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| Several of the world’s major cities are slowly sinking into the ocean, some at a staggering pace, and without any help from sea level rise. Here are a few of the cities most in danger of being overtaken by the sea. |
Jakarta
Jakarta is sinking faster than any other big city on the planet, faster even, than climate change is causing the sea to rise—so surreally fast that rivers sometimes flow upstream, ordinary rains regularly swamp neighborhoods and buildings slowly disappear undergound, swallowed up by the earth. 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.1
Different sections of the city—home to 10 million people within an urban area of 30 million—are subsiding at different rates, but most fall in the range of 3 to 10 centimeters every year. Over the years, that has added up to as much as four meters of surface elevation change. This has wreaked havoc on building foundations and other infrastructure. And as Jakarta sits on the coast, where a number of small rivers meet the sea, the flooding hazard is also real. This includes high-tide seawater flooding but also storm water flooding as rains captured by the sprawling city’s pavement struggles to drain seaward.2
Why the instability? Jakarta is a case of humans doing the wrong things in just the right place. River sediments deposited at the coast in places like this are naturally somewhat compressible. The actual weight of all the buildings and other construction at the surface is acting to compact the sediment a little, not unlike tampering down loose sand or soil in your yard. The biggest factor, though, is excessive groundwater pumping.
Within the sediment beneath Jakarta are several stacked aquifer layers that water can be pumped out of. Between the aquifer layers are impermeable capping layers. The use of well water in and around the city has caused the groundwater levels in the aquifers to drop tens of meters. As water level drops, the drained spaces lose that support and can collapse, compacting the sediment. In addition, the water pressure inside the impermeable capping layers can also drop during all this. This allows them to compress in a more reversible way—more like an air mattress deflating slightly. 2
London
London can’t blame its sinkage on skyscrapers or faulty infrastructure. It’s actually the result of the last ice age and a phenomenon called ‘glacial isostatic adjustment.’ London’s sinking is caused by the weight of the glaciers pressing down on Scotland 11,000 years ago. These depressed the north and allowed the south of the UK to relatively ‘soar.’ Since the UK’s glaciers have since melted, however, Scotland is now rising—at 0.04 inches per year—while the south of the UK is sinking back into the sea. 3
Dhaka
The capital of Bangladesh is sinking at a rate of a half-inch per yer. Like Jakarta, the situation is being exacerbated by groundwater extraction at in unsustainable rate, as well as shifting tectonic plates. 4
Bangkok
Bangkok finds itself in a precarious position. Currently sitting just five feet above sea level, and sinking at a rate of one inch per year, the city is projected to be submerged by 2030 unless drastic measures are taken. Bangkok does not suffer from the same groundwater issues as Jakarta and Dhaka, but its towering skyscrapers are, however causing the ground to cave in on itself. 4
New Orleans
