The alarming truth of California‘s land subsidence, revealed by a new, groundbreaking map developed with advanced remote-sensing techniques, is a major factor in the rising threat from sea level rise. Marin Govorcin is a NASA Jet Propulsion Laboratory remote sensing expert in Southern California. Her research highlights the unpredictability of land movement and its impact on coastal communities.
For accurate projections of sea level rise, it is important to understand these localized movements. They are driven by both natural processes, such as tectonic activity, and human actions, like groundwater pumping. The projections should take into account both the thermal expansion of the ocean and melting glaciers and ice sheets. According to current estimates, the sea level in California will rise between 6 and 14.5 inches by 2050 compared to 2000.
Govorcin said that in many areas vulnerable to sea level rise, like the land reclaimed beneath San Francisco’s city, the earth is sinking faster than the rate of rising water. He stressed the importance of including these factors when developing coastal infrastructure and planning.
Sea level rise models that rely on traditional tidal-gauge data may be limited in their spatial coverage, and they might not accurately reflect the changes occurring to land elevation. Satellite technology was used to track thousands of miles along the California coastline between 2015 and 2030, which provided unprecedented details on land movements.
To precisely measure ground movement, the research team combined radar data collected by Sentinel-1 satellites of the European Space Agency with velocity measurements taken from Earth-based Global Navigation Satellite System receiver stations. This integrated approach allowed for the identification of areas at risk from future sea-level rise, such as cities, beaches and aquifers.
The researchers found subsidence rates of over 0.4 inch per year in San Francisco Bay Area places like Bay Farm Island. Corte Madera. Foster City. and San Rafael. This was due to the sediment compacting. When factoring in this land sinking, the projected local sea level rise in the lowest-lying areas could surge to over 17 inches by 2050 – more than double the standard regional estimate of 7.4 inches, which is based solely on tidal gauge data.
The study also identified zones of localized downward movement in Big Sur Mountains and Palos Verdes Peninsula, Los Angeles. These areas were associated with slow moving landslides. In marshlands, lagoons and estuaries around Northern California’s San Francisco Bay and Monterey Bay, and the Russian River Estuary in Sonoma County there was evidence of subsidence.
Research also shows the influence that human activity has on the land movement. In parts of Los Angeles County or San Diego County the uncertainty in sea level predictions can be up to 15 inches due to groundwater extraction, oil and gas production. This requires ongoing monitoring and mitigation. As an example, the Central Valley of California can see up to 8 inches in subsidence each year due to fluctuations in groundwater.
Study also tracked the behavior of underground water reservoirs at locations like Chula Vista in San Diego County, Santa Ana in Orange County and Santa Clara Bay Area. The results revealed that these underground water reserves ebbs and flows in response to cycles in drought and rainfall and impact land elevation.
Intriguingly, the study discovered that the ground is also rising in certain areas. Santa Barbara’s groundwater basin has been steadily replenished since 2018, resulting in several millimeters per year of uplift. Long Beach also showed similar trends, with a high concentration of fluid injection and extraction activities related to gas and oil recoveries.
This important study has now informed California’s state policies and guidelines regarding sea level changes, resulting in more effective and knowledgeable coastal management strategies. California’s infrastructure and coastal communities need to be protected from the impact of both sea-level rise driven by climate changes and localized subsidence.
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Govorcin, M., Bekaert, D. P. S., Hamlington, B. D., Sangha, S. S., & Sweet, W. (2025). Variable vertical motion of land and its impact on projected sea-level rise. Science Advances, 11(5). https://doi.org/10.1126/sciadv.ads8163