Jakarta: Indonesia's capital sinking by up to 15cm a year, new research shows

It's one of the most densely populated cities in the world and home to more than 10 million people, but one of Asia's biggest cities could be virtually wiped off the map in 30 years.

That's because Jakarta — Indonesia's sprawling capital — is one of the fastest-sinking cities in the world, meaning large swathes of it could almost be entirely submerged by 2050.

It's a grim new prediction from experts at Bandung Institute of Technology (BIT), who say about 95 per cent of North Jakarta will be underwater in the next 32 years — forcing its 1.8 million residents to flee their homes.

The megacity sits on a swampy plain that has sunk more than 4m over the past three decades and it is so low that seven of the city's sewage-choked rivers actually have to flow uphill to reach Jakarta Bay.

It is now so bad that the BIT estimates the city is sinking by an average of 1-15cm a year and almost half the city now sits below sea level.

The situation is particularly dire in North Jakarta, a port city which has sunk 2.5m in 10 years and continues to sink by as much as 25cm a year in some parts — that's more than double the global average for coastal megacities.

One of the municipality's residents Fortuna Sophia said, at first glance, she can't tell her luxurious villa with a sea view is sinking.

However, she's lived there for four years and it has already flooded several times. Ominous cracks have also begun to appear on her home's walls and pillars every six months.

Photo / Supplied

"We just have to keep fixing it," she told the BBC. "The maintenance men say the cracks are caused by the shifting of the ground.

"The seawater flows in and covers the swimming pool entirely. We have to move all our furniture up to the first floor."

If vast sections of Jakarta — which generates more than 20 per cent of Indonesia's gross domestic product — were to be submerged, it would create an economic nightmare for the country's 261 million people.

Robert Sianipar, a former top official from the co-ordinating Ministry of Economic Affairs, told Reuters the impact of North Jakarta disappearing would be unthinkable.

Flooding is becoming increasingly frequent in Jakarta. Photo / AP

"If we abandon North Jakarta, that would cost $242 billion in assets — not to count the number of people and productivity that would have to be replaced," he said.

BIT lead researcher Heri Andreas said the sinking is partly down to the city's unreliable piped water. Most areas suffer problems with availability of piped water, leaving residents with no choice but to pump water from aquifers deep underground.

However, when this groundwater is pumped up, the land above sinks and subsides.

"The walkways are like waves, curving up and down. People can trip and fall," Ridwan of Muara Baru, who lives in one of the worst affected areas, told ASEAN Economist.

About three-quarters of residents rely on groundwater.

Reuters reports many of them are refusing to connect to the piped water distribution system because it is more expensive, is not always available and sometimes looks dirty coming out of the tap.

Experts say the only way to stop the city going underwater is to stop all groundwater extraction and solely rely on other sources of water, such as rain or river water or piped water from man-made reservoirs.

It all has serious repercussions for the city's residents who have already seen increased flooding in recent years and this is predicted to worsen as climate change causes sea levels to rise.

Recorded floods and severe storms in South-East Asia have risen sixfold, from fewer than 20 from 1960 to 1969 up to nearly 120 from 2000 to 2008, according to an Asian Development Bank study.

In February, more than 6500 residents in low-lying areas in Jakarta were evacuated to shelters following torrential rains which caused widespread floods across the Indonesian capital and landslides in satellite cities. They were among more than 11,000 people who were affected by the floods, officials said.

However, it was a devastating mega-storm in February 2007 which opened the Indonesian Government's eyes and forced it into action.

A strong monsoon storm coincided with a high tide and overwhelmed ramshackle coastal defences, pushing a wall of water from Jakarta Bay into the capital.

It was the first time a storm surge from the sea had flooded the city. Nearly half of Jakarta was covered by as much as 4m of muddy water.

At least 76 people were killed and 590,000 were left homeless. The cost of the damage reached $599 million.

However, none of this has deterred the property developers. More and more luxury apartments have populated the North Jakarta skyline regardless of the risks — meaning new residents are increasingly moving into the sinking area.

Indonesia's Association of Housing Development chief Eddy Ganefo told the BBC he had called for an end to development but "so long as we can sell apartments, development will continue".