City living to get more hot and bothered

Parts of Australia’s cities will be up to 3.7 degrees hotter by 2050, as urban expansion spawns ever more asphalt and concrete, new research suggests.

The ”urban heat island effect” – rising temperatures in built-up areas – will amplify climate change, particularly in the suburban fringes, according to researchers from the University of NSW.

”If you are living near the edge of a city today, you will notice the temperature change, mainly through the minimum temperature change at night,” said Daniel Argueso, the lead author of the study prepared at the Centre for Excellence in Climate System Science.

”There is also the fact that urban canyons prevent winds from moving around freely and cooling things down,” he said

Scientists have been studying the precise effects of urban heat for decades, although one simple way to test it is to touch a brick wall that has been in full sun for an afternoon but remains warm long into the evening.

As well as retaining heat longer than undisturbed earth or rock, artificial structures also absorb less moisture, meaning there is less cooling through evaporation.

In addition, cities produce more heat because there is a greater density of road traffic, electrical generators and industry, all of which generate small amounts of heat that add up, and hang around for extended periods.

”The ground heat flux daily cycle barely changes in the surrounding areas, but its amplitude increases considerably over areas of urbanisation,” according to the paper, Temperature Response to Future Urbanisation and Climate Change. ”This validates the picture of a surface with increased ground heat storage that is released later during the night.”

The researchers used climate models, which can estimate future temperature changes for the whole of Australia in two-kilometre-wide grid squares, and cross-referenced it with urban planning data.

The models were checked for accuracy by running simulations of temperature changes between 1990 and 2010, and they closely matched real-world observations over that period.

”The changes are noticeable all through the year, but they are especially marked during winter and spring, when minimum temperature increases over these areas could actually double the increase due to global warming alone by 2050,” the researchers wrote.

Some of the changes could be cushioned by simply planting more trees and planning for more parks and ponds.

The original release of this article first appeared on the website of Hangzhou Night Net.

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