State officials warned late Monday that extremely low runoff in California rivers could require even senior water rights holders to reduce their consumption this summer and fall.
The noticeby the State Water Resources Control Board, which regulates water rights, is informational only. But it is a "heads up" that formal curtailment orders could follow if water users don't begin taking action to conserve water now, said Les Grober, assistant deputy director for water rights at the board.
Even so-called "riparian" and "pre-1914" water rights holders, the most senior category in the state, could be affected. Such curtailment actions have not occurred since the drought of 1976-1977, considered the most severe in modern times.
"This is really a heads-up for a potentially critical condition," Grober said. "Junior water rights holders may not have water for crops. It's something the board is going to be watching over the next few months to see if further action is a good idea."
The notice was primarily targeted at farm water users in the Sacramento Valley, who generally hold the largest and most-senior water rights in the state. It came with a two-page list of conservation practices for "immediate consideration," including reusing irrigation runoff, reducing planted acreage, matching water delivery with crop demand, and other measures.
The Northern Sierra Nevada region, which provides much of California's total water supply through snowmelt, experienced the driest January-through-June period in 90 years. Major reservoirs in the region, the largest in the state, are at about 80 percent of average capacity and shrinking rapidly.
Grober said many area rivers would already be dry if not for the water being released from these reservoirs. Much of those releases are necessary to meet water quality and aquatic habitat requirements. In other words, water in some rivers may not be "natural" flow, which is what riparian and pre-1914 water rights holders are typically entitled to take.
Monday's notice was intended, in part, to caution these water rights holders that they may not be allowed to divert the water flowing by their land, because it is legally obligated to another purpose, Grober said.
"That is difficult to ascertain exactly when and where, and it also can be an arguable point," he acknowledged. "That's what the board is going to have to figure out."
Contact The Bee's Matt Weiser at (916) 321-1264. Follow him on Twitter @matt_weiser.