalities since 1900 than all other natural hazards combined.

Given the long history of hot weather in this country, we should be better prepared to tackle the threat of heat stress to public health and to our precious local wildlife, especially as future climate scenarios show summer heatwaves and winter warm spells will become longer, hotter and more frequent.

This is especially challenging news for Australians living in cities and suburbs, where the increasing frequency and severity of extreme heat events will only amplify the Urban Heat Island Effect.

Elderly people, children and those living on lower incomes or on the streets are especially at risk from rising temperatures in urban areas, because they are more vulnerable to heat-related stress and illness or less likely to use air-conditioning due to financial worries.

However, there are some simple and effective nature-based solutions for cooling our cities that deliver heaps of other benefits besides.

What is the urban heat island effect?

The ‘Urban Heat Island Effect’ is the established term for a phenomenon you’ve probably noticed yourself – cities and urban areas tend to be several degrees hotter than country areas. This localised warming is due to the large amounts of paved and dark-coloured surfaces like roads, roofs and car parks in our cities and urban areas.

These hard surfaces absorb the sun’s heat, causing the surface and ambient temperatures to rise. The hard surfaces also retain heat longer, meaning our cities can’t cool down at night.

The Urban Heat Island Effect becomes increasingly apparent with local population growth, as suburbs transition to having more paved surfaces and buildings per block than backyards and open green spaces.

What can nature in cities do about the Urban Heat Island Effect?

Tree planting is a simple and effective nature-based solution for cooling our cities. Trees in cities have many known benefits, including reduction of air temperature, glare and UV radiation. Street trees and other green infrastructure like parks, verges, green roofs and walls help by absorbing sunlight and shading hard surfaces, reducing the amount of heat that’s absorbed and released.

The trees, shrubs and grasses we plant are also natural cooling mechanisms – plants draw soil moisture up into their leaves, which then evaporates from the surface of the leaves and cools the air, much like an evaporative air conditioner. The Urban Heat Island Effect is reduced in suburbs that have good canopy cover and bigger backyards.

If our cities and urban areas are naturally cooler, then we don’t need to spend as much money and energy on running air-conditioners, which benefits our budgets, reduces our carbon footprint, and helps protect our most vulnerable citizens as well.

Besides tackling heat stress, planting more native vegetation in cities comes with lots of bonusses, like greater urban tree canopy cover and food resources for wildlife, better water quality in our urban rivers, green corridors that store carbon, and spaces that people want to spend time in as well.

We can go even further and say that greener cities promote better social connections. One study found there are always more people in the greener spaces, and larger groups of people interacting with one another. By drawing residents into spaces outside their homes, vegetation can promote interactions between neighbours, creating community ties.

By bringing nature back into cities and urban areas, we create places that are cooler, greener, friendlier and healthier for us to live.

How does Greening Australia’s work help combat the Urban Heat Island Effect?

Aside from our long-term goal to tackle climate change through our large-scale tree-planting projects, Greening Australia has short-term nature-based solutions as well.

Through our Nature in Cities program, we are strategically planting trees and other vegetation in built-up areas, to not only create habitat for animals but also to cool neighbourhoods suffering from the Urban Heat Island effect.

For example, through Our Park, Our Place, we are working on Noongar country with four of Perth’s lowest-canopy council areas to regenerate some local parks and to empower local residents to cool their neighbourhoods by restoring canopy cover and native vegetation plantings.

Through our Adelaide Green Cities project, we have been working with partners to engage local communities in practical demonstrations of how plants can help create a carbon neutral city. As part of this, the community has been helping restore the River Torrens/Karrawirra Parri corridor, with thousands of seedlings planted along the riverbanks to capture carbon, improve biodiversity, create new habitat and enhance water quality.

Also, through our Cooling the Schools project, we are working with schools and their communities to add plants to public parks and playgrounds across Sydney, prioritised by their vulnerability to the Urban Heat Island Effect. This will not only help cool neighbourhoods, but will also help provide connected habitat across the urban landscape for wildlife. We’ll also be reconnecting kids with nature and hopefully creating future environmental stewards.

For more information about any of these projects, please feel free to send us an online query.

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