California’s Sea Level Projections May Be Way Off—Thanks to Sinking Land

Rising and sinking land across the state of California could affect sea levels in the state in the coming decades, according to an analysis by researchers at NASA’s Jet Propulsion Laboratory.

The researchers studied satellite radar data to capture the vertical movement of land across more than one thousand miles (1,610 kilometers) of California coast. Comparing that data with historical observations of the same locations, the team found that land was subsiding and rising at levels much higher than regional estimates.

The team’s research—published last month in Science Advances—reveals the amount of surface motion on the ground using data from the European Space Agency’s Sentinel-1 satellites and ground-based receiving stations that are part of the Global Navigation Satellite System. The data was collected between 2015 and 2023 and shows how different areas across the state are rising and sinking. In the image below, areas in blue are subsiding, while areas in red are rising (the darker the red, the faster the rise).

According to a NASA JPL release, the San Francisco Bay Area is subsiding at a rate of more than 0.4 inches (10 millimeters) per year, in large part due to sediment compaction. The team posited in the study that local sea levels could rise by more than 17 inches (45 cm) by 2050 due to the subsidence, at least in the lowest-lying parts of San Rafael, Corte Madera, Foster City, and Bay Farm Island.

“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, a scientist at NASA JPL and lead author of the study, in an agency release.

The team also found hot spots of uplift (several millimeters per year) in the Santa Barbara groundwater basin and Long Beach.

In parts of L.A. and San Diego counties, the team found evidence that human drivers of land motion increase uncertainties in sea level projections by up to 15 inches (40 cm); human activities including groundwater extraction and hydrocarbon production make it harder to predict the motion of land.

Meanwhile, the team observed downward motion in land areas associated with landslides, such as the Palos Verdes Peninsula south of Los Angeles.

Future observations of elevation changes across North America will be aided by the JPL’s OPERA project (the Observational Products for End-Users from Remote Sensing Analysis). In tandem with the NISAR mission, a joint effort between NASA and the Indian space agency ISRO, OPERA will collect data on the elevation of North America, ensuring that the ever-changing surface of our continent can be carefully monitored.