After the overpumping of groundwater caused parts of Osaka, Japan, to sink by nearly 10 feet, new research shows the city is rising again — a phenomenon scientists once weren’t sure was even possible.
This could have major effects for coastal communities facing both land subsidence and rising seas.
Here’s what to know
According to Radio New Zealand, researchers set out to test whether land that sinks because of groundwater extraction can recover once groundwater levels rise — something scientists had long been unsure about. In Osaka, decades of groundwater rules followed a period in which parts of the city sank by nearly 3 meters (9 feet, 10 inches), and the land appears to be lifting.
New Zealand earth scientist and co-author Jesse Kearse said Osaka stood out as a particularly useful case because researchers could compare a long history of groundwater extraction with equally long records of the city’s vertical land movement.
“The city realised in the early part of the 20th century that they were taking far too much water from underneath the ground, running out of water, and the city dropped by close to 3 metres in some places — which is really extreme subsidence — as a response to groundwater extraction,” he said, per RNZ.
Using repeated satellite measurements alongside long-term monitoring from wells as deep as 500 meters (1,640 feet), the researchers tracked a slow return of groundwater. The data showed replenishment over the 50 to 60 years after Osaka imposed strict regulations in the 1960s.
“The city has bounced back up again. … Osaka is actually rising,” Kearse said, according to RNZ.
To explain the process, he likened what is happening beneath the city to “a gigantic water balloon.”
“When we take up water from underneath the ground, that balloon deflates and the city sinks,” he told RNZ. “But as the groundwater is replenished, that balloon reinflates and the city pops back up again — so it works in both directions.”
More background
Because sinking ground can worsen flooding tied to sea level rise, Kearse said the findings are especially important for coastal cities. He said the research is also relevant to places such as New Zealand, where, according to RNZ, close to 80% of the coastline is subsiding and demand for freshwater is likely to increase in the warmer climate.
For now, he said, there is no clear example in New Zealand of a city whose sinking can be directly pinned on excessive groundwater use.
“We’re not quite at that same stage as other countries around the world,” Kearse said, per RNZ.
When the ground sinks unevenly, it can stress essential infrastructure.
“If you’ve got pipes under the ground and some bits are moving differently to others, that can cause stress on the infrastructure,” Kearse told RNZ. “Roads are cracking, buildings are tilting — it’s not a good thing.”
The study also found that zones separating uplift from sinking often follow known fault lines. Kearse said those faults can act like underground dams, altering groundwater flow and concentrating damage in certain corridors.
What’s being done?
Osaka’s response was regulatory: strict groundwater rules that allowed underground water supplies to recover over half a century.
Kearse said scientists can predict “quite precisely” where damage is more likely to occur, giving cities a better chance to protect roads, pipes, and buildings before subsidence leads to failures.
Where can I learn more?
Land subsidence is reshaping cities, coastlines, and infrastructure around the world.
• In rural Arizona, towns are sinking 3 inches a year as groundwater depletion opens gaps and cracks.
• In Mexico City, the Metro faces mounting strain as neighborhoods sink 20 inches a year.
• Across China, major urban centers keep dropping as land subsidence becomes a national problem along vulnerable coasts.
• In many coastal hubs, the sheer weight of cities adds to sinking ground and flood risk.
• In New Orleans, sinking into the sea is compounding sea level rise and long-running infrastructure risks.
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AloJapan.com