EXPLAINER: How much will the rain help California's drought?

California has experienced a devastating, multi-year drought that’s depleted reservoirs, forced officials to plead with residents to conserve water and constrained supplies to vital farmland.

Suddenly, the state has been hit by a severe series of storms, with more expected in the coming days. The rain is soaking a state that desperately needs water, even as it takes a devastating human toll. Experts say it will help drought conditions, but it isn’t yet clear exactly how much. And the rain and snow won’t be enough to fix some of California’s long-term water problems that climate change is making worse.

“We are transitioning to a climate that is warming and more arid,” said Jeannie Jones, the interstate resources manager at California Department of Water Resources.

Here’s how the storms will affect California’s long struggle with drought:

WHERE IS THE RAIN HELPING?

California has experienced six atmospheric rivers in recent weeks and is bracing for as many as three more, with the wild weather set to continue for at least another week, Gov. Gavin Newsom said Tuesday from Santa Cruz County, where raging ocean water damaged an iconic wooden pier.

The storms have poured a tremendous amount of water on the state, especially in central California, including the San Francisco Bay Area and Sacramento Valley. Precipitation is 138% of average for this time of year, officials said. The storms have also dumped snow on the Sierra Nevada that run along California’s eastern border.

Most of the state's reservoirs remain below average for this time of year, but some have begun to fill, especially those close to the hard-hit Sacramento region and along parts of the Sierra Nevada. The reservoirs are essential for irrigating the Central Valley, a productive stretch of farmland that grows...