Groundwater and subsidence: why cities sink
About this app
Ground section of a model city: a well pumps, the pressure in the sand drops, water drains from the clay, the clay platelets move together and the surface sinks, mostly for good. Changing course stops the subsidence but hardly lifts the ground. Plus real rates from the radar study of 465 large cities: Medan, Bandung, Mexico City, Jakarta, Tehran, Berlin.
With explain mode: an AI tutor walks you through the app, points out what matters in the scene and answers your questions.
Why the ground under cities sinks
Many large cities stand on young layers of sand and clay. Groundwater in the sand is under pressure and carries part of the load. If wells pump out more water than flows back, that pressure drops. Water then slowly drains from the neighbouring clay layers, the effective stress in the clay rises and the clay platelets move closer together. The surface subsides. Once the pressure falls lower than ever before, this compaction is permanent; sand, by contrast, hardly deforms.
What the app shows
The app shows the ground section of a model city with a well, the pressure level and its cone of depression. A magnifier shows the clay platelets, and two charts track pressure level and subsidence over 60 years. The values are a model and drawn exaggerated. The second scenario shows real rates from a radar study of 465 large cities (Nature Cities 2026): Medan sinks 33 mm per year on average, Bandung 22 mm, single districts of Mexico City up to 21.7 cm, Berlin 0.2 mm.
Things to try
Play the years and watch the well casing rise out of the ground. Then halve the pumping: the city sinks half as fast. Change course in year 30 and refill the groundwater. Subsidence soon comes to a halt, but the ground rises by only a few centimetres. The dashed curve shows how far the city would have sunk without changing course.
Frequently asked questions
- Why do cities like Jakarta or Mexico City sink?
- The main cause is groundwater extraction from layers rich in clay. When the water pressure drops, the clay compacts and the surface settles. The weight of buildings and in places oil and gas extraction add to it. Jakarta at times sank by 20 to 28 cm per year, parts of Mexico City by up to 21.7 cm.
- Does the ground rise again when groundwater recovers?
- Only a little. Most of the compaction in the clay is permanent. When groundwater pressure rises, subsidence stops after a delay and only a small elastic part springs back. San José in California sank about 3.9 m until 1969 and stopped sinking once the groundwater rose again, without regaining its height.
- Do German cities sink too?
- Hardly. In the radar study of 465 large cities, German cities move by about 0.2 to 1.3 mm per year; Berlin is the most stable at 0.2 mm. On average European large cities sink by about 3 mm per year, Asian ones by about 33 mm.
- Are the numbers in the model city real?
- No, the model city is a model: the pressure level falls by 1.5 m per year, and each metre of drawdown causes 5 cm of permanent subsidence. Layers and subsidence are drawn exaggerated. The city values in the second scenario are real, with sources in the panel.
Subject: Geography & earth science
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