Bangkok is making preparations for a triple blow -- run-off from the North, heavy downpours and high tides -- all coinciding in the middle of the month.
The Bangkok Metropolitan Administration (BMA) has sounded the alarm as the run-off and the downpours could trigger widespread flooding worsened by the tides, deputy BMA spokesman Bensai Keeyapaj said Monday.
The BMA executives met Monday to discuss Bangkok's water situation.
Most vulnerable are communities along the Chao Phraya River which are not protected by flood walls.
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Also, in the past week, several low-lying spots east of Bangkok such as Min Buri and Lat Krabang have experienced flooding as canals have overflowed, she said.
Ms Bensai added more wet weather is in store for Bangkok in the coming days as a monsoon trough is lingering over the capital.
In Ayutthaya, provincial governor Sujin Chaichumsak said he has asked the irrigation authorities to open seven sluice gates to divert water from the Noi River into the 130,000-rai Phak Hai field where rice has already been harvested.
The area was now ready to be converted into a temporary kaem ling (monkey cheek) water-retention zone, he said.
The province had previously told the irrigation office that it could begin diverting the water into two other major clusters of paddy fields in Ayutthaya called the Bang Ban and Sena fields.
Water run-off from the North empties into the Gulf of Thailand through the Noi and Chao Phraya rivers.
Pathum Thani governor Surachai Khan-arsa, meanwhile, said the province was looking to divert at least 7 million cubic metres of water into the Rama IX reservoir project in Khlong Luang district which has a maximum retention capacity of 33 million cubic metres.
Although less water is now flowing downstream from the lower North and the upper part of the Central Plains, plenty more rain is on the way and will arrive from Tuesday until Saturday, said Thongplew Kongjun, deputy director-general of the Royal Irrigation Department (RID).
However, water experts maintain the current water situation is unlikely to lead to the major floods that devastated much of the country in 2011.
Chirapol Sintunawa, of Mahidol University's Faculty of Environment and Resource Studies, said a repeat of that disaster is unlikely.
However, the impact of the La Niña wet weather phenomenon in Southeast Asia could cause the rainy season in Thailand to drag on until early next year, and residents should be prepared.
He said with La Niña, storms could hit Thailand hard.
"Even though the floods are unlikely to cause huge damage as in 2011, several areas still run the risk of encountering more floods as more than two storms could be brewing to threaten the country in the same month," he said.
Some storms are predicted to form in Vietnam and possibly affect Thailand early next month, said Royol Chitradon, director of the Hydro and Agro Informatics Institute.