“Subsidence has been neglected in a lot of ways because it is slow moving. You don't recognize it until you start seeing damage,” says Michelle Sneed, a land subsidence specialist at the U.S. Geological Survey and coauthor on the paper. “The land sinking itself is not a problem. But if you're on the coast, it's a big problem. If you have infrastructure that crosses long areas, it's a big problem. If you have deep wells, they're collapsing because of subsidence. That's a problem.”For subsidence to become a problem, you need two things: The right kind of land, and an over-exploited aquifer. Aquifers hold water in between bits of sand, gravel, or clay. When the amount of clay in an aquifer is particularly high, the grains arrange themselves like plates thrown haphazardly in a sink—they’ve basically got random orientations, and the water fills in the spaces between the grains. But if you start extracting water from an aquifer, those spaces collapse and the grains draw closer together. “Those plates rearrange themselves into more like a stack of dinner plates that you put in your cupboard,” says Sneed. “It takes a lot less space, obviously, to stack the plates that way. And so that's the compaction of the aquifer system that then results in land subsidence at the surface.”
Long before climate change became recognized as one of the world’s major problems, water scarcity was widely recognized as a challenge for humanity.Unfortunately, the rise of awareness about the challenges of climate change had a perverse result when it came to the world working collectively to reduce global water scarcity.
But wouldn’t pumping more water back into the aquifer force the clay plates back to their random, spacey orientations? Unfortunately, no. “It'll press those grains apart a little bit—you'll get a little bit of expansion in the aquifer system represented as uplift on the land surface. But it's a tiny amount,” says Sneed. We’re talking maybe three quarters of an inch of movement. “They're still stacked like the plates in your cupboard,” she continues.
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So at this point you’ve got a double-barreled problem: The land has sunk and it won’t reinflate, and the aquifers won’t hold as much water as they once did, because they’ve compressed. “And that's an important point,” says Sneed. “As places around the world, including California, are starting to use aquifer systems as managed reservoirs, the compaction of them prior to now has reduced their ability to store water.”As the growing human population and more intense droughts brought on by climate change are putting ever more stress on water supplies, land is subsiding all over the world. Some parts of the Indonesian capital of Jakarta, for instance, are sinking as much as 10 inches a year , all while the seas are rising around it. Models estimate that in just three decades, 95 percent of North Jakarta could be underwater. The situation is so dire, Indonesia is planning to move its capital .