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How to make your home more resilient to heatwaves and severe storms in summer

Some parts of Australia are sweltering as a heatwave moves from Adelaide across to the east coast.

The City of Churches is no stranger to heatwaves.

In February 2017, the city experienced temperatures above 40 degrees Celsius for three consecutive days. At night, temperatures didn't drop below 30 degrees.

Michelle Leishman and colleagues at Macquarie University analysed images collected during the heatwave as part of a heat-mapping project of West Adelaide.

This is what the suburb of Mansfield Park looked like.

Adelaide heatwave

The analysis of the AdaptWest images highlighted the stark differences between urban (dark red) and vegetated areas (blue and purple).

In the heat of the day, roads and roofs reached up to 50 degrees.

During the night, bitumen roads continued to radiate heat.

This effect, known as the urban heat island, is well known. And Adelaide is not alone.

On January 4 last year, a temperature of 48.9 degrees C was recorded at Penrith in Sydney's west, making it the hottest place on Earth that day.

Both cities experienced severe storms either before or after the heatwaves.

Heatwaves and severe storms are features of the Australian summer, but as the climate warms, hot spells and heavy rainfall are predicted to become more frequent and more intense.

Here are some key changes you can make to your home that could help you weather the highs and lows of summer — and even save you some money.

Plant trees in your garden

While the buildings baked in Mansfield Park, large trees and grassy expanses reduced temperatures by between 5 and 6 degrees during the heatwave.

"If you think about the difference between 32 and 39 degrees, that makes a huge difference to people's thermal comfort," Professor Leishman says.

In West Adelaide, people's gardens covered about 20 per cent of the land, but they contained more than 40 per cent of the total tree cover.

While many government and city councils have urban greening programs, Professor Leishman says the focus is on public land such as parks, gardens and street trees. But expanding green areas in backyards could make a big difference to the heat island effect.

"Gardens are critically important to maintain and expand those urban forests and the benefits they provide, but there's very little concentration on gardens," Professor Leishman says.

Trees not only provide shade, but they also suck water up from the ground and release it through their foliage in a process called evapotranspiration.

Trees can also help reduce flash flooding and pollutant run-off during storms, and are important for maintaining biodiversity and wellbeing.

"It's become really obvious, especially after all our lockdowns, how important green spaces are for mental health and physical wellbeing," Professor Leishman says.

If you are planting a garden, Professor Leishman has a few tips to get you started:

  • plant deciduous trees on the northern or western sides — these provide shade in summer and allow light in in winter so you use less energy
  • trees can take a long time to grow, so start with a succession plan that includes grasses and shrubs
  • planting locations are important particularly for large trees. In the right location, they can develop deep anchoring roots so they are at less risk of toppling
  • keep trees maintained to reduce the risk of branches falling and litter building up
  • trees only provide a cooling effect if they are kept watered.

Many trees planted today in certain locations may not survive as the climate warms unless they are kept watered.

Professor Leishman and colleagues are currently investigating which species are suited to which area, and eventually hope to have an app that homeowners can use.

Go deeper: Tree loss is making for sweaty suburbs

Harvest stormwater in your backyard

Keeping water up to your plants in a heatwave or a prolonged drought can be a challenge.

But when it does rain, the amount of run-off in urban areas can increase by five to 10 times, damaging waterways and causing flash flooding, says Tim Fletcher of the University of Melbourne.

"Then, perversely, when it's not raining, we have a much drier landscape because we've let all that water go," Professor Fletcher says.

Several cities in Australia, including Adelaide, are now trialling systems to harvest stormwater, treat it in wetlands and store it to be reused at a later time.

There are also number of ways you can control stormwater around your home, not only to water your garden in dry times, but also to help prevent flash flooding.

One of these is to create a rain garden. These are specially constructed gardens where water is diverted from your downpipe to an area with loamy soil.

The water is used to support the plants or collected in an underdrain and sent slowly back into the stormwater system.

"They can be really nice natural-looking gardens, or they can be used as a vegetable garden," Professor Fletcher says.

He says there a few things to consider when constructing a rain garden, such as:

  • choosing plants that can tolerate both wet and dry conditions. Most states around Australia have recommended lists of plants for rain gardens for their particular region
  • constructing your garden for your climate. For instance, in places like Perth that experience long dry periods, build a saturated zone in the bottom. This keeps the water deep in the the soil and sustains plants for longer.

Another strategy is to use permeable paving surfaces such as porous asphalt, concrete or pavers separated by plants.

You can also design your driveway so water flows into the garden instead of going out into the street. You see this effect, known as 'green pick', on the edges of country roads.

But the most obvious thing you can do is store water in rain tanks.

"The technology around rainwater tanks has advanced so far," says Professor Fletcher, who uses a system that taps into weather forecasts from the Bureau of Meteorology.

The system allows him to monitor how much water is in the tank, and, if need be, release water ahead of a storm to help prevent flash flooding.

To make the most of stormwater coming off your roof, Professor Fletcher advises connecting your tank for as many uses as possible.

"Sometimes people put in a tank and just connect it to their garden water, but if you have it connected to toilet, hot water and laundry, you've now got quite a lot of uses being pulled out of it."

Go deeper: Chris made stormwater smart and saved money

Choose a light-coloured roof

Trees are important for providing shade, but you get to a point where the cooling benefit plateaus, says Deo Prasad of the CRC for Low Carbon Living.

And, he says, you need to plan your garden carefully to minimise the risk of falling branches or shading out areas for vegie gardens or solar.

Another major strategy to reduce temperatures in urban areas is to use light-coloured surfaces as roofs and roads.

"The difference between a black roof and a white roof in terms of the surface temperature would be 30-plus degrees," Professor Prasad says.

"Heat very quickly finds it way inside, particularly in black and dark-coloured metal, so you have to put a lot more insulation in the ceiling to offset that effect."

Meanwhile, dark asphalt can reach a peak surface temperature of between 48 and 67 degrees during the day and continue to radiate heat into the night, as seen in the heat maps above.

"If you have darker buildings ... or urban areas, they absorb and reradiate till much later in the day," Professor Prasad says.

"And if it is consecutive days of much higher temperatures, then it really heats up and continues to emit heat in the neighbourhood."

Many cities are now trialling light-coloured surfaces for roads and buildings and have regulations in place to ensure glare, particularly off glass surfaces, aren't an issue.

But, Professor Prasad says, there are no regulations in place in Australia for the introduction of light-coloured roofs.

"California introduced regulations on light roofs many decades ago," he points out.

Other changes to housing design that will make a difference according to Professor Prasad include:

  • considering the orientation of your house. Key living areas should be north-facing, which can be easily shaded in summer, but let the light in in winter. East- and west-facing facades are harder to shade, so they are best for rooms with smaller windows such as bathrooms or garages
  • thinking about the angle breezes come in from outside so you capture and circulate them inside your home
  • limiting the amount of glass facing the Sun, which causes overheating
  • installing insulation and double glazing to lower the impact of extremes.

Go deeper: High energy efficiency could be improved through simple tweaks

Put solar on the west as well

Heatwaves can put a lot of pressure on the electricity grid and your bank balance, especially if you use air conditioning to stay cool.

So if you are thinking about installing solar, consider putting some panels on the west-facing roof.

"In some places like Adelaide for example they have very actively encouraged west-facing solar ... because they had demand problem with the network," Professor Prasad says.

Traditionally everyone put panels on the north because you get sun until about 4 o'clock. But putting panels on the west side means you can take advantage of solar energy during peak periods.

"If you have sun generating solar on the west-facing panels, then you can get free energy until much later in the afternoon," Professor Prasad says.

"So your payback becomes good even if you generate for less time on the west."

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