Coastal cities in California are sinking

The combination of human activity and climate change is causing several regions of California to sink. New data also details how vertical land motion may play a larger part in rising sea levels than previously expected. These changes are increasingly likely to put communities at risk for heavy flooding in the future.

Sinking cities

The land beneath major coastal cities in California is sinking, which will likely have an effect on sea levels, according to a study published in the journal Science Advances. The implicated areas include parts of Los Angeles, San Diego and San Francisco. “In many parts of the world, like the reclaimed ground beneath San Francisco, the land is moving down faster than the sea itself is going up,” said Marin Govorcin, the lead author of the study and a remote sensing scientist at NASA’s Jet Propulsion Laboratory, in a NASA statement. There were also locations of uplift, like Santa Barbara.

Vertical land motion can be attributed to “natural processes, such as the movement of tectonic plates, and human factors, like the pumping of groundwater,” said Live Science. The most dramatic land sinking is happening in the Central Valley, “where the ground subsides as much as eight inches per year due to groundwater withdrawal amid drought,” said Smithsonian Magazine. “In regions of the Bay Area, the land dropped by more than 0.4 inches per year as the sediment became more compact.” On the flip side, Santa Barbara is rising because the groundwater in the region has been replenishing since 2018.

Human activity complicates the future of these regions. Things like hydrocarbon production and groundwater extraction “increase uncertainties in the sea level projections by up to 15 inches (40 centimeters) in parts of Los Angeles and San Diego counties,” said the NASA statement. “Reliable projections in these areas are challenging” due to the “unpredictable nature of human activities.”

Rising concern

Sinking land occurring in tandem with the rising sea spells trouble for California. By 2050, California sea levels are expected to rise between 6 and 14.5 inches higher than year 2000 levels. This may lead to an estimated $17.9 billion worth of flood damages to residential and commercial buildings, according to a 2018 California climate assessment, with coastal communities particularly at risk. The Science Advances study also found downward motion — associated with slow-moving landslides — is physically bringing the land closer to the Pacific Ocean. Most of the sea level rise is happening thanks to climate change, which causes glaciers and ice sheets to melt.

California is not the only location where land is sinking. Separate studies have found that Chicago and New York City are gradually sinking as well. As the years progress, many coastal communities around the world are likely to be in danger if they do not implement proper methods of preparation and climate change mitigation. These findings underscore the “importance of incorporating local VLM [Vertical Land Motion] with realistic uncertainties into relative sea level projections to improve and ensure effective coastal adaptation strategies,” the study said.