A severe heatwave baking parts of eastern Australia was expected to peak on Wednesday, affecting parts of western Sydney including Campbelltown, Liverpool, Parramatta and Penrith.
Wednesday was forecast to be Penrith’s fifth consecutive day above 35C, a new record for spring since records began in 1995. The mercury there hit 48.9C in January 2020, the highest temperature ever recorded in the Sydney basin.
During extreme heat events, western Sydney is typically 6C to 10C hotter than the rest of the city. Why is that, and can anything be done to make hot summers more bearable for western Sydney’s 2.7 million residents?
Why are temperatures so different between west and east?
There are several features that make western Sydney warmer than other parts of the city. Geographically, it sits in a flood plain, with the lowest point of a bowl being the Nepean and Hawkesbury rivers, according to Sebastian Pfautsch, a professor of urban planning and management at Western Sydney University.
Heat moving south-east from inland Australia gets trapped in the bowl, Pfautsch says. “It doesn’t really get pushed [east] over a ridge line that you can see from about the Hills shire all the way down to Campbelltown.”
Western Sydney also does not receive the cooling sea breezes that reach the eastern suburbs.
Dr Gloria Pignatta, a senior lecturer at the University of New South Wales school of built environment, says winds from the desert bring hot and dry air to western Sydney during summer.
“On still nights, temperature inversions can trap warm air in the western Sydney area, preventing overnight cooling. This increases the heat load for the following day,” she adds.
Urban design also plays a huge role. The urban heat island effect, in which urban centres are significantly warmer than rural areas (estimates vary from 1C to 13C), occurs because hard surfaces such as concrete and asphalt retain more heat than green areas.
“Urban expansion, urban densification, loss of green infrastructure, expansion of hard infrastructure, lots of black roofs, lots of black roads, all unshaded, lots more human activity, transport, but also manufacturing” – all these worsen the natural temperature discrepancy between eastern and western Sydney, Pfautsch says.
While western Sydney has abundant green cover compared to the eastern suburbs, in the form of native bush and farmland, Pfautsch notes the critical factor of rainfall in the east. “[It] gets up to 1,200mm to 1,300mm of rainfall each year, which means that green infrastructure has quite a bit of water that it can transpire, and therefore make the green spaces cool the area,” he says. “You don’t have that in western Sydney, where we have more green cover, but we only get about 700mm of rain annually. That means the whole system is … much drier.”
Less water for trees to transpire – to draw through their roots and evaporate through leaves – means more heat.
Will the extreme heat get worse?
The frequency and severity of extreme heatwaves are predicted to worsen due to the climate crisis. 2021 modelling projected that western Sydney and the Hawkesbury would experience an additional 10 to 20 days hotter than 35C annually by 2070.
In a study submitted for publication to the peer-reviewed journal Weather and Climate Extremes, Pfautsch’s analysis of western Sydney climate records between 2000 and 2020 suggests that in a worst-case scenario, western Sydney could have 160 days of temperatures exceeding 35C. “By 2060, you could have four months of consecutive day after day at or above 35C,” he says. “It’s just really scary. That’s only 35 years away.”
The analysis also showed that the likelihood of 40C days increased exponentially as the number of 35C days rose. “That’s why it’s so important we try everything in our arsenal to build cooler cities,” he says.
Is anything being done to adapt to the extreme heat?
The window of opportunity to take action to prevent extreme heat events has long passed, Pfautsch says. “It should have happened 20 years ago. Now all we can do to really keep people safe – because they die from heat – is to adapt.”
Increasing canopy cover from trees and good irrigation plays a role, Pignatta says, as does improving energy efficiency in buildings.
“More greening is not a ‘nice to have’ any more, it’s a must have,” Pfautsch says. “You can’t survive without it.”
Increasingly, councils and developers are also turning to climate-responsive urban design. Actions include intentionally creating shade using buildings, changing surfaces to lighter colours and more reflective materials, putting green roofs on high rise apartments, and orienting buildings and streets so they can be passively ventilated by wind.
“We see developers starting to take up the construction of [new suburbs] … where wind direction is taken into account to help blow the hot air out of these settlements as quickly as possible,” Pfautsch says.
In 2022, the Western Sydney Regional Organisation of Councils launched Cool Suburbs, an evidence-backed tool for design that takes heat resilience into account. It has already been used to assess planning projects in the City of Sydney and City of Blacktown, Pfautsch says.
