As part of a broader effort to improve understanding of sea level rise, researchers have published new estimates of California's vertical land motion -- also known as uplift and subsidence -- between 2015 and 2023. They detailed where land beneath major coastal cities, including parts of San Francisco, Los Angeles, and San Diego, is sinking. Locations of uplift were also observed.
The rising and sinking land, detected in the new analysis by researchers from NASA's Jet Propulsion Laboratory and the National Oceanic and Atmospheric Administration (NOAA), is visible in this map. Areas shown in blue are subsiding, with darker blue areas sinking faster than lighter blue ones. Areas shown in dark red are rising the fastest.
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.
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.
Read more about the research in an in-depth story by Sally Younger, NASA's Earth Science News Team.