Heatwave-related deaths in Perth are expected to more than double from 137 in 2011 to 378 by 2050 as the state faces increased warming due to climate change.
This prediction from the State of Australian Cities 2013 places Perth fourth in Australia for the number of annual heat-related deaths behind Brisbane, Melbourne and Adelaide.
Greening and density
Reducing vulnerability to heat-related illness and death is complex amidst plans for 50 per cent of Perth’s future residential development (or 154,000 homes) to increase in density to 15 dwellings a hectare by 2050.
While increasing density is critical in curbing the sprawl that characterises much of Perth’s urban residential development, the design of this infill is equally as important in safeguarding the resilience of the community to the effects of warming.
Dr Paul Barber, managing director of ArborCarbon, works with a number of local authorities across Australia in mapping the canopy cover of urban areas.
“How we design our new urban areas will have a profound impact on the well-being of communities that live within them,” Dr Barber said.
“Our work with LGAs has clearly shown large differences in the surface urban heat island effect between suburbs with lower and higher density housing. The high density areas have small blocks, large houses and very little room for canopy
“More important is how the canopy cover is changing over time and how rapidly it is changing. The best performing councils [in Perth] have remained roughly stable since 2012, and most have decreased substantially since that time.”
Greening and planning
In WA, residential development has largely been guided by the Liveable Neighbourhoods policy since being formally adopted in 2009. The policy’s main remit is to provide a sustainable urban structure, including guidelines for designing for higher density.
However, until a draft review was released in 2015, the policy included a guideline for verge widths at a maximum width of 4.5 metres, which left little room for the provision of street trees, who were competing for street space with utilities and parking. In 2015, a draft review was released, which has provided for a five-metre minimum verge width.
Protecting existing trees
While a number of councils are adopting greening plans or are signatories to the 202020 Vision to increase canopy cover, Dr Barber says that unless a commitment is made to retain existing trees through the development process, these initiatives will be unsuccessful.
“Conservation of our existing canopy cover is incredibly important and we are not doing that. Many councils are talking about increasing their canopy cover through large scale plantings,” Dr Barber said.
“In my opinion this is important. However, if we do not conserve our large trees, and we continue to remove them and cover our available planting space with hard surfaces, then we will never increase our canopy cover.”
Trees as assets
According to Bayswater councillor Chris Cornish, who has been active in supporting greater urban greening, the issue is serious and trees need to be valued as assets in order to be retained.
“It is incredibly serious. People are unnecessarily dying around Australia during heat waves; this is a public health issue yet is probably not fully appreciated,” Mr Cornish said. “The facts are very clear, temperatures are higher by two-plus degrees Celsius in urban areas.
“State governments all around Australia seem to be ignorant of the benefits trees bring. In WA, Main Roads and the Education Department have shown that they don’t give trees any regard whatsoever, they simply don’t enter the decision making equation.
“It is imperative that any proposal taken to a government department must have had a valuation applied to any trees being considered for destruction. People will place more weight on a financial asset – which is what trees are. I am convinced this needs to happen and it is a great pity it is not already. Shameful really.”
Local government action
Across Perth, a number of local governments are taking action by committing to an increase in canopy cover through the 202020 Vision, as well as developing individual urban forest strategies. Other local governments are creating protective mechanism for existing trees. The City of Cockburn has created a database of all existing street trees, as well as a significant tree register, including species situated within a road reserve along the proposed Perth Freight Link route.
A number of studies are underway, investigating the relationship between health, climate change and urban areas.
Curtin University’s Dr Helen Brown’s research on the complexity between health and climate change has influenced local government approaches to this issue. Dr Barber is currently undertaking research with a consortium of councils in South Australia to investigate the “relationship between urban canopy cover, urban heat, and the resilience of communities to climate change’’, which will assist local and state governments in increasing community resilience.
The impacts of planning and decision making will either compound or mitigate the effects of climate change in urban areas. According to Dr Barber, climate change is already impacting on existing tree populations, leading to their rapid decline and death, with newly planted species experiences high (greater than 75 per cent) failure rates.
“Decreased resilience of the communities living within our cities resulting in higher rates of hospital admissions, illness and avoidable death; and increased energy and water usage for maintenance of existing green spaces and cool zones. Not only will the climate become hotter and drier as a result of climate change, but our negative impacts on the urban forest canopy will greatly compound this.’’
This week the WA Greens launched an Urban Forest Strategy, which seeks to double Perth’s canopy cover by 2040. The ambitious strategy will aim to preserve 90 per cent of remaining urban bushland and significant trees and will establish an Aboriginal Stewardship committee to preserve cultural knowledge and practice.
“This project was born of a combination of sorrow and determination. Sorrow that across our city, community groups and volunteers are stretched to the limit defending local urban bushland treasures that shrink year by year,” Greens cities spokesperson Senator Scott Ludlam said.
“The impact of this uncontrolled clearing is starting to show. Not only are we losing the aesthetic and recreational benefits of living near green space, but our city is getting hotter. There can be as much as six degrees difference across Perth’s suburbs, depending on their canopy cover.”
As well as committing to increased canopy cover, the strategy responds to the pressure placed on and lack of protection for urban bushland and wetland areas threatened by development proposals, including the contentious Perth Freight Link.