Feature | June 9, 2023

US-German Satellites Show California Water Gains After Record Winter

A map of the western U.S. focused on California. In October 2022 on the left the map is red showing a major drought. In March 2023 on the right the map is now light blue showing drought recovery. There is a bar at the bottom labeled "Water Equivalent Height Anomaly (mm)" that goes from dark red to medium blue. The dark red is -300, white is 0, and medium blue is 300.

Thanks to a wet winter, California saw tremendous gains in the amount of water in the San Joaquin, Sacramento, and Tulare river basins (outlined in yellow) from October 2022 to March 2023, GRACE-FO data shows. The measurement includes water in lakes, rivers, reservoirs, snowpack, and groundwater aquifers. Credit: NASA’s Scientific Visualization Studio

After years of intense drought and diminishing groundwater, California just saw its greatest year-over-year water gains in two decades, according to data from the GRACE-FO (Gravity Recovery and Climate Experiment Follow-On) satellite mission, a partnership between NASA and the German Research Centre for Geosciences (GFZ). This past winter’s bonanza of atmospheric rivers alleviated some of the water deficit that the state incurred during periods of drought over the last 10 years, which included the three driest years on record in California.

Think of the state’s Central Valley region (outlined in yellow, above) as a giant swimming pool: GRACE-FO measurements include all the water contained in the lakes, rivers, soil, snowpack, and underground aquifers within that region. Between October 2022 and March 2023, storms provided enough water to raise the amount of water within the “swimming pool” by about 20 inches (about 500 millimeters). That’s about twice as much as the average winter water gain since satellite-based water storage measurements began in 2002 with the first GRACE mission.

This animation shows changes in the total amount of water within the California region outlined in yellow – including the Sacramento, San Joaquin, and Tulare river basins – from 2002 to 2023. The zero line on the graph represents the average amount of water in the region from 2004 to 2010. Credit: NASA’s Scientific Visualization Studio

While surface water basins are filling, underground stores of fresh water (aquifers) that are tapped for irrigation and other needs could take years to fully recharge. “One good winter of rain and snow won’t make up for years of extreme drought and extensive groundwater use,” said Felix Landerer, GRACE-FO project scientist at NASA’s Jet Propulsion Laboratory in Southern California. The GRACE-FO team will continue to track how California’s water storage evolves through the summer after the snowpack melts and water levels in the state’s lakes, rivers, and reservoirs start to recede during drier weather.

The observations were made possible through the unique sensing approach taken by both GRACE missions. As water moves around – in the form of ocean currents, falling rain, shifting groundwater, ice, and so on – it alters the planet’s mass near the surface, which changes Earth’s gravitational pull ever so slightly. GRACE-FO measures these subtle changes, enabling researchers to estimate changes in the total volume of water in an area.

Like its predecessor, the GRACE-FO mission consists of two identical satellites that fly one behind the other. As the lead satellite flies over an area with greater mass – such as an area with more water than another region – the slight change in gravity tugs it forward, increasing the distance between the two satellites. Microwave and laser instruments aboard the spacecraft precisely measure the minute distance changes between the two, revealing details about the overall mass of water that caused those changes.

The line graph shows seasonal changes in the total amount of water contained in California’s lakes, rivers, reservoirs, snowpack, and groundwater from 2002 to 2023. (The data gap from late 2017 to early 2018 coincides with the decommissioning of the GRACE mission and the launch of its successor, GRACE-FO.) Credit: NASA’s Scientific Visualization Studio

More About the Mission

GRACE (2002-2017) was a joint partnership between NASA and the German Aerospace Center, Deutsches Zentrum für Luft- und Raumfahrt. JPL managed the GRACE mission and manages the GRACE-FO mission for NASA’s Earth Science Division in the Science Mission Directorate in Washington. GRACE-FO is a collaboration between NASA and GFZ. Caltech in Pasadena, California, manages JPL for NASA.

More information on GRACE and GRACE-FO can be found here:



News Media Contacts

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