December has been bone dry in California, and it doesn’t look like it’s going to get much wetter by the time the 2018 rolls around.
Precipitation levels in Sacramento and most major California cities are below average for this time of year. The Sierra Nevada snowpack is just 37 percent of normal. The U.S. Drought Monitor says about one-third of California is either facing moderate drought conditions or is abnormally dry, with all of the dry areas lying south of the Sacramento-San Joaquin Delta. Extraordinarily arid conditions have helped fuel the wildfires in Southern California, where rainfall has been almost nonexistent. Arizona, Utah and parts of Nevada are also drier than usual.
With no rain or snow in the immediate National Weather Service forecast, it looks like December will be “kind of a bust, for the first of our three big months of precipitation,” said State Climatologist Michael Anderson. “That’s enough to get us paying closer attention.”
Still, climate experts and hydrologists say it’s way too early to sound the alarm about a new drought. Thanks to a wetter-than-usual November, total precipitation in Northern California is actually close to average for this time of year. Most of Northern California’s reservoirs, which are critical to keeping water flowing to cities and farms across the state during spring, summer and fall, are in good shape because of last winter’s record-breaking rain and snow.
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“Having as wet a winter as we did last year offers some buffer heading into this year,” Anderson said.
Plus, experts say, it’s not uncommon in California’s boom-and-bust wet seasons to have long periods of dry weather and still head into the summer months in decent shape. The winter of 2010-11 was extremely wet despite a lengthy dry spell. “Right in the middle of that year, in January and early February, there were six weeks with virtually no precipitation at all,” said Daniel McEvoy, climatologist with the Western Regional Climate Center in Reno.
California’s water years can be maddeningly difficult to predict. The reason is that California depends heavily on atmospheric rivers – heavy storms caused by high-powered winds dragging tropic moisture across the Pacific Ocean. Just a few of these storms, sometimes called “horizontal hurricanes,” can fill the state’s reservoirs, blanket the Sierra Nevada with snow and make the difference between a dry winter and a wet one.
A series of atmospheric rivers last winter produced the wettest season on record in Northern California, culminating with Gov. Jerry Brown declaring an end to the drought after five years.
This rainy season has been particularly confusing. The state Department of Water Resources’ closely-watched 8-station index, a series of gauges across the northern Sierra, has recorded 12.3 inches of rain and snow, or 94 percent of average. But the sensors that measure the Sierra snowpack, which generally are at higher elevations, show the snowfall has been well below normal.
David Rizzardo, chief of snow surveys and water supply forecasting at the Department of Water Resources, said in an email that the November storms were generally warm, resulting in a lot of rain but little snow. That distinction can prove critical. A healthy snowpack serves as the state’s largest reservoir as water melts and drains into the Central Valley during the long dry season.
Meanwhile, cities have been relatively short of rain. Sacramento has gotten just 56 percent of its normal rainfall for this date; Fresno is at 16 percent. Los Angeles is at 4 percent and has received just 0.01 inches of rain since the “water year” began Oct. 1.
The big X factor this winter has been the presence of a La Niña weather pattern, in which cooler ocean temperatures can produce relatively dry winters, particularly in the southern half of the state. The National Oceanic Atmospheric Administration said last month that long-term forecasts are pointing to a La Niña pattern this season that’s likely to bring “below-median precipitation across the southern tier of the United States.”
What’s more, a study by the University of Texas Institute for Geophysics suggests that back-to-back La Niña winters can produce even drier weather in the second year. California experienced La Niña last winter, despite all the rain.
The impact in the second year “on average ... tends to be stronger,” said Yuko Okumura, a research associate at the university and co-author of the study. But she added that “predicting each year’s impact can be very challenging.” Her research was published in the scientific journal Geophysical Research Letters.
With the Christmas holiday approaching, the relatively thin snowpack has forced the Sierra ski resorts to rely heavily on snow-making equipment. Some are still waiting to open for the season, such as Royal Gorge in Soda Springs, where the snow line is about 1,000 feet above the resort’s cross-country trails.
“We just need more snow at lower elevations to get things going,” Royal Gorge officials said on the resort’s website.
Most other resorts are doing better. “Luckily, the storms in late November provided a good base for many resorts to open, and the cold weather has enabled them to keep that snow (and whenever they can, make more),” said Mike Reitzell, president of the California Ski Industry Association, in email. “We are, however, very hopeful for additional snow before the holidays, a very important time for our resorts. Every season is different, and it looks like this one is just going to start off a little slower.”
Californians are continuing to feel the impact of the drought even though it’s officially over. Multiple cities still have outdoor watering restrictions in place. Sacramentans are limited to one day a week, for example.
And the state’s historic drought is still torturing the state’s forests. The U.S. Forest Service this week said that an additional 27 million trees, mostly conifers such as pines and firs, have died in California since November 2016. That brings the total number of trees that have died because of dry years and insects that prey on drought-weakened forests to 129 million.
Most of the problem is in the central and southern Sierra.
“The number of dead and dying trees has continued to rise, along with the risks to communities and firefighters if a wildfire breaks out in these areas,” said regional forester Randy Moore. “California’s trees have not yet recovered from the drought, and remain vulnerable to beetle attacks and increased wildfire threat.”