30 million people in the metro area, is pretty massive. Anyway, here's the detail:

&gt;The main cause: Jakartans are digging illegal wells, drip by drip draining the underground aquifers on which the city rests — like deflating a giant cushion underneath it. About 40 percent of Jakarta now lies below sea level.

That coupled with a rising Java Sea, it's time to retreat. The sad thing is that just 2 years ago the country was warning that they *only* had 10 years to stop the sinking. Turns out it actually was a lot less