Shane Coffield, a University of Maryland assistant research scientist working at NASA Goddard, estimates that about 40% more fires are burning around the Amazon city of Santarém than appear in the standard active-fire counts from NASA’s Fire Information for Resource Management System, known as FIRMS. His satellite analysis indicates roughly 50 to 70 uncontrolled fires in the Santarém region alone, a tally that official detection products do not fully capture.
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The finding sits inside a larger and worsening fire season. Smoke and flames rose sharply across the central and eastern Amazon starting in September 2026, and the plumes grew thick enough on Oct. 12 that NASA’s Aqua satellite imaged smoke streaming from fires on both sides of the Amazon River. Coffield’s estimate speaks to exactly that kind of day, when orbiting sensors see the least of what is burning beneath the smoke and the canopy.
How the hidden fires were found
The work was described in a NASA Earth Observatory report that ScienceDaily republished on Oct. 17. Coffield analyzed infrared heat signatures from the instrument behind VIIRS 375-meter active-fire data and searched for what he calls candidate fires: heat sources that fall below the thresholds used to flag a fire in official products. Those products already feed the FIRMS fire map, which many researchers and land managers use as their daily picture of where the Amazon is burning.
The gap is largest when conditions are worst. Coffield said that on some of the smokiest days the MODIS and VIIRS sensors return very few detections, and he added that the team knows such sparse counts cannot be right.
Dense smoke, clouds and the forest canopy all block or dilute the thermal signal, and slow-burning understory fires beneath the trees are the easiest to miss. Coffield told NASA he plans to share the candidate-fire locations with MapBiomas, the collaborative network that tracks fires and land use across the Amazon, so that people on the ground can check them. The 40% figure is his own estimate for the Santarém area, not a basin-wide correction. It comes from a NASA Earth Action project rather than a peer-reviewed paper, and the Earth Observatory report cites no journal article for it, so the number should be read as an expert estimate awaiting independent checking.
An El Niño drought feeding the burns
Douglas Morton, an Earth system scientist at NASA Goddard, frames the fires as part of a cascade of tropical burning set off by El Niño disruptions to rainfall. Describing the sequence, Morton said the Amazon is now seeing the second domino in that cascade fall, after fires elsewhere in the tropics. Indonesia has had fires and smoke since August, and hundreds of homes there were destroyed in October.
The drought numbers are stark. Brazil’s National Institute of Meteorology reported that rainfall in Manaus was 95% below normal in August and 60% below normal in September. Lightning causes less than 1% of fires in the region, so nearly every blaze burning now was started by people, and many of the large ones began as managed burns for grazing land or crop residue that then escaped into dry forest and pasture.
Morton called it striking and frustrating that the same forests are burning again, a reference to the 2015 to 2016 and 2023 El Niño events that produced similar sequences. His advice was blunt: given the intensity of this El Niño, he said, this is the year for people to avoid burning at all costs.
Smoke in Manaus and what comes next
The human cost is already visible downstream. City officials in Manaus, home to more than 2 million people, reported extremely poor air quality on Oct. 12, with fine particulate matter (PM2.5) above 135 micrograms per cubic meter. Schools closed and public events were canceled. Particles that small lodge deep in the lungs, which is why readings in that range draw closures rather than mere advisories.
Brazil’s own tallies show the scale. According to MercoPress, the National Institute for Space Research recorded 540 new hotspots in 48 hours, more than half of all of October 2025, and a state of emergency covers 36 municipalities in Amazonas. Environment Minister João Paulo Capobianco said after flying over the region that fires do not arise spontaneously in the Amazon biome. Integration Minister Waldez Góes said that deploying every available force to fight the fire is one task, while helping people who need humanitarian aid and medical care is another. The federal environmental agency Ibama sent four water-bombing aircraft, two helicopters and 290 firefighters, and the air force added two KC-390 aircraft.
A shortfall in detection matters because counts steer response: crews, warnings and enforcement follow the map, and a map that understates the burning on the smokiest days leaves the hardest-hit places looking quieter than they are.
The Earth Observatory expects the pattern to move. Fire activity is forecast to shift north in November and December 2026, toward Roraima, Amapá, northern Pará and parts of Venezuela, Guyana and Suriname, then south by August and September 2027 into the southern Amazon in Brazil and Paraguay. For Manaus and Santarém, fires are likely to persist until rains return, probably in December 2026 or January 2027.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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