Nan floods refocus debate over forests and watershed management
Nan retains about 736,000 hectares of forest cover alongside 128,000 hectares of bare mountains, while the North recorded Thailand's largest regional decline.
- Recent flooding in Nan province has sparked a debate on whether deforestation is the main cause of the floods, with other factors like heavy rain, terrain, and land-use changes also cited as contributors.
- Despite a large portion of the province remaining forested, Nan is among the top 10 Thai provinces for forest loss, with significant areas of "bare mountains" cleared for agriculture, which reduces the land's capacity to absorb water.
- The degradation of Nan's forests is a critical issue as they serve as the headwaters for the Chao Phraya River basin, supplying approximately 40% of its water and impacting flood risk and water security for millions downstream.
- Efforts to restore the degraded forests and watersheds are underway, but experts note that such ecological recovery is a long-term process expected to take at least 20 years to show significant results.
Flooding in Nan province has fuelled widespread online debate over deforestation and bare mountains, including whether forest loss is a major reason the province faces repeated floods.
Many Nan residents, however, argue that deforestation alone cannot explain the flooding.
Other contributing factors include terrain, heavy rain over a short period, land-use change, drainage systems, river conditions and climate change.
The debate raises broader questions about how much forest remains in Nan, the extent of its bare mountains and the role of its headwater forests in sustaining the Chao Phraya River basin.
Thailand records net decline in forest cover
Thailand’s latest forest figures remain a cause for concern.
Although forest cover increased in some provinces, the national total fell, reflecting pressure from land use, expanding communities and development projects that have altered forest areas.
Data from the Seub Nakhasathien Foundation, based on its analysis of data published in May 2026 under a 2025 project by the Forest Land Management Office of the Royal Forest Department to compile information on forest cover and forest types, showed that Thailand had 16,267,599.07 hectares of land retaining forest cover, equivalent to 31.43% of the country’s area.
This was down 18,044.39 hectares, or 0.11%, from 2024.
At the provincial level, Phetchabun recorded the country’s largest increase in land retaining forest cover, at 2,060.75 hectares, showing that some areas can still conserve and restore forests.
Chiang Mai recorded the largest decline, losing 5,486.73 hectares.
The North registered the largest regional decline, with a combined fall of 13,376.46 hectares.
Mae Hong Son, Tak and Nan were also among the provinces with the largest forest losses, while the Central and Southern regions together gained 1,379.89 hectares from 2024.
Nan ranked among the 10 provinces with the largest reductions in forest cover, losing 1,661.64 hectares.
Land-cover change data also showed that 42,688.68 hectares of Thailand’s forest cover were converted to other uses, while about 24,644.29 hectares returned to forest cover.
The main factors were the conversion of forest land to agriculture, expanding communities and buildings, and infrastructure projects, including roads and reservoirs in forest areas.
Wildfires and landslides also affected forest conditions.
However, the return of forest cover does not mean regenerated areas can entirely replace original forests.
Newly restored forests may have lower biodiversity and less complex ecosystems than the original natural forests, and their full ecological richness can take a long time to recover.
The figures published in 2026 therefore show more than whether Thailand has gained or lost forest.
They raise questions about the quality and integrity of the forests that remain and the rate at which natural forest is being lost, particularly in the North.
Nan retains extensive forests alongside bare mountains
Nan’s Provincial Office of Natural Resources and Environment said the province covers about 1,147,200 hectares.
Of this, about 736,000 hectares retain forest cover, which the office put at around 61% of the provincial area.
Legally designated forest areas, comprising national reserved forests and protected forests, total about 968,000 hectares, which it put at 79.81%.
The figures present another side of Nan.
Although the province is frequently discussed in connection with bare mountains and forest loss, most of its area remains within forest zones, with extensive areas still retaining forest cover.
The Royal Forest Department said Nan’s forests fall into two broad scientific categories: evergreen forests, comprising hill evergreen, dry evergreen and natural pine forests; and deciduous forests, comprising mixed deciduous and dry dipterocarp forests.
Extensive areas of hill evergreen, dry evergreen, mixed deciduous and dry dipterocarp forests occur along mountain ranges, particularly in Si Nan National Park and Doi Phu Kha National Park, both important headwater forest areas.
Bare mountains, however, remain a major challenge.
The Royal Initiative Discovery Foundation and Nan provincial authorities reported that Nan has about 128,000 hectares of bare mountains, equivalent to approximately 11% of the province.
More than 288,000 hectares of forest have been lost through land clearing for monoculture crops, particularly maize.
Forest restoration expected to take decades
Nan has begun pursuing several approaches to restore degraded areas, including the Nam Phang Model, the Nan Model and the idea of “putting hats and shoes on bare mountains”.
Measures also divide management areas into upstream, midstream and downstream zones and combine the Three Forests for Four Benefits project with support for ecological farming.
The aim is to reduce dependence on monoculture and encourage forms of agriculture more compatible with forests.
Restoring mountains and ecosystems, however, will not produce results within a few years.
The Royal Initiative Discovery Foundation said forest restoration takes at least 20 years before clear results begin to emerge.
Nan’s headwaters support the Chao Phraya basin
The Department of National Parks, Wildlife and Plant Conservation and a research team from the Khun Sathan Watershed Research Station said headwater forests on Nan’s peaks and ridges are the source of hundreds of small tributaries that converge to form the Nan River.
Headwater forests do more than provide green space.
They retain rainfall, slow its movement into streams, preserve soil moisture, prevent topsoil erosion and help filter sediment before it enters rivers.
When forests are destroyed, the land’s capacity to hold water declines, allowing rainwater to run off more quickly from higher ground during heavy rainfall.
During the dry season, less water remains stored in natural systems, reducing the capacity of headwater areas to release water continuously.
Information from the Royal Irrigation Department and research published in an international academic journal indicates that the Nan River is one of the main waterways feeding the Chao Phraya River.
It accounts for about 40% of the total water flowing through the Chao Phraya confluence in Nakhon Sawan and contributes about 57% of the sediment entering the river system.
The Nan River basin also encompasses farmland and water supplies for household use and consumption in Nan, Uttaradit, Sukhothai, Phitsanulok, Phichit and Nakhon Sawan.
Many residents and the agricultural sector depend on water resources from this basin.
Bare mountains and forest loss in Nan are therefore about more than slopes changing from green to brown; they are linked to the water system across the entire basin.
The central task may therefore be not to blame one side alone, but to protect the forests that remain, restore degraded land and manage headwater areas in earnest.
For those asking how closely forests and floods are connected, the answer may require looking beyond Nan’s mountains.
The Nan River continues downstream from its headwaters, sustaining people and the economy across several provinces in the Chao Phraya River basin.
