Natural hazards in Australia: heatwaves.

As part of a special issue on natural hazards, this paper reviews the current state of scientific knowledge of Australian heatwaves. Over recent years, progress has been made in understanding both the causes of and changes to heatwaves. Relationships between atmospheric heatwaves and large-scale and synoptic variability have been identified, with increasing trends in heatwave intensity, frequency and duration projected to continue throughout the 21st century. However, more research is required to further our understanding of the dynamical interactions of atmospheric heatwaves, particularly with the land surface. Research into marine heatwaves is still in its infancy, with little known about driving mechanisms, and observed and future changes. In order to address these knowledge gaps, recommendations include: focusing on a comprehensive assessment of atmospheric heatwave dynamics; understanding links with droughts; working towards a unified measurement framework; and investigating observed and future trends in marine heatwaves. Such work requires comprehensive and long-term collaboration activities. However, benefits will extend to the international community, thus addressing global grand challenges surrounding these extreme events.

Fig. 1 Heatwave schematic illustrating the various physical processes contributing to heatwaves, the interactions and feedbacks existing between them, and timescales on which they operate. Note that not all processes need to be present for a heatwave to occur (Fischer et al. 2007; Miralles et al. 2014). Coloured shading indicates the severity of a heatwave (red being more severe), the arrow thickness on the x-axis indicates the temporal length of key mechanisms, and the arrow on the y-axis indicates how the mechanisms on their various timescales may amplify heatwave severity. For example, A particular phase of climate modes may increase the likelihood of heatwaves, which then become more severe once other, shorter time-scale mechanisms (e.g. dry soil and high- pressure systems) also occur