Behind California's Historic Water Restrictions: Low Snowpack

Snow in mountains is only 6 percent of normal, worsening drought.

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Frank Gehrke of the California Department of Water Resources measures the snowpack in the mountains near Phillips, California, on April 1, 2015. But for the first time since measurements began in 1942, there was no snow at that location on this date.

When California Governor Jerry Brown announced unprecedented statewide water restrictions on Wednesday, he did so during a visit to the Sierra Nevada mountains, where snowpack is at the lowest level in recorded history.

Brown stood in a bare brown field that would normally be covered with several feet of snow at this time of year.

While many people think of drought as a prolonged lack of rain, in California the dryness has been driven by a lack of snowpack.

In normal years, California gets 70 percent of its precipitation from snow, says Tom Painter, a snow scientist with NASA's Jet Propulsion Laboratory in Pasadena, California. That snow eventually provides 75 to 80 percent of the state’s usable water, as it melts and fills rivers and reservoirs in the spring and summer. (Learn how California's snows have failed.)

I reported on how this cycle typically works—and how broad its effects are—last summer, in a story on new technology for measuring snowpack:

"California gets most of its precipitation for the year during the winter and early spring months. When that moisture falls as rain, it tends to run off the land quickly, and much of it ends up in the ocean. But when it falls as snow, it tends to stick to the mountains. It then melts slowly, so the water becomes available gradually and can recharge reservoirs and groundwater aquifers.

"That's water that serves tens of millions of people, grows about half of the fruits and nuts in the United States, produces hydropower, drives industry, supports recreation, and nourishes wildlife.

"As it stands, California can store only enough water in reservoirs to cover the state's needs for about a year and a half."

Data released this week by NASA show that the state’s snowpack was about 6 percent of normal levels. That’s about 40 percent of last year’s peak, which was itself just 24 percent of normal levels.

Dry Future?

California's drought has been getting worse every year, with no end in sight. The geologic record shows the state had experienced decades-long “megadroughts” in the distant past, so there’s no guarantee of a quick return to wetter years.

“The system still has some resiliency, so it's not that we're going to run out of water right away,” says Painter. “But we have to think in terms of buffering against the threat of long-term drought.” (Learn more about drought predictions.)

In the meantime, much of the state’s water needs have been supplied with groundwater. But that water comes with some hefty baggage, as my colleague Dennis Dimick recently reported:

"A new report from Stanford University says that nearly 60 percent of the state's water needs are now met by groundwater, up from 40 percent in years when normal amounts of rain and snow fall.

"Relying on groundwater to make up for shrinking surface water supplies comes at a rising price, and this hidden water found in California's Central Valley aquifers is the focus of what amounts to a new gold rush. ...

"In most years, aquifers recharge as rainfall and streamflow seep into unpaved ground. But during drought the water table—the depth at which water is found below the surface—drops as water is pumped from the ground faster than it can recharge."

California farmers continue to keep their crops alive by relying on that dwindling source of groundwater. In September, the state passed its first-ever restrictions on groundwater pumping as a result of the crisis, but those rules don’t have to go into full effect until 2040. Until then, a groundwater drilling boom runs apace in much of the state.

"If we don't get a bigger snowpack soon, we're going to be in trouble. I don't know what we're going to do," Floyd Arthur told National Geographic in August.

Arthur’s company now works around the clock drilling wells for farmers in the Central Valley, with a waiting list of over a year. When he moved to the region in the mid-20th century, the water table was a few feet below the surface, but now he frequently drills down 2,000 feet (600 meters) deep.

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