Gov. Arnold Schwarzenegger on Friday declared California's first-ever state of emergency in response to a drought, calling on city dwellers to immediately shave water consumption 20 percent and warning he may order statewide rationing if they don't.

"We could see, for the first time, the state invoking mandatory conservation," said Lester Snow, director of the California Department of Water Resources, in a conference call with news reporters following the declaration.

The state of emergency also frees up state money for providing assistance to communities and businesses slammed by severe cutbacks in water deliveries.

Snow cited a recent UC Davis study that estimates the three-year statewide drought could eliminate 95,000 farm jobs and result in $2.8 billion in economic losses in 2009.

And while most of that impact will be felt in the Central Valley, which grows half of the nation's fruits, vegetables and nuts, farmers in San Diego and Riverside counties will be affected, too.

"You're in a forest of stumped avocado trees," said Tim Quinn, executive director for the Sacramento-based Association of California Water Agencies.

In North San Diego County, avocado growers have been coping with the cutoff of 70 percent of their water by cutting all foliage off thousands of trees and literally turning them into stumps -- without killing them -- in a desperate bid to ride out the drought. Such trees can survive with minimal amounts of water and regrow.

The state of emergency follows Schwarzenegger's June 2008 declaration that California was gripped by a statewide drought. And it comes three days before state surveyors are poised to take a pivotal mountain snow measurement that is expected to provide a clear picture of how much water will be shipped south to Southern California from the State Water Project.

"We have a major snow survey scheduled for Monday that will update where we are, but we are still very far behind," Snow said.

State officials said it marked the first time that a state of emergency has been called because of drought. They said former Gov. Pete Wilson came close to declaring one in 1991, but the "March miracle" deluge that spring ended that drought.

In a statement, Schwarzenegger outlined why he declared an emergency.

"This drought is having a devastating impact on our people, our communities, our economy and our environment," Schwarzenegger said. "This is a crisis, just as severe as an earthquake or a raging wildfire."

Snow said that, across the state, 18 agencies that distribute water have already gone to mandatory conservation while 57 agencies -- including those serving San Diego and Riverside counties -- are asking residents to conserve voluntarily. Snow added the governor wants all of the distributing agencies to make saving water mandatory.

By that, Snow said he meant adopting utility rate structures that charge customers significantly more if they fail to conserve 20 percent and cracking down on people who hose off driveways or let sprinkler water run down the street. If mandatory measures aren't widely in place by March 30, he said, the governor may order rationing.

The San Diego County Water Authority, which distributes water to North County's cities and water districts, is scheduled to consider at its March 26 meeting whether to impose mandatory restrictions, said agency spokesman John Liarakos.

Meanwhile, the Western Municipal Water District, which serves the Interstate 15 corridor in western Riverside County, is poised to consider in April an ordinance that would fine customers for wasting water, said Tedi Jackson, a spokeswoman for the district.

Local agencies already were bracing for cutbacks.

The state announced late last year it likely would allocate just 15 percent of the amounts suppliers request for 2009. And that figure may hold up even though snow has been falling faster in recent weeks.

The winter got off to a particularly slow start. In late January, surveyors found that Sierra snow depth was 40 percent below average for that point in the season.

An avalanche of storms in the weeks since has beefed up accumulations, said Wendy Martin, the state's drought chief. And it is possible that, come Monday morning, snow levels will be close to the average total for the first of March, she said.

"The problem is, I don't think it's going to be enough," Martin said.

Even another "March miracle" comparable to the one that rescued the state in 1991 won't bail out the region.

The problem, Martin said, is California's reservoirs are less than one-third full. They are at their lowest levels since 1992. And it will take more than an average year to refill them.

"We have a pretty deep hole to dig out of," she said.

Martin said the low lake levels are compounded by concerns about an endangered fish, the delta smelt, that have spawned strict pumping limits for water headed south from the Sierra. The water that eventually winds up in Southern California is pumped from the Sacramento-San Joaquin Delta.

"If it rains like crazy, sure, we are going to up the allocation as much as we can," she said. "But we also are not going to overpromise. I don't think we are going to be anywhere near what people want us to deliver."

The 15 percent allocation sounds worse than it is. That's because it is a rare year when anyone gets what they ask for. Typically, Southern California gets 50 to 60 percent of what it asks for.

On the other hand, 15 percent is anything but typical. It is less than half of what the region received last year.

Martin said she is still wishing for a March miracle.

"But I'm not planning on it," she said.

Contact staff writer Dave Downey at (760) 745-6611, Ext. 2623, or ddowney@nctimes.com.