The Other
Sea-Level Rise
Coastal cities worry about the ocean coming up. In many of them, the bigger number is the ground going down — pulled out from under them, one well at a time.
Up to half a metre a year of sinking, by satellite radar — roughly 85× faster than the global ocean rose in 2024 (5.9 mm).
From creep to collapse
Every marker is measured sinking, on a log scale — each step to the right is ten times faster. The sea’s own rise sits near the slow end.
Log scale, millimetres per year. Ao et al. (2024) flag 3 mm/yr and 10 mm/yr as meaningful thresholds: 45% and 16% of urban land in 82 Chinese cities exceed them.
Where the ground is going
The same story on several continents: soft lakebed or delta clays, a growing city, and a straw into the aquifer below.
Schematic locator map. Dot size scales with the maximum measured rate; teal marks places that have largely stopped.
The ground stops when the pumps stop
Tokyo and Shanghai show the fix works. Mexico City shows what happens without it: the same fast rate, decade after decade.
Solid marks are documented values; dashed lines connect them and are simplified. Shanghai’s 1921–65 figure is a period average at the deepest point (2.6 m ÷ 44 yrs).
How far down
Total ground lost at the worst-hit spot in each place. The San Joaquin figure is from the famous USGS photo of Joseph Poland beside a pole marking where the ground was in 1925.
Why it happens. Water fills the pore spaces in buried clay and silt. Pump it out and the layers compact under their own weight — like squeezing a sponge that never springs back.
Why it’s permanent. Compacted clay mostly stays compacted. Chaussard et al. (2021) find “no hope for significant elevation and storage capacity recovery” in Mexico City.
Who is standing on it
Satellite surveys now see sinking in every big US city and nearly half of urban China.
of the world’s people live where the probability of subsidence is high
Chinese urban residents on ground sinking faster than 1 cm a year
US buildings at high risk of subsidence damage in 28 big cities
of the world’s regional aquifers show groundwater declines that have sped up since the 1980s
Also measured: ~34 million Americans live on sinking ground in the 28 largest US cities (Ohenhen et al. 2025); 45% of urban land in 82 Chinese cities sinks faster than 3 mm a year (Ao et al. 2024). And a projection: at current rates, about 95% of North Jakarta could be under water by 2050 (Bandung Institute of Technology). That is a model output, not a measurement.
What you can do
This is the one kind of sea-level rise cities can switch off locally, and fast.
- Stop pumping, and the fall stops. Tokyo and Shanghai cut groundwater use and switched to river water — sinking fell from centimetres to millimetres a year.
- But the lost ground doesn’t come back. Compacted clay does not re-expand: Mexico City’s elevation and aquifer storage losses are largely permanent.
- Count sinking land in flood maps. In delta cities the ground can drop faster than the sea rises, so projections that ignore subsidence understate the risk.
- Look up your own ground. Free satellite motion maps (e.g. the European Ground Motion Service, US InSAR studies) show whether your street is moving.