Planning Institute Reminds of the Importance of Urban Trees to Heat Management

Despite rising urban temperatures and severe heatwaves becoming the norm in Australia over the last few years, the planning process has inadvertently allowed the removal of nature’s natural air conditioners – trees.

Over the last 5 years heatwaves have become one of urban Australia’s silent killers, yet we seldom understand the scale of their impact because we only hear of the consequences retrospectively, usually in a statistical form.

For example, the heatwave that led to Victoria’s 2009 Black Saturday fires saw more than twice as many heat related deaths in urban Melbourne than deaths directly attributed to the fires themselves (374 ‘excess deaths’ as compared to 172 deaths in the bushfires). However because they happened quietly and statistically, they barely attracted attention.

Many heat related deaths in urban areas have two defining characteristics. They affect the elderly and occur most frequently in ‘heat islands’ - the untreed and unshaded areas of our cities. Both of these characteristics are presently on the rise, as figures indicate that our population is ageing such that by 2030 over 55’s will constitute 20% of the population.

Additionally, our urban and suburban areas are losing trees - and fast! Recent University of Melbourne research (G.M. Moore, “Valuing and Maintaining Urban Forest”, 2013) reveals that shade from trees can drop urban temperatures by up to 8°C, mitigating dangerous heat island effects.  Aside from this, they offer a huge range of other tangible benefits such as increased residential property values (up to 10%), reduced air conditioner use and costs (12-15%), extended life of road pavement (up to 200%), improved motorist behaviour, reduced erosion, and less storm damage to property by buffering winds.

It would seem illogical that tree cover in our cities and towns should decline at all, but that is exactly what is happening. Sadly, we have all played a role in this decline.

In order to keep houses affordable during the 1980’s and 90’s, homebuyers demanded ready-to-build-on-lots.  This demand on builders and developers resulted in expansive natural landscapes being reshaped, to create flat and cleared home building sites. Even today, some people within the community are not enamoured with trees.  It is commonplace to see up to 20% of freshly planted street trees in new estates pulled out by residents seeking a cleaner and uncluttered presentation to their homes.  

The invisible hand of liability and insurance has also become one of the secret designers of our cities. Large shade trees are seen as a risk because of the fear of falling limbs, or as objects that could potentially be struck by a car. Despite the real occurrence of these events being astronomically low, big trees are increasingly removed from gardens, streets, schools and parks in favour of head-height shrub species, if anything at all.

Initiatives for sustainable drainage have also seen the old practice of storing stormwater in a hole in the ground (a drainage sump) be rightly discontinued and replaced with shallow soakage basins.  The problem with this approach, however, is shallow basins can sometimes occupy areas as large as a soccer field, often at the cost of the trees that were there previously. Even tighter water allocations to new residential estates for establishing street and park trees can have a detrimental impact.

We know it is essential that we build walkable neighbourhoods to reduce our reliance on the car and for our own better health. Big shade trees are a critical ingredient to walkability; something which snaps into sharp focus for anyone contemplating a walk to their local shop or school on a hot day. But more than that, we need them to moderate the changing climate of our cities and towns to help save lives at risk through heat stress.

Fortunately, the solution is not insurmountable. It just calls for a commitment from all those people who care about the places in which we live – communities, developers, planners, designers, environmentalists and bureaucrats – to refocus on making our cities and towns greener, in order to achieve a cooler future.

It calls for the participants in the planning process to re-evaluate the priority given to trees in the design and management of our cities. It calls for ensuring that trees are no longer the ‘first cut’ to be made in the planning of our suburbs and cities, but the non-negotiable element that we protect above all else.

Written by Peter Ciemitis - PIA WA Urban Design Chapter Convenor