Indonesia’s underground peat fires are surging under El Niño and drought, raising fears of another destructive fire season.
Some fires race across the surface. Indonesia’s peat fires can do something more dangerous: disappear underground and keep burning.
Tropical peatland fires develop when carbon-rich wetland soils dry out enough to ignite. Instead of producing only fast-moving flames, these fires can smolder slowly at relatively low temperatures through deep layers of peat. That makes them extremely difficult to extinguish and especially damaging to air quality.
By one estimate, peat fires release three times more fine particulate matter than other tropical forest fires, along with five times more sulfur dioxide, three times more organic carbon, and twice as much methane and carbon monoxide. Fine particulate matter consists of tiny airborne particles that can travel deep into the lungs, making heavy peat smoke a serious health concern.
Satellites Track Indonesia’s Growing Fire Season
Indonesia’s 2026 fire season was already underway when the MODIS (Moderate Resolution Imaging Spectroradiometer) instrument aboard NASA’s Aqua satellite captured an image of the region on September 1, 2026.
On the accompanying fire map below, each red dot represents a “fire detection.” That does not necessarily mean each dot corresponds to a separate fire. Instead, it marks a satellite pixel where MODIS and an algorithm identified a thermal anomaly consistent with active burning. A single large fire can produce several detections.
Peat fires are a persistent threat in Indonesia, which contains about 36 percent of the world’s tropical peatlands. These landscapes normally hold large amounts of water, but severe drought can transform them into highly flammable fuel.
During particularly dry years over the past three decades, fires have burned across Indonesian peatlands for weeks or months, spreading thick smoke across large areas and disrupting everyday life for millions of people.
El Niño Is Making the Dry Season Drier
Indonesia experiences fires every year, but some of its most severe recent fire seasons occurred during El Niño, especially in 1997 and 2015.
El Niño changes patterns of ocean temperatures and atmospheric circulation across the tropical Pacific. In Indonesia, it often suppresses rainfall and intensifies the dry season. Conditions can become even drier when El Niño coincides with the positive phase of the Indian Ocean Dipole, another climate pattern that influences rainfall around the Indian Ocean.
In August, NOAA assessed El Niño as present and strengthening. A positive Indian Ocean Dipole was also underway.
“Indonesia is only about three weeks into its fire season, but we’re seeing fire activity track sharply upward, similar to 2015,” said Robert Field, a Columbia University researcher who developed a tool called the Global Fire Weather Database that produces experimental, real-time fire weather forecasts.
“The strong El Niño is making the dry season drier over the fire-prone parts of the country and exacerbating burning—just as we anticipated it would,” he said.
The comparison with 2015 is especially concerning. After burning for more than three months that year, fires across Indonesia had released 1.75 billion tons of greenhouse gas equivalents—more than Japan emits in a year.
As of September 2, Indonesia’s fires in 2026 had been burning for roughly a month and had already released about 10 percent as much as the total from the 2015 fires.
Fires Can Keep Burning Below Ground
Indonesia was also experiencing severe, widespread drought during the summer of 2026. According to the country’s meteorological agency, about 90 percent of Indonesia received little to no rain in early August.
Under normal conditions, peat deposits in Kalimantan, Sumatra, and Papua are wet enough to resist extensive burning. During drought, however, the water level can fall and expose dry peat to fire.
Once flames move below the surface, controlling them becomes much harder.
“Surface fires are less of a concern, but when fires get underground, they just won’t stop,” Field said. “They’ll keep burning until the rains come in October or November.”
That underground behavior is one of the reasons peat fires can persist for so long. Smoldering can continue even when obvious surface flames are limited, allowing fire to move through the soil where conventional firefighting is much more difficult.
The Worst Fires Can Be Harder to See From Space
Indonesia relies heavily on satellite observations to monitor active burning. The government uses data from NASA and NOAA instruments, including MODIS and VIIRS, to follow fires in near-real-time.
Indonesia’s Ministry of Forestry fire monitoring platform SiPongi, which uses MODIS and VIIRS observations, recorded 946 hotspots on August 31, 2026.
But satellites have important limitations.
Thick clouds and smoke can block the sensors’ view. Fires burning beneath forest vegetation can also be difficult to detect, while underground peat fires may be nearly invisible from above.
That creates an unusual problem: as smoke conditions become more severe, satellites can sometimes report fewer visible fires rather than more.
“The worst smoke events, paradoxically, can be the hardest to observe from space with MODIS and VIIRS,” said Mark Cochrane, an ecologist at the University of Maryland Center for Environmental Science who has conducted field research on peat fires in Indonesia for nearly a decade.
Decades of Drainage Made Peatlands More Flammable
Some of Indonesia’s vulnerability to peat fires can be traced back decades.
During the 1990s, extensive irrigation canals were constructed, and peat swamps were drained as part of efforts to create massive rice farms. Cochrane said that work substantially lowered the water table across wetland areas, leaving peat more vulnerable to drying and fire.
Oil palm plantations and other forms of plantation forestry are also widespread in the region.
After the unusually grim 2015 fire season, however, governments and other organizations began taking steps to reduce the danger. Some drainage canals have been dammed to help restore wet conditions in peatlands.
Authorities have also worked to strengthen firefighting capacity and reduce accidental human ignitions.
A Major Test of Fire Prevention Efforts
The 2026 fire season may show how well those measures work under extreme climate conditions.
“This year will be a real stress test of the measures that were put in place after 2015,” said Shi Jun Wee, a University of Maryland graduate student.
Wee is part of a team working with NASA and MapBiomas to improve fire detection. The researchers are developing new algorithms and techniques designed to identify more fires burning beneath the forest canopy than MODIS and VIIRS can currently detect.
Their approach uses shortwave infrared observations from Landsat and Sentinel-2 satellites. Shortwave infrared wavelengths can reveal heat and changes in vegetation that may be difficult to see in ordinary visible light.
As the fire season continues, Wee plans to follow conditions using NASA’s Worldview data browser, FIRMS (Fire Information for Resource Management System), HLS (Harmonized Landsat and Sentinel-2) observations, and GFED (Global Fire Emissions Database).
Hazardous Smoke Is Already Disrupting Daily Life
The effects are already being felt across Indonesia and neighboring countries.
Indonesian officials have warned that large portions of the population have been exposed to hazardous smoke. Some schools have begun moving classes online, while nine national parks have closed.
Heavy smoke has also disrupted air travel, with several flights delayed, according to news reports.
The broader challenge, Cochrane said, is maintaining attention on peat fires even after unusually severe seasons end.
“People tend to focus on these fires during an El Niño and then forget about them,” Cochrane said. “We need sustained focus, even during the years when they aren’t as bad, to solve this,” he said. “These fires create a tremendous amount of emissions.”
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