Photo credit: science.nasa.gov
As the Sierra Nevada mountains give way to the vast San Joaquin Valley in California, a critical investigative effort is underway, targeting the complex dynamics of snowmelt and its role in replenishing crucial groundwater supplies.
At the forefront of this endeavor is a NASA aircraft outfitted with advanced radar technology capable of detecting minute ground movements, highlighting an innovative approach to addressing one of the American West’s most significant water scarcity issues — the depletion of groundwater sources.
“The technology developed by NASA could revolutionize our understanding of where snowmelt contributes to groundwater recharge,” stated Erin Urquhart, who heads NASA’s Earth Action Water Resources program. “Such insights are essential for farmers, water managers, and policymakers tasked with ensuring sustainable water supplies for both agricultural and community needs.”
In late February, a NASA aircraft equipped with Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) embarked on the first of several planned flights over a 25-mile segment of the Tulare Basin. This area, where the foothills meet extensive farmland, is believed to be a critical factor in sustaining the region’s water resources.
The San Joaquin Valley largely depends on the melting of Sierra Nevada snow for its groundwater supply. “Historically, we’ve managed California’s water resources without a comprehensive understanding of how and where that meltwater infiltrates underground,” remarked Stanford University geophysicist and researcher Rosemary Knight, who is spearheading this initiative.
This intricate process is mostly hidden from view as water trickles through rock and soil, disappearing beneath cultivated fields and orchards. However, it tends to follow a predictable course, traveling toward rivers and streams, with some of it eventually seeping underground at the valley’s perimeter or as the waterways expand. As water moves through the soil, it creates slight pressures that can elevate the surface, changes too subtle for human detection but identifiable by NASA’s sophisticated radar technology.
“While synthetic aperture radar doesn’t directly capture water, we’re able to observe variations in surface elevation — even smaller than a centimeter — which indicate the presence of water,” explained Yunling Lou, head of the UAVSAR program at NASA’s Jet Propulsion Laboratory in Southern California.
These surface distortions lead to what Knight refers to as an “InSAR recharge signature.” By tracing the movement of these surface changes from the mountains into the valley, researchers aim to identify where groundwater replenishment takes place and quantify the natural recharge into the aquifer systems.
Previous satellite-based InSAR studies have illustrated seasonal land movements in the San Joaquin Valley, signaling how groundwater levels fluctuate with the seasons as snowmelt permeates the earth. However, these satellite observations lacked the resolution to pinpoint specific recharge routes. By integrating satellite imagery with data on subsurface sediments collected via an airborne electromagnetic system, Knight’s team has succeeded in mapping the underground pathways that facilitate aquifer recharge.
With the advanced UAVSAR system, researchers will acquire even finer-grained data, allowing for a more precise analysis of where and how rapidly water reabsorbs into the ground, thus rejuvenating the depleted aquifers.
California’s Central Valley is an agricultural powerhouse, responsible for over a third of the nation’s vegetables and two-thirds of its fruits and nuts, with the San Joaquin Valley being a key area where many farms depend heavily on groundwater, particularly during prolonged drought conditions.
In response to declining aquifer levels, water managers have been compelled to impose restrictions on groundwater extraction. As an alternative, some farmers have resorted to drilling deeper wells, which only exacerbates costs and accelerates resource depletion. “To optimize water management, understanding where recharge is occurring is crucial,” emphasized Aaron Fukuda, general manager of the Tulare Irrigation District, which oversees irrigation and groundwater projects in Tulare County.
“During dry seasons, when opportunities are limited, we can redirect flood releases to areas that efficiently recharge groundwater, while avoiding locations where water would just evaporate or take too long to penetrate the soil,” Fukuda elaborated. “In wetter years, like 2023, this becomes even more critical — ensuring that we quickly direct water into the ground minimizes flooding risks and maximizes absorption.”
Nasa’s continued efforts in monitoring Earth’s water resources incorporate various cutting-edge technologies that interlink to provide comprehensive insights into groundwater management challenges.
Next on the horizon is the NISAR mission, a collaboration between NASA and the Indian Space Research Organisation (ISRO), scheduled for launch in the coming months. It aims to deliver global-scale radar data capable of monitoring land and ice surface changes — including groundwater movement indicators — every 12 days.
Simultaneously, the GRACE satellites, operated through partnerships with the German Aerospace Center and NASA, have revolutionized groundwater monitoring by detecting minute fluctuations in Earth’s gravity. This allows for an expansive view of monthly water storage alterations across vast regions.
The GRACE and GRACE-FO missions have highlighted significant aquifer declines, particularly in California’s Central Valley, but due to their broader resolution, supplementary tools are necessary to identify recharge hotspots with greater accuracy.
Collectively, these technologies create a robust toolkit that connects large-scale monitoring with targeted water management strategies. NASA’s Western Water Applications Office (WWAO) plays an instrumental role in making this wealth of data accessible to water managers and other stakeholders, offering platforms such as the Visualization of In-situ and Remotely-Sensed Groundwater Observation (VIRGO) dashboard to support informed decision-making.
“Airborne initiatives like this one in the San Joaquin allow us to evaluate the practical applications of our technology in benefiting American communities,” stated Stephanie Granger, director of WWAO at NASA’s Jet Propulsion Laboratory. “We collaborate with local water authorities to explore tools that may reinforce water availability across the Western United States.”
Source
science.nasa.gov