In recent weeks, South-east Asia has been seeing persistent haze, with air quality in Singapore reaching the upper end of the moderate range and, on some days, the lower end of the unhealthy range.
Singapore’s 24-hour Pollutant Standards Index (PSI), which measures air quality, first entered the unhealthy range on the morning of Sept 4. The PSI went back up again this week, reaching 106 on the morning of Sept 10.
Air quality is considered unhealthy when the PSI is above 100, during which the National Environment Agency (NEA) advises the public to cut down on outdoor activities.
The last time the PSI hit unhealthy levels due to haze was in October 2023.
PSI levels in Singapore have not yet reached levels seen in 2015 or 2019
The haze has been caused by raging fires in Indonesia and if they continue, there is a risk of smoke haze affecting Singapore even further.
How did the haze reach Singapore’s shores again? It began with fires in the forests and peatlands of Sumatra and Kalimantan.
Dense smoke haze had been seen over southern and central Sumatra and various parts of Kalimantan on most days since Aug 21.
The smoke was then carried northwards by winds from the south, bringing haze towards Singapore.
Air quality breached unhealthy levels on Sept 4. Analysis by the Copernicus Atmosphere Monitoring Service showed aerosol plumes reaching Singapore and beyond.
This map shows fire hot spots detected in Indonesia in the week of Aug 31, based on data from NASA. The smoke reached Singapore as winds blew from the south.
Many fire hot spots were found within concession areas, where land is allocated for commercial use such as plantations. Some of these concessions overlap with peatlands, which are naturally wet ecosystems that can become highly flammable when they are drained for plantations.
In comparison, the fire hot spots detected during the week of Sept 21 – the peak week in 2015 – were concentrated in similar areas, although the number of hot spots was much higher.
Note: Concession areas are based on palm oil concession data from Global Forest Watch and wood pulp concession data from Trase, as well as data on mining business areas from Indonesia’s Ministry of Energy and Mineral Resources. The information is publicly available data and may not be comprehensive of all concession areas.
Forest fires in Indonesia are more easily ignited during the dry season, which typically runs from June to October. In 2026, the fire season is compounded by a “Godzilla” El Nino, which brings hotter and drier conditions.
The combination has stirred memories of 2015, which was also an El Nino year. Fires from Indonesia sent Singapore’s PSI to above 300 in September – into the hazardous range – prompting schools to close for a day. In Indonesia, the haze was linked to about half a million cases of respiratory infection.
How the number of fire hot spots in Indonesia compares across the years, as detected by NASA’s satellite
Source: NASA FIRMS, VIIRS/Suomi NPP active fire data, data as at Sept 10
Weather experts tell The Straits Times that a repeat of such a disaster in 2026 seems unlikely. This is because the current El Nino started later than the 2015 cycle. The El Nino in 2015 had an onset in April and a longer impact on the dry season than this year, said NEA.
In comparison, the 2026 El Nino started around June. The number of hot spots over Sumatra and Kalimantan so far is lower than in 2015.
NEA noted that there could still be periods of haze, especially during prolonged dry spells.
“The severity and duration of haze episodes will depend on how the ground situation subsequently develops and the extent of fires,” said the agency.
Here’s a comparison of Marina Barrage, before and during the haze this year
What is causing the widespread fires in Indonesia?
Fire is widely used as a cheaper option for agricultural land clearing by both smallholders and plantation companies, as burning costs far less than machines, said Dede Sulaeman, research lead for peatland monitoring at World Resources Institute Indonesia.
Many of the hot spots are seen on plantation land, called concessions, he added. “Concessions represent land with full control by companies, which should play a significant role in preventing fires and achieving a zero-fire target,” said Dede.
His colleague Muslih Biladi, a land use and supply chain analyst, said: “Many companies still struggle to keep fires from breaking out, and even large firms continue to see hot spots turn up in their subsidiaries’ concessions or in supplier areas near their production sites.”
Agricultural land in Sumatra and Kalimantan has been a tinderbox for decades since waterlogged peatlands were drained for plantations, making the land dry and flammable.
El Nino just amplifies human-caused burning. “The risk is therefore highest when human activities occur in already degraded or drained landscapes and coincide with prolonged drought,” Dede said.
What to do when the haze reaches unhealthy levels
Check the air quality before heading out and monitor Singapore’s 24-hour PSI and one-hour PM2.5 readings to understand current conditions.
NEA also provides health advisories based on PSI levels, including guidance on what you can do to protect yourself. Check NEA’s advisory for the latest recommendations.
When the PSI rises to unhealthy levels
Sources: MINISTRY OF MANPOWER, NATIONAL ENVIRONMENT AGENCY, MINISTRY OF EDUCATION