Most major Australian cities will be far hotter than forecast in coming years, as a lack of vegetation creates “heat islands,” especially in poorer areas, a new report warns.
- Most major cities lost green cover between 2013 and 2020
- “Heat islands” can form in built-up cities that trap warm air
- Temperatures are already set to rise because of climate change
The report, Temperature Check: Greening Australia’s Warming Cities, commissioned by the Australian Conservation Foundation, found green spaces in almost all major cities had declined in the last decade.
The country’s greenest capital, Hobart, was the only city to increase its green cover between 2013 and 2020 — but even then, it was only by 1 per cent.
The report said other capital cities had major work to do to increase vegetation, or avoid becoming almost unbearable in coming decades as climate change raises temperatures worldwide.
“Our research shows increasing urban vegetation will become essential for our three largest cities — Sydney, Melbourne and Brisbane — to reduce serious heatwave impacts by 2060-2080,” said the report’s author, Dr Lucy Richardson from the Monash Climate Change research communication hub.
Dr Richardson highlighted Western Sydney as one urban region at risk of becoming “unliveable”.
“If Western Sydney hits 50 degrees Celsius and then the urban heat island adds another 15 degrees — 65 degrees is not going to be liveable, so we need to act now,” Dr Richardson said.
The report explains in built-up cities, a lack of vegetation creates “‘heat islands” or pockets of warmer temperature, caused by air becoming trapped between buildings and other infrastructure.
Dark materials, including asphalt and steel, also absorb and retain more heat than natural materials.
It can also feel hotter because landscapes devoid of trees may give people fewer places to seek shelter.
The report found that Brisbane was one of the greenest cities with 54 per cent green cover in 2020.
Melbourne was found to be one of the least green cities, with just 23 per cent total tree cover, and Sydney had 34 per cent.
All three cities lost green cover between 2013 and 2020.
But, while the individual declines may not seem like much, the report said in a large city like Sydney, a 0.8 per cent drop could equal around 570 AFL football fields.
Meanwhile, according to a list of local government areas, green cover in the ACT almost halved from 2013 to 2020 to 34 per cent, Darwin has just 33 per cent, Perth 33 and Adelaide 27 per cent.
Poorer areas to suffer most
While warming cities will present a problem for most people, a “heat gap” has emerged between richer and poorer areas, the report said.
Typically, poorer areas have less green space and vegetation than wealthy suburbs.
“The areas which have lower socio-economic status tend to have less vegetation and because of the nature of the structure of the buildings, the layouts and designs of the areas, that’s where they tend to trap a lot more heat,” said Dr Richardson.
For example, the report showed the Blacktown local government area had just 22 per cent vegetation cover.
The city’s extra infrastructure could add a mean of 5.8 degrees Celsius on top of normal temperatures, the report found.
Meanwhile, Sydney’s Northern Beaches has 63 per cent tree cover and could expect its infrastructure to add a mean of just 1.1C.
“In those areas that are economically disadvantaged, they not only get hotter weather, they get the impact of the urban heat island effect that increases their temperature,” said Dr Paul Sinclair from the Australian Conservation Foundation.
“We need to start taking action now to make sure that our cities in the future are going to be liveable safe places for 90 per cent of the population.”
Planting for the future
In Logan City, south of Brisbane, Deputy Mayor John Raven said the local government area was committed to revegetation.
“We’ve been making sure that wherever developers are cutting down trees, they pay an offset to council so that we can revegetate areas that are of high environmental value, or areas historically damaged by farming or other activities, and restore them back to their original environmental values,” Mr Raven said.
But planting new trees to replace those that have been removed for development was not that simple.
“When we talk about revegetation, trying to compare one tree number to another is really fraught, because obviously, if I cut down a 100-year-old tree, that’s got a huge canopy and replace it with two tiny saplings, the community is not going to accept that,” he said.
Mr Raven said that although Logan City was experiencing a boom in affordable housing, it was possible to hold developers to account.
“We hope that other local governments and other cities across Australia will look to us and see the example that we’re setting,” he said.
In Brisbane’s northside, residents are taking matters into their own hands.
Gayle Dallaston has planted her nature strip with native trees and shrubs.
There are rules governing verge gardens and they vary by council, but many allow residents to replace lawns with larger plants.
“A lot of residents don’t know that they can do it, they don’t know that the guidelines are there,” Ms Dallaston said.
“I think we should be using every little bit of spare land that we can for habitat and for cooling the cities.
“Verges are the obvious place at the moment, and most of it is wasted land.”