Rising global population coexposure to heatwaves and landscape fire-sourced air pollution.

Landscape fires are increasingly threatening public health by causing substantial fire-sourced air pollution (SFAP), with risks amplified during heatwaves. We investigated the global spatial, temporal, and sociodemographic distribution of the population coexposure to heatwaves and SFAP from 2000 to 2019. We found that 52.4% of populated areas and 55.9% of the global population experienced increasing coexposure. On average, 916 million people per year were exposed to at least one coexposure day, increasing by 287 million people per decade. The global annual average exposed days per person was 1.3 days, rising from 1.0 days in 2000-2009 to 1.7 days in 2010-2019. Coexposure person-days increased by 5.5 billion per decade, of which 70.5% was attributable to increasing coexposure intensity and 29.5% to population growth. Countries with a low human development index (HDI) experienced the highest coexposure days per person and the greatest increases. These findings provide high-resolution data to inform health impact assessments and target mitigation and adaptation strategies.