Why peat fires are so hard to put out
Published 19 October 2026
Most of Indonesia's worst haze comes from burning peat, which smoulders underground for weeks. Why it smokes so much, and why water from above rarely stops it.
What peat is
Peat is soil made of plants that never finished rotting. In a swamp forest, leaves, wood and roots fall into ground that stays waterlogged all year, and without air the bacteria that would break them down cannot work. Over thousands of years the debris piles up into a dark, spongy layer that can be several metres deep.
Indonesia holds some of the largest tropical peatlands in the world, mostly in Sumatra, Kalimantan and Papua. Undisturbed, a peat swamp is too wet to burn: the water table sits at or near the surface, and the peat is more water than anything else.
How it dries out
Peat becomes fuel when it is drained. To grow crops, plantations and farms on peatland, canals are dug to lower the water table. Through the dry season the top of the peat dries out and starts to decompose, the ground sinks, and the dry layer gets thicker every year the canals keep draining it.
Central Kalimantan shows how long the effect lasts. In the 1990s the Mega Rice Project cut thousands of kilometres of canals through peat swamp around what is now Palangka Raya, to turn it into rice fields. The rice never took, but the canals kept draining, and the area has burned in dry years ever since.
Fire reaches dry peat in a few ways: land cleared by burning, fire that escapes from a field or a rubbish heap, or a surface fire in dry vegetation that reaches the ground beneath.
Why it smoulders instead of flaming
Once it catches, a peat fire behaves less like a forest fire and more like a charcoal burner. It creeps down and sideways through the dry layer, below the surface, with little or no visible flame. It burns slowly at a lower temperature, and that is exactly why it makes so much smoke: smouldering is incomplete burning, and incomplete burning gives off far more fine particles and carbon monoxide for each kilogram burned than an open flame does.
A peat fire can also burn for weeks and come back. Fire that seems out on the surface can keep moving underground and break out again somewhere else, sometimes after rain.
This is why haze from peat is so dense and so persistent, and why cities like Palangka Raya, Pekanbaru and Palembang can read Hazardous for days at a time in a bad season. Indonesia's haze season, explained covers the calendar and the weather behind it.
Why it is hard to put out
- The fire is underground. Water dropped from a helicopter soaks the surface and runs off or evaporates; the burning layer below can stay dry.
- The ground has to be soaked, not sprayed. Crews put out peat fires by pumping large volumes of water into the ground, often by pushing a lance into the peat, section by section. It is slow, heavy work, and in the dry season water itself is scarce near the fire.
- The fire front is hard to find. Smoke rises over a wide area while the burning edge moves unseen beneath it.
- Burned peat is gone. Peat that burns lowers the ground, and the land left behind often floods or stays degraded.
In practice, many peat fires end only when the rainy season raises the water table again.
Prevention: putting the water back
Because a wet peat swamp does not burn, the most effective defence is keeping peat wet. Blocking drainage canals with dams so they hold water instead of draining it, rewetting drained land, and replanting native swamp vegetation are the main tools. After the 2015 haze, Indonesia set up a national agency for peatland restoration, now the Peatland and Mangrove Restoration Agency (BRGM), to do exactly this.
Rewetting takes years to show, and it only works where the canals stay blocked. It is still the measure that addresses why the peat burns rather than the fire in front of you.
What the satellites see, and what they miss
The fire dots on Kabut's map are NASA FIRMS detections: points where a satellite measured more heat than its surroundings as it passed overhead. That works well for open flames, and less well for peat.
- Smouldering can be missed. A fire burning below the surface gives off less heat at the top than a flaming one, and may not register.
- Smoke and cloud hide the ground. On the worst haze days the smoke itself can stop a satellite seeing the fires beneath it.
- One fire can be many dots. A detection is a patch of ground, not a fire; a large burn appears as many detections, and the same fire is counted again on each pass.
- The data is hours old. Detections arrive about three hours after the satellite pass, which is why Kabut labels them "last 24h" and never "now".
So the hotspot count is a good sign of how much is burning and where, not a precise count of fires. Methodology explains how Kabut counts and de-duplicates them.