California – A high-stakes investigation is underway in California, not to catch a criminal, but to track the elusive journey of snowmelt replenishing vital groundwater reserves. NASA is deploying its cutting-edge technology to solve a critical water puzzle, one that could determine the future of agriculture in one of America’s most productive regions.
A NASA jet, equipped with the highly sensitive Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR), is conducting a series of flights over a 25-mile stretch of the Tulare Basin. This region, where foothills transition into farmland, is believed to hold the key to understanding how Sierra Nevada snowmelt seeps underground, recharging aquifers that are crucial for the San Joaquin Valley’s agricultural industry.
“NASA’s technology has the potential to give us unprecedented precision in measuring where snowmelt is recharging groundwater,” stated Erin Urquhart, program manager for NASA’s Earth Action Water Resources program. “This information is vital for farmers, water managers, and policymakers trying to make the best possible decisions to protect water supplies for agriculture and communities.”
The challenge lies in tracking the invisible process of water filtering through rock and sediment. As the snowmelt descends from the mountains, it flows into rivers and streams, eventually seeping underground at the valley’s edge. This underground movement creates subtle pressure, causing the surface to rise slightly—a change imperceptible to the human eye but detectable by NASA’s advanced radar.
“Synthetic aperture radar doesn’t directly see water,” explained Yunling Lou, who leads the UAVSAR program at NASA’s Jet Propulsion Laboratory. “We’re measuring changes in surface elevation—smaller than a centimeter—that tell us where the water is.”
These subtle surface bulges, or “InSAR recharge signatures,” are being meticulously tracked by researchers, led by Stanford University geophysicist Rosemary Knight. By mapping how these bulges migrate from the mountains into the valley, the team aims to pinpoint the precise locations of groundwater replenishment and quantify the amount of water recharging the system.
The San Joaquin Valley, which produces a significant portion of America’s fruits, nuts, and vegetables, relies heavily on groundwater, especially during drought years. As aquifer levels decline, water managers are forced to impose restrictions, and farmers are drilling deeper wells, driving up costs and depleting reserves.
“Knowing where recharge is happening is vital for smart water management,” said Aaron Fukuda, general manager of the Tulare Irrigation District. “In dry years, when we get limited opportunities, we can direct flood releases to areas that recharge efficiently, avoiding places where water would just evaporate or take too long to soak in. In wetter years, like 2023, it’s even more crucial—we need to move water into the ground as quickly as possible to prevent flooding and maximize the amount absorbed.”
NASA’s efforts extend beyond airborne radar. The upcoming NISAR mission and existing GRACE satellites offer complementary data, providing a comprehensive view of groundwater dynamics. The Western Water Applications Office (WWAO) further bridges the gap between data and practical application, ensuring water managers have access to the information they need.
“Airborne campaigns like this one in the San Joaquin test how our technology can deliver tangible benefits to American communities,” said Stephanie Granger, WWAO’s director at NASA’s Jet Propulsion Laboratory. “We partner with local water managers to evaluate tools that have the potential to strengthen water supplies across the Western United States.”
