Global Assessment of the Compound Effects of Hot, Dry Conditions and Fires on PM2.5 Levels using ERA5 and CAMS reanalysis

In recent years, attention has intensified on the interplay between environmental stressors, notably poor air quality, heatwaves, droughts, and fires, as exacerbated by climate change. These stressors, once viewed in isolation, are now recognized as interconnected phenomena forming a complex web of impacts with global repercussions. The compounding effects of these events have significant implications for ecosystems, economies, and public health worldwide. In this work, we present a comprehensive analysis of compound events of poor air quality, heatwaves, droughts, and fires on a global scale, shedding light on their interconnected nature, underlying drivers, and implications for ecosystems and societies worldwide.

We use meteorological data from ERA5 to compute heatwaves and droughts (using the Standardized Precipitation-Evapotranspiration Index – SPEI), Fire Radiative Power (FRP) from the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard Terra and Aqua sun-synchronous orbit satellites, and air quality data (particulate matter PM2.5) retrieved from the Copernicus Atmosphere Monitoring Service (CAMS) global reanalysis (EAC4). The horizontal resolution is preset at 0.75º × 0.75º, and the time window is between 2003 and 2022 at a daily basis. Compound events were identified based on the detection of pollution events, heatwaves, droughts, or FRP in various combinations, ranging from two to four events, within each cell of space and time.

Analysis revealed hotspots of compound events distributed across different regions worldwide. For instance, pollution and heatwaves were predominantly observed in India, the Arabian Peninsula, and eastern China, whereas heatwaves and fires were prevalent in the Brazilian Cerrado, northern Australia, and South African Savannas. The impacts of single and concurrent hot, dry, and fire events on particulate matter PM2.5 levels varied significantly by continent. Notably, North America and Asia exhibited pronounced pollution levels during simultaneous occurrence of these events compared to isolated pollution events.

The interaction between compound hot and dry events and wildfires poses a critical public health challenge, underscoring the interconnectedness of climate change, extreme weather events, and air pollution. Addressing these complex interrelationships necessitates comprehensive strategies integrating climate resilience, wildfire management, and air quality regulations to safeguard human health and well-being amidst a changing climate.

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020). This work was performed under the scope of project https://doi.org/10.54499/2022.09185.PTDC (DHEFEUS) and supported by national funds through FCT. DL and AR acknowledge FCT I.P./MCTES (Fundação para a Ciência e a Tecnologia) for the FCT https://doi.org/10.54499/2022.03183.CEECIND/CP1715/CT0004 and https://doi.org/10.54499/2022.01167.CEECIND/CP1722/CT0006, respectively.