Transboundary Haze in Singapore
It is not a storm, but for weeks at a time it can be the region's most disruptive weather-related hazard: a pall of smoke that turns the sky grey, stings the eyes, and pushes air quality into dangerous territory.
What causes the haze?
The haze is smoke carried to Singapore on regional winds, largely from land-clearing and agricultural fires in parts of Indonesia. When those fires burn through carbon-rich peatland, they smoulder for weeks and release vast amounts of fine particulate smoke. During the Southwest Monsoon, the prevailing winds can steer that smoke directly over Singapore, Malaysia, and neighbouring areas.
Why it clusters in the dry-spell months
Haze episodes typically strike between roughly June and October, during the Southwest Monsoon. Drier regional conditions make fires easier to start and sustain, and the wind direction favours smoke transport toward Singapore. Wetter years with fewer fires can pass with little haze at all; drought years, often linked to El Nino, tend to be the worst.
Major haze episodes
- 1997–1998: A severe, prolonged episode during a strong El Nino brought some of the worst regional haze on record and put the issue on the international agenda.
- June 2013: Singapore's air quality reached record-unhealthy levels, with the Pollutant Standards Index climbing into the hazardous range for the first time — a landmark event that dominated national life for days.
- 2015: Another severe, drawn-out El Nino-year episode affected the region for weeks, disrupting schools, flights, and outdoor life.
Reading the PSI
Singapore communicates air quality through the Pollutant Standards Index (PSI), reported over rolling periods and broken down by region. In broad terms:
| PSI | Category |
|---|---|
| 0–50 | Good |
| 51–100 | Moderate |
| 101–200 | Unhealthy |
| 201–300 | Very unhealthy |
| Above 300 | Hazardous |
Health advisories tighten as the PSI rises, especially for children, the elderly, and people with heart or lung conditions.
Protecting yourself during haze
- Check the latest PSI and the 24-hour reading, and follow NEA health advisories for your PSI band.
- Reduce strenuous outdoor activity when the PSI is unhealthy; stay indoors with windows closed when it is high.
- A properly fitted N95 mask filters fine haze particles; ordinary surgical masks do not.
- Those with respiratory or heart conditions should keep medication handy and seek care if symptoms worsen.