Each school was given a heat score. The hottest, with a score of 136, was All Saints Catholic College in Liverpool, followed by the Australian Islamic College in Mt Druitt, Delaney College and Holy Trinity Primary in Granville, and Liverpool Hospital School.
The researchers found Ponds High near Kellyville and Al Amanah College in Bankstown had shade covering just 2.4 per cent of their total grounds, while Al Faisal College’s Liverpool campus has no trees, and Amity College in Auburn has just 16 trees.
The project involved a study of nearly 1000 schools and the painstaking measurement of the hard surfaces, trees and shaded areas of 100 hundred schools from satellite images.
It is part of the Cooling the Schools program, launched by the environmental group Greening Australia, which commissioned Western Sydney University to study factors that were making schools vulnerable to excessive heat in the hottest parts of Sydney.
Researchers combined data on canopy and shade with other factors such as the so-called urban heat island effect – which sees some urban sites like schools grow even hotter than surrounding areas – and socio-economic data to identify its vulnerability to the impacts of Sydney’s climate.
The program will involve Greening Australia planting carefully-selected trees at 240 schools.
Greening Australia’s manager for its Nature in Cities program, Michael Vyse said the heat island effect had made some school playgrounds unbearable for children in parts of Sydney over summer.
“Planting trees is a sustainable and cost-effective way to provide shelter and natural cooling whilst also creating environmental benefits for local communities,” he said.
Heat has a significant impact on learning. Research has found that each increase of half a degree Celcius over a school year reduced performance in final exams by one per cent. Airconditioning corrects all the damaging effects.
Lead researcher at Western Sydney University Dr Sebastian Pfautsch said carefully planting trees on school grounds was more effective at cooling than providing artificial shade because their respiration – the transfer of moisture from the soil through their vascular system and into the air via leaves – actively cools the environment around them.
“Heat in schools is a critical topic that receives attention from the government, however, until now activities and funding programs have largely focused on what happens inside classrooms,” he said.
“Due to the impacts of climate change, outdoor heat has become a serious issue that must also be addressed.”
Dr Pfautsch said many schools had seen their canopy reduced over recent years due to fears about the dangers of limbs falling and the worry that they may contribute to allergies.
Western Sydney has been particularly hard hit by growing temperatures as the climate warms. On January 4 this year Penrith was the hottest place on earth for a period at around 3pm when the temperature hit 48.9 degrees, and this spring was the hottest on record.
Mr Vyse said the thousand of trees to be planted in the schools would be selected to be safe for the community, useful to the ecosystem and to cast shade. Most will be indigenous to the area where they are planted, but in some cases the need for trees that cast lots of shade in summer and little in winter – such as deciduous non-natives – may be considered.
Playgrounds can be especially hot because surfaces such as asphalt radiate heat and can reach 80 degrees. Children are more affected than adults because the centre of their bodies is closer to the ground, their metabolism is higher and they don’t sweat.
Dr Pfautsch said students in western Sydney were disadvantaged. Teachers kept children inside on hot days, but play and “the high value of learning activities in the outdoor space of school environments is increasingly recognised,” he said.
A spokesman for Sydney Catholic Schools said All Saints Catholic College managed the heat with airconditioning, covered walkways and undercroft areas. It also had plans to build new indoor and outdoor areas, and expand the green space.
A spokesman for the Catholic Education Diocese of Parramatta, which runs Delany College and Holy Trinity Primary, said both were long-established schools on small sites with hard surface areas.
The schools respond by airconditioning all learning environments, offering a covered learning area and shaded sail covers, and making indoor and shaded spaces available for students on very hot days.
“We continue to look at ways that we can mitigate against radiant heat in all of our schools, including the Granville schools,” he said.
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Nick O’Malley is National Environment and Climate Editor for The Sydney Morning Herald and The Age. He is also a senior writer and a former US correspondent.