More than half the world’s population has experienced simultaneous exposure to heatwaves and wildfires, and the number of people affected has risen sharply over two decades.
That striking statistic comes from research at Monash University in Australia, which examined global exposure to extreme heat and landscape fire pollution between 2000 and 2019.
It found that the number of people exposed to both hazards on the same day increased by 287 million over the study period, highlighting the growing overlap between extreme temperatures and wildfire smoke.
Led by Dr Yao Wu and Professors Yuming Guo and Shanshan Li, the research warns that climate warming could increase exposure to these combined events, raising concerns about their effects on respiratory and cardiovascular health.
Heatwaves and wildfires increasingly overlap
The researchers examined how exposure to heatwaves and wildfire pollution varied by region, over time, and across population groups.
Their findings show that almost 56% of the global population experienced increasing exposure to both hazards during the 20-year study period. Among people living in populated areas, the proportion was 52.4%.
Each year, an estimated 916 million people experienced at least one day when they were simultaneously exposed to a heatwave and pollution from landscape fires.
The number of people affected by these combined events increased by 287 million per decade, demonstrating the growing scale of the problem.
Exposure frequency also rose during the study. The global annual average increased from one day per person in 2000–2009 to 1.7 days in 2010–2019.
These figures show that heatwaves and wildfires are not simply separate environmental hazards. Their effects can coincide, exposing large populations to extreme temperatures and fire-related air pollution at the same time.
Combined exposure raises health concerns
The overlap between extreme heat and wildfire smoke presents particular risks for human health.
According to the researchers, respiratory and cardiovascular health risks associated with air pollution from landscape fires are amplified during prolonged periods of extreme temperatures.
This means that people exposed to wildfire pollution during a heatwave face the combined effects of two environmental stressors. The study highlights the scale of this simultaneous exposure and the potential consequences for public health.
The researchers warn that these risks could grow as climate warming makes heatwaves and wildfires more frequent and more likely to overlap.
Their findings underline the importance of understanding where heatwaves and wildfires coincide, how exposure changes over time, and which populations experience the greatest burden.
Which countries face the greatest exposure?
The study also identified the countries with the highest annual average numbers of person-days of simultaneous exposure to heatwaves and landscape fire smoke pollution.
The five countries with the highest averages were the Democratic Republic of the Congo, Indonesia, Mexico, Brazil, and the Russian Federation.
The results show that the combined effects of extreme heat and wildfire pollution span the globe, rather than being confined to regions commonly associated with severe heatwaves or major wildfires.
Climate warming could increase the risks
The research provides a global assessment of how exposure to heatwaves and wildfire pollution changed between 2000 and 2019.
With more than half the world’s population experiencing increasing exposure, the authors warn that climate warming could further intensify the problem.
As heatwaves and wildfires increasingly coincide, understanding their combined impact will be important for assessing the environmental and public health consequences of a warming climate.
