Gov. Jerry Brown on Sunday defended his order requiring Californians statewide to cut back on their water use in a historic mandate that spares those who consume the most — farmers.

As California endures a fourth year of drought, Brown's order this week requires towns and cities statewide to draw down water use by 25 percent compared with 2013 levels. While past reductions were voluntary, Brown said he is using his emergency powers to make the cuts mandatory.

Martha Raddatz, host of ABC's "This Week" public affairs program, asked Brown why the order doesn't extend to California farmers, who consume 80 percent of the state's water supply but make up less than 2 percent of the state's economy. Brown said farmers aren't using water frivolously on their lawns or taking long showers.

"They're providing most of the fruits and vegetables of America to a significant part of the world," he said.

Brown said that before the cutbacks, some California farmers had already been denied irrigation water from federal surface supplies, forcing them to leave hundreds of thousands of acres unplanted. Many vulnerable farm laborers are without work, he said. Farmers who don't have access to surface water have increased the amount of water pumped from limited groundwater supplies.

Brown announced the mandate on April 1 standing in the Sierra Nevada, where the snowpack measures at 5 percent of historical average, the lowest in 65 years of record-keeping.

Addressing agriculture, Brown said on the broadcast that farmers asserting century-old water rights deeply rooted in state law that allows them access to more water than others "are probably going to be examined."

After declaring a drought emergency in January 2014, Brown urged Californians to voluntarily cut their water use by 20 percent from the previous year. That resulted in great variations among communities and an overall reduction of about 10 percent statewide. Brown did the same as governor in 1977, during another severe drought, asking for a voluntary reduction of 25 percent.

The mandatory order will also require campuses, golf courses, cemeteries and other large landscapes to curb their water use.

"It is a wakeup call," Brown said. "It's requiring action and changes in behavior from the Oregon border all the way to the Mexican border. It affects lawns. It affects people's — how long they stay in the shower, how businesses use water."