BANGKOK: The Royal Irrigation Department says a powerful monsoon trough caused record rainfall of 630mm in three days, triggering severe floods across 10 southern Thai provinces
The Royal Irrigation Department (RID) says an intense monsoon trough has caused catastrophic flooding across ten southern provinces, with Hat Yai experiencing its most severe deluge in three centuries.
The Smart Water Operation Centre (SWOC) of the Royal Irrigation Department explained that the heavy flooding across the South since Nov 19, 2025 has been caused by the combined influence of a strong monsoon trough and a low-pressure cell covering the southern and lower southern regions.
This has triggered heavy to very heavy rainfall from Chumphon downwards, resulting in major flooding in 10 provinces including Chumphon,,Surat Thani, Nakhon Si Thammarat, Satun, Songkhla, Phatthalung, Trang, Narathiwat, Pattani and Yala.
Accumulated 24-hour rainfall in many areas exceeded 300–500 mm.
Why southern floods turned catastrophic as monsoon trough triggers heaviest rainfall in 300 years
Hatyai hit by its heaviest rainfall in 300 years
Songkhla province experienced intense rainfall across all districts, with Hat Yai recording its highest rainfall on Nov 21, 2025, measuring 335 mm, marking the heaviest single-day rainfall in 300 years.
The three-day accumulated rainfall from Nov 19–21 reached 630 mm, surpassing the historic 2010 Hatyai flood, which recorded 428 mm over the same period.
Flooding in Hatyai municipality saw water levels ranging from 0.50 to 2.50 metres.
Water levels in major and secondary rivers — as well as multiple canals — increased sharply, leading to overflow in many areas.
Khlong Phuminat Damri (Drainage Canal R.1) — a newly constructed canal designed to divert water from Khlong U-Taphao into Songkhla Lake
Khlong R.1 has a drainage capacity of 1,200 cubic metres per second, significantly reducing the volume of water flowing into Hatyai Municipality.
Although rainfall continues in some areas, it is showing a downward trend. If no new heavy rain occurs, officials expect the situation to ease and return to normal within three to five days.
The Royal Irrigation Department has deployed 32 water pumps, and 14 water-propulsion machines to accelerate drainage from the worst-hit zones.
Without Khlong R.1, Hat Yai would have been much worse
The RID noted that the rainfall this time exceeded the design capacity of Khlong Phuminat Damri (Khlong R.1).
However, the canal still played a crucial role in reducing the volume of water flowing into Hatyai district. Officials emphasised that without R.1, the flooding in Hatyai would likely have been far more severe than what occurred. - The Nation/ANN
