Farmers are feeling the impact of reduced water supplies.

The fourth consecutive year of drought doesn’t bode well for California, or for the United States for that matter, as the Golden State is the top agricultural state in the nation in terms of revenue and crop diversity from almonds to wine.

California Governor Jerry Brown on April 1 issued an executive order mandating a state-wide 25% reduction in water use (from a 2013 base). The order exempts agriculture, although some of the largest farming operations will have to submit water-use plans, and it wasn’t clear how farmers using municipal water in urban settings would be affected.

“This historic drought demands unprecedented actions,” Mr. Brown said. The state-wide mandate came after data showed urban residents trimmed their water use less than 3% in February, and after attempts to reduce water use through a state-wide drought declaration and mostly voluntary cutbacks in 2014 met with limited success and enforcement efforts from local municipalities.

It is the first ever state-wide mandate, which underscores the depth of the problem and government’s attempt to put “teeth” into the restrictions by including sizeable fines of up to $10,000 a day for water agencies that don’t meet conservation targets. Restrictions will vary from 10% to 35% based on local municipalities on past usage patterns, although the state water board still is working out final details.

The U.S. Department of Agriculture’s Natural Resources Conservation Service (N.R.C.S.) said the western snowpack, which accounts for most of seasonal water supply and typically peaks April 1, peaked earlier this year and was mostly melted, which will reduce streamflow later in the spring and summer.

“Almost all of the West coast continues to have record low snowpack,” N.R.C.S. hydrologist David Green said. “March was warm and dry in most of the West; as a result, snow is melting earlier than usual.”

A survey by the California Farm Water Coalition indicated about 42% of the state’s irrigated farmland already had received significant reductions to water supplies, and about 30%, or about 2.2 million acres, of irrigated farmland in the state will get no surface water at all.

California Farm Bureau president Paul Wenger said many of the state’s farmers were facing cuts of 60% to 100% of their water deliveries for the second year.

Some have expressed doubts the state edict will make much difference, and some have criticized Governor Brown for exempting agriculture, which they note uses 80% of the water but accounts for only 2% of the population. Almonds and rice were cited as heavy water users, but so were dairy and other operations.

“Contrary to so much of the media coverage lately, California agriculture is being devastated by the water restrictions caused by the drought,” said Richard Waycott, president and chief executive officer of the Almond Board of California.

Mr. Brown noted the importance of California agriculture to the state, the nation and the world as he responded to critics who cited the exemption for farmers. He said agriculture had suffered enough and was significantly impacted without the state mandate, although he left the door open to reconsider the agriculture exemption should the drought continue to worsen.

California produces about half of U.S.-grown fruits, nuts and vegetables and is the top milk-producing state, accounting for about 20% of U.S. supply. California is the only state that produces a number of crops (or a high percentage of total U.S. output), including almonds, artichokes, olives, pistachios, English walnuts, and others, as well as a majority of processing tomatoes, raisins, table and wine grapes and many others.

One dilemma California growers face is how to optimize use of the limited amount of water they expect to have. When they can, some have opted to forego seasonal crops but keep fruit and nut trees alive through irrigation since trees take a few years to reach maximum production. More than 400,000 acres were fallowed (unplanted) last year, and that may grow to over 600,000 acres this year or even double by some accounts.

Last year the impact of the third year of drought was reduced by heavy use of ground water to supplement short supplies of surface water. That was only a short-term fix as ground water was used faster than it was replenished. Also allaying significant price hikes of many fruits and vegetables was increased imports, helped in part by the strong dollar, which allows for the purchase of more foreign goods per dollar.

Forecasts of the impact the four-year drought on fruit, vegetable, nut and other high-value crop prices have been limited, in part because of uncertainty about California’s weather, imports and other factors. But there is general agreement prices will go up at some point. The question is when and by how much?