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Cindy Brown says her daughter Evie regularly leaves school sweated through and flushed. - ABC

A school is more than its classrooms — it's a place made for play and connection with the physical environment.

But when the hottest spot in a school is its playground, the future looks increasingly like one spent inside.

That's particularly the case if you're growing up in Western Sydney, where temperatures rose above 50 degrees Celsius last summer.

New research from Western Sydney University has revealed common surfaces used in central schoolyards, such as unshaded asphalt and artificial grass, recorded surface temperatures of more than 60C during days of extreme heat last year.

That makes them the top heat traps in schools.

The research marked the first time a public school's outdoor microclimate had been measured in detail, and revealed the extent of how poorly schools were designed to be heat sustainable as climate change endures.

"The core of the research is that we're just not designing heat-smart schools. Otherwise I wouldn't be taking surface temperatures of 70 degrees Celsius at any school," research lead Sebastian Pfautsch said.

With Western Sydney's population expected to swell by 1.8 million in the next 20 years, and several schools already reaching student capacity, Dr Pfautsch said he hoped the same mistakes would not be made at new schools.

"The newly built schools should incorporate climate-smart or heat-smart designs from the masterplan stage, so we really tackle the problem head-on by setting up tree canopy cover for decades to come," he said.

In 2019, the NSW Government opened 42 new and upgraded schools, with more than $1 billion invested and 130 school building projects underway in 2020.

"The schools already built have not addressed heat, particularly considering how common unshaded asphalt is in playgrounds or fake grass, which is a real burn hazard given we recorded temperatures close to 100 degrees."

Extreme heat kills more Australians than any other natural hazard combined, and young children are at particular risk because they sweat less, reducing their ability to cool down.

Last summer, Western Sydney saw 37 days over 35C compared to just six recorded in the east.

The disparity is becoming a portrait of growing climate inequality within suburbs, and parents like Cindy Brown are worried.

Her six-year old daughter Evie attends a primary school in Rydalmere which is covered in only concrete and artificial grass. Most of it is unshaded.

"Every week I'll pick her up and she's sweated through and flushed, and it's not even summer yet," Ms Brown said.

"It concerns me that she's not going to get the experience to play outside. Every year there's going to be more days where it's safer to be inside with air-conditioning than outside, and that will discourage kids from being active."

When Ms Brown began looking at schools in the area she found most were built without grass and tree areas.

"You don't really have much choice out here. I'm not sure why so many are built without greenery," she said.

In 2018, the NSW Government committed to the Cooler Schools program, a $500 million election promise to install air-conditioning in more than 900 schools by 2023.

Outside the classroom, the answer to cooling down is shade, which the research shows can reduce surface temperatures by 20C.

The best kind comes from low-risk trees and shade sails, with the lowest temperatures in schools recorded under tree canopies.

While covered outdoor learning areas (COLAs) are an immediate answer, their tin roofs emit heat into the surrounding environment, unlike trees that actively cool the air.

The research found jacarandas and weeping lilly pillys were the most appropriate tall trees to use for cover, and the weeping bottlebrush and Queensland brush box were ideal shorter tree species.

Tree canopy cover is one of the NSW Premier's priorities, with the state aiming to plant 1 million trees across Greater Sydney by 2022.

However, Dr Pfautsch said it could take years for trees to mature.

He suggested an idea that could be made compulsory: planting trees that are already big.

It is a technique known as large urban canopy retention (LUCR).

"It means that mature trees earmarked for felling as result of development are dug up and transplanted into the new location," he said.

"It has been done numerous times at Sydney Olympic Park with big fig trees and can be done with a number of species.

"The benefit is that you instantly have the shade of a tree that is many decades old. No waiting."

As Western Sydney continues to grow at rapid speed, heat resilience is at the forefront of the battle for it to be liveable for the people who call it home.

ABC