LOS ANGELES — Farmers with rights to California water dating back more than a century will face sharp cutbacks, the first reduction in their water use since 1977, state officials announced Friday. The officials said that rights dating to 1903 would be restricted, and that such restrictions would grow as the summer months go on, with the state facing a prolonged drought that shows few signs of easing.
“Demand in our key rivers systems are outstripping supply,” said Caren Trgovcich, the State Water Resources Control Board’s chief deputy director. “Other cuts may be imminent.”
It is too early to know the practical impact of the cuts, which prohibit farmers from taking surface water. State officials have warned of such curtailments for months, and many farmers and agricultural water districts prepared for them by increasing their reserves or digging new wells for groundwater.
Still, the dramatic move is a sign of how dire the drought has become, as the snowpack in the Sierra Nevada mountain range — which normally supplies water to the state through the summer months, as it melts — is at a historic low. Only once before in the state’s history have the most senior water rights been curtailed. But now, with the drought persisting into a fourth year, state officials say that more reductions for so-called senior water rights holders are nearly certain, and the need for additional cuts will be evaluated weekly.
The restrictions could cause the widespread fallowing of cropland in areas that have so far been largely exempt from cutbacks. The impact is likely to be felt far more broadly than it was in the 1970s, because the state now has more authority to impose cuts and a greater ability to measure how water from the Sacramento-San Joaquin River Delta is used.
“It’s going to be a different story for each of them and a struggle for each of them,” said Tom Howard, the executive director of the State Water Resources Control Board, referring to the senior water rights holders. “Some are going to have to stop irrigating crops, and there are others who have storage or wells they can fall back on.”
But the situation could deteriorate further, Mr. Howard said. “By the time this year ends, it might be much more broad-based and deeper,” he said.
While officials have said for months that water for the senior rights holders — those at the front of the line — would be curtailed, they had repeatedly put off such a decision amid the cooler and wetter weather of the last several weeks.
Earlier this year, Gov. Jerry Brown received repeated and intense criticism after he issued mandatory cuts on urban water use but exempted farmers. In a normal year, agriculture uses about 80 percent of the water consumed in the state. Farmers in the Central Valley have had their surface water allotment diminished or erased for the last several years, and instead have relied on water pumped from the ground.
Last month, the state reached an agreement with some farmers in the delta to voluntarily cut their use by 25 percent in exchange for a promise to not face more drastic cuts later during the growing season. Roughly half of the region’s 400 farmers eligible for the program signed on, according to state officials.
George Hartmann, a water rights lawyer who helped design the deal between state officials and the delta farmers, said that most growers had planned for such cuts. “We all knew this was going to happen,” he said. “The state had made it very clear that was part of their plans, so I doubt people spent a lot of money planting for something they weren’t sure they could grow.” But the most important impact may be the precedent the state board is setting, said Jeffrey Mount, a senior fellow at the Public Policy Institute of California. Several lawyers have already indicated that they will take the fight to court, arguing that the state board does not have the right to curb rights that date to before 1914, when California first began regulating water diversions.
“Litigation will be filed,” Mr. Hartmann said, “and I think the state welcomes it, so that this is resolved once and for all.”
Some 620,000 acres of land are expected to be fallowed in California this year, primarily in the Central Valley, according to statewide agricultural groups. The state has roughly 7.5 million acres of farmland, and the cuts in surface water are being felt unevenly, depending on the source of water.
“With every turn of the screw as water supplies shrink, more people suffer,” Paul Wenger, the president of the California Farm Bureau Federation, said in a statement. “Water shortages undermine rural economies, both in the short term and the long term, and these additional shortages will spread that impact to more people in more places.”
Peter Gleick, the president of the Pacific Institute, a nonprofit research institute that focuses on the environment, said that the biggest challenge for state officials would come in enforcing the restrictions, along with the thousands of other curtailment orders that it issued to more than 9,000 junior water rights holders earlier this year.
“This is an indication of how broadly water is used in California,” Mr. Gleick said. “These curtailments are the next step in spreading the growing pain of the drought to a growing number of users, and it is going to get worse as the hot summer drags on.”