A smoky haze is blanketing large parts of Southeast Asia, bringing grey skies and a lingering acrid smell now familiar to the local population. The haze—which occurs almost every year—is caused by smoke spreading from forest fires in Indonesia (as well as in Malaysia, but on a far smaller scale). More than 3600 fires had been detected on the islands of Sumatra and Borneo by weather satellites. This year, 2019, has seen some of the worst haze levels since 2015, when a state of emergency was declared in six Indonesian provinces. The haze has spread across Malaysia, Singapore, southern Thailand and the Philippines, causing a significant worsening of air quality.

Slash and burn

Forest burning usually peaks during Indonesia's dry season: July to October. Many farmers take advantage of the dry conditions to clear vegetation for cultivation, using the slash-and-burn method. Land is cleared by burning patches of forest. After a few years of planting crops, the rainforest soil loses its fertility, so the farmers clear a new area, leaving the previous land to return to its natural state. The fires the farmers start often flare out of control and spread into protected forested areas. The burnt land also becomes drier, which makes it easier to set alight the next time there are clearings.

Uncontrolled burning has accelerated in the last 30 years as more and more rainforest has been cleared to make way for expanding palm oil plantations. A recent fall in the price of palm oil has led some farmers to burn their plantations and replant them with vegetables or dragon fruit.

Tackling the fires

The Indonesian authorities have been dumping millions of litres of water in affected areas. But they struggle to put out the fires, many of which have been burning on lands rich in peat. A peat fire can burn underground for months, and requires a great deal of water to extinguish. Fires can spread underground and spring up in other places later.

It is in Indonesia itself where the impact of the haze is most severe. In Palangkaraya, the capital of central Kalimantan (Indonesian Borneo), the Air Quality Index (AQI) reached 2000 in September 2019—well above the hazardous level of 300.