Nan braces for more heavy rain with saturated soil increasing flood risk

The Office of the National Water Resources (ONWR) has warned Nan residents to prepare for another spell of heavy rain on Sunday (August 23), with saturated soil increasing the risk of further flash floods and rapid run-off even as river levels begin to stabilise and fall.

Deputy Prime Minister Songsak Thongsri chaired a meeting on Thursday (August 20) to review flooding across the Nan River basin, coordinate assistance for affected communities and develop measures to address the province’s recurring flood problems over the longer term.

Twenty-four-hour accumulated rainfall in Nan reached as high as 388 millimetres, triggering widespread flooding and run-off. At the time of the meeting, more than 12,900 households had been affected, with two deaths reported and one person still missing as search operations continued.

Prime Minister Anutin Charnvirakul had also assigned Deputy Prime Minister Yodchanan Wongsawat, who chairs the committee overseeing flood and drought prevention and response in northern Thailand, to monitor the relief operation closely.

Agencies ordered to step up monitoring and recovery

Songsak instructed officials to maintain strict surveillance, particularly in low-lying areas of Tha Wang Pha, Mueang Nan, Phu Phiang and Wiang Sa districts.

He issued eight sets of instructions involving national agencies and Nan provincial authorities. The Thai Meteorological Department was told to monitor weather conditions and use radar data to identify areas at risk of heavy rain in advance, while the Geo-Informatics and Space Technology Development Agency was assigned to map flood boundaries and assess affected areas using satellite data.

ONWR, the Royal Irrigation Department and the Hydro-Informatics Institute were directed to forecast the movement of floodwater, particularly towards Mueang Nan and downstream districts.

The Department of Mineral Resources was instructed to assess landslide-prone areas and coordinate with local volunteer and monitoring networks to issue warnings.

The Transport Ministry was told to inspect damaged roads, bridges and other infrastructure, as well as deploy machinery to clear routes blocked by landslides or debris.

The Provincial Electricity Authority was ordered to prepare contingency plans, personnel and equipment so damaged electricity systems could be restored quickly. The Public Relations Department was instructed to distribute clear and timely warnings, with particular attention to ensuring that vulnerable groups could access the information.

Nan provincial authorities, the Department of Disaster Prevention and Mitigation and other agencies were told to survey damage, install water pumps, accelerate relief and recovery work and monitor the risk of the Nan River overflowing in Wiang Sa district.

ONWR was also assigned to review lessons from the disaster and prepare urgent, short-, medium- and long-term plans for sustainable flood management in Nan.

River levels fall but downstream areas remain at risk

Chayan Muangsong, secretary-general of ONWR, reported that water levels in the Nan River around Tha Wang Pha and Mueang Nan districts had begun to stabilise and gradually decline.

However, authorities must continue monitoring floodwater moving from upstream areas towards lower parts of the province, particularly Wiang Sa, where water levels were still expected to rise.

Rainfall in Nan was forecast to ease between August 20 and 22 before heavy rain returned on August 23, particularly in the upper Nan River basin.

The areas requiring close monitoring include Pua, Song Khwae, Chiang Klang and Thung Chang districts, where 24-hour accumulated rainfall could reach between 50 and 70mm.

Chayan warned that the ground was already highly saturated. Even a moderate amount of additional rain could therefore become surface run-off and flow rapidly into rivers, causing water levels to rise again.

Authorities and residents in high-risk areas were urged to remain prepared and follow official warnings closely.