Do recent California storms herald a drought-busting winter?

Winter storms that showered California with much-needed rain and snow over the past week have managed to ease some severe drought conditions, but experts warned the state still has a long way to go to truly reverse its historic drought.

For many, the massive storm system that drenched parts of the West Coast with inch-deep rain and feet of snow was a reminder of seasons past, when it roiled traffic, unleashed rockfalls and unleashed a blizzard of “winter wonderland” posts on social media.

But as the state’s climate gets warmer and drier, sustained periods of rain and snow during the winter are becoming increasingly sporadic, experts say. Many fear a repeat of last year, when a similarly wet December gave way to California’s driest January to March on record.

“December has obviously started very well in terms of snowpack building up and even soaking other areas with rain,” said David Rizzardo, department chief of hydrology at the California Department of Water Resources. But “it’s definitely too early to tell, especially when at the moment it looks like we’re getting similar signals for a possible dry stretch ahead.”

There was cause for relief, however. Rizzardo said reservoir water levels had risen from the storms, including capacity increases at Lake Shasta and Lake Oroville of about 1% from the week before. The nationwide snow water equivalent, or amount of water contained in snow pack, was 223% of normal on Monday.

“There is no doubt that everything is beneficial and the alternative is certainly not what we want,” he said.

David Simeral, a research climatologist at the Western Regional Climate Center and one of the authors of the US Drought Monitor, said Thursday’s report will almost certainly show that “the drought is easing somewhat,” at least in the southern two-thirds of the state. Last Thursday’s update showed that 85% of the state was suffering from severe, extreme or extraordinary drought conditions, the three worst categories.

“The back-to-back storms we’ve had over the past few weeks have definitely had an impact on the drought, although they haven’t cleared the deficits,” he said. “We’ll wait and see how things develop, but I would definitely say there are some things to be optimistic about.”

Simeral said the storms also improved soil moisture, particularly around the coastal and trans-mountain ranges that run from the Bay Area to just above Los Angeles, where there has been heavy rainfall. Humidity levels there now range from the 80th to the 95th percentile, he said.

“These are really, really good numbers, but I don’t want to get too excited,” he said. “I’m cautiously optimistic as we move further into the winter months but as we know we can have good pre-season storms, especially from last year, and then the tap will be turned off in early January.”

A repeat of last year’s change from wet December to bone-dry January was a common concern among pundits.

“We’re reminded of that point last year — in late December, when we had really heavy snow,” said Rizzardo of the Department of Water Resources. “The weather and climate outlook looked pretty dry at the start of the calendar year and that is indeed what happened. We quickly fell back into ‘good try but still in the drought’ and that’s kind of a feeling right now.”

It’s something UCLA climate scientist Daniel Swain called “hydroclimate whiplash,” and he said it’s certainly possible again this year. Just a few weeks ago, conditions were so dry that state water agencies said they may only be able to allocate 5% of requested supplies to city water agencies in 2023.

“We had some decent water early in the season and now December is looking good for most of the state just based on what’s already happened,” Swain said. But there is a “slant in the odds of above-average dry conditions from January through spring.”

In fact, the National Oceanic and Atmospheric Administration’s seasonal forecasts still point to a dry start to the year across much of the West. Supporting this prediction is the rare third occurrence of La Niña, a tropical Pacific climate pattern associated with above-average dry conditions in California, particularly in the southern part of the state.

But while La Niña tends to be a reasonably reliable predictor of overall conditions, it “is sometimes overridden by other factors that are much more difficult to predict,” Swain said, including when and where high-pressure systems will manifest.

In addition, there are disturbances in the jet stream or the fast-flowing air currents in the upper layer of the atmosphere, which steer weather systems from west to east. Swain said the jet stream pattern is currently “upside down” due to extreme high pressure ridges in the Arctic, contributing to larger than normal forecast discrepancies.

Though many metrics look healthier than a week ago, Swain also noted that the reversal of the state’s severe drought in today’s warming climate is no longer just a matter of rain and snow. Evaporation demand – or the amount of water lost from the Earth’s surface to the atmosphere – increases as the state becomes warmer and drier.

“We recognize that it’s not just a question of precipitation,” he said. “As it gets warmer and the atmosphere increasingly demands more water from the landscape, it won’t be in equilibrium unless we get, on average, a lot more water from the sky than we used to, than we used to.”

That didn’t stop many Californians from celebrating the arrival of winter weather, however. Many people went to social media to share pictures of snowy mountains, misty foothills, fresh powder snow and frolicking pets. Even the Los Angeles River, so often reduced to a trickle, showed some flow.

The researchers said moisture of any kind is welcome. Thorough watering in early December can prevent the soil from stealing too much water later in the season, while heavy snow cover later in the year can mean a more reliable supply.

“It was a nice cold storm — one where places in the mountains didn’t have a problem seeing snow, as has been the norm for the last few years and decades,” Swain said. “We see fewer of these storms in a warming climate, but they do happen sometimes, and this was one of them.”

https://www.latimes.com/environment/story/2022-12-13/do-recent-california-storms-herald-a-drought-busting-winter Do recent California storms herald a drought-busting winter?

Alley Einstein

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