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Indonesia’s wildfire season has intensified into a regional health crisis, with fires across Sumatra and Borneo sending thick haze into neighbouring parts of Southeast Asia. More than 12.5 million people across seven Indonesian provinces had been exposed to smoke by September 9, while 113,336 people had been treated for respiratory illnesses linked to the fires, according to Indonesia’s health ministry. Reported cases more than doubled in just over a week. The fires have also disrupted schools and pushed air pollution to hazardous levels in parts of Malaysia, Singapore and the Philippines. Officials and researchers say an unusually strong El Niño has intensified drought and created conditions in which human-started fires can spread rapidly.
Fires Have Burned Hundreds of Thousands of Hectares
Indonesia’s forestry ministry recorded about 202,000 hectares of burned land between January and July, with 107,000 hectares burning in June alone. But the scale of the fires increased sharply during August. Environmental group YKAN estimated that another 600,000 hectares were damaged by fire during the month. Because the figures come from different sources and use different assessment methods, they should not be treated as a single official national total.
The scale of the fires is also showing up in atmospheric emissions. Between August 1 and September 8, Indonesia recorded 13,443 hotspots, compared with 9,454 during the same period in 2015, when the country experienced one of its most destructive fire seasons. Fire emissions were about 273% above the seasonal average. The current season has raised comparisons with Indonesia’s devastating 2015 fires, although the full extent of this year’s damage will depend on how long the dry conditions persist.
The emissions figure was still below the 21.7 million tonnes recorded during the same week in 2015, but the latest data underline the severity of the current season. The European Union’s Copernicus climate monitoring system also cautioned that emissions could be underestimated because underground peat fires are difficult for satellites to detect. The current fire season has been intensified by exceptionally hot and dry conditions associated with a strong El Niño.
Peat Fires Make the Crisis Harder to Control
A major reason the fires are proving difficult to extinguish is that many are burning through Indonesia’s extensive peatlands. Peat is made up of partially decomposed organic material accumulated over long periods. When these wetlands become sufficiently dry, fires can move through the peat below the surface, continuing to smoulder even when visible flames appear to have been extinguished.
These underground fires are particularly difficult for firefighters to detect and suppress and can produce large amounts of fine particulate pollution. Indonesia contains a substantial share of the world’s tropical peatlands, making the condition of these ecosystems especially important during severe droughts. More than 210,000 fire hotspots were detected in Indonesian peatland areas between January and August, according to data from the environmental organisation Pantau Gambut. The fires have been concentrated particularly in Kalimantan and Sumatra, where prolonged dry conditions have left peat and other vegetation highly vulnerable to ignition.
The immediate trigger for individual fires is not necessarily the climate phenomenon itself. El Niño creates the hot and dry conditions that allow human-started fires to escape and become much larger. Land clearing using fire has also been identified as a recurring factor in Indonesia’s wildfire seasons. The combination of dry weather, extensive peatlands and human ignition has made the current outbreak particularly difficult to contain.
Indonesia’s meteorological agency said on September 10 that high-confidence hotspots remained concentrated in Central Kalimantan, West Kalimantan, South Sumatra and South Papua. Over the preceding 10 days, Central Kalimantan recorded 2,526 such hotspots, followed by West Kalimantan with 2,102, South Sumatra with 1,180 and South Papua with 570. The agency said El Niño remained very strong and could persist into early 2027, while dry conditions and high temperatures continued to favour fires.
Haze Spreads Beyond Indonesia as Health Toll Mounts
The consequences are now extending well beyond the areas directly affected by the fires. Indonesia’s health ministry said respiratory illnesses linked to the fires rose from 50,891 cases on September 1 to 113,336 by September 9. More than 12.5 million people had been exposed to haze across seven provinces. Nearly one million masks, hundreds of oxygen concentrators and additional medical personnel had also been deployed to affected areas.
The fires have also disrupted education, with more than 1.4 million students shifted to remote learning in affected areas. In Palembang, more than 250,000 students across 1,030 schools were moved to online classes as air pollution worsened. The haze has continued to affect neighbouring countries. On Monday, September 14, Singapore’s 24-hour Pollutant Standards Index reached 117 in the central region, placing air quality in the unhealthy range. Smoke from fires in Sumatra and Kalimantan has also affected parts of Malaysia and southern Vietnam.
The worsening conditions have prompted an international firefighting response. Japan has deployed three CH-47 Chinook helicopters and personnel to West Kalimantan for aerial water-bombing operations from September 12 to 19, while Malaysia has offered firefighting assistance. With September remaining a critical period for Indonesia’s fire season, continued dry conditions and strong El Niño conditions could keep fire and haze risks elevated across the region.
References:
https://phys.org/news/2026-09-haze-indonesian-impacts-southeast-asia.html
Banner image: Photo by Joshua Kettle on Unsplash
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