Groundwater depletion is accelerating in the Central Valley

Scientists have discovered that groundwater depletion in California’s Central Valley accelerated dramatically during the drought as heavy agricultural pumping lowered aquifer levels to new lows and now threatens to deplete groundwater reserves.

The study shows that chronic declines in groundwater levels, which have plagued the Central Valley for decades, have worsened significantly in recent years, with a particularly rapid decline since 2019.

“We have a full-blown crisis,” said Jay Famiglietti, professor of hydrology and executive director of the University of Saskatchewan’s Global Institute for Water Security. “Groundwater in California, and groundwater across the southwestern United States, is disappearing much faster than most people realize.”

Famiglietti and other scientists found in their research, which was Published this month in the journal nature communication, Since 2019, the rate of groundwater depletion is 31% higher than in the last two droughts.

They also found that since 2003 the Central Valley has lost about 36 million acre-feet of groundwater, or about 1.3 times the full. Water conservation capacity Lake Mead, near Las Vegas, is the nation’s largest reservoir.

“The trajectory we’re on now is one for 100% extinction,” Famiglietti said. “This is water for future generations. And it’s disappearing.”

Historian of California Sustainable Groundwater Management Act Passed in 2014 with the intention of curbing overpumping and stabilizing aquifer levels. But the law, known as SGMA, gives many local organizations until 2040 to achieve sustainability goals.

Famiglietti said the findings indicate the timeline may be too long, pointing to the need to speed up implementation of regulations under the law. The current pace of groundwater loss is about five times faster than the long-term average since the 1960s.

“We see what appears to be a rush to pump as much groundwater as possible before the new restrictions take hold,” Famiglietti said. “My fear is that by the time SGMA is fully implemented, it will be too late. There will be nothing left to manage.”

Rush on groundwater comes in the middle The driest three-year period on record in California, Also a big one Mahakhara Worsened by global warming that has blanketed the American Southwest for 23 years.

During drought, when Less water is available From rivers and canals, agriculture in the central valley typically depends on groundwater for two-thirds or more of its water supply.

The study included nearly two decades of data analysis from two NASA satellite missions, including the latest one GRACE follow-on. The pair of satellites, launched into orbit in 2018, track changes in Earth’s gravity field to measure changes in the total amount of water above and below ground.

Scientists examined soil moisture, surface water and other data on snowpack to estimate groundwater loss and compared their results to an estimate. Computer model Developed by the US Geological Survey. They compared the current drought, from September 2019 to December 2021, with previous ones Mainly dry period From 2006-2011 and 2011-2017.

Data from the past two decades reveal a consistent drop in average water levels in a staircase-like pattern, with short wet periods that only temporarily slow the decline.

“Water stress levels in California are increasing,” said Pang-Wei Liu, a NASA scientist and lead author of the study. “The rate of groundwater depletion is accelerating, especially in these five, 10 years.”

The Central Valley is one of the world’s major agricultural regions, producing almonds, pistachios, grapes, walnuts, tangerines, rice and other crops, as well as livestock and dairy products.

The rapid pace of groundwater depletion has coincided with changes in crop production. State Crop Acreage Almond orchardAccording to federal data, increased from 760,000 acres Since 2011 1.3 million acres In 2021. Farmers planted more pistachio orchards.

Famiglietti said he thinks the recent acceleration in water table declines is likely driven, at least in part, by farmers planting lucrative garden crops and digging deep wells “before we hit the bottom” with restrictions under the Groundwater Act. Thousands since SGMA was passed New agricultural wells Drilled in the valley.

Pressure to dig more irrigation wells and rely more on groundwater has created problems for shallow domestic wells. This year there have been more than 1,400 dry wells State has been informed, The number is the highest since officials began tracking reports of dry wells in 2013.

The study shows it’s vital to move forward with implementation of the California law, which requires local agencies to develop groundwater plans and make progress toward their goals, said Felicia Marcus, a Stanford University researcher who previously led the state Water Resources Control Board. The study, he said, “is a stark reminder that we need to act, and we need to have a framework that enables people to act.”

Curbing overuse will be important, he said, as climate change brings more frequent and more severe dry spells.

“With SGMA, we have hope for a future where people’s children and grandchildren can farm and live in the Central Valley,” Marcus said. “Structure and regulation will be essential.”

Meanwhile, rural communities in the Central Valley continue to suffer the consequences of more well spills and drying. Many residents living with dry taps are relying on bottled water, household tanks, and truck-delivered water while they wait for a solution.

Part of the valley floor is sinking as a result of drainage of the aquifer. As the water table is lowered by leaving underground space in the gravel, sand and clay layers, the land collapses and permanently reduces the water storage capacity of the reservoir. In some parts of the valley, the land is submerged 1 foot per yearA problem that damaged canals and wells

The researchers found that the loss of groundwater is much greater than the loss of surface water, snow and soil moisture.

“California is losing water, and groundwater is the reason,” Famiglietti said. “This is really the tragedy of the common man.”

Scientists analyzed trends in three regions of the Central Valley — the Sacramento, San Joaquin and Tulare basins — and found that the northern Sacramento basin, which previously fared better than the southern region, is also experiencing groundwater depletion.

“The vast majority of California’s water is groundwater. The fact that it’s disappearing at a rate nearly five times faster than historical rates is the equivalent of uncontrolled withdrawals from a bank account,” Famiglietti said.

That water savings account, he said, is vital to getting through the drought and an important asset for California’s future. He said slowing withdrawals will be essential to retain groundwater for future generations.

Famiglietti, the study’s lead researcher, was previously a senior water scientist at NASA’s Jet Propulsion Laboratory. In past studies, he and other scientists have used NASA satellite measurements to assess how fast groundwater is being drained. California And Across the Colorado River Basin. he has Researched groundwater depletion In food-growing regions around the world, from South Asia to the Middle East to the Ogallala Aquifer beneath the Great Plains.

In January, he will start a new job as a professor at Arizona State University.

In many parts of the United States and other countries, groundwater remains poorly managed or completely unmanaged. As the wells draw down the water table, the drop in water table is largely invisible and underestimated. Using satellite measurements to track groundwater, Famiglietti and other researchers found Degradation is a widespread and growing problem In many parts of the world Major food producing regions.

A guiding objective of the research, Famiglietti said, is to “make the invisible visible.”

He said data across California and the Southwest paint a grim picture.

“The speed and scale of its disappearance is greater than any management project can replace,” Famiglietti said. “If that groundwater disappears, so will food production. That means less production, food shortages, higher food prices.”

More people are at risk of losing access to drinking water as more wells dry up as water levels drop, he said.

California’s groundwater laws promise to finally impose restrictions on agricultural water use in the Central Valley as local agencies move to implement them. Groundwater Sustainable Planning. For now, pumping is still not restricted in most areas.

Under the Act, sustainable groundwater management is defined as the management of water supplies in a manner that can be maintained “without causing undesired consequences” such as long-term depletion of groundwater levels. Researchers say that addressing groundwater shortages may require taking large swaths of farmland out of production.

Famiglietti said he thinks California has a historic opportunity to begin managing and conserving groundwater in the Central Valley before it’s gone.

“It’s disappearing fast,” he said. “This may be our last shot in California to get it right. And so we have to make sure it works.”

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