Winter Storms Ease Drought in California, for Now

Experts say that it’s too early to tell what will happen during the rest of the state’s rainy season, but that extreme drought is unlikely.

Heavy rain and snow has pounded California in recent weeks, causing floods, power outages, mudslides and other disruptions. But the storms have also filled reservoirs and deepened the snowpack in the Sierra Nevada mountain range, easing drought concerns in a state that is perpetually worried about not having enough water.

The near-constant pace of storms so far this winter has brought the state above-average precipitation, driving the storage level in most of California’s water reservoirs to well above normal for this point in the rainy season. Measurements show virtually no drought in the state.

“This is actually an exceptional wet period, something of the opposite of a drought,” said Daniel Swain, a climate scientist who works within the University of California system.

Mr. Swain said that it’s common in California for the state to recover from drought during the winter, the rainy season, although he added that it’s been a few years since the state has seen serious drought levels.

“If you miss out during winter, you’re not going to have another chance to replenish that water until at least the next winter,” he said.

While California’s wet season occurs from November through March, the bulk of snow, rain and hail falls during winter storms in December, January and February.

It remains to be seen how much more precipitation falls in the coming months, said Jeffrey Mount, a water policy expert at the Public Policy Institute of California.

“This is really like the second quarter of a football game,” Mr. Mount said. “We really don’t know what the outcome is going to be.”

Just a few heavy winter storms during the season can determine whether the following year will be wet or dry, according to experts. Climate change has led to more weather extremes in the state, including years of extreme wetness or dryness.

“California has always been a place where we have these big swings,” Mr. Swain said. “These recent swings have been at the upper end, beyond what we’ve seen in the historical record.”

Heavy rains are not always a net positive, he warned. While last winter was exceptionally dry for Southern California, he said, there was abundant precipitation the previous year. Those rains led to more vegetation growth, which then became fuel for the devastating wildfires last January.

“Could we see that emerge again next summer, next fall?” he said. “It’s possible, if we have an exceptionally hot summer or an exceptionally dry fall.”

What the current precipitation levels do indicate, Mr. Swain said, is that it is unlikely the state will enter extreme drought this year.

“It gives us some insurance,” he said. “Even if the tap shuts off early this winter or it doesn’t really turn on in a timely fashion next fall, we’re not going to have droughts that lead to water supply issues or agricultural curtailments or urban water restrictions.”

California also relies heavily on the accumulated mountain snowpack to melt and provide water during the state’s dry season. State meteorologists said recent snow in the Sierra Nevadas helped to build a “solid base” for the year’s snowpack.

“While California is in a better position now, it is still early in the season and our state’s water supply for this year will ultimately depend on a continued cadence of storms throughout winter and early spring,” Angelique Fabbiani-Leon, a hydrometeorologist at California’s Department of Water Resources, said in a statement last week.

In addition to a wetter season, California’s winter has been warmer than average this year, which could contribute to more rain than snow, and earlier melting of the snow that does accumulate.

Mr. Mount said the state depends on a slow release of water from the snowpack to refill reservoirs, usually beginning in April or May. “That’s coming earlier and earlier as things warm up,” he said.

Rainfall and snowmelt also contribute to recharging groundwater wells, which during drought years can account for two-thirds of California’s water supply. Such wells, which have become strained during previous dry years, are currently below their normal levels.

Michael Loik, a professor of environmental studies at the University of California at Santa Cruz, said Californians should continue to live with a conservative mind-set regarding water supply.

“Drought is the norm in California,” he said. “The next drought is just around the corner.”

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