Certain suburbs in Australia’s major cities are being left to swelter under higher temperatures – which could be reduced through one simple measure.
Monash University researchers have released a report today commissioned by the Australian Conservation Foundation that says Australia’s major cities need more trees and vegetation to reduce serious heatwave impacts.
The report notes there can be a “heat gap” or large differences in temperature between suburbs due to the amount of vegetation and built infrastructure.
For example, temperatures in the Sydney council area of Blacktown, which only has 22 per cent vegetation cover, are 5.8C higher due to extra heat from its built infrastructure.
This compares to Mosman, which has a moderately high level of vegetation (43 per cent) and which only experiences an extra 2.2C in temperature from its built environment.
The report says the variation between different areas of Sydney, is much higher than in Melbourne and Brisbane.
Experts say temperatures are forecast to soar during summer thanks to climate change, with hot summer days in Melbourne and Brisbane expected to regularly top 40C by 2060-2080, and up to 50C in Sydney.
Cities in particular will feel the brunt of increasing heatwaves thanks to a phenomenon known as the urban heat island effect (UHI).
The microclimate around cities is generally warmer due to a number of factors, including that high rise buildings and narrow streets create canyons where heat gets trapped. Materials such as concrete, asphalt, steel and glass also retain more heat than natural materials, and a lower proportion of tree cover or vegetation means there is less moisture to cool the air or to create shade.
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Areas where there are more people also tend to be warmer because of heat waste from the increased use of things like cars, factories and cooling systems.
“When temperatures go up, we strive to make ourselves more comfortable and rely on more airconditioning and refrigeration. This increases electricity usage and creates more waste heat, further contributing to the UHI effect,” the report states.
There are several ways to reduce the UHI effect including the use of reflective or super-cool materials, devices for solar control and shading, natural temperature sinks, or cooling systems that involve evaporation and transpiration.
However, one simple and cost-effective method is increasing the amount of trees, shrubs and even grass. These plants will help absorb sunlight, release water vapour that evaporates and cools the air, and provide shading.
This could be achieved through creating more open space, parks, wetlands, vertical greenery on building facades and vegetated roofs.
Sadly, the amount of vegetation has declined in all major cities except for Hobart, which is the only capital city to have more tree cover in 2020 than it did in 2013.
In Sydney, there was a 0.8 per cent decline in vegetation cover during this period, and while this may seem small, it is equal to 12.2sq km – or about 570 AFL football fields.
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“Heatwaves kill more Australians than any other natural disaster and these will get more severe as our climate continues to change,” report co-author Dr Lucy Richardson of Monash University said.
“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.
“Natural infrastructure takes time to establish to its maximum effectiveness, so acting early is critical for meeting future needs.”
ACF campaigns director Paul Sinclair said Australia’s national environmental law had not been effective in preventing the destruction of native trees.
“In the first 17 years that Australia had a national environment law, 20,212 hectares of urban threatened species habitat – that’s 11,400 MCG footy grounds – was destroyed,” he said.
“Decisions made by Australian governments in the coming months will either lock in permanent and escalating damage to the ecological systems that sustain human health and livelihoods, or they will promote a healthier, fairer and greener world.”
The Monash research is the first study to examine the cumulative effects of future climate change and the UHI effect at local government level across Australia’s three largest cities.
It may come as a surprise but this city, considered one of the most beautiful in the world, is one of Australia’s least green capitals.
It has an overall 34 per cent vegetation cover and experiences an extra 5.5C in hotter temperatures due to heat trapped by the city’s infrastructure.
The extra heat in some areas can reach as high as 13.5C.
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Improving the city’s vegetation cover is especially important as the hottest summer days are expected to increase to between 41.7C and 50C for 2060-2080 under a business-as-usual scenario.
In comparison, the summer’s hottest days over the last 50 years at Sydney’s Observatory Hill station averaged 39.1°C.
Sydney can expect around 56 of its average days to reach over 30C each year by 2060–2080, with around 15 average days over 35C and two average days over 40C.
Mosman and North Sydney are expected to have the highest predicted temperature peak, at 50C. The lowest peak was expected to be Burwood at 47.9C.
However, when looking at average temperatures, Blacktown was expected to have the highest mean summer temperature of 31.3C.
Brisbane is one of Australia’s greenest capital cities with 54 per cent overall vegetation cover.
On average the city experiences an extra 1C temperature due to heat being trapped by the city’s built infrastructure.
However, this can be as high as 6.1C extra in some areas.
Predictions suggest the city’s hottest summer days will sit between 38.3C and 41.8C by 2060–2080, under a business-as-usual scenario.
In comparison, summer’s hottest days over the last 50 years at the Brisbane Airport station averaged 35°C.
There will be around 137 average days over 30C each year and around 14 average days over 35C each year.
This is considerably hotter than the long-term average of 30C and the average for the 2019–2020 summer, which was 30.9C.
Melbourne is one of Australia’s least green capital cities with 23 per cent overall vegetation cover.
The city’s temperatures are typically 5.5C higher due to heat being trapped by the city’s built infrastructure.
This can climb to as much as 13.5C of extra heat in some areas.
Predictions suggest the city’s hottest summer days will sit between 42.9C and 49.4C by 2060-2080, under a business-as-usual scenario.
Casey would have the coolest maximum hottest summer days at 47C, compared with the highest hottest days predicted for Maribyrnong and Brimbank, both reaching 49.4C.
At the moment, summer’s hottest days over the last 50 years at Melbourne’s Olympic Park station averaged 41.9C.
Melbourne should expect around 48 average days to reach over 30C each year, with 17 average days over 35C and three average days over 40C.
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