California Governor Jerry Brown on Sunday defended tough new measures aimed at combatting a crippling four-year drought, but which critics say are far too lenient on the state's farmers.

Brown on Wednesday announced sweeping water restrictions for the first time in the state's history to counter what officials called the most devastating dryspell on record.

The decision that many of the draconian restrictions would not apply to agriculture reflects how hard the industry has already been hit, he told ABC television's "This Week" program.

"Look, the farmers have fallowed hundreds of thousands of acres of land. They're pulling up vines and trees. Farmworkers who are at the very low end of the economic scale here are out of work," he said.

"There are people in agriculture that are really suffering."

The executive action taken by the California governor aims to achieve a 25 percent reduction in water usage across cities and towns throughout California.

The reductions would be achieved by ramping up enforcement to prevent wasteful water use, while investing in technologies designed to make California more drought-resilient.

The measures also order college campuses, golf courses, cemeteries and other large consumers of water to significantly cut their use.

"If they don't comply, people can be fined $500 a day," Brown told ABC.

The drought has left huge swaths of California's landscape unrecognizable, with normally brimming lakes and rivers now dry and losses to the state's agricultural industry estimated at several billion dollars.

But critics cited figures circulating in the US media that farming uses 80 percent of California's water but accounts for less than two percent of its economy.

Brown confirmed those figures, but said agriculture's importance to California belies its relatively small share of the state's domestic product.

"If you don't want to produce any food and import it from some other place, theoretically, you could" impose water restrictions on agriculture, he said.

"But that would displace hundreds of thousands of people and I don't think it's needed."

He conceded that while technological improvements can help the farm industry use water more efficiently, but nevertheless rejected -- for now -- the idea of imposing water restrictions.

"They're not watering their lawn or taking long showers. They're providing most of the fruits and vegetables of America to a significant part of the world," he said.

But, Brown added, "if things continue at this level, that's probably going to be examined."