SAN FRANCISCO — Californians were warned against abandoning conservation efforts Tuesday as several weeks of storms spawned by El Niño began hitting the West Coast.

Heavy rain and snow are welcome after four years of drought in California, despite their potential for causing flash floods and mudslides. But even a very wet winter won’t be enough to replenish water supplies depleted by four years of drought.

The powerful El Niño system — a warming pattern that lifts vast amounts of precipitation from the Pacific Ocean, funnels it across North America and alters weather worldwide — is expected to cause unusual US weather for months.

As much as 15 inches of rain could fall in the next 16 days in Northern California, with about 2 feet of snow expected in the highest points of the Sierra Nevada, said Johnny Powell, a forecaster with the National Weather Service.

In Southern California, between 2 and 3.5 inches of rain is predicted to fall across the coastal and valley areas, and up to 5 inches in the mountains.

Flash flooding and flows of mud and debris were a concern in places around the state, especially in wildfire burn areas.

Altogether, the storms should bring massive amounts of rain and snow to a very parched state this month, but water managers won’t be able to fully estimate this year’s snowmelt until April 1, when the snowpack is at its deepest.

California’s water deficit remains so profound that a ‘‘steady parade of storms’’ like these will be needed for years to come to end the relentless drought, said Mike Anderson, climatologist for the state’s Department of Water Resources.

Associated Press