When Fire Weather Translates into Biomass-Burning Particulate Emissions Across South American Ecoregions

Biomass burning is a major source of particulate matter and trace gases in South America, yet the extent to which favorable meteorological conditions for fire occurrence translate into atmospheric emissions varies among ecosystems and emission inventories. This study evaluates the ecoregional coupling between the Fire Weather Index (FWI) and biomass-burning total particulate matter (TPM) emissions across 96 Level III ecoregions of South America. Historical daily FWI data for 1981–2024 were combined with TPM emissions from the Global Fire Assimilation System (GFAS), Global Fire Emissions Database (GFED), and Quick Fire Emissions Dataset (QFED) for 2003–2024. Raw monthly FWI and TPM were strongly associated, with median Spearman correlation coefficients (ρ) ranging from 0.73 to 0.76 across inventories. After removal of the mean seasonal cycle, median correlations decreased to 0.42–0.49, indicating that shared seasonality explains part, but not all, of the observed relationship. Positive coupling between FWI anomalies and TPM anomalies remained significant after autocorrelation adjustment and false discovery rate (FDR) correction in 84–88 ecoregions per inventory, while 84 of the 96 ecoregions showed robust agreement across emission-estimation approaches. Monthly mean FWI generally outperformed the frequency of days exceeding the 95th-percentile (P95) fire-weather threshold as an overall predictor of TPM variability; nevertheless, high-emission months contained approximately 5.6–6.6 times more extreme FWI days than other months. Hyper-arid ecoregions exhibited pronounced decoupling despite very high climatological FWI values, consistent with fuel limitation, whereas many tropical, savanna, wetland, and transitional ecoregions showed strong coupling. These results distinguish meteorological fire danger from realized particulate emissions and identify the regions where favorable fire-weather conditions most consistently translate into biomass-burning atmospheric emissions.