San Francisco is sinking, and it's worse than we thought
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San Francisco is sinking, and new research shows it's more widespread — and riskier — than was once suspected.
Why it matters: Land subsidence is an invisible but growing threat to urban infrastructure — cracking roads, destabilizing buildings and making low-lying areas even more flood-prone.
- In San Francisco, it combines with sea level rise, seismic instability and aging buildings and infrastructure to heighten long-term risk.
Driving the news: In a new peer-reviewed study published in Nature, researchers analyzed six years of satellite radar data in the 28 most-populous U.S. cities.
- They found that 25 are subsiding, affecting more than 33 million people — over 10% of the U.S. population — who live on sinking land.
Zoom in: Over 92% of San Francisco's land area is sinking at measurable rates, and some faster than others, per the study.
- SF is sinking by almost 1 millimeter (0.04 inches) on average per year, though that figure reaches as high as 10 millimeters (0.4 inches) for some neighborhoods.
- Tectonic activity and sediment compaction appear to be the dominant drivers in San Francisco — not groundwater pumping, which is a primary culprit elsewhere — the study notes.
- Parts of the region built on landfill — such as Treasure Island, SoMa, the eastern bayshore and San Francisco International Airport — are seeing the highest rates of subsidence.
The big picture: Subsidence has long been associated with sinking cities such as Jakarta, Indonesia; New Orleans and Houston — the fastest-sinking of the 28 studied — but new research shows it's a widespread issue across the U.S.
- Whereas natural processes influence urban land subsidence in the United States, most of the sinking land results from human-driven activities, with 80% of the subsidence associated with groundwater withdrawals.
What they're saying: The researchers behind the study are urging cities to factor subsidence into zoning, infrastructure upgrades and flood planning.
- They're also calling for long-term ground monitoring and public outreach to ensure communities are prepared for slow but damaging shifts.
- Uneven sinking puts stress on buildings, leading to cracks, warped frames or even structural failure, researcher Manoochehr Shirzaei told New Scientist.
- "We need to start treating subsidence like the slow-moving disaster it is."
State of play: San Francisco, like other Bay Area cities, has worked in recent years to counter land instability and shore up the waterfront.
- Planned actions include bolstering critical infrastructure and implementing land use controls in areas like Bayview-Hunter's Point, which served as a dumping ground for toxic waste for years and is highly vulnerable to sea level rise.
- The city already requires protections against flood damage for new construction and significant renovations to buildings in designated flood hazard areas.
Stunning stat: By 2050, sea levels in low-lying parts of the Bay could rise by as much as 17 inches compared with 2000 levels, per a February NASA report.
Worthy of your time: Homeowners, renters and businesses in San Francisco are eligible for federally subsidized flood insurance through the city's participation in the National Flood Insurance Program.
What to watch: The San Francisco Bay Conservation & Development Commission adopted a regional shoreline adaptation plan last December aimed at guiding local governments in their efforts to address rising sea levels.
- California law requires all cities and counties along the coast and bayshore to submit a subregional plan by 2034.
Editor's note: This story has been corrected to show 1 millimeter is equivalent to 0.04 inches (not 0.4).