Researchers from NASA's Jet Propulsion Laboratory in Southern California and the National Oceanic and Atmospheric Administration (NOAA) analyzed vertical land motion – also known as uplift and subsidence – along the California coast between 2015 and 2023. They detailed where land beneath major coastal cities, including parts of San Francisco, Los Angeles, and San Diego, is sinking (indicated in blue in this visualization of the data). Locations of uplift (shown in red) were also observed.

Causes for the motion include human-driven activities such as groundwater withdrawal and wastewater injection as well as natural dynamics like tectonic activity. Understanding these local elevation changes can help communities adapt to rising sea levels in their area. The researchers pinpointed hot spots – including cities, beaches, and aquifers – at greater exposure to rising seas in coming decades. Sea level rise can exacerbate issues like nuisance flooding and saltwater intrusion.

To gather the data, the researchers employed a remote sensing technique called interferometric synthetic aperture radar (InSAR), which combines two or more 3D observations of the same region to reveal surface motion down to fractions of inches. They used the radars on the ESA (European Space Agency) Sentinel-1 satellites, as well as motion velocity data from ground-based receiving stations in the Global Navigation Satellite System.