Central Valley farmers created a groundwater deficit large enough to fill an empty Shasta Lake seven times in order to keep their profitable orchards alive during California’s epic five-year drought.
The massive scale of California’s groundwater pumping is outlined in a study released Wednesday by researchers at UCLA and the University of Houston. The researchers conclude that California’s pending groundwater regulations remain woefully behind what is necessary to bring the state’s groundwater levels back into balance.
“Pumping groundwater during a drought isn’t an unreasonable strategy,” said Dennis Lettenmaier, the UCLA professor of geography who led the study. “The problem is: Do to you have a strategy to make it sustainable, which means putting it back in? As near as I can tell, the answer to that is ‘no.’ ”
Farming groups say they had no choice but to drill and pump so much during the drought because state and federal regulators limited their surface water deliveries to protect endangered fish.
“There’s no reason that we can’t recover from the current amount of groundwater pumping or overdraft that’s existing now,” said Mike Wade, the executive director of the California Farm Water Coalition. “The answer is providing sufficient surface supply to meet those agricultural and urban water supply needs.”
To do that, Wade said, farmers are aggressively advocating for new reservoirs to prepare for the next drought. Wade said they’re also diligently preparing to comply with the state’s pending groundwater laws when they start to take effect three years from now.
To estimate pumping rates during the two droughts that struck the state in the past decade, the researchers used NASA satellite data and “water-balance estimates,” which take into account how much water crops need during at temperatures, as well as rainfall, snowmelt and soil-moisture capacity. The first drought the researchers studied lasted from 2007 to 2009. The more severe drought ran from 2012 to last winter.
In the first drought, the researchers estimated farmers pumped enough for a net loss of 16.5 cubic kilometers of water. In the more severe drought, they pumped a net loss of 40 cubic kilometers, according to the study published in Geophysical Research Letters. The study provided net figures because some groundwater is recharged even in drought years.
Sixteen cubic kilometers of water is enough to fill Shasta Lake – the state’s largest reservoir – to capacity almost three separate times. Forty cubic kilometers is enough to fill Shasta seven times.
Lettenmaier said pumping rates doubled during the most recent drought, even though the total amount of irrigated acres of farmland shrunk by 7 percent.
The reason? The drought was hotter and Central Valley farmers were transitioning from row crops such as tomatoes and cotton to more high-value, thirsty nut-tree crops such as almonds, pistachios and walnuts. Unlike row crops, trees are permanent, and can’t be fallowed in dry periods.
Much of the the past 17 years has been dry with only a few wet winters in between, so the wet winter California just experienced only goes so far to recharge the state’s groundwater deficit, said Thomas Harter, a groundwater expert with the UC Davis Center for Watershed Sciences. Harter was not affiliated with the study.
“We’re close to 10 years in the hole or maybe more,” Harter said. “Just one winter is going to give us some back, but it’s not going to give most of what we’ve lost in these droughts. We would need many more above average to wet winters to make up what we’ve lost.”
Meanwhile, an increase in pumping has exacerbated a number of problems in the Central Valley. Huge swaths of the valley floor have sunk substantially through a process known as subsidence. In some areas, bridges and concrete canals have started to collapse. Researchers said overpumping also has raised costs for farmers as they burn electricity and spend tens of thousands of dollars on new pumps to pull water from deeper and deeper in the earth.
The findings come on the heels of a Sacramento Bee investigation published last summer that revealed new wells were going in faster and deeper than ever during the drought in California’s southern Central Valley farmbelt.
The Bee found that farmers dug about 2,500 wells in the San Joaquin Valley in 2015 alone, the highest number on record. That was five times the annual average for the previous 30 years, according to The Bee’s analysis of state and local data.
As farmers ramped up drilling and installed larger, more powerful pumps, aquifers that had quietly flourished beneath the soil for thousands of years were dropping at dangerous rates. The well drilling has exacted a substantial human cost in some of California’s poorest rural communities – the ones populated by workers who tend the fields kept green by all that groundwater.
Falling water tables increase risks from underground pollutants, and in some cases municipal drinking-water wells fail altogether. By one estimate, about 30 percent of the communities in Tulare County had problems with failing wells during the drought.
Similar concerns prompted Gov. Jerry Brown to sign a bill in 2014 that placed the first-ever limits on California groundwater pumping. But the legislation won’t kick in until 2020, and won’t become fully implemented for another 20 years.
Lettenmaier, the study’s lead author, said his team’s findings remain just as relevant now even as the state’s reservoirs are mostly full after a remarkably wet winter. For the first time in years, most California farmers are expecting full surface-water deliveries.
“The best time to be thinking about drought planning is when you don’t have drought,” he said, “but of course it never happens that way.”