This year was awful, but lately I’ve been getting a sinking feeling that things are going to get even worse. A new study shows that sinking feeling is all too reasonable, because land is literally subsiding in on itself.
A new study, published in Science on New Year’s Eve, suggests that by 2040, some 4.6 million square miles (12 million square kilometers), or 8% of the Earth’s ground surface, could be impacted by subsidence. That would affect a staggering 635 million people.
The phenomenon can be caused by natural occurrences like earthquakes and sinkhole formation, but is exacerbated by human actions, especially the extraction of oil, natural gas, minerals, and groundwater. The authors conducted a large-scale review of scientific literature on subsidence, which also revealed at least 200 locations across 34 countries saw land subsidence due to groundwater depletion in the past century. Globally, groundwater pumping is “by far the single largest cause” of the phenomenon, according to the U.S. Geological Survey.
They then created combined spatial and statistical analyses to create a model that projects future global subsistence, based on the last decade’s trends and other factors, including the added stress of drought on water supply, as well as the increasing demand for water for human consumption and industry due to population growth.
“Our results identify 1,596 major cities, or about 22% of the world’s 7,343 major cities that are in potential subsidence areas,” the study says. Fifty-seven percent of those urban areas are also prone to flooding, a threat which is exacerbated by subsidence.
The areas most likely to sink are concentrated in and around densely populated, urban centers and highly irrigated areas—places where there are high levels of groundwater extraction. Among the areas worst hit will be Asia’s North China Plain; the Gulf of Mexico coastal plain; river deltas in Vietnam, Egypt, and the Netherlands; and inland sedimentary basins of Mexico, Iran, and the Mediterranean.
Though the effects will be seen all over the world, 86% of the people likely to be impacted live in Asia, “which is about 10 times the combined exposed population of North America and Europe,” the report says. “India and China share the top two rankings of potential subsidence in terms of spatial extent and exposed population.”
Subsidence is already having measurable effects around the world. Jakarta, Indonesia, for instance, is sinking 10 inches (25.4 centimeters) per year, and has already seen some buildings sink straight into the ground. Subsidence there has also massively increased the risk of flooding like what happened at the start 2020. Even more gradually subsiding landscapes can pose huge risks, including permanently reducing access to groundwater storage capacity, causing fractures to form in the ground, damaging buildings and other infrastructure, and increasing vulnerability to floods and other disasters.
The authors say their findings are “a key first step toward formulating effective land subsidence policies that are lacking in most countries worldwide.” To get a handle on this little-known but crucial issue, the authors call for increased monitoring of ground levels worldwide. Currently, for instance, the only countries that publish the cost of subsidence to their economies are China and the Netherlands.
World leaders can also take steps to mitigate the harm subsidence could cause by preparing flood plans. In addition, the authors call on them to develop alternate supplies of water to reduce the risk of sinking land in the first place. That includes restrictions on groundwater usage, including clamping down most on water-guzzling industries like agribusiness and livestock harvesting, textile production, car manufacturing, and oil and gas extraction (which should be wound down immediately for climate reasons, anyway).
The findings are particularly urgent because as ground levels are sinking, sea levels are rising. That means many areas along the numerous coasts will be even more likely to flood. None of this will be easy, and world leaders will certainly run into political issues in imposing new rules. But if we don’t act, many of us will be sunk.