Scientists have been generating striking visualizations of coastal flooding for years, showing cities already submerged beneath the waves. Those grim forecasts are edging closer to reality. A new study focused on two California megacities—Los Angeles and San Francisco—finds a worrying pattern: some coastal areas are sinking, and local sea-level rise could be more than double earlier predictions.
This analysis, from researchers at NASA and NOAA, measured coastal subsidence with satellite radar. In the most affected places—like San Rafael and Foster City in the San Francisco Bay area—the land is sinking by more than 10 millimeters each year. Over the next 25 years, that could mean sea levels in those spots rise by 45 centimeters or more—about twice the 19 centimeters experts previously expected. In Los Angeles, coastal land is projected to be roughly 15 centimeters lower than current sea-level forecasts indicate, according to Live Science.
“In many parts of the world— including coastal areas around San Francisco—land is sinking faster than sea levels are rising,” said Marin Govorchin, a remote sensing specialist at NASA’s Jet Propulsion Laboratory.
The study points to vertical land movement—the rise and fall of land—as a major factor. That movement comes from natural processes such as tectonic shifts and from human causes, notably groundwater extraction. At the same time, climate change is raising sea levels: extra heat melts glaciers and ice sheets, adds water to the oceans, and pushes coastlines inland. The combined effect threatens coastal communities worldwide.
To track vertical land movement, researchers analyzed radar data from the European Space Agency’s Sentinel-1 satellites and land-motion measurements from the Global Navigation Satellite System. The most extreme subsidence was seen in central California, where aggressive groundwater pumping makes parts of the Central Valley sink by as much as 20 centimeters a year. Scientists warn that vertical land movement is hard to predict, but the study shows it must be included in forecasts of coastal inundation.
The findings appear in the journal Science Advances.
