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
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New Orleans
New Orleans and surrounding areas continue to sink at highly variable rates due to a combination of natural geographic and human-induced processes, according to a NASA/university study using NASA airborne radar.
The observed rates of sinking, otherwise known as subsidence, were generally consistent with, but somewhat higher than, previous studies conducted using different radar data.5
While the study cites may contributing factors for the regional subsidence, the primary contributors were found to be groundwater pumping and dewatering (surface water pumping to lower the water table, which prevents standing water and soggy ground).
Other Places
Arizona State University geophysicist Manoochehr Shirzaei, who studies land subsidence says, “Almost every coastal city around the world builds on loose sediment, and all of them are subsiding, regardless of pumping groundwater. In fact, vertical land motion is as important as sea level rise, but unfortunately it gets very little attention, because the process is slow.” 6
Consider the San Francisco Bay Area. Last year, Shirzaei published a study that showed most of its coastline is sinking around 0.07 inches a year, not because of groundwater drainage but because of the natural settling of soils or landfill. That's tiny compared to Jakarta's 10 inches of annual shrinkage, s And well short of Mexico City, perhaps sinking at a foot a year. Also notable: California's Central Valley, which has sunk almost 30 feet in places due to groundwater over exploitation. This adds up over time—the analysis estimated that the San Francisco airport could be underwater by 2100. This is the inevitable consequence of building on landfill. 7
Shanghai has experienced more than two meters of subsidence due to groundwater pumping and construction on compressible sediments—just like Jakarta.2
In many cases, the location of a city was chosen without any idea of the future scale of population living there. Bad development decisions, and a lack of recognition of the carrying capacities of the land are definite causes of the problem. 3
References
Michael Kimmelman, “Jakarta is sinking so fast, it could end up under water,” The New York Times, December 21, 2017
Scott K. Johnson, “Jakarta has sunk by up to 4 meters, forcing Indonesia to build a new capital,” arstechnica.com, August 27, 2019
Elen Diskin, “These 5 major cities are sinking rapidly into the sea,”matadornetwork.com, December 5, 2018.
Katherine Kramer, “Sinking cities, rising seas,” christianaid.org.uk, October 5, 2018
Tony Greicius, “New study maps rate of New Orleans sinking,” nasa.gov, May 16, 2016
Matt Simon, “Jakarta is sinking. Now Indonesia has to find a new capital,” wired.com, May 2, 2019
Manoochehr Shirzaei and Roland Burgmann, “Global climate change and local land subsidence exacerbate inundation risk to the San Francisco Bay Area,” Science Advances, March 7, 2018
Jack Dini is author of Challenging Environmental Mythology. He has also written for American Council on Science and Health, Environment & Climate News, and Hawaii Reporter.
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. 
