3 reasons Jakarta is the fastest sinking city in the world

One of the most densely populated cities in the world, Jakarta is disappearing into the ground, literally. Researchers at the Bandung Institute of Technology say that by 2050 about 95% of North Jakarta will be submerged.

North Jakarta, a port city, has sunk 2.5m in 10 years and continues to sink by as much as 25cm a year in some parts, more than double the global average for coastal megacities. According to a media report, Jakarta is sinking by an average of 1-15cm a year and almost half the city now sits below sea level.

Not just the north part, the rest of Jakarta is sinking too, even if at a slower rate. The report says that in West Jakarta, the ground is sinking by as much as 15cm annually, by 10cm annually in the east, 2 cm in Central Jakarta and just 1cm in South Jakarta.

Here is why Jakarta is the fastest sinking city in the world -

• Groundwater exploitation
Since piped water isn't reliable, is sporadically available and costly, people are forced to pump water from the aquifers. Excessive use of groundwater causes the land above it to sink and this leads to land subsidence, a phenomenon where rock and sediment pancake on top of each other. The report says that Jakarta government does not even publish data on the volume of groundwater use. Governor, Basuki Tjajaja Purnama, had in 2014 said that illegal use of groundwater had reached alarming levels.

A 2009 decree to restore the water tables by the Ministry of Environment failed as it did not have any mechanism to enforce it. According to the decree, homeowners and commercial buildings were required to store rainwater in 3-foot-deep biopore cylinders on their properties to absorb and store rainwater.

• Poor planning
Economic development has worsened the effects of the subsidence, says another media report. The impact of subsidence, due mainly to groundwater extraction, is greater when populations tend to increase near low lying areas. It says that in 2010, the number of people living in vulnerable coastal areas in Indonesia was 47.2 million - one of the highest globally, and up 35 per cent since 1990. 
Unchecked urbanisation without proper groundwater recharge can have devastating effects. The 2015 floods in Chennai in Tamil Nadu were seen as a result of the same. 

• Climate change
Coastal cities are affected because of rising sea levels caused by climate change. The report says that increased sea levels occur because of thermal expansion - the water expanding because of extra heat - and the melting of polar ice. Experts suggest reintroducing mangroves and rejuvenating reservoirs actually part of old Jakarta.

All the issues combined together exacerbate the effects. Since the growing urban population increases the water demand, climate change will make supply more variable. This will further increase groundwater exploitation. Robert Mcdonald, scientist at the US-based environmental organisation The Nature Conservancy had told Down To Earth that by 2050, 36 per cent of the world's cities will face water crisis.

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