Why San Diego is sinking, along with other major U.S. cities
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An aerial view of the city. Photo: Joe Sohm/Visions of America/Universal Images Group via Getty Images
San Diego is sinking by the millimeter, and new research shows it's more widespread — and riskier — than once suspected.
Why it matters: Land subsidence is an invisible but growing threat to urban infrastructure — cracking roads, destabilizing buildings and bridges, and raising flood risks.
- In San Diego, it amplifies the impacts of sea-level rise, which can worsen coastal flooding and erosion, particularly during storms.
The big picture: A peer-reviewed study published this month in Nature, found that 25 of the 28 most populous U.S. cities are subsiding, affecting more than 33 million people — over 10% of the U.S. population — who live on sinking land.
- The most affected areas are in Texas, particularly Houston, Fort Worth and Dallas.
Zoom in: San Diego is sinking about 1 millimeter per year — the highest rate of the four California cities analyzed.
- About 90% of the city's land is sinking, but it's more severe (as much as 7mm) in South San Diego, parts of Point Loma and southeastern city neighborhoods.
- Most of the buildings here have a low risk of serious structural damage, with only a small fraction falling into the "high" or "very high" risk category.
State of play: Groundwater extraction for drinking and agriculture is the primary cause of land subsidence nationwide and in San Diego, according to the report.
- When water is pumped from the ground, the pressure in aquifers or wells decreases and can cause the ground to sink.
- San Diego is particularly sensitive to groundwater depletion due to its geology and a history of extraction, so it's at greater risk of sinking when those levels drop.
Between the lines: California has struggled to replenish its groundwater stores, in part because of overpumping and a lack of infrastructure, Cal Matters reports. That's true despite wet winters and a state law intended to protect and restore the state's groundwater.
What's next: Researchers urge cities to factor subsidence into zoning, infrastructure upgrades and flood planning.
- They also call for long-term ground monitoring and public outreach to ensure communities are prepared for slow but damaging shifts.
The bottom line: "We need to start treating subsidence like the slow-moving disaster it is," researcher Manoochehr Shirzaei told New Scientist.