• Western Australia experienced a series of heatwaves in December 2021 – January 2022.
  • The coastal town of Onslow, Western Australia, equalled Australia’s hottest day at 50.7°C.

Western Australia experienced a series of heatwaves over the 2021-2022 summer period, starting on 17th December and 12th January, and in the south-west, starting on 23rd December and 18th January of the Pilbara region.

These led to several records, including the equal hottest day in Australia of 50.7°C, at Onslow on 13th January, and Perth recording six days in a row above 40°C between 18th and 23rd January – the longest run of such days for any month in 123 years of observations.

This marked Perth’s 11th day over 40°C for the 2021-22 summer and exceeded the previous record of 7 summer days over 40°C, set in the 2015-16 summer. For Marble Bar, a total of 16 days of maximum temperatures above 45°C in December is the highest count for that month on record, and the second highest for any month.

During this heatwave, a strong high-pressure system over the Great Australian Bight created easterly winds that brought hot and dry weather from the desert to Perth. Additionally, a west coast trough – an extended region of low atmospheric pressure – was situated either just along the west coast, or slightly offshore.

The combination of the high over the Bight and the coastal trough resulted in easterly to north easterly winds, which acted to block the afternoon sea breeze, causing it to weaken and form later, allowing heat to build up over the land for most of the day.

Schematic of the Pilbara heatwave of November-December 2021. Source: ARC Centre of Excellence for Climate Extremes.

Heatwaves are one of the most significant natural hazards in Australia in terms of loss of life. They can negatively impact infrastructure, agriculture, ecosystems as well as health.

Heatwave conditions are expected to continue to worsen as the climate warms. The ARC Centre of Excellence for Climate Extremes is continuing to research links between heatwaves and weather systems, soil moisture and climate change.

Main research contact: Dr Tess Parker | Tess.Parker@monash.edu