California Sinking Faster Than Thought, Aquifers Could Permanently Shrink

California is sinking even faster than scientists had
thought, new NASA satellite imagery shows.
Some areas of the Golden State are sinking more than 2
inches (5.1 centimeters) per month, the imagery reveals.
Though the sinking, called subsidence, has long been a
problem in California, the rate is accelerating because
the state's extreme drought is fueling voracious
groundwater pumping.
"Because of increased pumping, groundwater levels are
reaching record lows — up to 100 feet (30 meters) lower
than previous records," Mark Cowin, director of
California's Department of Water Resources, 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."
What's more, this furious groundwater pumping could
have long-term consequences. If the land shrinks too
much, and for too long, it can permanently lose its
ability to store groundwater , the researchers said.
The state's sinking isn't new: California has long
suffered from subsidence, and some parts are now a few
dozen feet lower than they were in 1925, according to
the U.S. Geological Survey .
But the state's worst drought on record — 97 percent of
the state is facing moderate to exceptional drought —
has only accelerated the trend. To quantify this
accelerated sinking, researchers at the Department of
Water Resources and NASA's Jet Propulsion Laboratory
in Pasadena, California, compared satellite imagery of
California over time. Thanks to images taken from both
satellites and airplanes using a remote-sensing
technique called interferometric synthetic aperture radar
(InSAR), which uses radar to measure elevation
differences, researchers can now map changes in the
surface height of the ground with incredible precision.
For the current study, the team stitched together
imagery from Japan's satellite-based Phased Array type
L-band Synthetic Aperture Radar and Canada's Earth
Observation satellite Radarsat-2, as well as NASA's
airplane-based Uninhabited Aerial Vehicle Synthetic
Aperture Radar.
Certain hotspots are shrinking at an astonishing rate —
regions of the Tulare Basin, which includes Fresno, sank
13 inches (33 cm) in just eight months, they found. The
Sacramento Valley is sinking about 0.5 inches (1.3 cm)
per month. And the California Aqueduct — an intricate
network of pipes, canals and tunnels that funnels water
from high in the Sierra Nevada mountains in northern
and central California to Southern California — has sunk
12.5 inches (32 cm), and most of that was just in the
past four months, according to the new study.
The unquenchable thirst for groundwater in certain
regions is largely a result of agriculture: Most of the
state's agricultural production resides in the fast-
sinking regions around some of the state's most
endangered river systems — the San Joaquin and
Sacramento rivers. As the heat and lack of rainfall have
depleted surface-water supplies, farmers have turned to
groundwater to keep their crops afloat.
Subsidence isn't just an aesthetic problem; bridges and
highways can sink and crack in dangerous ways, and
flood-control structures can be compromised. In the San
Joaquin Valley, the sinking Earth has destroyed the
outer shell around thousands of privately drilled wells.
"Groundwater acts as a savings account to provide
supplies during drought, but the NASA report shows the
consequences of excessive withdrawals as we head into
the fifth year of historic drought," Corwin said. "We will
work together with counties, local water districts, and
affected communities to identify ways to slow the rate of
subsidence and protect vital infrastructure such as
canals, pumping stations, bridges and wells."