Over the past 100 years, heatwaves have caused more deaths than any other natural hazard according to professor Will Steffen of the Climate Council.
Sparkling skyscrapers and bright lights might make for a beautiful skyline, but on the city ground, the removal of trees and vegetation is turning up the heat in our cities, and it is killing us.
Sydney is projected to experience an average of four additional days above 35 degrees Celsius per year, which will continue to rise to 11 additional days per year by 2070 according to AdaptNSW.
Gail Hall, an author of The Growing Green Guide reveals that Melbourne can be six degrees hotter than its surrounding suburbs.
Trees and vegetation which help in cooling spaces have made way for apartment towers and poorly planned spaces with hard surfaces, dark roofs and pavement. This heat also keeps air conditioners on for longer, consuming masses of energy, all of which are now playing havoc with our health.
Brent Jacobs, research director at the Institute for Sustainable Futures at the University of Technology offers some stark statistics on how critical vegetation and in particular trees are for our urban lifestyle.
Jacobs was a researcher on the study Where Are All The Trees?
The report summarises the findings of Australia’s Urban Tree Canopy and was developed to support the 202020 Vision project, a national initiative that plans to see a 20 per cent increase in urban green space by 2020.
Trees offer a better quality of life, improved air quality, cooling, acoustics, thermal protection, biophilia, and carbon sequestering, and they can help reduce heat impacted death, particularly when it comes to our most vulnerable community members.
The Death Toll
Jacobs notes that a 2010 review of 113 European and North American studies of heatwave effects shows an over-representation in mortality rates of the bedridden, hospitalised, pensioners, the socially isolated and those confined to their home on a daily basis.
“As changes to temperature extremes often result in more severe impacts than changes to average temperatures, an increase in heatwaves places the communities at a heightened risk,” said Jacobs.
Adriana Keating and John Handmer of the Centre for Risk and Community Safety at RMIT state that if we do not adapt, heatwaves could cause an estimated additional 6214 deaths (or 402 deaths annually) by 2050 in Victoria alone.
In The Age, it was noted that Melbourne alone averaged approximately 200 heat-related deaths in 2013, in comparison to the state road toll of 242 deaths. By 2030, the number of deaths as a result of heat is expected to double.
Furthermore “an increase of one to two degrees celsius in average temperature is estimated to increase the number of heat-related deaths among the elderly in Australia’s capital cities by over 80 per cent,” said Jacobs.
“There is a also a link between heat and mental showing that hospital admissions for mental and behavioural disorders rises during heat waves.
“There are hidden impacts too, such as increases in domestic violence during heat waves probably caused by increased alcohol consumption. For many affects we don’t collect heat related statistics – but anecdotal evidence suggests increase in behavioural issues).”
Helen Brown from Curtin University’s School of Public Health conducted a study in 2013 reiterating the need to act now.
“The way societies react to these risks today will influence the extent to which current and future generations are affected. While climate change is a global phenomenon, adaptation is a local affair," she noted. “Our research established that increases in extreme heat in Perth, would pose the greatest risk to human health associated with climate change.”
The costs are not just physical. In the City of Melbourne alone, an analysis found that “the total economic cost to community due to hot weather is estimated to be $1.8 billion in present value terms. Approximately one-third of these impacts are due to heatwaves. Of the total heat impact, the urban heat island effect contributes approximately $300 million in present value.”
Another recent estimate placed the annual economic burden to the Australian workforce of heat waves at around US$6.2 billion or around 0.4 per cent of Australia’s GDP.
Return of The Trees
So just how important are trees in cooling the city? Jacobs identifies two critical points:
- They provide shade at ground level for whatever is underneath their canopy. No matter whether it's grass paved surfaces or roads, they reduce the surface temperature at ground level which cools the places people move around in.
- They use moisture from the soil in transpiration (evaporation of water from their leaves). They do this to keep themselves cool, but it also keeps the environment cool.
Jacobs also points to patterns of tree canopy cover in cities like Sydney where past development has removed tree canopy and notes that newer suburbs (peri-urban areas) that were once used for farming are now being converted into residential developments.
“The land has already been cleared of trees – but the open space is filled with hard surfaces and most of the remaining natural landscape is lost,” he said.
Jacobs also states that while many Sydney suburbs have a lot of variation in tree cover such as open space, parks, creeks the mapping work demonstrated that the cooling effect of these areas doesn’t extend far into residential areas or have an ample impact on the urban heat islands.
“We need to incorporate trees into the residential and commercial areas,” he said.
While the effects of climate change are generally cited as the primary cause of increasing urban heat, Jacobs notes that property affordability is also to blame.
“There is pressure to keep costs of new housing down to make these areas affordable but this often means that while the purchase cost of the house or apartment may be low, the running costs (power and maintenance) are passed on to the property owner,” he said.
He also identified three other major concerns:
- Existing built environments that didn’t account for urban heat in the construction - trees and vegetation are removed and replaced with hard surfaces and dark surfaces which absorb heat and materials. These surfaces are impermeable to rainfall so it runs off instead of being stored in the soil for later evaporation.
- New suburbs are following the same patterns as above and where buildings occupy a larger proportion of land area. There is also less open space in backyards than we had in the 1960s and 70s, when people could grow gardens and revegetate.
- We have high-rise urban renewal projects, particularly along major roads, where there is no provision for green space and the thermal performance of buildings isn’t really part of the design. Therefore, air conditioning remains heavily relied on for thermal comfort for residents.
Residents are encouraged to seek council approval before removing trees, but nationally there has been a rise in bush fire protection schemes that provide approval and guidelines.
NSW Rural Fire Service’s 10/50 vegetation clearing strategy is designed to prepare people allowing them to clear trees on their property within 10 metres of a home without seeking approval and clear underlying vegetation such as shrubs (but not trees) on their property within 50 metres of a home, without seeking approval.
Jacobs says the scheme is being abused by some homeowners, particularly where trees might obscure views.
“The Nature Conservation Council estimates that the 10/50 rule resulted in the senseless loss of hundreds of landmark trees in Sydney suburbs and regional towns without any meaningful improvement in bush fire risk,” he said. “In fact, in areas where councils have been recording vegetation removal under the 10/50 rule, less than five per cent of trees removed were for legitimate fire risk purposes. Most trees removed have been to improve views or facilitate development, not reduce bush fire risk."
The rule is now under review.
DEPI in Victoria also has the 10/50 rule for areas covered by the Bushfire Management Overlay.
The entitlement also has a 10/30 rule for 21 metropolitan municipalities, allowing residents to clear any vegetation on their property, including trees, within 10 metres of a house and any vegetation except for trees within 30 metres for bush fire protection. Houses built or approved after September 10, 2009 need a planning permit.
“The issue for urban heat is that while removing trees may reduce some of the risk to homes from bush fire, it actually increases the exposure to urban heat,” Jacobs warns.
The Queensland Government defines a "tree" as any woody perennial plant or any plant resembling a tree in form and size (shrub, palm etc.) and even has a policy to protect dead trees.
Queensland legislation features a Natural Assets Local Law 2003 that includes a Vegetation Protection Order (VPO).
So along with council instructions, there are also a host of resources for people to contribute to the “urban tree canopy.”
Jacobs cites green cover recommendations such as the NSW Office of Environment and Heritage (2015) Urban Green Cover in NSW Technical Guidelines.
Melbourne has the Growing Green Guide which is Australia’s first guide to green roofs and walls. This was designed for the private sector (planners, designers, developers and homeowners) in adding to the city’s green infrastructure and to encourage innovation in urban greening.
So What Is Australia Doing About It?
Jacobs commends projects such as Sydney’s Central Park, The Goods Line and Darling Harbour’s redevelopment.
He warns, however, that it’s not all up to our cities. It is crucial to encourage urban greening in the suburbs, where population-based development is booming.
“Many of these councils are struggling to maintain services from their rates base so it’s understandable that they want to attract developers, but they need to be aware that urban heat could be a time bomb," he notes.
"Unless we build heat mitigation into new developments, through water sensitive urban design and the retention of trees in the urban landscape, we are creating liveability problems for those communities in the future."
Penrith City Council has developed a Cooling the City strategy which provides a road map to address pressures on the community from increasing urban heat.
But the worst of it? Many of us still don't understand the implications if we don’t make changes today.
“Most people recognise that it’s hot but its too easy to go inside and turn on their air conditioner. But I think the impact on vulnerable community members of heat waves are still largely hidden," Jacobs notes.
"At the moment, for the disadvantaged in our communities, particularly the elderly, the chronically ill and the housebound, the cost of cooling is too high – they can’t afford to run air conditioning so they suffer in silence.”