From The Conversation: Heatwaves — Australia’s biggest natural killers — are getting more frequent and hotter thanks to climate change. One day cities such as Melbourne may see unprecedented heat, perhaps 48°C or higher.
But our research shows that smart urban design can create refuges in cities that could feel more than 10°C cooler, and without increasing energy use.
Recently the Victorian Auditor-General released a report that found Victoria is not adequately prepared to deal with heat disasters.
While this report focused on the ability of our services to respond to and communicate about extreme heat events, it also raises an important question: how do we better prepare our cities for more frequent and hotter heat waves?
With increasing predicted temperatures and the impact of the urban heat island effect (where urban space is much hotter than surrounding areas) to consider, there is increasing pressure on Australian cities to support the health of their populations during extreme heat events.
Whilst it’s important to make sure our emergency services are able to cope in the best way possible, this is a reactive response that will help manage crisis situations. Reinforcing the electricity grid to make sure that outages are minimised is also valuable.
However, proactively dealing with mitigation of extreme heat can take the pressure off services, minimise expense and most importantly, reduce heat stress.
How do we mitigate extreme heat?
There is an important body of work on reducing the urban heat island effect, particularly through urban greening infrastructure and building performance. A notable example of green infrastructure is the Melbourne Urban Forest Strategy.
Urban forests have been found to be very effective methods for city heat mitigation. However, vegetation takes a long time to grow and may not be as appropriate in every part of a city, so we need a greater diversity of solutions.
It is important to design at the street level scale: particularly in those places used the most. The spaces between buildings are necessary to urban functionality and where people spend most outdoor time.
A recent study in Sydney found that streetscapes have higher minimum temperatures than rooftops indicating the importance of cooling this highly used part of the city. Streets, train stations, even car parks can be designed to contribute towards much cooler experiences.
Keeping cool on the streets
Research on urban microclimates from around the world has shown that we can control the thermal comfort of smaller spaces, without using more energy (see also here and here). This is not just about reducing the absolute temperature, it’s also about making people feel comfortable.
The experience of temperature is controlled by both personal and environmental factors. Combinations of air temperature, wind, humidity and radiated heat will change the feeling, or apparent temperature, of the weather.
We can create spaces with optimum comfort levels through a combination of shading, reduced heat build up in materials, humidity and wind management. Rather than trying to change the temperature of the whole city, we can provide heat refuges at street level to make the city more functional on hot days.
We know that a comprehensive toolkit is needed to understand how we can cool the city in different places. Trees and greening are important but aren’t practical everywhere, and certainly not when they are used in isolation.
Designs that also include redirecting wind, controlling humidity and water and that consider thermal qualities of materials are necessary. There are also further opportunities for enhanced cooling that use virtually no energy.
For example, geothermal cooling (where wind is tunnelled underground and cooled by the earth) and misting are two tools that can actively reinforce cool space within cities.
A winning design
In a recent Street14 ideas competition run by the Australian Institute of Landscape Architects and Kingston City council we tested these design ideas on a site in the Melbourne suburb of Moorabbin. Our entry won Best Urban Tactic, you can watch the video below.
Our research using on site temperature and humidity sensors revealed temperature differences of up to 10°C across a small urban block. In addition, whilst exposed sites were the hottest, they were also often the quickest to cool off.
This gives us big clues into designing urban spaces for use across a whole day, where it’s important to minimise heat build-up but also to encourage rapid heat loss.
Key to this idea of designing microclimates is designing responses to the local conditions.
In Moorabbin, having the sensors on site was important because it meant we weren’t designing using generalised ideas, but instead able to work with the specific events on site.
This kind of work on design with atmospheric conditions is beginning to be explored in cities around the world.
Examples include climate engineers Transsolar, who were instrumental in demonstrating that Qatar’s 2022 World Cup bid was viable, showing how well designed stadia could mitigate the extreme temperatures of a Qatar summer (see also here).
In Taiwan construction is underway on the Jade Eco Park, a climatically controlled park that works to vary temperature, humidity and to provide clean air within microclimates to counter or enhance local climatic conditions.
Australian cities, with very particular weather conditions, need responsive design solutions that work with those kinds of factors.
For example, Melbourne’s very dry summers are more suited to cooling tactics that involve evaporation than other more humid capital cities.
Urban design can create spaces of heat refuge at street level within cities. Tram stops, train stations and streets that need to be used even during the most extreme heatwave are places that can be cooled.
If we can drop the temperature of these spaces by even a few degrees, we can save lives.