Emerging Opportunities for Green Infrastructure

Keeping our Cities Liveable: Addressing Urban Heat Island Effect and Biodiversity

Our Australian Cities are often recognised as some of the most liveable in the world, but two emerging issues threaten to slowly and insidiously chip away at those accolades. Urban Heat Island Effect (UHIE) and biodiversity loss threaten the comfort and resilience of our homes.

Our cities are primarily concrete, which causes several issues for our comfort, safety, and the survival of local flora and fauna in a heating climate. The presence of biodiversity in our cities, especially trees with leafy canopies, promotes milder temperatures and greater air humidity. This presence of green improves thermal comfort for a greater sense of well-being and adverse impacts on human health, energy consumption, and urban infrastructure.

Research shows that urban forests have temperatures that are on average 2° degrees celsius lower that unforested urban areas.

The addition of trees and other vegetation to the built environment provides the greatest benefit in mitigating the UHIE. Through the process of transpiration and the provision of shade, trees help reduce day and nighttime temperatures, especially during summer. They shade streets and footpaths, and their leaves reflect more sunlight and absorb less heat than built materials, reducing the heat absorbed by the built environment. During transpiration, plants draw water from the soil and release moisture through their leaves into the air.

Tree canopies and root systems reduce stormwater flows and nutrient loads that end up in our waterways. They intercept and mitigate the impact of heavy rainfalls. Healthy tree roots help reduce the nitrogen, phosphorus, and heavy metal content in stormwater.

Biodiversity is a superpower of the natural world and we need to leverage its magic in our cities in our efforts to battle climate change and maintain liveability. Benefits of biodiversity in our urban environment include improve air quality, disease resistance, food security, and extreme weather regulation.

Small Spaces with Big Impact

We need to reimagine the role and function of our turf medians and verges, remnant land, easements, and desolate carparks, to meet the pressures posed by climate change, population growth, and urban heating on our cities, services, and community. Collectively, the reimagining, revegetation, and re-wilding of these spaces will be an important link in the chain of green infrastructure within our cities.

Streets make up the largest proportion of our publicly available space. Most streets were designed with efficient car movement in mind, and we need to continue to reimagine them for everyone (people, plants, bugs, and wildlife). They are our most democratic and truly public spaces; the essential arteries of our cities’ green infrastructure.

Green streets incorporate multiple elements with the potential to offer a diverse range of habitats to greatly increase urban biodiversity. Habitat types include trees, wetlands and pools, and vegetated areas. These can be incorporated into a relatively small area and offer a potential habitat to microbes, invertebrates, reptiles, mammals, and birds including some of our rarer or protected species. Biodiversity value of a green street increases with the inclusion of low planting of wildflowers, indigenous planting, and the incorporation of diverse microhabitats (such as varied ground topography, planting, and water availability).

A great example of how we might achieve this strategy in a coordinated way is the City of Melbourne’s Urban Forest Strategy, a format that has been adopted by many LGA’s across the country to help address the significant challenges facing our urban centres. The strategy aims to:

•  increase canopy cover from 22% to 40% by 2040
• increase forest diversity with no more than 5% of one tree species, no more than 10% of one genus and no more than 20% of any one family
• improve vegetation health, soil moisture rates and biodiversity

The strategy relies on a reimagination of the City’s central medians, intersections, verge buildouts, rooftops, remnant, and underutilised land to achieve these outcomes. Flexible and all-encompassing strategies such as this help to galvanise anyone with a vested interest in improving the health of our cities, no matter the scale. This sort of coordination is critical for establishing an effective green infrastructure in our cities.