Parts of California Are Sinking, and It Could Worsen the Effects of Sea-Level Rise, NASA Study Finds

Parts of California’s coastline are sinking, according to a NASA-led study published earlier this year in Science Advances. That’s bad news for sea-level rise, which poses a flood risk along the shore even without the land subsiding.

“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,” Marin Govorcin, the study’s lead author and a remote sensing scientist at NASA’s Jet Propulsion Laboratory, says in a statement.

The study pinpoints specific areas in the state where the ground is shifting up or down. These movements—called vertical land motion—are driven by both human and natural causes, such as groundwater pumping or the actions of tectonic plates. To measure these changes, researchers used satellite radar data collected by the European Space Agency and motion velocity data from the Global Navigation Satellite System. They compared observations of the same sites between 2015 and 2023.

Statewide, the most dramatic sinking of land is happening in the Central Valley, where the ground subsides as much as eight inches per year due to groundwater withdrawal amid drought, according to the statement. In regions of the Bay Area, the land dropped by more than 0.4 inches per year as the sediment became more compact.

That “seemingly modest” drop, as NASA notes in the statement, can still expose coastal areas to more waves and allow more saltwater to infiltrate the land or get into underground aquifers. Accounting for the sinking coastlines, the scientists predict sea levels in the Bay Area could rise more than twice as much as previously thought in those hotspots.

“By 2050, sea levels in California are expected to increase between 6 and 14.5 inches (15 and 37 centimeters) higher than year 2000 levels,” according to the statement. These rises are mainly driven by melting glaciers and ice sheets, as well as warming oceans, but the land also plays a role.

Sea-level rise poses a big threat to California. As the ocean creeps higher, coastal flooding will happen more frequently, explains Laura Engeman, a coastal resilience specialist with the Center for Climate Change Impacts and Adaptation at the Scripps Institution of Oceanography, in a post. Some areas will flood permanently. And it’s going to be costly: 20 inches of sea-level rise could damage $17.9 billion worth of buildings, according to a 2018 climate assessment.

Some parts of the state, like the Big Sur mountains and Los Angeles’ Palos Verdes Peninsula, are descending due to slow-moving landslides likely caused by erosion. That Los Angeles community shifted as much as four inches downward every week between September 18 and October 17, 2024, the lab found.

“The speed is more than enough to put human life and infrastructure at risk,” says Alexander Handwerger, a landslide scientist at the Jet Propulsion Laboratory, to Julia Jacobo at ABC News. The Palos Verdes Peninsula has been moving with landslides for at least 60 years, but its motion recently sped up because of heavy precipitation in 2023 and early 2024.

Other recent studies have also shed light on California’s geological issues. A study published in November by scientists at Stanford University found that the San Joaquin Valley, a major agricultural region in the central part of the state, is sinking at a record-breaking pace because of groundwater pumping.

“Never before has it been so rapid for such a long period of time,” Matthew Lees, the study’s lead author, told Ian James at the Los Angeles Times when the paper came out.

Additional urban areas, including Chicago and New York City, are also sinking due to settling or shifting ground and the weight of their buildings.

The NASA scientists say their findings are being used to inform updated sea-level rise guidance for the state of California.

Sara Hashemi | READ MORE

Sara Hashemi is a science writer and fact-checker currently based in New York City. Her work has appeared in Sierra, The Body, Maisonneuve magazine and more.