It's crucial that future urban developments have solid strategies to help cool cities, making use of ongoing research and statistics.
Over the past year, Australia has moved closer to bringing cooler cities to our doorstep, achieved through collaboration with Australian researchers, industry and local government leaders working together to plan ways in which to combat climate change and the urban heat island (UHI) effect.
Collaboration is the key to making change and combating rising urban temperatures, especially as studies worldwide show that a higher average temperature of two to 12 degrees Celsius exists in highly-urbanised areas compared to their rural surroundings.
We all need to work together to design cooler outdoor spaces utilising trees and vegetation, whilst creating surfaces and buildings that take into account their position to the sun whilst using innovative heat mitigating materials.
As part of this collaborative approach, in August 2017 Australian industry, local government leaders and researchers came together at a national forum to review this progress and where Australia’s first guide to urban cooling was launched and discussed.
The guide is designed to keep city dwellers cooler during hot weather by helping landscape architects, urban designers, planners, local authorities, government agencies and developers mitigate these UHIs and microclimates created by our urban environment.
The guide’s author and research leader, UNSW’s Dr Paul Osmond, said the document brings together data from a three-year project studying urban microclimates, covers different climate zones that define cities across Australia, and provides a toolkit for planners to use.
“The range of urban landscapes that the guide covers include dense inner cities, middle ring and outer suburbs with a focus on design intervention, including streetscapes, plazas, squares and malls,” he said.
“The importance of design which embraces vegetation cover, particularly tree canopy; the use of shade to minimise heat; and the orientation of these elements are also key to cooling. Interventions may be active, such as misting systems and awnings, or passive, like street trees, green roofs, water bodies, cool roofs and facades.
“All these elements have an effect on urban temperatures. For example, radiant temperatures in urban parks with sufficient irrigation can be two to four degrees Celsius cooler compared with adjacent unvegetated or built-up areas, while air temperature reduction may be up to two degrees Celsius according to a park’s extent and the proportion of trees. This is is known as the park cool island effect.”
Overall, urban climates are ultimately created from a balance between the heat of the sun and heat lost from walls, roofs and ground; by heat exchange via air movement between ground, buildings and atmosphere; and by heat generation within the city itself, for example from motor transport. Therefore the guide has a framework of urban form, climate type and the nature of intervention.
Building materials are a key contributor of UHI, so collaborating with companies like BlueScope Steel, a leader in sustainable, reflective materials, is a must. Their products can reflect heat off buildings to reduce inside temperatures, and when combined with surrounding vegetation, trees and landscape design, this helps reduce the UHI impact. Urban development must have trees and vegetation, as trees use solar energy to drive photosynthesis and evapotranspiration, while leaves and branches provide shade to keep everything beneath cool and protected against the harsh heat of the sun.
If you really want to experience how vegetation and trees work to cool a city, when in Sydney on a very hot day visit Wendy Whiteley’s Secret Garden in Lavender Bay, near North Sydney, and take a walk down into the park. You can literally feel yourself get cooler as the vegetation gets denser and you get lower. This garden is a great example of a cool oasis, with incredible views, in the middle of a busy city.
There are of course many other materials that impact UHI, one being what we walk on each day – paving – which in the past may have not been considered an issue.
According to the guide, surfaces like asphalt have a low solar reflectance of five to 20 per cent, so they can reach high temperatures of between 48 and 67 degrees Celsius, whilst other common paving surfaces like concrete have a reflectance of around 25 to 40 per cent, so their surface temperatures can get up to 65 degrees Celsius. Cool pavement materials – where the structure offer reflectiveness and permeability to air and water – store less heat compared to conventional products.
Increased reflectance, heat emittance and permeability to air and water are basic characteristics of cool paving and utilising lighter pigments and aggregates in asphalt, concrete, and other types of block pavers can increase their reflectance up to 30 per cent. However, the area of cool materials is in constant development with new material coatings being added to help further address cooling surfaces.
Overall, the guide is a major milestone for urban development, said Brett Pollard of HASSELL.
“Improving liveability, health and well-being are critical challenges for our cities, especially in light of our rapidly changing climate,” he said. “This guide will provide built environment professionals with evidence based design strategies that can be directly applied to projects, no matter what scale, and ultimately help keep our cities cool.”
The guide is also a prime example of positive collaboration, combining high quality research with the input of industry and government partners such as HASSELL, AECOM and Office of Environment and Heritage (OEH), who were instrumental in helping producing a tool which reflects the needs of end-users.
Collaboration is the key to a future where urban planning takes into account all that is required to keep our cities cool and carbon neutral.