Parts of Thailand's capital could be underwater by 2030 unless the government takes steps to prevent disaster, say experts

Among the pressing challenges facing the new government of Thailand, brought to power by the July elections, is the fact that Bangkok is steadily sinking. The gloomiest forecasts suggest parts of the Thai capital may be underwater by 2030, but experts are also critical of the lack of any clear policy to prevent impending disaster.

Several factors – climate change, rising sea levels, coastal erosion, shifting clay soil – are threatening the great city on the Chao Phraya delta, founded in 1782 by the first monarch belonging to the Chakri dynasty, which is still ruling today.

The population has greatly increased, with about 10 million people now living in the city and its suburbs. Even the weight of the skyscrapers, constantly on the rise in a conurbation in the throes of perpetual change, is contributing to Bangkok's gradual immersion. Much of the metropolis is now below sea level and the ground is subsiding by 1.5 to 5cm a year.

In the medium to long term more than 1m buildings, 90% of which are residential, are under threat from the rising sea level. In due course the ground floors of buildings could be awash with 10cm of water for part of the year, according to the Asian Institute of Technology.

In the port of Samunt Prakan, about 15 km downstream from the capital, the residents of detached houses along the river already spend several months a year up to their ankles in water.

A joint report published in December by the World Bank, the Asian Development Bank and Japan's International Co-operation Agency highlighted the threat from climate change to three Asian megacities: Bangkok, Ho Chi Minh City and Manila.

Illegal tapping of groundwater is one of the causes of the capital's misfortunes, according to Jan Bojo, a World Bank expert based there. Not all the specialists endorse this view, but they do agree the situation is bound to deteriorate over the next few years. Smith Dharmasaroja, the head of the National Disaster Warning Centre, is predicting that by 2100 Bangkok will have become a new Atlantis. Dharmasaroja's forecasts are taken seriously: in the 1990s he predicted the fearful tsunami that devastated countries around the Indian Ocean in 2004.

Dharmasaroja maintains that "no decision has been taken" at government level "to stop the problem". And, he adds, if nothing is done Bangkok could be underwater by 2030.

One of the solutions he has suggested is to build a series of dykes along the coast of the Gulf of Thailand, a scheme that would cost over $2bn. He says work should start immediately, otherwise it will be too late to halt the chain of events leading to disaster.

Anond Snidvongs, an oceanographer and specialist on climate-change impacts in south-east Asia, takes a more cautious line. "No one can predict how long it will take for Bangkok to be flooded and how this process will unfold," he says. He sees no point in building huge dykes. "The rise in sea level is not that great and climate change only plays a fairly small part – about one-fifth – in the current scenario," he adds.

"It's pointless," he stresses, "to try to protect the coastline, which is being eroded by three to four centimetres a year. But there are plenty of other ways of combating flooding, such as better management of building land in the city."

Niramon Kulsrisombat, a town planner and lecturer in urban and regional planning at Chulalongkorn University, confirms that "floods have always occurred, Bangkok having been built on sodden terrain 1.5 metres below sea level".

A network of khlongs (canals), fields and allotments used to soak up flooding, but with recent urbanisation many buildings have taken their place and the water is trapped.

"Government efforts have focused on raising barriers 2.8 metres high along various stretches of the Chao Phraya," Kulsrisombat explains, "but this has just done even more damage to the traditional appearance of a settlement where people lived on the water in houses on stilts."

Snidvongs thinks the key factor in saving the city is co-ordinating measures. "We absolutely need to achieve a consensus so that the million or so people who will be directly affected by flooding in the medium or long term can agree on the principles underpinning any solutions," he says.

In short, the scientists who spend their time scrutinising Bangkok must tighten up their diagnosis, the better to prepare for rescuing the Thai capital.

This article originally appeared in Le Monde