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Impacts of Vertical Land Motion on California’s Sea Levels
The variations in land elevation may appear minor—measured in fractions of an inch annually—but these changes can significantly influence local risks associated with flooding, wave activity, and saltwater intrusion.
Understanding sea level rise involves more than just monitoring ocean heights; the land along coastlines is also subject to gradual shifts. A NASA-led research team focusing on California has revealed how even slight vertical land movement can have profound effects on local sea levels over the coming years.
Predictions for 2050 indicate that sea levels in California may rise by between 6 and 14.5 inches (15 to 37 centimeters) above the levels recorded in 2000. This increase is primarily attributed to factors such as the melting of glaciers and ice sheets, along with the thermal expansion of oceans caused by rising temperatures. The team emphasizes that as coastal regions strategize their adaptation responses, incorporating insights into how land elevation influences these changes will be crucial. The outcomes of their research are informing updated state guidance.
“In many global regions, including areas like the reclaimed land in San Francisco, we are witnessing land subsiding more rapidly than sea levels are rising,” explained lead researcher Marin Govorcin, a remote sensing expert at NASA’s Jet Propulsion Laboratory in Southern California.
The recent study sheds light on the unpredictable nature of vertical land motion, which can result from both anthropogenic activities—like groundwater extraction and wastewater injection—and natural processes such as tectonic shifts. The research highlights that utilizing direct satellite data can enhance our understanding of vertical movements and their relationship with rising sea levels. Traditional models based on tide gauges fail to capture the full scope of dynamic land movements on a local level.
The collaborative effort between JPL and the National Oceanic and Atmospheric Administration (NOAA) employed satellite radar technology to meticulously map vertical movements along over a thousand miles of California’s coastline. The research team identified several vulnerable areas—comprising cities, beaches, and aquifers—more susceptible to sea level rise in the near future.
To detect minute land changes from space, the scientists analyzed radar data from the European Space Agency’s Sentinel-1 satellites in conjunction with data from ground-based Global Navigation Satellite System (GNSS) stations. They utilized a technique known as interferometric synthetic aperture radar (InSAR) to compare observations of specific locations from 2015 to 2023.
Focusing on the San Francisco Bay Area—specifically regions such as San Rafael, Corte Madera, Foster City, and Bay Farm Island—the team identified areas where land is subsiding at a rate exceeding 0.4 inches (10 millimeters) per year primarily due to sediment compaction. When factoring in this subsidence, projections indicate that local sea levels may rise by over 17 inches (45 centimeters) by 2050, a significant increase compared to the regional forecast of 7.4 inches (19 centimeters) based solely on tide gauge data.
Conversely, not all California coastal areas are experiencing decline; some regions, like the Santa Barbara groundwater basin, have noted uplift of several millimeters annually since 2018. Uplift was also observed in Long Beach, which undergoes fluid extraction and injection related to oil and gas operations.
The study further indicates that human activities contribute to uncertainties in sea level estimates, potentially increasing projections by as much as 15 inches (40 centimeters) in parts of Los Angeles and San Diego counties. The unpredictable nature of these human-induced movements, such as hydrocarbon extraction and groundwater depletion, underscores the necessity for continuous monitoring of land shifts.
In central California, particularly in regions prone to significant subsidence like the Central Valley, groundwater withdrawal contributes to land sinks of up to 8 inches (20 centimeters) annually. The interplay between periods of drought and precipitation alters the levels of underground aquifers, with similar patterns observed in Santa Clara, Santa Ana, and Chula Vista.
Along rugged coastal areas such as the Big Sur Mountains and Palos Verdes Peninsula, researchers identified localized downward movements tied to slow-moving landslides. In Northern California, sinking patterns were also noted in marshlands and lagoons around San Francisco Bay and the Russian River estuary in Sonoma County, likely exacerbated by erosion.
A variety of stakeholders, including scientists, policymakers, and the general public, can keep track of these environmental changes through the JPL-driven OPERA (Observational Products for End-Users from Remote Sensing Analysis) initiative. This project provides detailed insights into land elevation changes across North America, highlighting the dynamics of subsidence, tectonics, and landslides.
The OPERA project is set to benefit from cutting-edge InSAR data from the forthcoming NISAR (NASA-Indian Space Research Organization Synthetic Aperture Radar) mission, anticipated to launch soon.
Source
www.nasa.gov