Australia is considered as a “land of climate extremes”. This is true especially for our cities, which have at times become hubs of extreme temperatures in summer. This past summer was the second-hottest on record for Australia, following the 2018-19 record, with average temperatures increasing more than 2°C maximum above the long-term average.
Long and Frequent heatwaves are having serious impacts on energy consumption, labour productivity, public health, and also the economy.
Cities already face a problem even without global warming, the urban heat island effect, whereby inner urban areas are much hotter than the surrounding rural areas. Urban heat islands are caused mainly by factors such as energy consumption,pollution, industrial activities, asphalt roads, large dark concrete buildings, and closely spaced structures.
Australia’s major cities shows Evidence that average temperatures are 2-10°C higher in highly urbanized areas than in their rural surroundings.
Policymakers and Governments can use a variety of cooling strategies combined with community engagement, adaptation and education measures to cool Australian cities.
1. Green infrastructure
Green infrastructure includes parks, community gardens,street trees, green roofs and vertical gardens. In subtropical and tropical climate zones, like much of Australia, green infrastructure is a cost-effective cooling strategy.
Evidence suggests that about 10% increase in tree canopy cover can lower afternoon ambient temperatures by as much as 1-1.5 C. Similarly, in parks with adequate irrigation ambient temperatures can be 1-1.5°C lower than nearby or built-up or un-vegetated areas.
Street tree canopy cover can be increased by planting more shade trees on footpaths, lanes and street medians. Where there is little space for street trees and parks, green roofs and walls may be viable options.
2. Water-sensitive urban design
The use of water has been used as a way to cool cities for thousands of years. Water-based landscapes such as lakes, rivers, wetlands and bioswales can reduce urban ambient temperatures by 1-2°C. This is a result of evaporative cooling snd water heat retention.
In addition to natural water bodies, various other water-based technologies are now available for both decorative and climatic reasons. Examples include passive water systems, like pools, ponds and fountains, and active or hybrid systems, such as sprinklers and evaporative wind towers. Active and passive systems can decrease ambient temperatures by about 3-8°C.
Water-based systems are usually combined with green infrastructure to enhance urban cooling, improve air quality, aid in flood management and provide attractive public spaces.
3.Use of Cool materials
Building materials are major contributors to the urban heat island effect. The use of cool materials on streets, roofs and pavements is an important cooling strategy. A cool surface material has low heat capacity,low heat conductivity, high solar reflectance and high permeability.
Evidence shows that using cool materials for roofs and facades can reduce indoor temperature by 2-5°C, improve indoor comfort and cut energy use.
Cool materials commonly applied to buildings include elastomeric, white paints, acrylic or polyurethane coating, ethylene propylenediene tetrolymer membrane, polyvinyl chloride,chlorinated polyethylene, thermoplastic polyolefin, and chlorosulfonated polyethylene.
Lighter aggregates and binders in asphalt and concrete, permeable pavers made from foam concrete, permeable asphalt and resin concrete are standard cool pavement materials.
Shading can greatly improve outdoor thermal comfort and decrease radiant temperature. Providing shading on streets, building entries and public venues using greenery, artificial structures or a combination of both can increase outdoor thermal comfort and block solar radiation. Examples of artificial structures include temporary shades, sunshades and shades using solar panels.
5. Combined cooling strategies
Performance analysis of various projects in Australia suggests the cooling potential of the combined use of the different strategies discussed above is much higher than the sum of the contributions of each individual technology. The average maximum temperature reduction with just one technology is around close to 1.5°C. When two or more technologies are used together the reduction exceeds to 2.5°C.
6. Behaviour changes
People through their use of air conditioning are significant contributors to urban heat. The waste heat from air conditioners heats up surrounding outdoor spaces.
Projections show cooling demand in Australian cities may vastly increase by up to 275% by 2050. Such a trend will have a great impact on increasing electricity use as well as on urban climate. If this is powered by fossil fuels, it will add billions of tons of carbon pollution.
Climate-responsive building design and adaptive design techniques in existing buildings can minimize occupants’ demand for cooling energy by reducing indoor and outdoor temperatures.
Cities must take a holistic, long-term approach
Local governments can prepare for and respond to heat events through emergency response plans. However, emergency responses alone cannot address other challenges of urban heat, including human vulnerability, energy disruptions and the economic costs of lower workplace productivity and infrastructure failures.
Long-term cooling strategies are needed to keep buildings, city residents and communities cool and save energy, health and economic costs.