A new report from Thailand's government says that Bangkok, its capital city and home to some 14 million people, could be underwater in the next 15 years thanks to a combination of sinking land and rising global sea levels.

The conclusion comes from Thailand's National Reform Council, which issued a report last week that warned "immediate and costly solutions are needed to avert a catastrophe," caused by "excessive pumping from the [underground] aquifer, the weight of mushrooming development and rising sea levels," the Bangkok Post reports.

The city, much of which lies at an elevation of just under 5 feet above sea level, already is sinking at a rate of 2 centimeters (about 0.8 inches) every year. Should it continue at this rate for the rest of this century, by 2100 "Bangkok will be fully submerged and unliveable," the Global Post reports.

(MORE: The World's Fastest-Sinking Cities)

This sinking, called subsidence by the scientists who study it, is accelerated by the sheer number, size and weight of all the buildings pressing down on the land all around Bangkok, according to the NRC committee that issued last week's report.

"There are about 700 buildings with 20 floors or more and 4,000 buildings with 8-20 floors in Bangkok," said Witthaya Kulsomboom, the head of the committee. "There are also many electric railways. These could cause the submergence of parts of Bangkok and surrounding areas in the future."

Relocation of the capital will have to be considered, Kulsomboom added, especially if development continues unabated and groundwater continues to be pumped from underneath the city.

Among the committee's recommendations were the construction of a seawall to protect the greater Bangkok area from rising seas, estimated to cost about 500 billion Thai baht – or about $14.3 billion in U.S. dollars.