Short note 2020

This is a storm in a teacup. "Leafy" areas are prestigious in Australia and more trees are being planted to capture that prestige. I myself have planted nine trees that are now very tall.

But trees take a while to grow so new plantings in new suburbs will take a while to grow. When they do grow up, the new suburbs too will be cooler

Note that this is just about suburbia. Worldwide there has been a great upsurge of tree planting as agriculture has become more efficient and the land released goes under pine plantations

Huge swathes of our suburbs are in danger of becoming virtually unliveable with residents jumping from “aircon to aircon via a car with aircon” to avoid the searing heat.

That’s one of the conclusions of a new report that has also found that in just seven years the number of trees in 69 per cent of urban areas has dramatically dropped. Without enough trees shading city streets, temperatures can be as much as 10C hotter.

And one of the biggest culprits of cranking up the heat in our suburbs is homeowners clearing trees to build, among other things, swimming pools – ironically to cool down on hot days.

Associate Professor Joe Hurley from RMIT’s Centre for Urban Research said city greenery not only helped put the lid on heat, it was also key in managing stormwater and provided physical and mental health benefits.

Heatwaves are a hallmark of an Australian summer. But they're getting hotter, becoming more frequent, and lasting longer.

“Green cover should be managed as critical infrastructure alongside communications, transport, water and the electricity network,” he told news.com.au.

“But all too often trees are traded away for other demands like urban development. It can end up being about having tree or something else when we should manage our cities better so we can have green cities.”

Prof Hurley is the lead author of Where Will all the Trees be, a new RMIT report, released today, which looked at tree cover across hundreds of Australian local government areas (LGAs).

It found Cairns had the most green cover at 83 per cent while Wyndham, in Melbourne’s south west which includes Werribee, had the least at just 5.4 per cent.

“The bad news is between 2013 and 2020 the majority of LGAs have lost green cover. The more encouraging news is that from 2016, the majority are now gaining cover, that’s a good sign that the longer term trend is being turned around – but they still haven’t made up the losses,” said Prof Hurley.

Other studies have shown trees can have a dramatic effect on the ambient temperature of cities. Urban areas are often hotter than surrounding country areas anyway due to “grey cover”, the preponderance of hard surfaces like asphalt and metal roofs that help crank up the mercury. Lack of canopy can make this issue worse.

A vivid example from Melbourne illustrates this. Thermal images of Royal Parade show the surface temperature of the road fully exposed to the sun as surpassing 65C; yet just meters away a tree shaded area is around 30C cooler.

The air temperature of urban areas with more trees can be around 4C cooler than those without. On a more local level, the air temperature in an treeless car park can be 10C higher than a nearby shady street.

“We can’t say ‘stop developing and just plant trees’ so what’s exciting about Parramatta is how it is increasing urban tree canopy to create better neighbourhoods while becoming a major urban centre,” said Prof Hurley.

“The answer is to prioritise green infrastructure alongside development. As cities grow, we can make them greener – it’s not an either, or.”

https://www.news.com.au/technology/environment/lack-of-trees-exacerbates-extreme-heat-effects-in-australian-suburbs/news-story/0825f8746b7e3e25be04e21140da4637