Greening Australia’s cities

The urban greening movement is about making our urban environments cooler, more liveable and socially connected. Urban greening increases the amount of green infrastructure in and around urban areas, aiming to create mutually beneficial relationships between city dwellers and their environments. The world is learning more about climate change every day, which has led to green space initiatives being prioritised in urban planning. Projects like living walls, green roofs and tree planting are growing in scale as we come to realise we need to act fast.

Hotter cities

Adding to the impact of heatwaves and rising average temperatures is the increasing urbanisation of our cities, which creates large numbers of heat-generating hard surfaces in the form of buildings, roads and car parks, and impacts our stormwater runoff. Combined with the heat generated by traffic and industrial activity, it creates artificial warmth and so-called heat islands, resulting in urban areas having much higher temperatures than their rural surroundings.

Hotter cities compel residents to rely on air conditioners to remain cool, which further strains energy demands.

Urban greening can have significant effects on temperatures and energy use throughout a city, with major savings on electricity as well as added protection of critical infrastructure.

In Melbourne, there is a large percentage of hot spots that are more than 10°C warmer than non-urban conditions. Such heat islands can rapidly lead to tangible health impacts on their residents. The death toll in Australia from heatwaves alone has exceeded that for any other environmental disaster, including floods, bushfires, and cyclones, and the same is true for Europe and the U.S.

The power of plants

Plants can help cool cities through the water that evaporates from their leaves and by shading surfaces that otherwise might absorb heat. This evaporative cooling effect is achieved by evapotranspiration – the evaporation of water from within leaves. This is a very energy and cost-efficient way to regulate outdoor air temperature and can provide significant relief to people during heatwaves.

Plants also help keep harmful pollutants at bay, by trapping particles in the wax or cuticles of their leaves. Trees and vegetation in our streets absorb carbon dioxide and release oxygen, providing cleaner air to breathe.

The Japanese preventative healthcare practice of Shinrin-yoku, or ‘forest bathing’, is modelled on a recognition of the many benefits of immersion in natural spaces. Numerous studies have uncovered multiple social, psychological and health benefits of human exposure to green spaces. These include stress and anxiety reduction, lowered risk of depression, improved cognitive functioning and greater physical and mental wellbeing overall.

Green cities are healthier and more pleasant places to live, not just for people but for all other species. They act as vital refuges for rapidly vanishing biodiversity.

Many flora and fauna species have been lost or are threatened due to urban growth and roadways, and whole ecosystems have been destroyed or fragmented. Planting more trees can promote biodiversity, improve habitat and create the migration corridors necessary to ensure the health of existing wildlife populations. Of course, urban greening alone will not be enough to meet all the daunting challenges ahead but it would be a great start.

Whilst other countries around the world have a government system that can mandate this type of green infrastructure on a broad scale, the different levels of government in Australia pose a challenge to achieving consistent outcomes. With impactful initiatives such as the NSW Greening Our City program that aims to plant more than five million trees by 2030 and Melbourne’s Urban Forest Strategy, with an overall target of 40% canopy cover by 2040, it appears we are heading in the right direction.

Plant selection is also a major consideration. Planners need to think about the changing climate conditions of their cities, what types of greenery will thrive best in these environments and the ongoing maintenance of these sites. Special care and attention are required to maintain existing trees that are showing signs of suffering from a hotter, drier climate and to areas where wildfire plays a significant risk to our existing urban canopy.

Greening cities is more than just a technical challenge. It requires greater leadership and political commitment, integrated planning, community participation and long-term thinking.

Melbourne’s Urban Forest Strategy

1. Increase canopy cover 40% by 2040.

2. Increase diversity – no more than 5% of a single tree species, 10% of a genus or 20% of a family.

3. Improve vegetation health by 90%.

4. Improve soil moisture.

5. Improve biodiversity.

6. Inform and consult with the community

Written by Kerry Reber, Diggers education and events manager.