What happened in 2026
Between January and late March 2026, monitoring agencies recorded well over 2,000 fire hotspots across Chiang Mai province, with a sharp spike in late March when 158 individual wildfires were logged across 15 districts in a single day — nearly five times the count from the day before. On multiple days in March, independent air-quality tracker IQAir ranked Chiang Mai among the top few most polluted major cities in the world, with the AQI (Air Quality Index) exceeding 150 — the threshold classed as "unhealthy" — and PM2.5 (fine particulate matter) as the dominant pollutant. Provincial authorities declared some districts, including Samoeng and Hot, wildfire disaster zones and deployed firefighting helicopters, alongside a blanket ban on open burning across the province from 1 February to 31 May.
Why this happens every year
Chiang Mai's poor air quality each dry season comes overwhelmingly from biomass burning rather than the traffic- or industry-driven smog of other big cities: agricultural residue burning (rice, sugarcane and maize fields being cleared ahead of planting), forest fires in the surrounding hills, and smoke drifting in from similar burning across neighbouring countries. Geography compounds it — Chiang Mai sits in a bowl of mountains that traps smoke rather than letting it disperse. The pattern is consistent enough that it has an informal local name: "burning season," running roughly from mid-February through April, peaking in March.
What it means if you're planning a trip
If you have real flexibility, the cool season (November–February) and the rainy season (June–October) both avoid the worst of it — see our full best time to visit guide. If your dates are fixed and they fall in burning season, it doesn't necessarily mean cancelling: air quality is genuinely variable day to day even within the season, and outdoor plans (hiking Doi Inthanon, visiting hilltop temples) are the activities most worth checking a real-time reading before committing to.
- Check a live reading before you travel and again once you arrive — conditions can shift meaningfully within days.
- An N95 or KN95 respirator, not a surgical mask, is what actually filters PM2.5 effectively if you need to be outside on a bad-AQI day.
- Anyone with asthma, other respiratory conditions, or travelling with young children or older relatives should weigh this season more heavily than a typical visitor would.
- Indoor and half-day options (museums, cafés, cooking classes, spas — see cooking classes and massage & spas) are reasonable ways to structure a day around a bad-air afternoon.
Millions of people live in Chiang Mai year-round, including through burning season, and locals go about ordinary life through it — this is a real seasonal environmental issue worth planning around, not a reason to avoid the city altogether outside those months.