man walking street by bare tree

We talk about greening our cities, but new research has found that over the past three years metropolitan areas have lost greenery equivalent in size to the city of Brisbane – and it’s our poorer suburbs facing the greatest impacts, often 10°C hotter than more affluent areas.

The Where Should All the Trees Go? report, produced by RMIT, University of Western Australia and CSIRO Data 61, analysed greenness across Australian metropolitan areas to identity priority areas for greening.

While rates of greening were predicted to have been stable over the 3–8-year period since similar studies were conducted, the research found there had been a 2.6 per cent decline, equating to 1586 square kilometres.

“None of the [local government areas] have increased their green land cover over the period studied by a significant amount,” the research report said, “and the majority have lost green cover.”

Lead author Associate Professor Marco Amati from the RMIT Centre for Urban Research said local government greening efforts had not been as successful as hoped.

“We found there has been a major decline in canopy coverage.”

A key finding was that liveability in terms of access to green space and concentration of heat due to the urban heat island effect were spread unevenly across metropolitan areas.

In terms of spatial patterns there were no hard and fast rules as to which areas were losing the most tree cover – so you couldn’t say outer suburbs were losing more greenery than inner suburbs over the whole of Australia.

But there was a strong, consistent correlation between low canopy cover, heat and socioeconomic disadvantage.

“As they lose vegetation, urban areas start to act like heat sponges,” Dr Amati said.

“Our study showed areas identified as less affluent are at risk of having urban hotspots that are more than 10 degrees higher than those found in wealthier areas.”

Extreme heat anomalies were identified in many areas of relative socio-economic disadvantage, including Sydney’s west, Melbourne’s west and outer areas of Perth.

“In contrast, areas exhibiting lower relative surface temperatures in Melbourne and Sydney are related to the presence of national parks and socio-economic affluence as measured by the SEIFA Index of Economic Resources,” the report said.

To identify the areas of socioeconomic and health disadvantage coinciding with a lack of green cover and high heat, the team developed a Vulnerability to Heat, poor Health, Economic Disadvantage and Access (VHHEDA) index.

“Using this index, we found that green spaces and heat concentration in Australia are spread unevenly, which is contributing to an uneven spread of economic and health circumstances,” Dr Amati said.

Report co-author Dr Bryan Boruff from the University of Western Australia said there were a number of factors that could explain the findings, including changing neighbourhood trends such as increased infill development.

“Local governments showing the greatest green space losses across Perth lie in a band that stretches from inland Melville to coastal East Fremantle where the traditional Aussie backyard is losing ground to densification and infill,” Dr Boruff said.

Other factors the report mentioned included bushfire mitigation policies such as NSW’s 10/50 rule, consumer trends towards small gardens and greenfield development on the edge of urban areas.

“While it is known that the Australian backyard is disappearing, much more research is required to understand the factors influencing this unanticipated trend to help get our urban greening back on track,” Dr Boruff said.

The report recommended that breaking up patches of high heat anomalies could be achieved through “planting corridors”, which it said should be a key component in strategic planning of green infrastructure in large metropolitan areas.

It said while industrial facilities and infrastructure like airports presented limited opportunities for greening, “large areas of railway land, roofs that could be greened and major highways could be important locations for reducing urban heat”.

The next stage of the research project will be working out how much potential greening area there is to mitigate the hot spots across our metropolitan areas.

The Fifth Estate is holding The Green Rebellion Goes West event into the future of development in Sydney’s West on 29 September, where this topic is bound to be discussed. Tickets are still available.

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