October 7, 20254 min readSouth Africa’s Coast Is Rising—And Scientists Have a New Explanation WhyHuman water management contributes to sinking land across the globe, and it may also be responsible for an unexpected riseBy Avery Schuyler Nunn edited by Sarah Lewin FrasierLand rising along South Africa’s coast may be closely tied to humans’ use of water. For decades geologists thought the slow rise of South Africa’s southern coast was driven by forces deep below—buoyant plumes of molten rock ascending through Earth’s mantle and heaving the crust upward over millions of years. But now satellite data and precise GPS measurements are tilting such assumptions off their axis. A study in the Journal of Geophysical Research: Solid Earth suggests this land rise may have less to do with deep tectonic forces and more to do with missing groundwater just under our feet.Human activity has long been depleting South Africa’s groundwater. In 2018, after grappling with severe droughts for years, the country came close to a full-blown water emergency when Cape Town was nearly the world’s first major city to literally run out of water—a scenario dubbed “Day Zero.” For several months that year the city’s residents faced the very real prospect of having to regularly queue for critically limited water supplies, an outcome staved off only by timely rainfall and intensive water-saving campaigns. The extreme shortage resulted from a combination of climate change and unsustainable water use, which drained surface reservoirs and placed mounting pressure on aquifers across the region.The recent study hypothesizes that the ground, once compressed by the sheer weight of the surface water and groundwater above it, is now expanding like a foam mattress relieved of pressure. Using GPS and satellite gravity data from between 2000 and 2021, the researchers detected a roughly six-millimeter rise in the land surface—a shift that coincides with humans’ depletion of South Africa’s water reserves and periods of drought.On supporting science journalismIf you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.“Sometimes the first explanation isn’t necessarily the right one,” says University of Bonn geodesist Christian Mielke, the study’s lead author. “Perhaps it isn’t plate tectonics after all.”That misunderstanding, not necessarily the rising land itself, may be the most striking thing about South Africa’s situation. What was once chalked up to the slow churning of Earth’s mysterious and inaccessible interior may instead reflect human activity, especially our management—or mismanagement—of water.“The presence of water, either as ice and snow on the land surface or as groundwater below, and the removal of that water are intimately tied to the deformation of the ground’s surface,” says Stanford University geophysicist Rosemary Knight. In most places around the globe, this process usually leads to sinking, called land subsidence, to fill the gap.But in South Africa, the new study suggests, that tie between water and land movement shows up in a surprising way. During the rainy season, rivers and reservoirs fill, adding weight that presses the crust down. In the dry months, much of that water either evaporates or gets pumped away, and the land rebounds upward. Over time the long-term loss of groundwater tips the balance toward uplift rather than sinking.This “seasonal breathing” is the giveaway that the cause is probably not solely a mantle plume. If molten rock were pushing upward, the motion would be steady, not tied to rainfall cycles. The expansion, if verified, could be yet another example of the ways human water use is reshaping the planet.From 1945 to 1970 more than 13,000 square kilometers of California’s San Joaquin Valley, once hailed as a “land of milk and honey” for Dust Bowl migrants, sank by at least 30 centimeters—and in some places by nearly nine meters. The San Joaquin sinking has only sped up since then, and parts of the valley drop more than 30 centimeters a year during severe droughts. On average, the pace has accelerated by 70 percent from the mid-20th century.Something similar is happening to the Chesapeake Bay, which, with its sweeping estuaries and lush tidal wetlands, is one of the U.S. East Coast’s most ecologically significant regions. Here land subsidence—driven by both groundwater extraction from aquifers and the lingering effects of ancient glacial shifts—is accelerating flood risk and relative sea-level rise. Satellite data, tide gauge records and projections from the Intergovernmental Panel on Climate Change suggest that by 2100 the combination of subsidence and sea-level rise could inundate up to 1,100 square kilometers of the Chesapeake Bay’s coastline.Mielke notes that such findings highlight the complexity of the planet’s response to human-induced environmental change. The consequences are still gradually being uncovered, and the implications may be profound. As climate change accelerates, land movements could exacerbate other challenges, especially in coastal areas with rising seas.To monitor such hidden shifts on a global scale, scientists use the GRACE satellite mission (Gravity Recovery and Climate Experiment) to detect changes in Earth’s mass by measuring minuscule variations in gravity. Because water has weight, depleting or replenishing groundwater subtly alters the planet’s gravitational field, which GRACE can detect from orbit.Knight and other researchers are looking for ways to keep land from shifting on such a vast scale by maintaining a careful balance. “Basically you get subsidence when water out exceeds water in,” Knight says. “And for water in, the term that’s used is ‘recharge.’”Some recharge happens naturally as rain or snowmelt soaks into the soil, but this precipitation isn’t enough to offset decades of groundwater extraction and current demand. That’s why places such as California are now turning to managed aquifer recharge: strategically spreading excess surface water (such as winter floodwaters) across land where it can percolate into the ground and rebuild depleted reserves, or injecting water directly into aquifers. Estimates suggest there is space underground for a total amount of water 30 times the volume of California’s Shasta Lake, enough to begin reversing the land’s descent.As Knight puts it, the solution can’t be about just cutting back on groundwater pumping. It must involve replenishment: restoring water to the ground from which it was drawn.It’s Time to Stand Up for ScienceIf you enjoyed this article, I’d like to ask for your support. Scientific American has served as an advocate for science and industry for 180 years, and right now may be the most critical moment in that two-century history.I’ve been a Scientific American subscriber since I was 12 years old, and it helped shape the way I look at the world. 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Human water management contributes to sinking land across the globe, and it may also be responsible for an unexpected rise