Our backyards should be safe and inviting spaces all year round, including during the summer months.
Authors
- Pui Kwan Cheung
Research Fellow in Urban Microclimates, The University of Melbourne
- Stephen Livesley
Professor in Urban Horticulture, The University of Melbourne
But the choices we make about garden design and maintenance, such as whether to have artificial turf or real grass for a lawn, can have serious consequences. Children, elderly people and pets are particularly susceptible to burns from contact with artificial turf on a hot day.
Watering your lawn or planting a shady tree can also dramatically change how hot your backyard feels in summer. Ultimately, these factors will influence how much time you and your family spend outside.
No matter where in the world you live, it is never too late to find out how to make your backyard safer and cooler next summer.
The case against artificial turf
Artificial turf or synthetic grass, commonly used on sports fields, has become popular in private outdoor spaces such as backyards.
People may think it's cheaper and easier to maintain than real turf. Perhaps they like the idea of saving water and having the look of lawn without the hassle of mowing and fertilising it.
But this type of plastic surface is known to become very hot on a sunny day.
We wanted to find out just how hot artificial turf can get in a suburban backyard over summer.
So we set up an experiment to compare the temperatures of artificial turf, dry natural turf, and watered natural turf in Melbourne. We took surface temperature measurements continuously for 51 days during the summer of 2023-24.
The research was part of a project demonstrating the benefits of green space in residential properties. The project received funding from Horticulture Innovation Australia, a grower-owned not-for-profit research and development corporation. That funding, in part, came from three water authorities.
Feeling the heat
In adults, irreversible burns occur when the skin is in contact with a surface that is 48°C or hotter for ten minutes.
The temperature needed to cause skin burns in children is approximately 2°C lower, because their skin is thinner and more sensitive .
Contact skin burns due to the high surface temperature of artificial turf has been identified as a health risk.
In our latest research , the artificial turf reached a scorching 72°C, which is sufficient to cause irreversible skin burns in just ten seconds. In contrast, the real turf was never hot enough to cause such burns (maximum temperature of 39°C).
Over the course of our experiment, the artificial turf was hot enough to cause adults irreversible skin burns for almost four hours a day. While adults might be expected to move away from the heat before it burns, vulnerable people such as babies and the elderly, as well as pets, are most at risk because they may be unable to move away.
We also took measurements in real backyards on a hot sunny summer's day. We compared the risk of skin burns on four different surfaces: artificial turf, mulch, timber and real turf. The only surface that did not get hot enough to cause skin burns in adults was real turf.
Why should I water the lawn?
Grass and other plants release water vapour from little holes in their leaves into the atmosphere. This process helps the plant maintain a liveable leaf temperature on a hot day, but it also cools the air around the leaves.
It is a good idea to water your lawn throughout summer for two reasons:
well-watered lawn is healthier, stays green for longer, and has more leaves to release water vapour into the air ("transpire").
more water is available to evaporate from the soil and leaves , adding to the cooling effect.
If you're worried about wasting drinking water on your lawn, you can install a rainwater tank or household water recycling plant . Having access to alternative water sources will become increasingly important as the world warms and the climate dries.
What about shade?
The most effective way to make you feel cooler in your backyard is to provide adequate shade. This reduces the amount of sun energy hitting your body or the ground, heating the surface and warming the surrounding air.
A single tree can lower the level of heat stress from extreme to moderate. This may be the difference between wanting to spend time outside on a hot day and avoiding your backyard altogether.
Even small trees can still make you feel cooler, if they provide some shade.
However, too-dense tree canopy cover may prevent air flow - so there is a happy medium. Air flow is necessary to move the heat away from your backyard and cool your body down.
Taking all the above measures will keep your backyard safe and cool throughout summer. This will allow you and your family to spend more quality time in your backyard, cool your home, and improve your quality of life.
Pui Kwan Cheung receives funding from Horticulture Innovation Australia (Hort Innovation) for the research project "demonstrating the benefits of increasing available green infrastructure in residential homes", which is relevant to this article. The project involves co-investment from South East Water, Greater Western Water, Yarra Valley Water, the Department of Energy, Environment and Climate Action (Victoria), Department of Planning, Housing and Infrastructure (New South Wales), The University of Melbourne, and the Australian Government. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture.
Stephen Livesley receives funding from Horticulture Innovation Australia, the Australian Research Council and various water authorities.
