FRESNO, Calif. (KSEE/KGPE) – Experts from NASA say a previously unmeasured underground source accounts for about 10% of all the water that enters the highly-productive Central Valley farmland each year.

The NASA study shows an average of four million acre-feet of water is delivered through the soil and fractured rocks under California’s Sierra Nevada mountains to the Central Valley annually.

Federal officials say the Central Valley encompasses only 1% of the nation’s farmland but produces 40% of the country’s fruits, vegetables, and nuts annually – but that is only possible because of the intensive groundwater pumping for irrigation as well as river and stream flows captured in reservoirs.

However, experts say growers who are pumping more water than can be replenished by natural sources are causing the ground level to sink and requiring wells to be drilled deeper and deeper. They estimate that the Central Valley lost about 1.8 million acre-feet of groundwater per year between 2006 and 2021.

After decades of pumping, underground water resources are dwindling. Wells in the Tulare Basin now must be drilled as much as 3,500 feet (over 1,000 meters) deep to find adequate water

Report from the NASA’s Jet Propulsion Laboratory published in April 2022

With water getting to be more scarce in the Central Valley due to climate change and human use, federal officials say studies like this offer a chance to better protect the remaining resources.

In the study led by scientist Donald Argus of NASA’s Jet Propulsion Laboratory in Southern California, researchers said they found that groundwater volumes fluctuate more widely between dry and wet years than had been previously known.

To find out more about NASA’s water studies click here.