UC Davis report says we use five times more water than we've got

California is in a state of extreme hydrologic debt.

More than five times the water that actually flows from the mountains each year has been promised by water agencies to various users, according to a new report authored by researchers with UC Davis and UC Merced.

In making long-term agreements with farms, industries, cities and environmental needs, the California Department of Water Resources and the U.S. Bureau of Reclamation have promised to deliver 370 million acre-feet of water each year from a system of watersheds that only produces 70 million acre-feet, according to the paper published last week in the journal Environmental Research Letters.

Co-author Ted Grantham, until recently with the UC Davis Center for Watershed Sciences and now with the U.S. Geological Survey, told SN&R this overallocation has occurred through a variety of ways.

Some people report using more water than they actually do each year, so that when their allotment gets cut in dry years they still receive their needed share.

Other times, water is “double accounted,” which means it is used first in fields before it drains back into a river.

And some users simply misreport their use, said Grantham, who co-authored the paper with UC Merced professor Joshua Viers.

Their study was based on records from California’s water-rights system, meant to serve as an accounting book for the state’s water bank. However, California’s water-accounting records do not factor in groundwater, which is essentially treated as a free-for-all resource.

Brian Stranko, with The Nature Conservancy, says it’s been estimated that in the average year, 40 percent of all water used in the state for human needs is pumped from the ground. In a drought year, that figure can increase to 60 percent, he says. This uncertainty further confuses any efforts to accurately track and regulate water use. Moreover, use of groundwater depletes surface-water supplies.

He points out that using groundwater actually depletes reservoirs.

“When people draw water up from their wells, [water managers] have to release more water from Lake Shasta to keep river levels up,” Stranko said.

He also explained that when water is taken from the ground, levels of nearby streams and lakes may drop, too. But California imposes no restrictions or requirements on groundwater use, and farmers and other users whose surface-water supplies are cut during dry times may revert freely to wells to generate water.

“It was written into law in 1914 that groundwater is unrelated to surface water, and that’s a misconception that’s finally being recognized,” Stranko said.

How much water can be sustainably removed from subsurface reserves is not yet known, but Stranko says water experts believe that Californians overdraw from wells by about 2 million acre-feet per year. As a result, land is sinking in places, a process which Stranko says permanently shrinks the potential capacity of an underground reservoir.

Two proposed laws, Assembly Bill 1739 (introduced by local Assemblyman Roger Dickinson) and Senate Bill 1168—which passed through the state Legislature this week and await Gov. Jerry Brown’s signature—aim to create a system of regulating groundwater use by requiring registration of and reporting on wells. Opponents have characterized the bills as impeding on landowners’ rights, while supporters have argued that the water under one person’s land must be recognized as being a part of the state’s collective reservoir and, therefore, belonging to everyone.

The current drought has underscored the problem of California’s overallocated water supply, since authorities intending to cut back water rations don’t always know exactly how much a given user is consuming. Grantham says watersheds, small creeks and fish tend to lose out under such uncertain conditions.

Environmental groups want officials to take more accurate notes on where water is going and how much is left for natural resources.

“They need to develop a transparent accounting system for the water,” said Zeke Grader, a board member with the Golden Gate Salmon Association, a group immersed in a constant battle to maintain sufficient river flows for Chinook salmon.

Grantham told SN&R that “it’s hard to maintain stream flows in a lot of places because no one really knows how much water is being used.”

And unless new state laws crack down on unregulated groundwater use, developing an accurate accounting system for the state’s water supply cannot be fully accomplished, according to Stranko.

“We’ve recognized that we’ve overalloacted our surface water,” he said. “Now, we need to think about the groundwater.” Each, he says, is an important part of the equation.