Near-record rainfall has battered California for weeks, sparking floods and landslides as the state struggles to cope with so much water. But scientists say even this much precipitation won't reverse the western U.S. state's decades-long drought.

A parade of atmospheric rivers, massive flows of moisture dragged through the skies from the oceans, has unleashed staggering volumes of rain and snow since December.

San Francisco got more rain in the last two weeks than it has done in any similar period for 150 years, while the Sierra Nevada mountains have been buried in as much as 10.5 meters of snow.

Peter Gleick, co-founder of the Pacific Institute in Oakland, a research organization that specializes in water issues, says it's difficult to quantify exactly how much water has fallen from the sky.

"But we're definitely talking about trillions of gallons," he said. "There's no doubt that the water we're getting now is a great help in eliminating the drought... But it is too soon to say that the drought is over." He believes it has to wait until the end of winter to know for sure.

The western United States is in its 23rd year of drought, with major rivers and reservoirs at a fraction of capacity. 

California's largest reservoir, Lake Shashta, is only 42 percent full, official data shows, even after all this rain.

The monster snowpack in the Sierra Nevada mountains is currently twice what it normally is in January, which may help to provide the gradual run-off that drip-feeds reservoirs in drier months.

Beyond its reservoirs and snow reserves, the state faces a much deeper-seated problem with its depleted groundwater, says Nicholas Pinter, a geologist from University of California, Davis.

About half of measured wells in California have seen their water levels decline over the past 20 years, according to a report from the California Natural Resources Agency released in October.

And the torrents of rain that have fallen are not all that effective at recharging them – the soil became saturated quickly, so instead of being absorbed, subsequent downpours just ran off.

"Groundwater is like our retirement account. It's slow to go in and we have to withdraw it very, very carefully," says Pinter.

California's vast agricultural sector is a heavy user of this underground water. That intense need, coupled with big cities like Los Angeles that have nowhere near enough of their own water to support their populations, means almost no matter how much it rains, it will not be enough.

"We will never end the discussion of drought in California because drought in California is largely driven by water demand," says Pinter.

(With input from AFP)

(If you want to contribute and have specific expertise, please contact us at nature@cgtn.com.)