CHIANG RAI— On Monday, dark clouds pressed low over the Thai-Myanmar border as Mae Sai residents stacked sandbags and watched the Sai River rise. The fading tail of Typhoon Bualoi, the 20th storm in a fierce Pacific season, had moved west after striking northern Vietnam, dropping constant rain across northern Thailand.
In a town already hit by repeated floods this year, streets swelled into shallow pools, and recovery slipped back into survival.
The Thai Meteorological Department warned early Tuesday of thunderstorms over 60% of the North, and pockets of heavy rain up to 150 millimetres in 24 hours. Flash floods, forest runoff, and river surges were likely in Chiang Rai, Phayao, Nan, and nearby provinces.
Mae Sai, a hard-working border town where Thai baht and Myanmar kyat change hands under misty hills, has endured a year of punishing storms. The first big flood hit in late April after 118.8 millimetres of overnight rain, forcing midnight evacuations and swamping roads in Mai Lung Khon.
In May, waters rose again before dawn, sweeping through Ban Tham Pha Jom and other riverside communities. The municipality opened four shelters in temples and district halls. Acting mayor Wannasilp Jirakas warned residents to treat floodwater as contaminated, with arsenic a concern from upstream sources, and urged families to boil water to prevent disease.
July brought more hardship. On the 27th, another 118.8 millimetre downpour pushed officials to move the elderly and bedridden from Ban Pham Kwai Muang Dang, while district chief Warayut Khomboon scrambled teams to plug embankment gaps.
Sai River Rising
He said the Sai river rose without warning, surprising even those on watch. By August, forecasts hinted at more storms, and people in town were tired and short of cash. More than 200 households have been damaged this year.
Erosion has chewed up roads, and losses approach 4 billion baht, echoing the historic 2024 floods linked to Typhoon Yagi’s remnants. That disaster shut Chiang Rai Airport for a day and stranded travellers, and many levees remain in need of repair.
Bualoi, a Category 1 typhoon, made landfall in Quang Binh, Vietnam, on 29 September, then weakened over Laos. Thailand avoided a direct hit, yet the storm energized the southwest monsoon trough, strengthened by cooler air aloft, and fed moisture into the North for roughly 10 days from 20 September.
The Department of Disaster Prevention and Mitigation sent Cell Broadcast alerts to phones across Chiang Rai, warning of flash floods and quick rises along waterways near foothills and lowlands.
In Mae Sai, swollen tributaries in Myanmar channelled an estimated 50 cubic metres per second into the river, easily breaching sandbag lines and turning the border bridge area into a churning obstacle.
Relief volunteers in orange vests delivered rice, instant noodles, and water filters. At the same time, public anger grew over upstream impacts in Myanmar’s Shan State.
A surge in gold and rare earth mining, led by Chinese-linked operators in areas controlled by armed groups such as the United Wa State Army, has stripped hillsides near the Sai River’s sources.
Srip Mining in Myanmar
Global Witness satellite analysis points to a widening “sacrifice zone” where mining areas expanded from 26,000 hectares in 2018 to 46,700 in 2024, with hotspots at Pang War and Mong Hsat close to the headwaters. Open pits and chemical use have removed forest cover that once soaked up heavy rain.
Environmental advocates warn that with vegetation gone, rainfall flushes straight into streams, and acids and ammonium sulphate used in rare earth extraction increase erosion. During intense monsoon bursts, runoff turns into silt-loaded torrents.
Rains from Bualoi have sped this up, pushing mud and toxins downstream. Arsenic levels in the Sai reportedly reach four times the WHO guideline. Mercury and cyanide have entered fish stocks.
In Mae Sai, this year’s floodwaters often appear orange-yellow and can irritate skin on contact. Local fishers have reported rashes after rescue work and water contact, saying the river that once fed families now harms them.
Analysts link the mining boom to Myanmar’s turmoil since the 2021 coup. With sanctions biting, the junta is seen to allow operations that finance militias, while China, which dominates global rare earth processing, shifts dirty extraction over the border.
Mining Damages Chiang Rai Rivers
At least 20 new sites have appeared in southern Shan State, with reports of high levels of toxic waste per tonne of rare earth mined. The fallout crosses borders. About 1.2 million people in Chiang Rai rely on the Sai and Kok rivers for water, now at risk from arsenic and other pollutants.
The Mekong downstream shows early signs of the same stress, raising alarms for Laos and Cambodia. Environmental groups call it organized environmental crime and want action at the ASEAN level.
In Mae Sai’s shelters, including Wat Phromwihan temple, families sleep under tarps and on thin mats. A young monk, Phra Maha Nikhom, leads prayers for dry weather and stable ground.
Chiang Rai’s Governor sent 500 troops to reinforce sandbag walls and put excavators to work dredging channels, a task slowed by the lack of cooperation on upstream works inside Myanmar.
DDPM chief Anuchin Charoenpak has asked Naypyidaw to coordinate, yet conflict and mistrust have stalled progress. He has said Thailand cannot solve the upstream blockages alone.
As Bualoi’s showers eased to a drizzle by evening, Mae Sai could only take a short breath. Forecasts point to a wetter 2026 with La Niña conditions likely. People want more than short-term fixes.
They want cross-border limits on mining near headwaters, funds for replanting from Beijing, and clear testing of water quality. Local council member Bundit Pantarakon told a crowd at the bridge that the river is in decline and that without help from neighbours, everyone along its banks will pay the price.
For now, the Sai keeps moving, brown and swollen. In a border town shaped by trade and storms, people count on grit, community, and a break in the rain.
