In a recent study, scientists have found that a previously unmeasured source, the water that seeps through soil and fractured rock beneath California’s Sierra Nevada mountains, and which delivers an average of 4 million acres (5 km3) of water to the state’s Central Valley each year, represents that source. Groundwater accounts for about 10% of all water that enters these highly productive farmlands each year from every source including river flows and precipitation.
According to the site,PhysIn a 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 was previously understood.
Scientists noticed a greater loss of groundwater during drought years than was estimated by previous studies Argus and his colleagues report that the Central Valley lost about 1.8 million acres (2.2 km3) of groundwater annually between 2006 and 2021.
There is no way to directly measure the total volume of water in and under the center of the valley, but the gravity recovery and climate experiment satellites (GRACE) And GRACE Follow-On (GRACE FO) It can accurately measure how much that volume has changed from month to month. And it works Argus and colleagues for several years to integrate the data GRACE These with notes from Research Network GPS that measures how high and low the earth’s surfaces are. In central California, these movements are largely caused by increases and decreases in groundwater.
and use Argus previously used GPS to quantify the volume of changing waters in the deep Sierra, but in this new study he and his colleagues used measurements of GPS And GRACE The groundwater change for the mountains was subtracted from the groundwater changes in both the mountains and the valley to get a more accurate estimate of the change in the valley alone, then they compared this number using the water balance model.
The Central Valley includes only 1% of the agricultural land in the United States, but produces 40% of the country’s table fruits, vegetables, and nuts annually.
This is only possible because of the intense pumping of groundwater for irrigation and the flow of rivers and streams being captured in reservoirs. For at least 60 years, farmers have been pumping more water from aquifers than can be replenished by natural sources, causing ground level sinking and requiring excavation. Wells are getting deeper and deeper, and with water scarcity in the Central Valley increasing due to climate change and human use, a more detailed understanding of the natural movement of groundwater offers an opportunity to better protect the remaining resources.