Background Globally, drowning is a leading cause of injury-related harm, which is heavily impacted by environmental conditions. In Australia, fatal unintentional drowning peaks in summer, yet the impact of prolonged periods of hot weather (heatwave) on fatal drowning has not previously been explored.

Methods Using a case-crossover approach, we examined the difference in drowning risk between heatwave and non-heatwave days for the Australian state of Queensland from 2010 to 2019. Heatwave data, measured by the excess heat factor, were acquired from the Bureau of Meteorology. Incidence rate ratios (IRRs) were calculated by sex, age of drowning decedent, category of drowning incident (International Classification of Diseases−10 codes) and heatwave severity. Excess drowning mortality during heatwaves was also calculated.

Results Analyses reveal increased fatal drowning risk during heatwave for males (IRR 1.22, 95% CI 0.92 to 1.61), people aged 65+ years (IRR 1.36, 95% CI 0.83 to 2.24), unintentional drowning (IRR 1.28, 95% CI 0.98 to 1.69) and during severe heatwaves (IRR 1.26, 95% CI0.88 to 1.82). There were 13 excess drowning deaths due to heatwave over the study period.

Discussion The findings confirm an increased risk of fatal drowning during heatwaves. With increased likelihood and severity of heatwaves, this information should be used to inform drowning prevention, in particular the timing of public awareness campaigns and patrolling of supervised aquatic locations.

Conclusions Water safety and patrolling organisations, as well as first responders, need to prepare for more drowning deaths during heatwave conditions. In addition, drowning prevention education ahead of heatwaves is needed for recreational swimmers, and older people, particularly those with comorbidities which may be further exacerbated by a heatwave.