AUSTRALIAN cities are 5C hotter compared to surrounding areas because of a phenomenon known as the ‘Urban Island Heat’ effect that could eventually turn them into death traps.

Densely populated urban areas including Sydney, Melbourne and Brisbane are baring the brunt of the UHI across the country and not even a looming winter can stop it.

The UHI occurs when natural permeable surfaces including grass, plants or bush land are replaced with concrete, asphalt and infrastructure.

According to the Centre for Science Education (UCAR), urban development causes surfaces that were once permeable and moist to become impermeable and dry. They heat up during the day and retain the warmth but infrastructure prevents it from escaping into the cold night.

These changes cause urban regions to become warmer than their rural surroundings, forming an “island” of higher temperatures in the area.

“These surfaces absorb — rather than reflect — the sun’s heat, causing surface temperatures and overall ambient temperatures to rise,” according to a statement from UCAR.

“Displacing trees and vegetation minimised the natural cooling effects of shading and evaporation of water from soil and leaves.

“Tall buildings and narrow streets can heat air trapped between them and reduce air flow. Waste heat from vehicles, factories, and air conditioners may add warmth to their surroundings, further exacerbating the heat island effect.”

The UHI is perpetuated by residents in urban areas who suffer from the effects and increase usage of electric fans and airconditioners for relief. The increased energy demands strain resources which often leads to ‘rolling blackouts’ or power outages and contributed to an even hotter UHI.

But that’s not the only significant impact of the phenomenon.

According to UNSW researchers, extreme city heat could cause train lines to crumble and could cause heat stress, damaging our organs.

“Since 1900, extreme heat events have killed more Australians than bushfires, cyclones, earthquakes, floods and severe storms combined,” the researchers said.

WHAT’S BEING DONE ABOUT IT?

Watering pavement before a heatwave could also be the answer to bringing down the temperature in urban heat islands. It’s popular in Japan and is being considered in Paris, but some researchers believe it could cause extra humidity and heat stress.

Several experts have recommended changing the colour of roof tiles as another way to reduce urban heat. Dark tiles absorb more heat than lighter colours.

The Cool Streets initiative was developed by landscape architect Dr Libby Gallagher, whose PhD found changes to street design could reduce CO2 emissions, cool neighbourhoods and reduce power bills for residents.

Dr Brent Jacobs, research director at the Institute of Sustainable Futures at UTS, said temperatures were rising faster in western Sydney than in the east due to climate change and urban development. Eco-friendly developments with a focus on green space in Sydney suburbs including Waterloo and Green Square are being put in place in a bid to cool the areas down.

In 2014, Melbourne City Council found temperature variations of up to 4C degrees between the city centre and suburbs because of the UHI.

Melbourne City Council loses about 1500 trees a year through old age, heat stress, development and vandalism. It replaces them with 3000 new trees annually as part of an urban-forest strategy.

In Brisbane, suburbs including Windsor, Wilston and Milton, will be hotter by 2023 if the city concentrates on an infill development plan, according to new research by Queensland University of Technology.

But the findings published in the Land Use Policy journal showed that if a sprawl development instead occurred, inner-city suburbs including Fortitude Valley could be significantly cooler in 2023, compared to 2004.

Dr Liton Kamruzzaman, from the Science and Engineering Faculty, said the findings found the number of suburbs suffering from extreme UHI effect was increasing.

“[It has increased] from 10 per cent in 1991 to 20 per cent in 2013, and this trend will continue if effective planning policies are not introduced,” he told the Brisbane Times.

Last year the then acting Minister for Cities Greg Hunt announced a plan to create cool and green cities and pledged to plant more trees each decade up until 2050 and would look at building greenery on to rooftops.

Globally, 2016 was the hottest year yet and it continues to get warmer.

The hottest year on record was 2015 before it was overtaken last year, and this year could end up being even hotter than the last.

Many other places around the world are affected by the UHI.

Downtown New York City is an urban heat island, a built-up area with temperatures that are higher than the rural areas surrounding it.

According to the Environmental Protection Agency, the annual air temperature of a city with one million people can be 1—3C warmer than its surroundings.

The Heat Island Group has previously reported that the UHI around Los Angeles, California in the US costs the city $US100 million a year in energy.

Climate and water outlook: May - July 2017 Climate and water outlook: May - July 2017

megan.palin@news.com.au