NAN - Flood-hit areas of this northern province could face renewed danger this weekend, with another round of rain forecast for Sunday, raising concerns about landslides and flash floods as communities recover from this week’s devastating flooding.

Water levels were stabilising on Thursday and gradually receding after torrential rain inundated large parts of the province.

While water levels in Nan municipality had begun to decline, flooding remained severe in parts of Wiang Sa district, Seree Supratid, director of the Climate Change and Disaster Centre at Rangsit University, said on Thursday.

Mr Seree said conditions should improve over the next two days, with water levels expected to fall significantly on Friday and Saturday. The Nan River is likely to drop below its banks on Friday.

However, forecasters are monitoring a low-pressure system over northern Vietnam that could bring another spell of rain to northern Thailand on Sunday.

“The current forecast indicates another batch of rain on Aug 23, but the situation must be updated daily to determine whether it will follow the same pattern as this week’s event,” Mr Seree said.

He said the main concern was that soil across Nan and parts of the lower North was already saturated after days of heavy rainfall.

“The ground can no longer absorb much more water, creating a risk of landslides and flash floods, particularly in upper areas. This must be closely monitored.”

The warning comes after severe flooding swept through Nan this week following rainfall of up to 380 millimetres in some areas. Two people were killed and parts of Pua, Tha Wang Pha, Muang, Phu Phiang and Wiang Sa districts were inundated.

Authorities have begun recovery operations in upstream districts where floodwaters are receding, while relief efforts continue further downstream.

Mr Seree, also vice-president of the National Disaster Warning Council Foundation, also called for stronger coordination between central and local authorities in disaster preparedness and response.

He said cell broadcast alerts and other national warning systems can only provide broad-area warnings, while local authorities are better placed to identify vulnerable communities, assess local risks and direct residents to evacuation centres.

Despite warnings being issued between 4 and 6am, fatalities still occurred, suggesting gaps between official alerts and people receiving or acting on them, he said.

Mr Seree urged local administrations to establish emergency war rooms to work alongside central agencies and improve communications during disasters.

He also said changing land use and environmental conditions had increased flood risks.

In the past, rainfall of 100 to 200 millimetres might not have caused major flooding, but altered landscapes now mean much lower rainfall totals can trigger flood events.

“Each locality has a different capacity to absorb water. Local authorities need their own warning systems and risk assessments. Otherwise, these problems will continue to recur, with more deaths and greater damage,” he said. (Story continues below)

Volunteers take part in a project to rehabilitate deforested land on a hill in Nan Noi district of Nan province in 2018. (Bangkok Post File Photo)

Forest loss blamed

Separately, environmental academic Sonthi Kotchawat said Nan’s recurring floods reflected long-term environmental degradation, with deforestation and encroachment into protected forest areas contributing to frequent flooding, particularly in Pua district.

Large areas of natural forest had been converted into monoculture farmland, especially maize plantations on steep mountain slopes, reducing the land’s ability to absorb rainfall, said Mr Sonthi, a member of Thai Environmental Academics Club.

He cited data showing Nan has nearly 800,000 rai devoted to maize cultivation, while around 1.8 million rai or 24% of the province’s 7.6 million rai of forest land had been converted into “bald mountains” through agricultural expansion.

Combined with steep terrain and intense monsoon rainfall, the loss of forest cover has accelerated runoff into rivers and low-lying communities, increasing the risk of flash floods and river overflows.

Although reforestation and sustainable farming programmes have expanded in recent years, large areas of degraded land remain vulnerable to erosion and rapid runoff during heavy storms, Mr Sonthi added.