Thailand’s reservoirs 72% full as 6 provinces face flood risk until September 21
Thailand’s reservoirs were 72% full on September 20, as forecasts warned of over 200mm of rain across three days in parts of six provinces
- Thailand's Office of the National Water Resources (ONWR) has warned of potential flash floods and rapid runoff in six provinces between September 19-21.
- The warning identifies ten specific districts within the provinces of Trat, Kanchanaburi, Chaiyaphum, Sa Kaeo, Nakhon Ratchasima, and Buri Ram where rainfall could exceed 200mm.
- Residents in the at-risk areas, particularly low-lying communities, are advised to monitor weather updates and prepare for possible riverbank overflows.
- The warning comes as Thailand's nationwide reservoir storage is reported to be at 72% of total capacity.
The Office of the National Water Resources (ONWR) warned that heavy rainfall could trigger flash floods and rapid runoff in parts of six Thai provinces during September 19–21, 2026. The agency’s September 20 water report also put nationwide reservoir storage at 72% of capacity.
Ten districts face rainfall totals above 200mm
ONWR identified ten districts where accumulated rainfall could exceed 200mm over September 19–21, creating a risk of flash floods and runoff from higher ground.
Residents in the identified areas were advised to monitor weather information, prepare for possible riverbank overflows and take care when travelling through places affected by standing water. Low-lying communities and areas receiving runoff near foothills warranted particular attention.
ONWR said it was monitoring conditions with relevant agencies and coordinating with the Thai Meteorological Department (TMD), the Department of Disaster Prevention and Mitigation (DDPM) and local administrations. The monitoring focused particularly on the six provinces, with the aim of limiting harm to people and property.
National reservoir storage reaches 57,818 million cubic metres
Thailand’s reservoirs held a combined 57,818 million cubic metres of water, equivalent to 72% of total storage capacity, in the September 20 report.
Usable water amounted to 33,696 million cubic metres. Bangkok Biznews’s account also gave a figure of 60% for usable water, but did not specify the capacity measure used to calculate that percentage.
The western region had the highest reservoir storage relative to capacity, at 86%. Regional figures were:
Rain forecast to ease during September 21–25
Rainfall across Thailand was expected to decrease overall during September 21–25, although heavy downpours could still occur in some areas.
The forecast cited a monsoon trough shifting northwards across the lower Central region and the East towards a low-pressure area over the central South China Sea. A moderate south-westerly monsoon was also continuing to cover the Andaman Sea and the Gulf of Thailand.
For September 20, the report identified a continuing risk of heavy rain in upper northern and upper northeastern Thailand, the lower Central region, the upper South and the East.
Sukhothai recorded the largest rainfall total among the regional maxima listed in the September 20 report, at 126mm. The figures were:
The rainfall had prompted monitoring of accumulating water in vulnerable areas. Related coverage details the heavy-rain and flood risks in Bangkok and eastern Thailand on September 20.
Three key eastern reservoirs hold 50–77% of capacity
The report assessed water supplies in the Eastern Economic Corridor (EEC) as sufficient for domestic and industrial use. The corridor is an important area for industry, agriculture and tourism.
Storage at three key reservoirs stood as follows:
Prasae had the highest storage level of the three, both by volume and as a proportion of capacity.
Water availability in the EEC remained adequate to meet household and industrial requirements while supporting water management through the latter part of the rainy season.
