Bangkok residents are being warned about the potential for severe flooding as the capital is expected to be hit hard by torrential rainfall in September to November.

The heavy rain is predicted due to the influence of the La Nina climate phenomenon which will likely boost the capital's rainfall pattern this year to levels last seen in 1983, when some of the worst floods ever hit Bangkok, said Thanawat Jarupongsakul, head of the Unit for Disaster and Land Information Studies, Chulalongkorn University.

Bangpoo Industrial Estate has become an unpleasant place to commute and work this week, although many factories closed on Tuesday because of the floods. (Photo by Somchai Poomlard)

"We expect there will be storms coming from the Gulf of Thailand heading directly to the capital and heavy downpours of at least 200 millimetres are possible during September to November," he told a seminar on "Urban Policy to Respond To Climate Change" organised by the Thailand Environment Institute yesterday.

"It means we might face breakdowns in infrastructure in the capital. Infrastructure for commuters, especially the subway, might be seriously affected," said the expert.

He said the rainfall pattern this year would likely be very similar to that in 1983. The storms begin near the Ca Mau Peninsula in Vietnam and pass through Cambodia over the Gulf of Thailand before heading directly to the capital.

Flood levels could potentially be higher than one metre in some parts of the capital and could last for a few days or up to a week. Everywhere in the capital is at risk of inundation, Mr Thanawat said. He said the amount of rainfall this week which caused sudden flooding in several areas of Bangkok reached close to 100mm. Imagine what could happen if the rainfall reached 200mm or more, he warned.

Although the Bangkok Metropolitan Administration has built a giant tunnel for water drainage, this cannot operate at full capacity due to garbage blocking the flow of water, he said. Meanwhile, the bulk of the water drainage system in the capital is old, having been built around 40 years ago.

Thongchai Roachnakanan, a city-planning expert, said Bangkok's water drainage system cannot handle the extreme weather caused by climate change as it was designed to drain only 60 cubic metres per second, which is virtually useless if there is heavy rain.

What the capital needs to cope with the extreme weather is a system which can effectively drain water at a rate of at least 100 cu m/second, he said.

Mr Thongchai said allowance for climate change has not been included in city-planning regulations, adding that increasing the amount of green areas and waterways is one way to solve the situation over the long term.

"A suitable system is not being implemented because parties are not aware flooding is a serious problem for the capital. They think it just involves abrupt flooding, which comes and goes. People just live with it," he said.