Dry December brings drought back to mind
Memories of perpetual blue sky and months on end without rain faded quickly after last winter’s drought-busting storms. But with a bone-dry December and a good chance of sunshine well into the New Year, many Californians are getting flashbacks.
While it may be too soon to start talking drought again, water managers are frustrated to see the first month of the state’s peak rain season slip by with little precipitation.
Reservoirs have only just recovered from the five dry years. Fields and forests are still bouncing back. And the giant aquifers beneath much of California, which were overpumped during recent water shortages, remain frighteningly low. Skiers, meanwhile, risk going another year without a white Christmas in
With no rain in sight, Jay Liu walks Harry along the trails at the Dougherty Hills open space in Dublin.
Tahoe.
This week, the widely watched U.S. Drought Monitor classified 44 percent of the state as “abnormally dry,” and climate experts warn that rain and snow are needed soon to protect large swaths from descending into the next category of “moderate drought.”
The Bay Area has been so parched that the
National Weather Service’s local office issued a rare December red flag warning for high wildfire danger from Friday night to Sunday morning.
“When one of the rainy months is a bust, it’s certainly noticeable,” said Mike Anderson, state climatologist at the California Department of Water Resources. “I wouldn’t call it concern yet. But we’re certainly paying attention.”
The dry skies are a result of a stubborn mass of air over the West Coast that is blocking east-moving storms from making landfall. It’s the same high-pressure pattern that became notorious during the drought and was coined the “Ridiculously Resilient Ridge.”
Forecasters say the ridge is likely to sit tight for the rest of the month, though there’s a slight chance it will break down or shift — and invite in wet weather — during the middle of next week.
“How can this be?” tweeted the weather service’s office in Southern California, where dry hills and valleys along with powerful winds have fed a string of devastating wildfires. “No precipitation over most of CA while the majority of North America gets wet in the next two weeks.”
High-pressure patterns are not typically this persistent. But climate experts say they may be getting more dogged and more common with global warming. Scientists have linked the drying air masses to the swirling glut of greenhouse gases as well as to melting sea ice in the Arctic. The extent of the relationships is still being studied.
The current atmospheric ridge is also strengthened by a La Niña system that has taken hold. The weather service said Thursday that La Niña’s signature cool ocean temperatures and swift westerly trade winds in the equatorial Pacific have intensified, with an 80 percent chance of remaining through winter.
Strong La Niñas have historically pushed the Pacific storm track northward, meaning that when wet fronts develop, they’re less likely to bear down on California, especially the southern part.
The Climate Prediction Center, a division of the weather service that focuses on long-range forecasts, is expecting San Francisco and places to the south to be slightly drier than usual through February.
“The fact that it’s been dry goes along with what our expectations have been,” said Mike Halpert, the center’s deputy director. “It’s certainly going to rain at some point. But you’re smack dab in the rainy season right now, and every week that goes by is one week closer to the end of the rainy season.”
California gets about half its annual precipitation in December, January and February.
Fortunately for those worried about the slow start to the season, the arrival of rain is inconsistent as a rule. Most of the state’s precipitation comes from a handful of big storms, often called atmospheric rivers, which can move rainfall totals back to normal in a matter of days.
“We’ve seen some years where the rainy season didn’t kick off until January and we were still OK,” Halpert said.
Since the start of the rain year, measured between July 1 and June 30, San Francisco has seen 3.27 inches of rain, or 49 percent of average, according to the weather service. In December, 0.02 of an inch has fallen, barely enough to dampen the streets.
Southern California has been even drier. Los Angeles has seen just 0.18 of an inch since July, about 7 percent of average. Amid the arid conditions, fires have scorched some 400 square miles between San Diego and Santa Barbara this month. Hundreds of homes have been destroyed.
The San Joaquin Valley has been slightly better off. Fresno has received about a half inch of rain since July, roughly 22 percent of average.
The bright spot is well to the north. The eight-station precipitation index, which measures rainfall in the northern Sierra Nevada where much of the state’s drinking water comes from, is at 90 percent of average.
The other piece of good news, said Anderson, the state climatologist, is that most of California’s big reservoirs are still holding lots of water from last winter. This cache should satisfy water demands even if the weather remains dry, at least for a while, he said.
California’s woodlands and agricultural fields are a different story. Hundreds of millions of trees were killed or weakened by the drought, and forests and the wildlife that depend on them would benefit from rain. So would farmland that was fallowed because of water shortages.
Aquifers in the Central Valley, which were pumped so relentlessly over the past seven years that the ground sank, also need more rain to recover.
Meanwhile, snowpack in the Sierra stands at just 34 percent of average. The snow is important because it holds water that melts into reservoirs long after the rainy season has ended. It’s also invaluable for ski resorts, which were hit hard during the drought.
“I’m not too worried,” said Steve Anderson, a forecaster for the weather service in Monterey. “Even though the month of December has been dry so far, we still have time to make up the rain deficit.”