LOS ANGELES — Four years of a historic drought that has left California parched forced Gov. Jerry Brown on Wednesday to declare the first mandatory water restrictions in the state’s history.

He ordered the State Water Resources Control Board to enact mandatory cuts in water use by 25 percent, which could save 1.5 million acre-feet of water over nine months. An acre-foot contains 325,851 gallons of water.

Brown issued the executive order while visiting the Phillips Station in the Sierra Nevada — an area that would normally be blanketed with snow more than 60 inches deep at this time of year.

"Today we are standing on dry grass where there should be 5 feet of snow. This historic drought demands unprecedented action," he said in a statement.

"Therefore, I'm issuing an executive order mandating substantial water reductions across our state. As Californians, we must pull together and save water in every way possible."

Snowpack measurements registered at about 5 percent of the state average on a day when it’s usually at its peak. Levels are the lowest they have been in more than 70 years.

Without snow, California’s reservoirs will not fill up. Runoff from melting snow usually accounts for 30 percent of the state’s water supply.

Brown on Wednesday called for the replacement of 50 million square feet of lawns with drought-tolerant landscaping and the creation of a statewide consumer rebate program to replace old appliances with water- and energy-efficient models.

Campuses, golf courses, cemeteries and other large landscaped locations have been asked to make significant cuts in water use. And new homes and developments have been barred from irrigating with potable water unless water-efficient drip irrigation systems are used. Brown also barred watering of ornamental grass on public street medians.

Moreover, local water agencies have been asked to adjust rates — higher rates for higher users — to encourage water cuts and discourage waste.

"We’re very happy to see mandatory conservation," said Sara Aminzadeh, the executive director of the California Coastkeeper Alliance. "Voluntary conservation wasn’t working well enough."

However, she expressed concern that the restrictions are based on a percentage of prior usage rather than gallons per capita. That means those who used a lot of water before the mandatory cuts will be allowed to use more water than others.

Per capita quotas "would provide a more equitable approach," Aminzadeh said.

Historically, the state has preferred to let local districts manage how they want to reach their goals rather than dictate specific rules.

Agricultural users are now also required to report more detailed water use information to state regulators, which can help them catch illegal water diversions and water waste.

"We know that in order to address the drought effectively, we need much better information both on how much water we are using and at what rate," said Adrienne Alvord, California and Western states director at the Union of Concerned Scientists, in a statement. "This is a critical requirement that we need to make permanent, since we know that you can't manage what you don't measure."

Water agencies also have to report what they’re doing to conserve water and how they’re enforcing user guidelines.

In March the state water board toughened restrictions by ordering urban districts to limit the number of days residents may water their yards. Brown and state legislators passed a $1 billion emergency drought relief plan that includes funding for long-term alternatives, such as desalination and sewage water recycling.

The state must focus on modernizing water management systems to deal with climate change, Alvord said.

"While the governor's water reduction actions are crucial and even more may be necessary if the drought continues, it is also important for Californians to keep in mind that in a warming climate we are entering a new era, and water managers and state planners need to incorporate future projections into their scenarios," she added.