Is the wet weather streak enough to combat the drought?

‘We need more storms, and we can’t be sure it’s coming’

Just weeks after dire warnings of a dry winter and dwindling snowpack prompted state and local officials to rein in water supplies for the coming year, the Bay Area has been soaked to the bone.

A series of winter storms brought a deluge of rain and snow to Northern California, culminating in above-average precipitation for the month of December, with more rain and cold weather in the forecast for the Bay Area next week.

December’s drenching capped off one of the driest water years on record, but Californians are not yet out of the woods in overcoming drought conditions or dampening wildfire threats, experts say.

“It’s been a wet, cool December, but not close to record-breaking,” said Jan Null, longtime Bay Area meteorologist and founder of Golden Gate Weather Services. “We are off to a really good start. We’re running way ahead of normal levels — almost twice normal right now. But January, February and March — we just need to keep the drumbeat.”

California’s climate is notorious for snapping between wet and dry years, and climate change is increasing this variability. Recent research shows shortened, more intense precipitation periods could become the new normal in a warming world, spelling challenges for California’s water supplies in years to come.

“With climate change, we’re seeing more extreme events,” said Jay Lund, professor of civil and environmental engineering at the University of California, Davis. “But that’s really on top of the normal, very high variability that California has.”

After a year marked by empty wells, dried riverbeds and water curtailments, the burst of wet weather is a welcomed change. But the question remains: Will this season’s storms be enough?

“We’ve already got enough precipitation that it’s pretty clear it’s not going to be another 2021,” said Lund. But there’s still a gaping deficit. “We entered this wet season starting in October, with nearly empty reservoirs and pretty low groundwater levels after two years of lots of extra pumping. And so, everybody was pretty worried.”

That worry extended to San Francisco. In late November, Mayor London Breed declared a water shortage emergency and issued a voluntary 10% reduction in water use across the regional system managed by the San Francisco Public Utilities Commission (SFPUC).

Despite the rainfall, many Northern California reservoirs, which provide water throughout the state via a complex system of dams, canals and pipes, remain drier than historical averages, according to data from the California Department of Water Resources (DWR).

“The water supply outlook for customers of the SFPUC’s Regional Water System remains somewhat uncertain, despite this recent precipitation,” said Steven Ritchie, assistant general manager for SFPUC’s Water Enterprise. “While the recent rain and snow are positive, there is still uncertainty around the state’s actions to curtail our Tuolumne River diversions.”

On average, the bulk of California’s annual precipitation falls from November through March, with most of the state’s snow, hail, and rain falling between December and February. According to DWR, just a handful of atmospheric rivers — or lack thereof — during the winter season can determine if the year will be wet or dry.

But recent studies have shown that autumn precipitation is in decline, driven by November precipitation decreases, historically the wettest autumn month.

Rising temperatures and shifting precipitation patterns also complicate drought conditions and lengthen wildfire seasons. Studies show even with wetter winters, warming spring temperatures can exacerbate wildfires by drying out underbrush, shrubs and grasses, which can easily ignite during the dry season. Higher temperatures also cause soil moisture to evaporate faster, making wildfire seasons last longer.

Sean de Guzman, Chief of the California Department of Water Resources Snow Surveys and Water Supply Forecasting Section, walks in the deep snow during the measurement phase of the first media snow survey of the 2022 season at Phillips Station in the Sierra Nevada Mountains on Thursday, Dec. 30, 2021. The state snowpack is currently at 160% of average. (Andrew Innerarity/California Department of Water Resources)

Sean de Guzman, Chief of the California Department of Water Resources Snow Surveys and Water Supply Forecasting Section, walks in the deep snow during the measurement phase of the first media snow survey of the 2022 season at Phillips Station in the Sierra Nevada Mountains on Thursday, Dec. 30, 2021. The state snowpack is currently at 160% of average. (Andrew Innerarity/California Department of Water Resources)

Still, there are some signs of hope for the year ahead. While this month’s teeth-chattering whiteout conditions snarled traffic, blanketed roads and stranded motorists on major highways, surveys conducted by DWR Thursday showed the statewide snowpack is 160% of average for this period.

“We could not have asked for a better December in terms of Sierra snow and rain,” said DWR Director Karla Nemeth. “But Californians need to be aware that even these big storms may not refill our major reservoirs during the next few months. We need more storms and average temperatures this winter and spring, and we can’t be sure it’s coming.”

Experts think it’s likely Californians will emerge from this snow-capped winter into continued dry conditions. “There’s some reasonable probability of there being a drought this year,” said Lund. “It’s much diminished from what it was before, but even with that, there’s still going to be these problems of groundwater overdraft, water for salmon, streams, things like that. So, we have a lot of reasons to reduce our water use.”

“This is California,” he said. “You should always be careful with water.”

jwolfrom@sfexaminer.com

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