Urban overheating is a growing problem, and UNSW researchers have created a national index to measure and then mitigate heat vulnerability in Australia’s towns and cities.
Parts of Western Sydney experience dangerously high temperatures in summer due to the urban heat island effect, exacerbated by high-density developments, dark roofs and a lack of trees and green spaces. Photo: Nearmap, 2024
On hot days, heat exhaustion can hit quickly, bringing light-headedness, sweat and muscle cramps. If a person is unable to cool down at this point, they might feel nauseous and their heart might race. And if these symptoms are untreated, heat exhaustion can escalate to heatstroke, which can lead to death.
The elderly, the young, and those with pre-existing health conditions are the most at risk.
Heat has a history of making a devastating impact on people. Between 1900 and 2010, extreme heat events claimed more Australian lives than the total number of deaths from all other natural hazards combined.
With 2023 the hottest year ever recorded on Earth, Australia’s summers are getting hotter and more dangerous. For example, it is expected that Sydney and Melbourne will have 50 °C+ summer days in the near future, with Western Sydney already reaching 48.9 °C in January 2020.
What is Heat Vulnerability?
Urban heat is linked not just to increased deaths and emergency admissions, but also increased energy and water consumption, as people try to cool down.
Some communities are more vulnerable to the effects of heat. This can be due to living in towns and cities more impacted by the Urban Heat Island effect – where high-density urban areas have increased ambient temperature compared to surrounding suburban or rural areas – and also because they have less access to cooling resources such as air-conditioning (with the cost of running air-conditioners an additional barrier to consider).
Heat vulnerability measurements quantify the effects of high temperatures on communities, including heat-related illness, energy consumption and outdoor thermal environments.
Understanding heat vulnerability and selecting appropriate mitigation and adaptation strategies to reduce it has become increasingly important due to the impacts of climate change. It is now a policy and planning priority for all levels of government in Australia.
And that’s where UNSW researcher Associate Professor Lan Ding and her colleagues at UNSW’s High Performance Architecture team are making an impact.
A/Prof. Ding is leading a project to create a National Heat Vulnerability Observatory Index (NaVHO) to provide a standardised approach to data collection and measurement of heat vulnerability, which includes the impact of the built environment, as it identifies areas where populations are more vulnerable to the adverse effects of urban heat and informs effective cooling interventions in the built environment.
The data is then used to model the impact of different heat mitigation strategies and advise local authorities about which would be most effective in their locations.
“Addressing the impacts of urban heat vulnerability is critical for Australia to plan for resilient, sustainable communities to combat climate change,” says A/Prof. Ding.
“Concerningly, many of the places in Australia that are most vulnerable to extreme heat have been designed without enough of the features that mitigate heat, such as urban surface treatments, green spaces and trees with water irrigation, and water-cooling systems.
“This exacerbates the urban heat island (UHI) effect and thereby intensifies the health, economic and environmental impacts of extreme heat for these populations.”
What is a National Heat Vulnerability Observatory Index?
The NaHVO is a partnership between the NSW Department of Climate Change, Energy, the Environment and Water and UNSW's High Performance Architecture team, and has an advisory committee with representatives from government, industry and academia.
It was set up in 2023 to develop national benchmark datasets and an innovative, robust and consistent methodology to measure heat vulnerability in Australian towns and cities.
“The ability to monitor heat vulnerability and identify cooling opportunities is so important,” says Prof. Ding.
“It will help prioritise effective heat vulnerability investments and measure the impact of policy and investments over time. And it will support urban planners, developers and architects to design smart, climate resilient towns and cities.”
While there are a range of mitigation and adaptation interventions that can be used to reduce the impact of heating in urban environments, the challenge for decision makers is how to know the specific impact those interventions will have in their town or city, because of the unique attributes of every location.
“The NaHVO enables those responsible for communities, from the national government down to local government, to see and measure the effects of urban overheating. And, importantly, to receive advice on cooling strategies and location-specific data on the impact of implementation of these strategies,” says Prof. Ding.
The impact of the National Heat Vulnerability Observatory
The researchers have just completed phase 1 of the project, where they built town-specific datasets for areas of Dubbo Region and Maitland City measuring heat vulnerability. They then modelled the potential effects of heat mitigation strategies and other planning decisions on those locations.
In both cities the team were able to use the multi-disciplinary benchmark datasets to model how the use of cool materials (on roads, pavements and roofs) and increased urban greenery (through planting and irrigation) would reduce heat.
The project team also conducted ‘microscale’ cooling potential analysis as part of the pilot.
Dubbo Regional Council chose Southlakes, as it represents the types of new residential developments planned for Dubbo, and South Dubbo to understand and reduce heat vulnerability in existing areas of Dubbo.
In Southlakes, various subdivision scenarios have been analysed. The results indicate that reducing lot sizes while increasing building density leads to increased outdoor air and surface temperatures. However, implementing a combination of mitigation strategies can effectively reduce the heat effects associated with increased building density.
Maitland City Council identified Aberglasslyn as one of the key areas vulnerable to heat. During heatwaves, the suburb experiences higher air temperature and surface temperatures than surrounding areas, primarily due to dark roofs and low tree canopy coverage along its streets.
Cooling interventions, such as replacing dark roofs with cool roofs, can significantly reduce energy consumption for space cooling while mitigating heat effects across the suburb.
“We were able to compare the impact of scenarios, from altering subdivision lot sizes in a new development to changing the materials of roofing and hard surfaces, and provide data specific to those locations that showed how different decisions would affect temperatures and therefore everything from energy consumption to the health of the community,” says Prof. Ding.
Modelling showed that the use of cool roofs, cool pavement, greenery with water irrigation, water-misting and outdoor shading could reduce air temperature by 1.6 °C in the areas studied in Maitland and 2 °C in the areas looked at in Dubbo and the surface temperature by over 10 °C in each location.
Having successfully shown the impact of the NaHVO in Dubbo and Maitland the team is setting up to expand the project to a further 21 cities in Australia.
“The more cities we collect benchmark data from, the more robust the NaHVO will be,” says A/Prof. Ding.