Climate change danger 'exaggerated' in tidal flooding in Gulf of Thailand

Bangkok Post 25 Jul 10;

Land subsidence, not climate change, is the biggest factor causing tidal flooding, a researcher says.

Subsidence is the main cause of coastal tidal flooding and coastal line erosion along the upper Gulf of Thailand, says Thanawat Jarupongsakul, head of the unit for disaster and land information studies at Chulalongkorn University's science faculty.

Many people believe that climate change causes rising sea levels, which could one day inundate Bangkok and neighbouring provinces, he said.

But according to his study, climate change accounted for less than 10% of the risk.

Another cause was low levels of estuary sediment, a key element in strengthening tidal mudflats which act as a barrier against erosion.

"We have found that 82.5% of the flooding is due to land subsidence," Mr Thanawat told a recent seminar on rising sea levels organised by Chulalongkorn University.

Land subsidence is getting worse, especially in Samut Prakan, Samut Sakhon, Samut Songkhram and Chachoengsao provinces, which are close to the upper Gulf of Thailand.

Although those provinces have a similar rate of land subsidence, losing three centimetres a year on average, the problem is worsening because of powerful coastal tidal flooding, he said.

In 1984, Bangkok experienced high levels of land subsidence, losing over 10 centimetres of shoreline that year, caused by uncontrolled underground water pumping, as the city tried to keep its people supplied with water.

A regulation was imposed banning underground water pumping in Bangkok, which alleviated the problem.

"We can do nothing about rising sea levels. We can do nothing about falling levels of sediment.

"But what we can do is prevent land subsidence," Mr Thanawat said.

In 2007, the intergovernmental panel on climate change said world sea levels were rising on average about three millimetres a year, with 2.4 millimetres in Malaysia, 2.5 millimetres in Vietnam, 7.8 millimetres in Bangladesh and 4.1 millimetres in Thailand.

Mr Thanawat said that if nothing was done about land erosion, Thailand could end up losing 8.2 kilometres of shoreline a year by next century.