Elevation changes appear to be small – the scores are inches per year, but they can increase or reduce local flood risk, wave exposure and saltwater intrusion.

Tracking and predicting sea level rises does not just involve measuring our ocean altitude: land along the coastal line also rises at elevation. Through California as a case study, a team led by NASA shows that seemingly moderate vertical land movements may significantly affect local sea levels in the coming decades.

By 2050, California sea levels are expected to rise by 6 to 14.5 feet (15 cm and 37 cm) from 2000 levels. Melting glaciers and ice caps and warm seawater mainly drive the rise. The team said that as coastal communities develop adaptation strategies, they can also benefit from a better understanding of land roles. These findings have been used in updated guidelines for the country.

“In many parts of the world, like the recycling ground below San Francisco, this land moves down faster than the sea itself,” said Marin Govoring, a remote sensing scientist at NASA’s Jet Propulsion Laboratory in Southern California, Southern California. .

This new study illustrates how vertical land movement is unpredictable in terms of scale and velocity. It is caused by natural factors such as groundwater pumping and wastewater injection and structural activities. The researchers demonstrate how direct satellite observations improve estimates of vertical land motion and relative sea level rise. The current model based on tidal gauge measurements cannot cover every location and all dynamic land movements within a given area.

Researchers at JPL and the National Oceanic and Atmospheric Administration (NOAA) used satellite radar to track more than a thousand miles of the California coast and descended with new details. They identified the hot spot - Including cities, beaches and aquifers - In the coming decades, the oceans will be more in contact now and for decades to come.

To capture local motion one inch from space, the team analyzed radar measurements performed by ESA (European Space Agency's Sentinel-1 satellite) and movement speed data from ground receiving stations in the global navigation satellite system. The researchers compared multiple observations at the same location between 2015 and 2023 using a processing technique called Interference Synthetic Aperture Radar (INSAR).

Homecoming in the San Francisco Bay Area - Specifically, San Rafael, Cote Madeira, Foster City and Bay Farm Island - The team found that the land fell at a steady rate of more than 0.4 inches (10 mm) per year due to sediment compaction. By 2050, local sea levels may increase by more than 17 inches (45 cm). This is this settlement in the lowest part of these areas. This is more than twice the estimate of the 7.4-inch (19 cm) area based solely on tidal gauge projections.

Not all coastal areas in California are sinking. Researchers have mapped uplift hotspots several millimeters a year in the Santa Barbara groundwater basin, which has been replenishing steadily since 2018. They also observed bulges on Long Beach, where liquid extraction and injection occurred in oil and gas production.

Scientists further calculated how human-induced local land movement drivers increase uncertainty in sea level forecasts by 15 inches (40 cm) in parts of Los Angeles and San Diego counties. Reliable predictions in these areas are challenging because the unpredictable nature of human activities, such as hydrocarbon production and groundwater extraction, require continuous monitoring of land movement.

In central California, the quick link section of the Central Valley (gradually lowered by up to 8 inches or 20 cm per year), land movement is affected by groundwater evacuation. During periods of drought and precipitation, subterranean aquifers can be absorbed alternately or inflated. This fluctuation has also been observed in the aquifers of Santa Clara in San Francisco Bay Area, Orange County and Chula Vista in San Diego County.

Along solid coastal terrain, such as San Francisco and the Big Sur Mountains in San Francisco and Los Angeles, the team pointed to local areas associated with slow moving landslides Sports area. In Northern California, they also discovered the downswing trends in swamps and lagoons near San Francisco and Monterey Bay, as well as the Russian River estuaries in Sonoma County. Erosion in these areas may be a key factor.

Scientists, decision makers and the public can monitor these and other changes through JPL-led operas (observation products from end users of remote sensing analysis). The Opera project details the height changes in land surfaces in North America and sheds light on dynamic processes including settlement, tectonics and landslides.

The opera project will utilize other state-of-the-art INS INAR data from the upcoming Nisar (NASA-Indian Space Research Organization Synthetic Aperture Radar) and is expected to be released in the coming months.

Jane Lee/Andrew King
Jet Propulsion Laboratory in Pasadena, California.
818-354-0307 / 626-379-6874
jane.j.lee@jpl.nasa.gov / andrew.wang@jpl.nasa.gov

Written by Sally Younger

2025-015