Scientists have uncovered dramatic shifts in California’s coastal landscape, revealing areas that are either sinking or rising.

Using satellite and radar technology, researchers mapped land motion from 2015 to 2023, showing how factors like groundwater withdrawal and natural erosion influence the state’s shoreline. These vertical shifts impact how communities will experience sea level rise, making it crucial to understand which areas are at greater risk of flooding and saltwater intrusion in the coming decades.

Tracking California’s Shifting Coastline

To better understand the impact of sea level rise, researchers have released new estimates of California’s vertical land motion — also known as uplift and subsidence — between 2015 and 2023. Their findings highlight areas where land beneath major coastal cities, including parts of San Francisco, Los Angeles, and San Diego, is sinking. Some regions are also experiencing uplift.

This land movement was identified through a new analysis conducted by scientists from NASA’s Jet Propulsion Laboratory (JPL) and the National Oceanic and Atmospheric Administration (NOAA). Their findings are visualized in the map above, where blue areas indicate subsidence — darker shades representing faster sinking — while dark red marks the fastest-rising locations.

High-Tech Tools Reveal the Movement

Data for the map are based on 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. The researchers 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.

Causes for the motion include human-driven activities as well as natural dynamics. For example, areas of sinking land in coastal California cities and in parts of the Central Valley are caused by factors like soil compaction, erosion, and groundwater withdrawal. The scientists also tracked areas of uplift, including in Long Beach, a site of oil and gas production.

The Stakes for Coastal Communities

In coastal areas, understanding local elevation changes can help communities adapt to rising sea levels. The researchers pinpointed hot spots—including cities, beaches, and aquifers—with greater exposure to rising seas in coming decades. Sea level rise can exacerbate issues like nuisance flooding and saltwater intrusion.

Explore Further: Sinking Cities, Surging Seas – A NASA Discovery That Redefines Coastal Risk

Reference: “Variable vertical land motion and its impacts on sea level rise projections” by Marin Govorcin, David P. S. Bekaert, Benjamin D. Hamlington, Simran S. Sangha and William Sweet, 29 January 2025, Science Advances.
DOI: 10.1126/sciadv.ads8163