Since 1900, extreme heat events have killed more people in Australia than the sum of all other natural hazards (Coates et al, 2014).
A heatwave is a period of three or more consecutive days of extreme heat. Heatwaves are likely to increase in frequency and intensity due to climate change.
Frequency of heatwaves
Across Australia, heatwaves are becoming hotter, longer and more frequent (Bureau of Meteorology, 2018).
Since 1910, the number and frequency of days of extreme heat have increased, as shown in Figure 1.
Figure 1: the number and frequency of extreme heat events in Australia from 1910 to 2010
By the 2050s, if the current rate of global warming continues, Victoria could experience around double the number of very hot days each year compared with the 1986–2005 average (Department of Environment, Land, Water and Planning 2019).
Figure 2 shows the 2050 projections for the number of very hot days per year in three selected cities: Melbourne, Bairnsdale and Mildura compared with the 1986–2005 average.
Figure 2: Number of very hot days per year in three Victorian cities comparing the 1981–2010 average with projections for 2050s.
There are also reports that Victoria is tracking towards the worst end of climate projections, with potentially devastating impacts on Victorians, the economy and society (Department of Environment, Land, Water and Planning 2019).
While anyone can be affected by heatwaves, people particularly susceptible include the elderly and very young, people with existing chronic health conditions, low-income households, people who are socially isolated and those who are required to be physically active for employment (Department of Health and Human Services 2018a).
The health impacts of extreme heat and heatwaves can be significant. Extreme heat increases the incidence of illness, most commonly in the form of:
- heat cramps, heat exhaustion and heat stroke
- exacerbation of a pre-existing medical condition
- gastroenteritis, in connection with poor food handling (Department of Health and Human Services, 2018a).
Heatstroke is a medical emergency that can result in permanent damage to vital organs, or even death, if not treated immediately (Department of Health and Human Services 2018a).
Extreme heat can also exacerbate pre-existing medical conditions, including heart and kidney disease, asthma and other respiratory illnesses (Department of Health and Human Services 2018a).
In 2009 and again in 2014, major heatwaves resulted in catastrophic impacts upon the health of Victorians. In both instances, heatwaves resulted in loss of life, with an estimated 374 excess deaths in 2009 and 167 in 2014 (Department of Health and Human Services 2018a).
Extreme heat affects all parts of the health system, with ambulance, emergency departments and community health sectors particularly affected (Natural Capital Economics 2018).
In 2018, it was estimated that heatwaves cost Victoria $87 million annually, with these costs projected to increase significantly as climate change increases the severity and frequency of heatwaves (Natural Capital Economics, 2018).
These economic impacts are felt across the Victorian economy, including in the construction, electricity, health, manufacturing, mining, tourism, transport, agriculture and water sectors, with the greatest impact experienced by the agriculture sector (Natural Capital Economics 2018). The impact on agriculture will lead to higher food production costs for Victoria.
Increased frequency and severity of heatwaves affects the ability of individuals to pay energy bills.
Many Victorians already struggle to pay energy bills (Victorian Council of Social Service, 2017), and the number of people expected to experience ‘bill stress’ during summer will increase as heatwave frequency and severity increase.
Extreme heat days in Victoria
The Chief Health Officer issues a heat health alert when the heat health temperature threshold is reached for a specific weather forecast district.
Victoria’s heat health temperature thresholds are based on academic research, past experience and practice.
Heat health temperature thresholds are the average temperature above which substantial increases in mortality in weather forecast districts can be expected (Department of Health and Human Services, 2018b).
For the 2016–17 summer season, the Chief Health Officer issued heat health alerts for six days, three of which were consecutive from 8–10 February 2017 (Department of Health and Human Services, 2018b).
Observed temperatures from the Bureau of Meteorology indicate that extreme heat occurred on all six of these days.
For the 2017–18 summer season, heat health alerts were issued for 10 days. Eight of these actually experienced extreme heat (Department of Health and Human Services, 2018b). This is shown in Figure 3.
There were two periods of heatwave with three or more days of extreme heat forecast: 18–21 January 2018 and 26–28 January 2018.
Figure 3: Number of forecast and observed extreme heat days in Victoria during summer seasons 2016–17 and 2017–18 as indicated by heat health alerts
Find out more
For more information about climate change and its impacts upon health, access the Chief Health Officer's Climate change page.
Bureau of Meteorology 2018, Understanding heatwaves, Bureau of Meteorology, Canberra.
Coates L, Haynes K, O'Brien J, McAneney J and Dimer de Oliveira F 2014, 'Exploring 167 years of vulnerability: An examination of extreme heat events in Australia 1844-2010', Environmental Science & Policy, vol 42, Oct 2014.
Department of Health and Human Services 2018a, Survive the , retrieved from Better Health Channel.
Department of Health and Human Services 2018b, Heat health alerts. State Government of Victoria, Melbourne.
Department of Environment, Land, Water and Planning 2019, Victoria’s climate science report 2019. State Government of Victoria, Melbourne.
Natural Capital Economics 2018, Heatwaves in Victoria: a vulnerability assessment, unpublished report prepared for Victorian Department of Environment, Land, Water and Planning, Melbourne.
Victorian Council of Social Service 2017, Power struggles: everyday battles to stay connected. Victorian Council of Social Service, Melbourne.
Reviewed 11 March 2023