What is a heatwave?

Heatwaves are extended periods of hot days and nights and are increasing as a consequence of climate change. Even if they receive far less public attention than floods, cyclones or bushfires, heatwaves kill more people than any other natural disaster and seriously damage our health, ecosystems, agricutlure, infrastructure and communities.

in summer

Heatwaves get more attention during the hotter months of the year when they have greater impacts on things like human health, native wildlife, pets and infrastructure.

But also
in winter

Heatwaves can also occur during the cooler months too. A heatwave in winter won't reach 40°c and might only be a run of a few days a little over 20°c, but it's warm relative to the time of year. These kind of events can have disastrous impacts on our crops, by interfering with reproductive cycles and harvesting dates.

How do we measure heatwaves?

We look at periods of at least 3 days in a row where each day is in the top 10% for that day of the year, at each location.

Once we identify these days, three of them must be in a consecutive window to be considered a heatwave. One individual, or two days in a row, while still quite extreme, are not prolonged enough the be considered a heatwave

Characteristics of a Heatwave

By investigating heatwaves using different charactersitcs, we're able to understand more about what drives them, as well as provide the most appropriate information to those that need it most (e.g. health researchers, ecologists, engineers). For individual heatwaves, we might be interested in the following characteristics.


How long it went for


How hot it got compared to what we usually expect


The hottest part of the heatwave


How much area it covered


When the season started and finished


How many overall events there were

How are
heatwaves changing
in Australia?

Heatwaves in Australia are becoming hotter, longer, more frequent, and occurring earlier.

The changes in Australian heatwaves are part of a long-term global trend towards more heatwaves and hot weather in many regions, a trend that is very likely influenced by human-driven climate change.

Impacts of Heatwaves

Who (and what) feel the effects of extreme heat, and how? The short answer is "everyone", but in the interest of thoroughness let's break it down a bit further.

Direct Impacts on Human Health

Even if they receive far less public attention than floods, cyclones or bushfires, heatwaves kill more people than any other natural disaster and seriously damage our health, ecosystems, agriculture, infrastructure and communities.

Mortality numbers due to heatwaves in the world in the last few years:

  • Over 370 people were killed in SE Australia during the heatwave that preceded the black Saturday bushfires in 2009
  • 750 deaths were attributed of the Chicago heatwave in 1995
  • 70 000 people were killed by the 2003 European heatwave
  • 11000 people died as a direct result of the prolonged heat during Russia in 2010, with another 45 000 deaths from the smog and bushfires associated with the heatwave

number of deaths attributed to the 2003 European summer heatwave

How can the heat kill people?

Our bodies operate at a core temperature of 37°C and must maintain that temperature within a very narrow range.

If core body temperature rises to 38°C for several hours, heat exhaustion occurs, and mental and physical capacity becomes impaired.

If core temperature goes above 42°C, even for just a few hours, heat stroke and death can result.

Sport, events and tourism

Sport is also feeling the heat.

During the 2014 Australian Open tennis tournament, play was suspended on 16 January after the temperature exceeded 43°C.

While players sweltered in extreme temperatures, off-court ambulancestreated almost 1000 tennis fans for heat exhaustion in the first few days.

Tennis athletes were also affected, and showed symptoms of heat stroke such as hallucinations and collapsing.


Extreme heat can have significant impacts on infrastructure and essential services, especially electricity transmission and transport systems.

Financial losses from the 2009 heatwave in Australia have been estimated at $800 million, mainly due to power outages and disruptions to the transport system. Also during the 2009 heatwave, Melbourne train lines literally buckled because of the heat.

Energy demand increases dramatically as workplaces and houses run air conditioning at peak levels, which can result in rolling brownouts or blackouts. In some instances energy demand is so high that substations can catch alight because of the pressure.

Hospital facilities are also tested as members of the general public experience heat stroke. Any strain on public health infrastructure may continue for a number of days after the heatwave.


Heatwaves can have significant impacts on agricultural crops and livestock. High temperatures over several days can reduce the crop yield through direct and indirect effects. The direct effect is through damage to crop's reproductive parts, responsible for producing grain. Indirectly, extreme temperatures increase plant water stress, cessation of photosynthesis and possibly death.

For example, wine grape production in 2008-09 was around 7% lower than the 2007-08 harvest.

Natural Ecosystems

Plants and animals, like humans, are susceptible to extreme heat events. In periods of extreme heat, birds may lose up to 5% of their body mass per hour and rapidly reach their limit of dehydration tolerance.


Birds dead in Western Australia on January 2009, mostly zebra finches and budgerigars


Black cockatoos dead in January 2014 due to temperatures up to 48°C


flying foxes dead since 1994 along the east coast of Australia.

Population decline
and eventual extintion

Some of Australia's most iconic marsupials are also at risk during extended periods of hot weather, increasing the risk of population decline and eventual extintion.

Marine Ecosystems

Marine organisms are also affected by the impacts of severe heat. Heatwaves can occur in the surface waters of the ocean, sometimes leading to dramatic impacts on marine ecosystems.

When coral reefs are subject to sea surface temperatures more than 1-2°C above average summer maximum temperatures, the corals can bleach and die. The Great Barrier Reef has lost 50% of its coral cover in the last 30 years.

Underwater kelp forests are also permanently damaged when a marine heatwave occurs over their habitats. In 2011, a small but intense marine heatwave occurred off the coast of WA, named the 'Ningaloo Nino'. For 2 weeks, the water was as high as 4°c warmer than normal. This caused irreversible damage to the delicate ecosystems in this area, killing many fish and bleaching coral.


Of coral cover lost in the Great Barrier Reef
during the past 30 years

Future projections of extreme heat

With greenhouse gas concentrations in the atmosphere continuing to rise, extreme hot weather will become even more severe. Under a scenario of continuing high emissions—the track that we are currently on—the type of extreme hot weather we now regard as unusual will become a normal pattern in many regions, occurring every year or two.

Implications of severe heatwaves and hot weather

The prospect of increasing extreme heat events and heatwaves has important implications for our health and health services, our economy, our infrastructure and our environment.

It has been estimated that heatwaves could cause an additional 402 deaths annually by 2050 in Victoria alone. This translates to an additional $218 million loss per year

Heatwaves will increase further in their intensity, frequency and duration throughout the 21st Century. And this includes winter events during cooler seasons as well. We know, for example, that human induced climate change has at least doubled the chance of a European heatwave similar to 2003, and increased the likelihood of Australian summers as extreme as 2012/2013 by up to 5-fold. These risks will only increase further as we increase our greenhouse gas emissions.


deaths per year estimated by 2050 in Victoria alone

Even if we think that we can't help...

Our ability to reduce greenhouse gas emissions rapidly and deeply will strongly influence this scenario of high emissions.

The choices we make over this decade will largely determine the severity of the extreme heat that our children and grandchildren will experience.

We cannot wait to make greenhouse gas emission reductions later, when extreme events have already become unmanageable. That will be too late.

How can we reduce greenhouse emissions?

There are a lot of small, simple ways you can help to reduce greenshouse emissions. Trying to take advantage of more public transport rather than driving our car, using energy efficient lighting and appliances or even reducing the amount of appliances you have in your home.

Ten ways to reduce greenhouse gases

Burning fossil fuels such as natural gas, coal, oil and gasoline raises the level of carbon dioxide in the atmosphere, and carbon dioxide is a major contributor to the greenhouse effect and global warming. You can help to reduce the demand for fossil fuels, which in turn reduces global warming, by using energy more wisely.

Find out now