By Ivana Mowry-Mora
A NASA-led study shows that parts of California’s coastline are sinking faster than the ocean is rising, amplifying local sea level rise. Using satellite data, researchers have pinpointed locations where the ground is subsiding at alarming rates, putting coastal cities at risk of flooding far sooner than expected. The discovery forces a reassessment of global sea level projections, highlighting that some regions could face double the previously estimated rise by 2050.
A recent study, published on January 29, 2025, in Science Advances, examines how vertical land motion—the rising and sinking of Earth’s surface—affects local sea level projections. The research, led by Marin Govorcin of NASA’s Jet Propulsion Laboratory (JPL), used interferometric synthetic aperture radar (InSAR) from ESA’s Sentinel-1 satellites to track land elevation changes along California’s coast from 2015 to 2023.
Their findings reveal that many areas are sinking at rates exceeding 0.4 inches (10 millimeters) per year, significantly worsening the impact of sea level rise. In places like San Francisco Bay, where land is compacting, local sea levels could rise more than 17 inches (45 cm) by 2050—more than double previous estimates based solely on ocean levels. The study highlights the critical need to factor in land movement when predicting future flooding risks.
The study reveals that vertical land motion varies widely in both speed and scale. Land subsidence is not just caused by natural tectonic shifts—human activities are playing a major role in making coastal land sink faster than ever before. Practices such as groundwater extraction, oil and gas drilling, and rapid urbanization are all contributing to this hidden crisis. For example, in the middle of California, the fast-sinking parts of the Central Valley (subsiding as much as 8 inches, or 20 centimeters, per year) are influenced by groundwater withdrawal for agriculture. Periods of drought and precipitation can alternately draw down or inflate underground aquifers.
Understanding land motion is now essential for predicting the true impacts of sea level rise. Unlike tide gauge models, which have limited coverage, satellite data can capture land shifts across entire regions, offering a clearer picture of the dynamic forces shaping coastlines. NASA’s OPERA (Observational Products for End-Users from Remote Sensing Analysis) project is using satellite-based monitoring to track elevational changes across North America. This data will help governments and city planners make informed decisions about coastal resilience.
