JPL
Careers
Education
Science & Technology
JPL Logo
JPL Logo
Earth
.

NASA Measures Underground Water Flowing From Sierra to Central Valley

Jan. 23, 2023

Water flowing deep underground from the Sierra Nevada into California’s Central Valley provides 10% of all water entering the valley, an amount measured for the first time in a new NASA study. The region relies heavily on underground water for crop irrigation.

Credit: Cloud Cap / Adobe Stock

This source accounts for about 10% of all the water that enters this highly productive farmland, including rivers and rain.

In a recent study, scientists found that a previously unmeasured source – water percolating through soil and fractured rock below California’s Sierra Nevada mountains – delivers an average of 4 million acre feet (5 cubic kilometers) of water to the state’s Central Valley each year. This underground source accounts for about 10% of all the water that enters this highly productive farmland each year from every source (including river inflows and precipitation).

The Central Valley encompasses only 1% of U.S. farmland but produces 40% of the nation’s table fruits, vegetables, and nuts annually. That’s only possible because of intensive groundwater pumping for irrigation and river and stream flow captured in reservoirs. For at least 60 years, growers have been pumping more water from aquifers than can be replenished by natural sources, causing the ground level to sink and requiring wells to be drilled deeper and deeper.

As water grows more scarce in the Central Valley due to climate change and human use, a more detailed understanding of the natural movement of groundwater offers a chance to better protect the remaining resources.

In the recently published study led by scientist Donald Argus of NASA’s Jet Propulsion Laboratory in Southern California, researchers found that groundwater volume fluctuates more widely between dry and wet years than had been previously understood. In particular, the scientists observed a greater loss of groundwater during dry years than earlier studies had estimated. Argus and colleagues estimated that the Central Valley lost about 1.8 million acre feet (2.2 cubic kilometers) of groundwater per year between 2006 to 2021.

Get the Latest JPL News

SUBSCRIBE TO THE NEWSLETTER

There is no way to directly measure the total volume of water on and under the Central Valley, but the satellites of the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE FO) missions can accurately measure how much that volume changes from month to month. Argus and colleagues have been working for several years to combine such GRACE data with observations from a GPS research network that measures how land surfaces rise and subside. In central California, those motions are largely caused by increases and decreases in underground water.

Argus had previously used GPS to quantify the changing volume of water deep within the Sierra. For this new study, he and his co-authors used both GPS and GRACE measurements and subtracted the mountain groundwater change from the groundwater changes in both the mountains and the valley to obtain a more accurate estimate of change in the valley alone.

Then they compared that number with an estimate that co-author Sarfaraz Alam, a postdoctoral scholar at Stanford University, had calculated using a water-balance model. Such models attempt to account for all water entering and leaving an area from all processes, including river flows, precipitation, evaporation, and pumping from wells. The difference between the model’s estimate and their new result, they believe, must come from the one process that was not included in the water-balance model: groundwater flowing from the mountains into the valley.

The volume of the inflow was surprising, according to Argus, because researchers believed they already had a good understanding of the amount of water entering and leaving the Central Valley. “We now know how much groundwater is going into and coming out of the aquifers during each season of the year, and during periods of drought and episodes of heavy precipitation,” Argus said. This new understanding could be used, for example, to modify existing restrictions on watering during dry years versus wet years to better match usage with the available groundwater resources.

News Media Contact

Jane J. Lee / Andrew Wang

Jet Propulsion Laboratory, Pasadena, Calif.

818-354-0307 / 626-379-6874

jane.j.lee@jpl.nasa.gov / andrew.wang@jpl.nasa.gov

Written by Carol Rasmussen

2023-006

Related News

Earth .

Scientists Track Tropical Landslide Creeping Below an African City

Earth .

NASA Scientists and Satellites Make Sense of Earth’s Subtle Motions

Climate Change .

NASA Space Missions Pinpoint Sources of CO2 Emissions on Earth

Earth .

Watch the Latest Water Satellite Unfold Itself in Space

Earth .

NASA Awards Launch Services Contract for Sentinel-6B Mission

Earth .

NASA Launches International Mission to Survey Earth’s Water

Climate Change .

NASA Sensors to Help Detect Methane Emitted by Landfills

Earth .

Latest International Water Satellite Packs an Engineering Punch

Earth .

Water-Tracking SWOT Satellite Encapsulated in Rocket Payload Fairing

Climate Change .

Water Mission to Gauge Alaskan Rivers on Front Lines of Climate Change

Explore More

Image .

London, England Parks

Mission .

Surface Water and Ocean Topography

Image .

Potosi, Bolivia

Image .

California Atmospheric River Storms Captured by NASA's AIRS

Image .

Eriskay Island, Scotland

Image .

Airborne NASA Radar Maps Mauna Loa Lava Changes in Hawaii

Image .

Satellite Data Shows Ground Motion From Mauna Loa Volcano Eruption

Image .

Takawangha Volcano, Alaska

Image .

NASA's AIRS Instrument Tracks Volcanic Sulfur Dioxide Plume from Mauna Loa Eruption

Image .

SWOT Satellite will Improve Clarity and Detail of Sea Height Measurements

About JPL
Who We Are
Executive Council
Directors
Careers
Internships
The JPL Story
JPL Achievements
Documentary Series
Annual Reports
Missions
Current
Past
Future
All
News
All
Earth
Solar System
Stars and Galaxies
Subscribe to JPL News
Galleries
Images
Videos
Audio
Podcasts
Apps
Visions of the Future
Slice of History
Robotics at JPL
Events
Lecture Series
Team Competitions
Speakers Bureau
Calendar
Visit
Public Tours
Virtual Tour
Directions and Maps
Topics
JPL Life
Solar System
Mars
Earth
Climate Change
Exoplanets
Stars and Galaxies
Robotics
More
Asteroid Watch
NASA's Eyes Visualizations
Universe - Internal Newsletter
Social Media
Get the Latest from JPL
Follow Us

JPL is a federally funded research and development center managed for NASA by Caltech.

More from JPL
Careers Education Science & Technology Acquisitions JPL Store
Careers
Education
Science & Technology
Acquisitions
JPL Store
Related NASA Sites
Basics of Spaceflight
Climate Kids
Earth / Global Climate Change
Exoplanet Exploration
Mars Exploration
Solar System Exploration
Space Place
NASA's Eyes Visualization Project
Voyager Interstellar Mission
NASA
Caltech
Privacy
Image Policy
FAQ
Feedback
Site Managers: Veronica McGregor, Randal Jackson
Site Editors: Tony Greicius, Naomi Hartono
CL#: 21-0018