Global Compound Climate Events: Intensified Air Pollution During Simultaneous Extreme Events

The increasing frequency and intensity of extreme environmental and climatic stressors, such as heatwaves, droughts, wildfires, and air pollution episodes, highlight the urgency of understanding their interconnected nature. Traditionally studied in isolation, these stressors often interact in complex ways, amplifying their individual and cumulative impacts on ecosystems, economies, and public health. This study explores the global occurrence of compound events involving heatwaves, droughts, wildfires, and poor air quality, identifying their key drivers, spatial distribution, and associated consequences.

ERA5 reanalysis were used to identify drought periods using the Standardized Precipitation-Evapotranspiration Index (SPEI) and detected heatwaves based on temperature anomalies. Fire activity was assessed using Fire Radiative Power (FRP) data from the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Terra and Aqua satellites, while air pollution levels, specifically particulate matter (PM2.5), were derived from the Copernicus Atmosphere Monitoring Service (CAMS) global reanalysis (EAC4). The co-occurrence of these phenomena was analyzed to pinpoint regions experiencing compound hot, dry, fire, and pollution events.

Our findings reveal distinct global hotspots where multiple stressors interact. Heatwaves and air pollution events were predominantly observed in regions such as India, the Arabian Peninsula, and eastern China. Meanwhile, the Brazilian Cerrado, northern Australia, and South African savannas frequently experienced simultaneous heatwave and wildfire occurrences. The Mediterranean region, particularly Greece, Portugal, and Italy, exhibited a high prevalence of concurrent heat, drought, wildfire, and air pollution episodes. Notably, in North America and Asia, PM2.5 concentrations reached significantly higher levels during simultaneous extreme events compared to isolated pollution occurrences.

The interplay of compound hot and dry conditions with wildfires, and ultimately with pollution events, presents critical challenges for public health and environmental management. The cascading effects of these interactions underscore the need for integrated approaches that encompass climate adaptation strategies, wildfire risk mitigation, and stringent air quality regulations. Understanding these linkages is essential for formulating policies that enhance climate resilience and safeguard communities against the escalating threats posed by climate-driven extreme events.

This research was funded by the Portuguese Fundação para a Ciência e a Tecnologia, FCT, I.P./MCTES through national funds (PIDDAC): UID/50019/2025 and LA/P/0068/2020 https://doi.org/10.54499/LA/P/0068/2020. This study was conducted within 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 for grants https://doi.org/10.54499/2022.03183.CEECIND/CP1715/CT0004 and https://doi.org/10.54499/2022.01167.CEECIND/CP1722/CT0006, respectively.