Hot in the City

SERIES 33 | Episode 02

Costa’s visiting a public park in Merrylands, Western Sydney. It’s a classic park you might find in cities and suburbs around the country. But this park is playing a wider role in research looking at the impact of heat in our public places.

Dr Sebastian Pfautsch is an Associate Professor for Urban Studies at Western Sydney University, and he specialises in heat in urban areas.

Australia’s climate is getting hotter. Not only does this represent a risk to the environment, it’s also a risk to our health, and the suitability of the cities we live in.

“Heat in general is natural disaster killer number 1 in Australia. It kills more than all others put together; bushfires, floods, cyclones. It impacts people, the health system transport, the environment, the economy. Trains go slower, people go to work slower. It trickles into various aspects of life, how you look after yourself, social interactions, it’s quite incredible” says urban heat expert Dr Sebastian Pfautsch. In our cities, hard surfaces like roads and footpaths absorb and store  heat from the sun, exacerbating heatwaves, while densification often removes shade-giving trees.

“Heat is real. In heatwaves there can be a 12-13 degree gradient between suburbs.”

As part of his research Sebastian has started measuring heat. Through a network of loggers and heat sensors, Sebastian has been benchmarking temperature levels across Sydney’s west. The results have been concerning. “I recorded on one day Penrith was the hottest place on earth at 52 degrees, with 6 days of 50 degrees. Unbearable”.

At the park in Merrylands, Sebastian has recorded temperatures of 90°C on surfaces in an innocuous suburban playground.

After recording the dangerous heat levels at the playground, Sebastian worked with council to make simple adjustments to make the playground more safe. Shade sails were erected, and surfaces replaced with ones that mitigate heat load. Resulting measured temperatures are now within safe limits.  But Sebastian says the real insurance policy is the landscaping. “The sails are really temporary, the plants will grow and provide even better shading and cooling through transpiration”

Species planted include Eucalyptus moluccana, Lophostemon and Callistemons. The orientation of the plantings is north and west, to shield against the brunt of afternoon sun.

Sebastian refers to trees as “natural air conditioners”. By releasing water into the air through the process of transpiration, trees cool the surrounding area.

The project is focused on Sydney’s West because it experiences higher temperatures during heatwaves. This is due to it being further from the coast, receiving less rainfall, as well as the compounding effect of urban development. This is was Sebastian calls “green to grey”.

“The rates of urbanisation and greenfield transformation are at their highest in western Sydney. When we do that we introduce hard surfaces with concrete and roads, and this increases the amount of heat these environments store. Everyone wants a big house on a small block. Some of these developments there might only be 50cm between houses- there’s no space left to plant trees, even in retrospect.”

But Sebastian’s research has shown that there’s important differences in the kind of cooling offered by different trees. “The first is different types of ‘canopy architecture’, which is the way light is intercepted as it enters the tree-it’s different for different species. If you think about eucalyptus the leaves are arranged at the end in tufts, so the canopy is very sparse. If we think of a fig like a moreton bay it has a very dark canopy, so very little light and heat is getting through to surfaces underneath, and this provides more cooling”.

“Another is ‘leaf angle’, eucalyptus leaves are more pendulous. They’ve evolved in a hot dry climate, so they want to avoid sunshine and heating. This habit means more sun reaches the ground. If you look at a London Plane Tree the leaves are planar and flat; they’re deciduous leaves that have evolved to accumulate as much sun and energy as they can, and so less light gets through”.

These characteristics can be used strategically depending on the shade (and therefore cooling) outcome you’re trying to achieve.

Sebastian wants to this approach rolled out to every street, backyard and playground to help cool our cities.

Sebastian also says “Most of them are short to medium height trees. They can be planted on the northern and western side of houses to shade walls and windows, but they also make a lovely addition to any front yard or verge where most of the listed species provide decorative flowers besides cooling.

Figs and paperbarks would also be good options to grow medium to tall trees.”

* Check before planting: this may be an environmental weed in your area

Filmed on Dharug Country | Merrylands, NSW