Planning to cope with extreme heat

10 Feb, 2018 04:00 AM
 New research shows that ambient temperatures can be reduced in cropped land with lighter-coloured or no-till paddocks that absorbe less heat.
New research shows that ambient temperatures can be reduced in cropped land with lighter-coloured or no-till paddocks that absorbe less heat.

HEATWAVES are happening more often and researchers are responding with practical climate engineering strategies to take the edge off the impacts of extreme hot spells.

Modifying the land surface in urban and agricultural areas can reduce extreme temperatures by up to two to three degrees Celsius, according to the findings from a collaborative international study led by ETH University Zurich, Switzeralnd, with researchers from Australia’s Centre of Excellence for Climate Extremes, University of Tasmania, CSIRO and the United States.

Centre of Excellence for Climate System Science director, Andy Pitman, said land modification may be able to knock the “critical last two degrees” off a severe heat spike .

“We’re not suggesting this would have profound implications and cool all of Australia right down,” Mr Pitman said.

Potential techniques for climate engineering include crop varieties bred to be lighter in colour, use of more reflective mulch, leaving lighter stubble on cropped land or no-till practices that produce soils that absorb less heat.

The centre contributed to the research and is investigating local applications for urban and rural landscapes but more work is needed to develop specific applications.

“I would stress that we’re not telling farmers how to function, or suggesting they should lay bright plastic across the land,” Mr Pitman said.

“We’re saying there’s potential to use simple techniques to moderate extreme temperatures.”

Mr Pitman said techniques needed to be applied across a lot of land.

“We’re talking about vast scales, like across a wheatbelt, and making it slightly more reflective to the parts of sunlight that aren’t used for photosynthesis,” he said.

Mr Pitman said further research was needed to understand local impacts and practical applications.

An obvious commercial benefit would be when climate engineering is used to moderate an extreme heatwave that would otherwise have risked plant losses.

While Europe’s extreme events are relatively cool compared to the scorchers of inland Australia, it can be severely impacted by significant temperature spikes like the 2003 heatwave that claimed more than 70,000 lives.

Much of the work to date on this climate engineering method has been done in Europe, in both farming areas like the Black Sea wheat region and urban environments.

“These are not new strategies, but the clever thing we did in this research was to tease out that the impacts of these methods has most impact at the extreme end of temperatures,” Mr Pitman said.

“People in the Mediterranean have had light coloured roofs for many hundreds of years.

“There’s a strange thing about Australia that we seem to like black roofs.

“It’s not a cost thing, it’s purely taste.

“Even half a degree cooler in a city can provide considerable value, like cooling the temperature by half a degree and prevent the electricity grid exceeding a threshold and causing a brownout.”

There is another factor in the differences between extreme heat events in Australia and Europe, but more work is needed to determine the significance of its impacts.

Water evaporating from tree leaves into the atmosphere (transpiration) has a modest cooling effect.

But native European trees cannot transpire under extreme heat.

But in Australia Eucalypts have evolved to cope.

“Normal trees can’t transpire if they’re heat stressed,” Mr Pitman said,

“But eucalyptus aren’t normal.

“Like the animals here are really weird relative to the northern hemisphere, our vegetation is similarly weird.

“Eucalypts respond to extreme heat by sweating as a strategy to cool themselves down.

“They’ve adapted to almost always have access to water and they have a range of strategies to cope with extreme heat that most people in the bush already understand.

“The first response is pumping water into the atmosphere, which involves putting out volatile organic compounds – which is why the Blue Mountains look blue.

“And they let their leaves droop so they are almost vertical to the sun, to absorb less heat.”

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