Parched California's reservoirs have been slowly gaining some volume after heavier rains than usual, but it is too soon to determine how this might impact the state's severe drought.

"Reservoirs across the state are at higher levels than last year. March has been a very good month thanks to El Nino," Doug Carlson, spokesman for the Department of Water Resources, told AFP, referring to the weather pattern.

The Shasta reservoir was up to 81 percent of its capacity, and there is a similar outlook at Oroville.

But "it's too soon to say how this will impact the drought," Carlson said of the severe drought that has already lasted four years.

The El Nino weather pattern is associated with a sustained period of warming in the central and eastern tropical Pacific, which can spark deadly and costly climate extremes.

In December, the UN weather agency warned that the phenomenon, triggered by a warming in sea surface temperatures in the Pacific Ocean, was the worst in more than 15 years.

California has imposed water use restrictions, and fines those who won't cooperate.