Australian city designs must change in face of deadlier heatwaves: experts

Updated

Australian cities need to prepare for more frequent, intense and longer-lasting heatwaves, experts say, which could lead to restrictions on black roads and roofs that contribute to dangerous heat traps.

Heatwaves already kill more Australians than bushfires and cyclones and meteorologists say a looming El Nino weather system could push up summer temperatures later this year.

Scientists are investigating ways to lower the temperatures of Australian cities, including using light-coloured bitumen, planting more trees and floating the idea of banning black roofs.

"Australians regularly overestimate their ability to withstand extreme heat," Professor Liz Hanna, an environmental health expert from the Australian National University, told Lateline.

"We think we know how to handle it because we live in a hot country but we're now dealing with unprecedented extremes.

"We have to take heat as a health issue far more seriously."

Extreme heat 'could kill hundreds in a few days'

By 2050, an extreme heat event in Melbourne could kill more than 1,000 people in a few days unless there is better preparation, according to a Federal Government report looking at extreme heat events.

Scientists say cities can exacerbate extreme heat by four to seven degrees Celsius, especially overnight, triggering unnecessary deaths.

In some small urban spaces or microclimates, temperatures can jump more dramatically, says Professor Nigel Tapper, an urban climate specialist from Monash University.

"If we're in an urban canyon where the forecast air temperature is 35 degrees and the sun is beating down onto hard, dark surfaces, then surface temperatures might be up to 70 degrees," he said.

"That means the temperature you feel walking around is more like 45 or 50 degrees."

Dark roofs and roads don't make sense: expert

Black roads and roofs dominate many new housing developments and can be 30 degrees hotter on the surface than forecast air temperatures.

Professor Liz Hanna says this does not make sense in Australia's climate.

"We drive around and shake our heads in dismay at the silliness of this, the cost of retrofitting these houses and the poor, miserable people in the future who will have high electricity bills because they'll be forced to cool their houses artificially," she said.

The worst-affected cities include Perth, Adelaide, Melbourne and Sydney's western suburbs which endure drier and more intense heat extremes.

Professor Tapper and other researchers have determined the maximum temperature threshold beyond which death rates spike. It is different in each city because people acclimatise to local conditions.

Overnight minimum temperatures also have a significant impact on death rates.

City Maximum temperature threshold for excess mortality (degrees Celsius) Canberra 33 Hobart 35 Brisbane 36 Darwin 37 Sydney 38 Melbourne 39 Adelaide 42 Perth 44

(Source: National Climate Change Adaptation Research Facility)

The Melbourne City Council and other academic researchers assessed the 2009 heatwaves - that included three days over 43C – and found there were 374 deaths during the period.

There were also more than 1,000 other emergency callouts, blackouts, mass public transport strandings and bushfires costing hundreds of millions of dollars.

Heatwaves are also linked to more episodes of mental illness, foodborne disease and violence.

Independent Melbourne City Councillor Arron Wood says Melbourne got a timely reminder last summer.

"We had a reminder of that just last summer when we had a whole week over 40 degrees and again public transport tracks buckled, we had people stuck in lifts all over the city and outdoor sites shut down," he said.

"You get the feeling that we're only one step away from real trouble in a heatwave."

Trees can cool cities

However, almost all of these impacts, including deaths, are preventable with deliberate planning to cool cities.

The right kind of design could enable cities to offset up to four degrees Celsius - which is one of the upper projections for global warming.

Cr Wood says Melbourne City Council plans to cool the city centre by four degrees in 20 years by using a variety of strategies including more trees and vegetation.

He says trees are natural air conditioners and just one can make a radical difference to temperature.

"We're aiming to increase our urban forest by doubling canopy cover to bring down the urban heat island effect," Cr Wood said.

"We also want to think smarter about how to use more green roofs and walls and facades. Our trees and parks are the first line of defence against heat."

Stormwater could make cities greener and cooler

But for cities like Melbourne to stay green it means a big shift in the use of water.

During the last prolonged drought in south-eastern Australia, parks and gardens were allowed to dry out. This time there are plans to capture and recycle stormwater.

"Five hundred billion litres of water falls on this city every year and we capture just 1 per cent," Cr Wood said.

Sydney sustainability campaigner Michael Mobbs cools his inner-city neighbourhood with street gardens that use recycled water.

"When it was over 42 degrees last year it was only 32 degrees out here," he said.

Mr Mobbs is also promoting trials of lighter-coloured bitumen that he says can reduce temperatures by two to four degrees.

"It's about 10 to 15 per cent more expensive right now but as it becomes more commonly used, the price will drop," he said.

White roofs can reflect 80 per cent of the sun's heat and are also being trialled.

"I think it's time to ban black roofs and black roads. They don't make sense," Mr Mobbs said.

He says people should prepare now for possible heatwaves this summer.

Other cheap solutions include planting vines on western walls where they act like insulation, installing outdoor blinds, and maintaining well-watered green areas on and near houses.

"We need to use better design because just a few degrees can help save lives," Professor Tapper said.

People most vulnerable to heatwaves include the elderly, the sick, the obese, the mentally ill, the very young, the poor and socially isolated and those who work outdoors.

Professor Tapper and a team of researchers have mapped the most at-risk suburbs in each capital city by combining demographic vulnerability with urban hotspots.

Click on the map to find out how different suburbs rate.

Topics: urban-development-and-planning, weather, environment, environmental-impact, environmental-management, environmental-policy, environmental-technology, community-and-society, health, environmental-health, building-and-construction, industry, australia, sydney-2000, nsw, melbourne-3000, vic, wa, perth-6000, adelaide-5000, sa, canberra-2600, act, tas, hobart-7000, nt, qld, brisbane-4000

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