Ů��С��Ƶ

The fires that raged through Indonesia last year were the world’s worst since 1997. They generated a smoke plume so large that it wrapped itself halfway around the equator – fallout on a scale usually associated only with volcanic eruptions.

Fire and smoke billowing from the peat fires, triggered by oil palm plantation owners and other farmers who clear surplus vegetation by setting it alight also generated 1.5 billion tonnes of carbon dioxide – more than the total 2013 emissions of Japan.

The massive equatorial plume was identifiable by satellites designed to detect carbon monoxide, another major pollutant generated by the fires, which lasted from July to November. The plume stretched from East Africa to the western Pacific Ocean and persisted for two months.

“I don’t know of any other sources other than volcanoes that have had such a pronounced signature as we saw with the carbon monoxide stretching halfway around the world at the equator,” says of Columbia University in New York.

Field estimates that as many as 15 million citizens of Indonesia and its neighbours –including Singapore, Malaysia and southern Thailand – were at risk of respiratory damage from the constant fumes. “Once the fire escapes underground into the peat, it produces smoke until the monsoon returns, and people downwind are exposed to this smoke,” he says.

Weather patterns

Field used data from five different satellite instruments that monitor fire activity and the composition of the smoke generated. “We wanted to understand how 2015 compared with previous events and the drought conditions under which they happened,” he says.

By combining the satellite data with meteorological records, Field established that Indonesian fires often occur in association with the ultra-dry conditions in the region that accompany El Niño, a major cyclical weather system. These dry out the underlying peat to the point at which it can catch fire and can’t be extinguished until monsoon rains arrive months later. A next step might be to refine the predictions further by including the combined effects of high temperatures and low humidity on peat moisture, says Field.

He also found that less than 4 millimetres of rain per day during the annual dry season, from August to November – combined with El Niño conditions – seems to be a “tipping point” beyond which fires can to suddenly take off.

This, says Field, could help predict when fires will take off, and guide measures to discourage fire-lighting.

“We can anticipate El Niño events further and further in advance, and having a threshold to gauge these forecasts against can provide a starting trigger for advanced prevention and preparedness measures,” Field says. “The more lead time, the better, but the real test will be the next time it’s drier than normal.”

No improvement

To minimise the risk of fires, farmers should halt the practice of burning on top of peat, Field says. “Fire has to be eliminated on peatlands, which in general need to be rehabilitated.”

Others who study peat fires echo the warning. “To me, the most significant finding here is that almost 20 years after the devastating fires during the 1997 El Niño, the Indonesian landscape is still equally or even more vulnerable to droughts leading to large fire events,” says Guido van der Werf of VU Amsterdam in the Netherlands.

“That basically means no progress has been made in mitigating the vulnerability of the landscape even though in the meantime, other large fire events have occurred,” he says.

The El Niño weather system has now given way to a much wetter La Niña system, which should keep the peat too wet to catch fire this year, says Field.

Journal reference: PNAS, DOI: 10.1073/pnas.1524888113

Read more: Indonesia forced to act as wildfire haze chokes South-East Asia