Described as “one of the more notable structural depressions in the world,” the Central Valley is surrounded by mountain ranges: the Coast Range to the west, the Sierra Nevada to the east, the Tehachapi Mountains to the south, and the Cascade Range to the north. The Central Valley consists of the Sacramento Valley in the northern one-third and the San Joaquin Valley in the southern two-thirds. The two valleys meet in the Delta area.
The Central Valley produces around a quarter of the nation’s food. Nineteen counties comprise the Central Valley, with 6.5 million people, 20,000 square miles, over 35,000 farms, and almost six million harvested acres. Those 19 counties include eight of the top 10 agricultural counties in the state. And one of those counties, Tulare County, is the largest dairy-producing county in the country. As of May 2022, Tulare County had marketings of 790.8 million pounds, which equals the combined milk marketings of the smallest 1,264 counties. Fresno County, smack dab in the middle of the Central Valley, is the top agricultural county in the United States.
Groundwater problems in the Central Valley
Around 75 percent of California’s and 17 percent of the nation’s irrigated land is in the Central Valley. About 20 percent of the nation’s groundwater demand comes from pumping Central Valley aquifers, making it the second most pumped aquifer system in the U.S.
According to a study published in the AGU journal, overpumping in the Central Valley will lead to depletion. Water Resources Researchers discovered that the state’s last two droughts caused dismal groundwater storage recovery, and less than a third of groundwater recovered during droughts occurred from 2012 to 2016.
Researchers also found that it would take six to eight years to fully recover over-drafted groundwater when wet years with above-average rainfall follow drought years. However, that scenario is unlikely because the state’s climate is becoming increasingly hotter and drier. There is less than a 20 percent chance of full recovery over 20 years following a drought if the climate stays hotter and drier.
Researchers found that after the 2006 to 2009 drought, only 34 percent of 19 cubic kilometers of groundwater was recovered. After the 2012 to 2016 drought, only 19 percent of 28 cubic kilometers was recovered. The researchers attributed low groundwater recovery in the post-2016 drought period to overdraft compared to limited water availability. Researchers also found that groundwater extraction caps could significantly improve aquifer resistance to drought. However, that poses a big problem for Central Valley agriculture.
Thirsty crops and dwindling groundwater
Almonds, a water-thirsty crop, are one of the top crops in the Central Valley and California’s top agricultural export. The almond acreage in California in 2020 was around 1.6 million acres, 5.3 percent higher than in 2019 at 1.5 million acres. Five Central Valley counties, all located in the San Joaquin Valley, accounted for 73 percent of almond acreage. In 2021, almond production only decreased by around 10 percent amid the drought.
The entire Central Valley is under drought conditions, ranging from extreme to exceptional (the worst category). In 2021, drought caused reduced surface water deliveries to farms. Farmers received no allocations from the Central Valley Project and State Water Project. The total surface water deliveries for Central Valley farms decreased by 5.5 million acre-feet in 2021, which is 41 percent below the 2002 to 2016 average. Direct economic costs of drought for California agriculture, much of which is in the Central Valley, are estimated at $1.2 billion.
In the Central Valley and throughout the west, climate change, drought, and dwindling water supplies are coming together in a perfect storm. Sound water management, conservation, and planning are critical to the people and agriculture of the valley.
Image credit: BertaIV, courtesy of Flickr