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Mandatory garden space for urban housing developments and combatting the urban heat island effect

March 15, 2017 at 11:50 pm John Englart 1 comment

Saving the trees in backyard gardens in our cities is critically important to slow the increasing rise of temperatures in the urban environment. Under the refreshed Plan for Melbourne, the State government is bringing in new minimum mandatory garden rules for housing development. The real issue that no-one is discussing, is how to encourage the increase in the private forest canopy in our cities.

Rising temperatures due to climate change are making our cities hotter. Climate change is amplifying the urban heat island effect. All the built surfaces in the city are absorbing heat during the day and creating a substantial increase in urban temperatures as compared to similar rural areas. This is particularly exacerbated during extreme heat events and heatwaves and poses a major heat health threat to the population.

Increasing tree canopy cover and increasing soil moisture in the urban environment are major methods for reducing the urban heat island effect.

Trees provide shade and evapo-transpiration cooling down the microclimate. As these three academics point out in The Conversation, Our cities need more trees and water, not less, to stay liveable.

Urban trees are worth much more than they cost. They add to urban sustainability through ameliorating the heat island effect, reducing stormwater runoff, providing shade, filtering pollution, reducing energy use. Green vistas are known to improve attention and office work productivity.

Melbourne City and many municipal council’s have recognised the threat of the urban heat island effect when combined with rising temperatures and more frequent extreme heat events associated with climate change and have adopted urban forest and street landscaping strategies.

For example, Melbourne City Council adopted an Urban Forest strategy in 2011 with a target to increase public realm canopy cover from 22 per cent at present to 40 per cent by 2040. Tree canopy covers about 22 per cent of Melbourne city’s public streets and park areas, while canopy cover in the private realm is only about 3 per cent.

Landscaping streets now incorporates more water sensitive urban design to try to capture rainfall to retain it as soil moisture in parks and vegetation, and slow it’s path into stormwater drains.

All this focus on improving public areas is important, but the private sphere is far more problematic. While efforts are being made to increase the urban tree canopy through streetscape landscaping, increased housing density development is reducing the tree canopy on private land.

There is a disjuncture between the public and private. In some urban areas the urban forest canopy in total is shrinking.

Melbourne is forecast to grow to 8 million people by 2051 and middle suburbs, with established infrastructure, will come under increasing pressure to house more people, according to this Age article. Plan Melbourne establishes a target of about 70 per cent increased housing in established suburbs, and 30 per cent on the urban fringe.

There are good reasons to increase housing density to maximise the efficiencies of infrastructure such as public transport, schools, hospitals. But we need to be careful it does not come at the expense of our total urban tree canopy that incorporates both the public and private realms.

On the one hand here in Moreland we have a well developed street landscape policy (2012-2022) that includes the policy of planting 5000 new trees every year. Moreland Council officers are presently developing a comprehensive Urban Forest policy.

At it’s September 2014 meeting Moreland Council adopted a report on increasing vegetation tree canopy and resolved “to support and fund current initiatives aligned with the management of climate change and the Urban Heat Island Effect.”

But Moreland is seeing significant urban consolidation and development. There are more high rise building development in the south of the municipality. In the northern suburbs subdivision and development of the traditional suburban family house and block often creates additional housing as villa units and townhouses but with little garden space.

As part of doing an inventory for the Moreland Street Landscape Strategy it was found that street trees provide only 2.5 per cent of the canopy cover across the Moreland municipality and yet their contribution has increased by 400 per cent since 1989.

Even more concerning, it was found that since 2010 there has been a 25 per cent decline in private tree canopy across Moreland municipality due to urban consolidation.

This is a trend that is exacerbating the urban heat island affect. While our streets might be becoming greener the number of trees and extent of the forest canopy as part of our private urban gardens is shrinking.

This is a huge planning issue when we need to be increasing vegetation and forest canopy in the urban environment, not only on public land and streetscapes but also on the private land where we live and work.

The state government’s Plan Melbourne, up to the present, hasn’t taken into account the reduction in private garden space due to development. Plan Melbourne was supposed to provide a blueprint for ensuring our suburbs developed and grew in a consistent and environmentally sustainable manner. But often garden space, private space for trees, suffered as a result of development.

The Melbourne Plan strategy sets out a goal of 70 per cent of new housing in established areas. Neighbourhood residential zones will have maximum mandatory height limits of nine metres, and general residential zones will have a maximum mandatory height of eleven metres. These limits can be varied by application to VCAT, which almost always seems to side with development proposals ignoring wider community and sustainability criteria.

Part of the change that Minister for Planning Richard Wynne announced is that caps on how many dwellings can be built on a block will be lifted, but with new requirements for developments to have a mandatory percentage of garden space.

Under the new rules, blocks between 400-500 square metres require a 25 per cent minimum garden area, blocks between 501-600 metres need 30 per cent, and blocks larger than 650 square metres must have a 35 per cent garden area.

This is partly aimed to stop houses being built in fence to fence development, but it may provide an impetus for increasing private trees to provide shade and reduce household energy costs.

“We’ve refreshed the vision and plugged the gaps, ensuring Victoria has plans to cater for population growth, deal with climate change and deliver a record pipeline of infrastructure.” said Minister for Planning Richard Wynne.

He accused the previous Liberal Government of missing the mark with Plan Melbourne, as it didn’t address the need to plan to manage population growth without allowing over-development. The previous Liberal National party government lead by Premier Baillieu, then Premier Napthine weren’t serious on climate change emasculating the state’s Climate change act and doing little to reduce the state’s emissions or encourage renewables.

Richard Wynne says this measure is all about giving Victorians access to backyard outdoor space and giving kids opportunities to form their childhood memories in backyards.

“These are once-in-a-generation changes to suburban residential zones and are all about protecting the much-loved Aussie backyard.” he said.

I worry less about childhood backyard memories, and more about keeping our homes, our city at a liveable temperature. The opportunity for more trees also improves urban biodiversity, aesthetics and a stimulating environment for children.

While the mandatory changes for garden space in new development is important, the the problem remains: how to encourage more tree canopy on private land, especially in sub-divisional development.

Entry filed under: heatwave, news.