Drought Conditions in California are Causing Severe Subsidence

As California continues pumping groundwater to combat the historic drought they are facing, land in the San Joaquin Valley is sinking at an increased rate of 2 inches more per month. The California Department of Water Resources released a NASA report illustrating their findings.

"Because of increased pumping, groundwater levels are reaching record lows -- up to 100 feet (30 meters) lower than previous records," Department of Water Resources Director Mark Cowin said in a statement. "As extensive groundwater pumping continues, the land is sinking more rapidly and this puts nearby infrastructure at greater risk of costly damage."

NASA compared satellite images taken of Earth's surface over time to discover this increased rate of subsidence. Interferometric synthetic aperture radar (InSAR) observations from satellite and aircraft platforms have been used over the past few years to produce maps of subsidence with approximately centimeter-level accuracy. Using multiple scenes, researchers at NASA's Jet Propulsion Laboratory (JPL) were able to produce time histories and profiles of subsidence at selected locations to show the variation over time. 

"This study represents an unprecedented use of multiple satellites and aircraft to map subsidence in California and address a practical problem we're all facing," said JPL research scientist and report co-author Tom Farr in the statement. 

From the images, they found that the area near Corcoran in the Tulare basin sank 13 inches in just eight months, which is about 1.6 inches per month. They also discovered that an area in the Sacramento Valley was sinking faster than in previous measurements, at approximately half an inch per month. Additionally, they found that areas near the California Aqueduct have sunk up to 12.5 inches, eight of which occurred throughout just four months in 2014.

"Subsidence is directly impacting the California Aqueduct, and this NASA technology is ideal for identifying which areas are subsiding the most in order to focus monitoring and repair efforts," said Cathleen Jones, JPL research scientist and study co-author, in the statement. "Knowledge is power, and in this case knowledge can save water and help the state better maintain this critical element of the state's water delivery system."

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