Sonoma County residents will likely be facing mandatory water conservation measures by sometime in April if there is no significant rain before then, officials said Tuesday.

"It seems to me that drastic times call for drastic measures," Supervisor Shirlee Zane said as the supervisors approved a drought emergency declaration that will make the county eligible for state and federal disaster assistance.

Healdsburg and Cloverdale have already imposed mandatory conservation because they are dependent on the water coming from Lake Mendocino, which is at just 41 percent of its capacity. The Sonoma County Water Agency has cut releases from the reservoir into the upper Russian River to a trickle in order to preserve whatever it can behind the dam.

But there is growing concern about the supply at the much larger Lake Sonoma, which serves more than 600,000 customers in the cities south of Healdsburg, including parts of Marin County. That reservoir, designed to hold a three-year supply of water, is down to just 67 percent of its capacity and is less than a year away from the level at which the water agency would be forced to impose a 30 percent cut on the municipalities that buy the water and distribute it to residential and business customers.

In early April, "we're going to take a hard look at Lake Sonoma .<TH>.<TH>. our objective is to extend that water pool into November," when the rainy season should have started again, Water Agency General Manager Grant Davis told the supervisors.

Until the so-far lackluster rainy season wraps up, however, the agency won't know how much water it will have in the reservoir to meet the dry summer months, and therefore it isn't clear yet how much the agency might need to do to hold off the steep mandatory cuts as long as possible.

A key advisory panel, which includes members from all the water systems that buy from the Water Agency, will look at the reservoir levels at a meeting April 7 and may recommend less draconian mandatory measures to stretch the supply, Davis said.

The governor has already called for water customers to cut their consumption voluntarily by at least 20 percent, and most area municipalities are already asking their customers to follow his advice. None of the cities relying on Lake Sonoma have made such restrictions mandatory yet.

The agency has launched an unprecedented mid-winter conservation campaign, with ads bearing the slogan "There's a drought on, turn the water off." The county is hoping that Tuesday's drought declaration could open the door to state and federal funding for projects such as replacing toilets and other water fixtures in area homes.

The declaration could also make it easier for ranchers and farmers to apply for emergency assistance programs. Agriculture Commissioner Tony Linegar says losses to area farmers are at least $6.2 million and he is projecting a near-total loss for grain and hay farmers, a particularly difficult and expensive prospect for ranchers trying to feed livestock that would normally eat on pasture land until well into the summer.

"Hay is getting more and more difficult to find, particularly organic hay," he told the supervisors.

The region is in its third straight dry year, but 2013 was unusual dry, with less than 9 inches recorded in Santa Rosa. That is certainly the driest year since records were first kept in the 19th century and may be the driest year in about 400 years, according to a study of North Coast tree rings by researchers at the University of Arizona.

Even 1977, the worst drought year in recent memory, saw about 15 inches of rain in Santa Rosa, according to Press Democrat records. The yearly average is more than 32 inches.

A heavy rainstorm in early February, the first significant precipitation in almost 14 months, gave farmers and water managers a small amount of breathing room, but the drinking water reservoirs remain at alarmingly low levels.

The National Weather Service is predicting two significant storms between Wednesday and the weekend, but even those storms will not end the drought, even if they add a little extra water in the reservoirs.

"Rain brings amnesia," Board of Supervisors Chairman David Rabbitt said, counseling against excessive optimism in the face of a wet weekend. "We need to have inches, inches, of rain just to get back to the worst place we've been" in previous droughts.

You can reach Staff Writer Sean Scully at 521-5313 or sean.scully@pressdemocrat.com. On Twitter @BeerCountry.