Most of the time we discuss climate change as affecting cities and the people who live in them. Less well known is that cities – specifically their planning and design – also create climate change through the urban heat island. Encouragingly, this means that cities can provide climate solutions. Why are we not discussing this? The following is the first of two articles on this topic.
Throughout 2019, cities across the world witnessed their hottest summers ever. While heatwaves have always been part of summer conditions in Australia, what we are witnessing now is not normal and major cities have experienced unprecedented intensity and duration of hot days. Climate change and will continue to exacerbate heatwaves and their impacts.
But cities themselves also contribute to climate change through the urban heat island (UHI) effect. Research shows that UHI can add 2-4 degree Celsius in urban areas compared to outer suburbs, and as much as 15 degree Celsius compared to parklands or rural areas. Heat is trapped in cities creating a “heat bubble” or meso-climate.
UHI is caused by a potent mix of poor urban design, high density building stock, reduction in wind speed, materials with high thermal mass, low albedo and low permeability, poor landscaping and pollutants from industry and traffic.
So many planning solutions contribute to the UHI
UHI can happen all year round, It can increase the risk of death from heat stress and heat stroke, especially among vulnerable people
The burden of extreme heat is typically borne by low-income groups who cannot afford to cool their homes.
Shockingly, between 1890 and 2013, extreme heat killed more Australians than all other natural hazards combined (except
epidemics). For example, while the 2009 Black Saturday bushfires resulted in the deaths of 174 people, the heatwave that preceded the fires is estimated to have resulted in of 980 deaths in Victoria and South Australia.
Survival of the precious natural environment within cities is also threatened, with fauna such as butterflies, moths, honeybees and koalas dying due to heat stress.
Economically, heat stress has livelihood implications for people who work outside, and puts pressure on residents’ back pockets through higher energy costs for cooling. Buildings and physical infrastructure can also be affected by heat stress and cause cracks, buckling or failures in exposed infrastructure – such as roads, bridges and rail lines.
Those who can (including the authors!), crank up their cooling system within the home and workplace, increasing energy consumption and putting pressure on the city’s energy system.
This can make matters worse. Especially if the aircon is run on coal fired electricity. Aircon units also spew hot air to the outside, which further heats the city (see Figure).
We are stuck in a reinforcing feedback loop between climate change and UHI effect. For Australia – the driest continent on earth – UHI has further implications on food and water security.
We’ll need 1 billion new houses by 2050 – but there’s not much by way of climate centred design
In 2018, the Global Facility for Disaster Reduction and Recovery (GFDRR) predicted that the world will need nearly 1 billion new dwellings by 2050, equating to a doubling of the current building stock. We are building new cities and densifying existing ones at an accelerated rate, but we are not designing them with UHI and climate change adaptation in mind.
One of our research projects, the Tarnagulla community resilience action plan confirms that housing and infrastructure constitute one of the most pressing needs for communities, yet, they are mal-adapted to our changing climate, putting lives at risk.
Without concerted actions, UHI will cost us our lives, liveability of our cities and the planet we call our home.
What can we do about the UHI effect?
There are a myriad of strategies being adopted by cities across the world to reduce UHI and adapt to climate change.
Green roofs and walls, increasing green space and canopy cover, urban farms, storing stormwater and increasing groundwater percolation, and expansion of highly reflective pavements are just some of the strategies being used, globally.
However, research suggests that the effectiveness of such strategies is largely dependent on the environmental conditions such as local climatology, geography and surface topology, and therefore, strategies applied at local-scale do not necessarily reduce city-level UHI effect.
We must accept scientific evidence and work collaboratively
Decisions must be evidence-based and be supported by political goodwill to allow for change to happen.
Concerted action is required from state and local governments (especially amongst planners and urban designers), the private sector (especially architects and developers), researchers, the not-for-profit sector, and finally from city residents themselves.
Resilience thinking can help
UHI and outdoor air quality (OAQ) are complex problems that require resilience thinking to understand how and where to make positive change.
For example, addressing the UHI effect requires understanding the interrelations between urban morphology (grey infrastructure), green-blue infrastructure, local climatic conditions, and economic and political conditions and trends.
Nature based solutions
A third key principle is the massive potential for nature-based solutions for reducing the UHI effect.
These initiatives include green infrastructure such as street trees, parks and backyard gardens, and blue infrastructure such as water sensitive urban design and allowing rainwater to percolate in the soil. Not only does more green and blue space reduce heat, it has significant other for city residents and local biodiversity.
Currently, in one of the action-research projects Climate Resilient Honiara, we have adopted nature-based solutions to develop strategic actions to build resilience of those living in rapidly urbanising and fast-growing capital city of the Solomon Islands, from current and future climate impacts and natural hazards.
Underlying nature-based solutions is the acknowledgment that the health of ecosystems and the biodiversity that comprises them is fundamental to human settlements and human survival.
What would this look like in practice?
Australian cities could develop cooling strategies to promote cooling landscaping such as providing shade, including water features, and supporting biodiversity. Such a strategy would also explore amending planning policies and updating building codes that haven’t changed in 50 years.
Land-use planning that reduces, or at least does not increase, the UHI effect in Australian cities would include adjusting the ratio of green-blue infrastructure to grey-infrastructure (that is land cover), pattern of land-use, and density of building stock.
Urban design, building regulations and the building design standards also need to be updated.
Low albedo building materials and pavements, and increasing porous or high-water permeable pavements, could make a significant impact.
We could mandate green canopy cover and (extensive or intensive) green roofs, and encourage vertical greenery and green pavements. As our cities grow vertically, green roofs have proven to be an effective strategy to reduce outdoor air temperature and energy consumption.
Australian cities can learn from our neighbours such as Singapore, which leads South-East Asia in reducing UHI effect.
”Cooling Singapore” is a collaborative research project involving government, consultants and researchers, that has developed a comprehensive catalogue of 86 strategies for cooling, grouped into seven clusters: vegetation, urban geometry, water features and bodies, materials and surfaces, shading, transport, and energy.
The government has mandated in the Building Control Authority,, inclusion of green infrastructure at multiple building levels and has also developed climate-responsive design guidelines.
Together, these strategies has helped Singapore achieve 14th ranking internationally and first ranking in Asia in 2018, for their environmental health and ecosystem vitality, as per the Environmental Performance Index, developed by Yale University and the United Nations.
Event: If you are interested in shaping the future cities while living in a changing climate, come and join RMIT lecturers and researchers at a panel discussion as part of Sustainable Living Festival on 19th Feb 2020. Register here.
Dr Mittul Vahanvati is lecturer and research fellow at RMIT University, the School of Global, Urban and Social Studies. Her research and practice focuses on long-term effectiveness of disaster recovery, which sits at the intersection of environmentally sustainable buildings and community resilience. She specialises in co-production approaches and designing reconstruction programs for long-term community resilience and has been based in Australia, Switzerland and India..
Dr Adriana Keating is a Research Fellow in the Centre for Urban Research. Her research focuses on the human dimensions of disasters and climate change adaptation. She is an expert in disaster resilience, and her work utilises systems analysis, and measurement and decision-support methodologies.
Helen Cheng is a practising Australian architect in Singapore, studying Masters of International Urban and Environmental Management, focusing her research on Singapore building practice, strategies and policy implementation.
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