Our deathtrap sizzling suburbs revealed
VAST tracts of Australia's major cities are unnecessarily overheating leading to a potential health crisis for residents.
New research has found otherwise identical suburbs, and even streets lying side-by-side, are not sharing the heat load equally. Some are sweltering with surface heat temperatures up to 20C higher than the neighbourhood next door.
The worst affected areas include parts of Melbourne and Adelaide.
All too often it's poorer outer suburbs that end up far hotter than inner city enclaves.
And while one seemingly simple solution could cool down our streets, bureaucratic red tape and risk-averse councils are shunning the idea.
The analysis comes from 202020 Vision, a national initiative that includes state and local governments, universities and business, which aims to increase urban green spaces by 20 per cent by 2020.
It has said tree cover on suburban streets has declined by 35 per cent in eight years. Fewer trees mean less shade and less shade means hotter streets. That can have a negative effect on everything from anti-social behaviour to health.
"If heat continues to rise it can have profound concerns about health impacts," Griffith University urban and environmental planner Dr Tony Matthews told news.com.au.
"The concern is that in the future that heat will get more extreme and the heat stress will hit people a lot harder.
"And heat stress can be deadly; it's nothing to be sniffed at."
This week Sydney has sweltered through a heatwave that has lasted for more than 10 days while Melbourne has seen a "one-in-10-year heat event" as temperatures soared past 40C in the CBD.
202020 Vision has compiled a heat vulnerability index looking at each state as well all local government areas (LGA) to assess the total number of hot days, the ability of the local population to remain healthy in the heat and the extent of green space.
AUSTRALIA'S MOST HEAT-VULNERABLE SUBURBS
Nine LGAs were found to be Australia's most vulnerable to heat stress: Hume, Darebin and the city of Ballarat in Victoria; Gawler, Port Adelaide Enfield, West Torrens, Playford and Charles Sturt in South Australia and Belmont in Perth.
Large chunks of Sydney only just escaped being in the most heat-vulnerable category. Rockdale, Holroyd, Canterbury, Botany Bay and Blacktown all scored poorly for heat stress.
Launceston was the most heat-vulnerable council in Tasmania. Logan, Ipswich and Toowoomba took out the dubious honours in Queensland.
Most cities contain "urban heat islands" (UHI) where the surface and air temperatures can rise substantially higher than other areas and stay hotter for longer due to human impact.
"The main reason cities suffer from the UHI effect is because they are constructed from steel, concrete and aggregate that absorb heat. At a hot time of year, the extent of that is exaggerated as the materials release heat back into environment," Dr Matthews said.
Airports, with their large runways and terminals, are often UHIs.
Vehicles and airconditioners further pump up the temperature, tipping the scales from bearable to blistering.
URBAN HEAT CONTINENTS
Worse though, some cities now contained substantial "urban heat continents" where UHIs had joined together. In Sydney, a huge heat continent now stretches in three directions with Parramatta at its centre and bordered by Botany Bay, Liverpool and the Hills District.
Melbourne has a heat continent that surrounds Sunbury and Melton in the west.
Dr Matthews said that above 42C a "tolerability threshold" is reached where infrastructure, like train tracks, begins to potentially facture and melt. And people don't fare particularly well either.
"Overall, Sydney is quite green as are Melbourne and Brisbane. Perth and Adelaide are not that green while the Gold Coast and a lot of regional cities are playing catch-up," Dr Matthews said.
The report found tree and shrub canopy cover nationally had reduced by 2.1 per cent in four years, the equivalent of 162,000 Melbourne Cricket Grounds.
Over eight years, 35 per cent of councils has seen a "significant decline" in canopy with only four per cent seeing a notable increase in foliage.
In 2017, climate scientist Dr Elizabeth Hanna said a combination of heat and humidity could mean Darwin is "not a viable place to live" in the future. There the council is busily attempting to bring down surface temperatures by reducing hard spaces and shade streets.
POSHEST SUBURBS THE COOLEST
The least heat-stressed LGAs were often those in the ritziest areas including Woollahra, Mosman and Kuring-Gai in Sydney, Bayside in Melbourne and Claremont in Perth.
Posher 'burbs were often closer to the coast where sea breezes helped cool the locals. But Dr Matthews said that wasn't the only reason.
"There's also often a correlation of how well-off suburbs are and how much greenery they have. People with a bit of money tend to live in suburbs that are well established with mature greenery.
"A lot of newly developed suburbs on the urban fringe have low levels of greenery because lot sizes have been reduced so you get lots of houses, very few gardens and nature strips are given over to street parking. These newer suburbs tend to be much hotter."
Urban greening could be more trees on streets but also green roofs, parks and plantings on the side of buildings.
Parramatta, in Sydney's west, is at the centre of a heat continent that spreads out in three directions.
The city council has an aim to increase street tree cover from 33 per cent to 40 per cent by 2050. It shared with news.com.au thermal images taken after a string of consecutive hot days of two parallel streets, one with trees and the other without.
"The thermal images show that the heavily treed street has much lower day and night temperatures. This in turn reduces the nearby air temperature, making the street a more pleasant place to walk along," a council spokesman said.
Parramatta city chiefs reckon the shade provided by trees could be enough to bring surface temperatures down by as much as 20 degrees while air temperatures could reduce by between two and five degrees.
ROADBLOCKS TO GREENER STREETS
The report said councils including the City of Sydney and Blacktown in NSW, Yarra in Melbourne, Townsville in Queensland and Armadale in Western Australia were seeing the biggest canopy increases.
But many councils, and property owners, are frustrating efforts to make our suburbs greener and cooler, Dr Matthews said.
"There is the fear of liability by councils of, for instance, underground tree roots or if tree branches fall."
More trees could also lead to more wildlife and human conflicts, such as possums on roofs and birds pooing on cars. But he said these were "pretty minor" concerns compared to the overall benefits. And hardier species could lessen the likelihood of branches falling.
GREENER STREETS, LESS CRIME
Urban greening wasn't just about cooler streets, Dr Matthews said. Soil can help soak up torrential rain taking pressure of stormwater drains. More vegetation and parks can improve the mental health of locals and encourage exercise. Even crime can go down, he said.
"You would think the opposite would happen as trees limit sight lines but there is strong research that suggests more greenery has the effect of bringing down crime levels as it prompts people to behave a little bit better.
"Let's not say trees are the solution to crime, but more evident urban greenery can have a positive effect."
But a key benefit remains taking the edge of the heat. However, can trees really help mitigate the effects of rising temperatures?
"If the world is 30C hotter by 2100, a few trees won't be much help, but if the global temperature rise in 100 years is only 1C hotter that's still significant but those consequences might be kept in check by urban greenery," said Dr Matthews.
"And that's the thing: Do you do nothing or try and do something? I believe we should try and do something that at least helps human happiness and that alone is a reason enough to go ahead."