Amazon droughts intensify wildfire pollution and estimated health risks

A study estimates that drought years bring larger increases in fire-related fine particles, ozone and premature mortality across the region.

Editorial illustration — not from the study.

The researchers combined satellite observations of fires with fire-emissions data and an atmospheric chemistry model to examine how droughts and deforestation affected Amazon air quality. They compared simulations with fires included against simulations without fires during the July–November dry season.

In years without drought, fires accounted for about half of regional carbon monoxide and fine-particle pollution and one-third of ozone. During drought years, their estimated contributions rose to 60–80% for carbon monoxide and fine particles and 50% for ozone. Health-risk calculations also indicated larger fire-related increases in premature mortality during drought years.

How drought changed pollution

During non-drought years, biomass burning contributed about 50% of regional carbon monoxide and fine-particle pollution and 33% of ozone during the dry season. During drought years, those contributions increased to 60–80% for carbon monoxide and fine particles and 50% for ozone.

Pollutant levels were significantly correlated with drought intensity. Using an exposure-and-health-risk model, the researchers estimated that fire-related fine-particle exposure was associated with a 6.0% increase in premature mortality in non-drought years and an 8.9% increase in drought years. For ozone, the corresponding estimates were 18.6% and 24.4%. These are modeled estimates of premature mortality, not direct counts of deaths observed in the study.

Why the risk matters

The findings indicate that droughts can amplify the air-quality effects of Amazon fires, increasing exposure to fine particles and ozone even when deforestation rates remain stable. That makes drought conditions relevant to wildfire planning and climate adaptation efforts intended to reduce risks to public health.

Evidence and caveats

The study used satellite fire observations, the Global Fire Emissions Database and the GEOS-Chem High Performance atmospheric chemistry model to simulate pollution from 2010 to 2015. It also used the Global Exposure Mortality Model and exposure-response relationships to estimate health effects.

The results are model-based estimates for the six-year study period, rather than direct measurements of premature deaths caused by fires. The abstract reports significant correlations between drought intensity and pollutant levels, but does not establish that every observed association is causal. The abstract also does not provide details on geographic variation, uncertainty ranges or how individual exposure was measured.

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