Penrith deals with urban heat
James Dunn
Updated May 28, 2015 – 2.39pm, first published at 12.15am
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Any sleeping dog will tell you that the shade is the best place to be in the harsh heat of the Australian summer, but Penrith City Council wanted to look further than that: it wanted to see how its urban tree cover might mitigate that heat – and conversely, how a lack of tree cover might worsen it.
In one of the first studies of its kind, the council – with funding assistance from the NSW state government and support from Local Government NSW – set out to map its local government area to see what effect heat had on its population, and to investigate if it needed to be mitigated, and how that might be done.
The council engaged the Institute for Sustainable Futures (ISF) at the University of Technology, Sydney (UTS) to analyse CSIRO thermal mapping of Penrith to identify the areas of higher heat, and whether those coincided with concentrations of its more vulnerable communities –that is, the old and disadvantaged.
Penrith's Nepean River is a naturally cooler area, but built-up zones create the 'urban heat island' effect. Wolter Peeters
The ISF study analysed five suburbs, with 16 identified hotspots, which had levels of tree cover as low as 2.5 per cent, and high proportions of sealed surfaces. Candice Delaney, senior research consultant at the ISF, says that while the site-specific causes of heat can include the level of tree cover, water absorption and the surface albedo (reflection) value, the geometry of urban areas, topography and wind direction are also influential. "In spite of this complexity, the study showed that the presence of tree cover explains 55 per cent of the variation in surface temperature in 16 Penrith hotspots," Delaney says.
Poorer groups harder hit
"The residential areas throughout the study were shown to be consistently hot, placing housebound groups at risk, regardless of their socioeconomic standing. However, we found that people in a lower socioeconomic bracket, who were already vulnerable to the impacts of heat, were more at risk."
In residential areas of Penrith with high levels of tree and grass cover, the temperatures were significantly cooler, she says. These cooler areas presented a "stark thermal contrast" to neighbouring hotspots.
Carl Spears, principal communications officer at Penrith City Council, says the study has given the council "broad priority areas to further investigate". He says while the city's beautiful natural areas, especially near the Nepean River, are naturally cooler, urban areas create the well-recognised "urban heat island" effect.
"This affects all urban areas and cities, but Penrith is at the forefront of doing something about it. We think it is important to find ways to cool our city and make it even more liveable into the future," Spears says.
Penrith's strategy to combat urban heat islands, titled "Cooling the City", recognises areas where vulnerable groups live, as well as those where people congregate – for example, schools, childcare centres and transport nodes.
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