We may not think of heatwaves as big contributors to the nations mortality rate but research shows that extreme temperatures currently contribute to the deaths of over 1000 people aged over 65 each year across Australia (McMichael et al., 2003). They have been described as “silent killers”, causing more deaths since the 1890s than bushfires, cyclones, earthquakes, floods and severe storms combined. In fact, from 1844 to 2010, extreme heat events have been responsible for at least 5332 fatalities in Australia and, since 1900, 4555: more than the combined total of deaths from all other natural hazards. Over 30% of those deaths occurred in just nine events.
Before we look at the changing distribution of heatwave frequency and duration, it's best to define what the term means and how it is measured.
A heatwave is described by the Australian Bureau of Meteorology as three or more days of high maximum and minimum temperatures that are unusual for a given location (BOM, 2016). A heat wave always includes the combination of intensity and duration of high temperature periods.
Heatwaves are primarily controlled by changes in temperature. Globally, for example, mean seasonal changes in temperature is responsible for 95% of projected heatwave changes in most regions (Argueso et al., 2016).
See the animation below for projected increases in annual temperature for Queensland
Fortunately, there seems to be good agreement about the nature of weather systems driving heatwaves in Australia. In many cases a high-pressure system sits next to the region experiencing the heatwave, pushing hot air from the centre of Australia towards that region. The location of the high depends on the region experiencing the heatwave, but there is always one there.
These high-pressure systems are created and sustained by other weather influences farther afield, for instance. We know for instance that heatwaves in Melbourne are coupled with tropical cyclones to the northwest of Australia.
Other, longer-term variables can affect not just individual heatwaves but their patterns, timing and severity too. So heatwaves are likely to be much longer and more frequent during El Niño than La Niña phases over much of northern and eastern Australia. However, this does not influence heatwaves over Australia’s far southeast – here, the most important driver is changes to wind patterns over the Southern Ocean.
Significantly more heatwave days, and longer and more intense events are observed over northern and eastern Australia during El Niño compared to La Niña (Perkins et al. 2015), yet different relationships occur in the southeast (Trewin 2009; Parker et al. 2014; Boschat et al. 2015).
But there is still a gap in our understanding of how future changes to patterns such as El Niño will influence our heatwaves.
Point and click to the figure elements to read original scientific publications about heatwave drivers.
Future surface temperature and heatwaves are projected to increase substantially across Queensland’s regions. However, our ability to mitigate greenhouse gases emissions may affect future surface temperature and hence heatwaves duration and frequency. The video bellow shows how surface temperature and heatwaves are projected to change across three distinct climatic regions within Queensland under moderate (RCP 4.5) and high (RCP 8.5) emissions scenarios.
The maps below show how heatwaves duration and frequency are projected to intensify across Queensland’s local government areas under moderate (RCP 4.5) and high (RCP 8.5) emissions scenarios based on climate models simulations.
Climate models point out that the frequency of heatwaves may exceed 18 days in 2030, with duration of up to 9 days in Mount Isa and Torres Strait Islands.
Heatwaves may become as frequent as 10% of the year in 2050 in Brisbane, Gold Coast and Noosa. A single heatwave event may last up to two weeks in these locations.
In 2070 a heatwave event can last more than three weeks in Rockhampton and more than five weeks in Mackay.
In 2090 heatwaves may experience a massive intensification in the tropics, occurring one third of the year and lasting more than 50 days in Townsville, Cairns and Torres Strait Islands.
Analysis integrating observations and projections for South East Queensland suggest that the mean number of heatwave days (expressed as a % of the year) will increase from less than 2 over the reference period to 17 in 2070 and 25 in 2090.
Similar trends are observed for heatwave duration which last about 6 days during the reference period but increases to 12-22 days in 2070 depending on our greenhouse gases emissions.
This means that by the end of this century a ‘heatwave’ could last more than one entire month in the absence of strong mitigation measures.
Point and click to a local government area in the map below and check the plots to understand how do climate models project future heatwaves across Queensland’s regions.
Heatwaves have direct impacts on mortality amongst the elderly and young but they also cause numerous indirect impacts such as stress on electricity networks, emergency services, hospitals and infrastructure stresses such as road damage and transport delays when railway lines buckled under the extreme conditions. The impacts of severe heatwaves are likely to affect all sectors of the Australian community, from the general public to government organizations and industries, health, utilities, commerce, agriculture and infrastructure.
These impacts have led state governments and other bodies to investigate heatwave management strategies, while the Bureau of Meteorology have developed a heatwave forecast service for Australia. The Climate council have also summarized the extreme temperatures during the summer of 2016/2017.
In general, getting better prepared for the effects future heatwaves involves making progress in the following five principal adaptation areas:
The Queensland Government has recently launched the Queensland State Heatwaves Risk Assessment 2019 (SHRA) – a detailed macro level risk assessment for heatwave. The project was a partnership between Queensland Fire and Emergency Services (QFES), Queensland Health and the Department of Environment and Science (DES). It was a collaborative effort across Governments and non-government organisations across the public and private sectors and involved substantial engagement at state and regional level.
The SHRA represents the most comprehensive analysis of future climate risk undertaken for a natural hazard risk assessment in Queensland. It is underpinned by a robust scientific basis, enabling all stakeholders including State agencies, disaster management groups, infrastructure owners and town planners to understand, plan for, and reduce the risk from heatwaves.
Some useful links in terms of public safety messaging and State level planning from the Queensland Government (incl. Q Health) are included below: