Chiang Mai, Thailand's second-largest city, is nestled in a network of narrow valleys in the country's northern highlands. Known for panoramic mountain views, the historic city has seen clear skies become a rarity in recent decades, with smoke increasingly darkening the dry season skies, particularly in March and April.
On April 22, 2026, NASA's satellite captured a smoky view of the city and surrounding region, with haze partially obscuring valleys and ridges that would normally be visible. The smoke likely comes from small agricultural and forest fires lit to clear crop debris or maintain ecosystems. Satellite sensors detected few fires in January 2026, but detections surged in February, March, and April. Fire activity typically peaks in March and fades by May as seasonal rains roll in.
Research says smoke from biomass burning is a top contributor to poor air quality in northern Thailand during the dry season. One estimate suggests about 70 percent of fine particulate matter (PM2.5) in Chiang Mai in April comes from biomass burning. Other culprits include vehicles, power plants, industry, and charcoal burning for cooking and heating. Geography doesn't help: surrounding mountains block airflow and encourage temperature inversions that trap local pollution and haze in the valleys.
On the same day the satellite image was taken, ground-level air quality sensors recorded "unhealthy" and "very unhealthy" PM2.5 levels throughout Chiang Mai and the region, per the World Air Quality Index project. Prolonged exposure to such pollution can contribute to respiratory and cardiovascular diseases and other health problems.
News reports indicate the haze is hurting tourism, with international traveler numbers to Chiang Mai dropping. After over a month of persistent haze, tourist arrivals in the town of Pai, a popular backpacker destination northwest of Chiang Mai, were down 90 percent, according to a local newspaper.
Unusually warm and dry conditions have gripped the region recently, according to meteorologists at the ASEAN Specialised Meteorological Centre (ASMC). On March 27, the group warned of a "high risk" of severe transboundary haze and raised its alert level to three, the highest on the scale. In late March, ASMC noted that dry conditions were forecast to persist over most of the Mekong sub-region, with prevailing winds expected from the south or southwest. "Under these conditions," ASMC noted, "the hotspot and smoke haze situation could escalate further."