News•February 3, 2014

Time is Running Out for California Drought Relief

The California drought, now reaching into its 13th month, grows more devastating with each passing day and there is no sign of significant relief in sight.

More than halfway through the state's wet season and the Sierra Nevada snowcap all but non-existent, California's prospects for making up its precipitation deficit are slim. The snowcap will yield precious little water and the state would need to get an average of about a foot or more of rain in the next two months to make up the difference. Forecasts are not offering much hope of that.

Comparison of the water content in California's mountain snowpack so far this year, compared to the state's wettest and driest years. (The data is divided by region.)
Click image to enlarge. Credit: Climate Central using CDWR data.

The California drought reached another grim milestone on Friday when the state announced that for the first time in the 54-year history of the State Water Project it may not be able to allocate water to the nearly 25 million Californians who depend on the vast system of dams and reservoirs for supplemental water supplies. The Department of Water Resources also said it planned to reduce allocations to farmland by 50 percent, the maximum extent allowable by law.

The State Water Project provides supplemental water to two-thirds of the state’s population and about 750,000 acres of farmland, according to the California Department of Water Resources.

“If we are to have any hope of coping with continued dry weather and balancing multiple needs, we must act now to preserve what water remains in our reservoirs,” Mark Cowin, Department of Water Resources director, said in a press release. Officials said the communities that depend in part on the State Water Project’s water also have other sources, so the potential for a zero allocation does not mean that taps will run dry.

The stakes are high for California, the country’s most populous state with 38 million residents. It has a $44.7 billion agricultural industry that generates more than $100 billion in related economic activity. California produces nearly half of all U.S.-grown fruits, nuts, and vegetables and it is the leading dairy state. The state’s farm cash receipts in 2012 were $13 billion more than that of Iowa, the No. 2 agricultural state. Because California farms depend heavily on irrigation to sustain production during the dry season, drought constitutes a dire threat to the state’s economy.

The federal government has designated nearly 9 percent of the state as being in “exceptional drought,” the worst category. It’s the first time in the 15-year history of the Drought Monitor that any California territory had reached that status. Longer-running records indicate the 13-month drought, which is part of a 3-year dry period, is equal to or worse than any other short-term drought and is among the top 10 worst droughts to hit California in the past 500 years, based on tree-ring records and instrument data. The drought is part of a broader Western drought that has lasted for roughly 13 years, raising the specter of a modern-day “megadrought” akin to events that doomed some ancient civilizations.

The National Weather Service’s Climate Prediction Center is forecasting a continued likelihood of drier-than-average conditions across much of California through the months of February and March, which are typically the last two months the state sees widespread heavy precipitation before the dry season sets in.

Drought Monitor map of California, showing the area of “exceptional drought” conditions in dark red.
Credit: U.S. Drought Monitor.

According to Victor Murphy, a NWS meteorologist in Dallas, the month of February has not been kind to California during the past two years, and offers little hope of relief this year, either. “The past two Februarys have cumulatively been the third driest back-to-back Februaries on record,” Murphy said in an email conversation. “A third consecutive dry February would be devastating.”

A dry February would put all the pressure on receiving abundant rainfall and mountain snow during March in order to avert a water crisis this summer, and it becomes far less likely that an entire wet season’s worth of water will come in such a short timespan. As a sign of the pessimism across the state, water restrictions in many communities are already going into effect.

Looming on the horizon is the prospect of a wildfire-filled summer with a perfect storm of water management challenges as the state’s competing water users, from dairy farmers to residents of downtown Los Angeles, clash over access to a diminished supply. Already this winter, wildfires have been running far above average.

In 2013, California saw a greater number of wildfires compared to the 2003-2012 average, but fewer acres burned than average. Climate change has been linked to increased wildfires in the Western U.S., particularly an increase in the frequency of large wildfires in California and other states.

Once February and March roll past, California typically sees a dropoff of about 50 percent in rainfall amounts between March and April, Murphy said. That makes the next two months a make-or-break period. “It’s safe to say they’re on the clock,” Murphy said. “The clock runs out on April 1.”

Blame the “resilient ridge”

The current drought began in January of 2013, Murphy said, when the spigot of Pacific storms suddenly shut off, but at the time, the state had accumulated enough of a snowpack from a wet fall and early winter to make it through the dry season. But following the driest calendar year on record since 1895, and with a snowpack water content that as of Jan. 30 was just 12 percent of average for this time of year (a record low), the state has little, if any, such reserve to fall back on this year.

“Now more than ever, we all need to save every drop we can in our homes and places of work,” Cowin said.

Water managers are facing the most serious crisis since 1976-77, when drought conditions forced the state to institute a new system of water management policies. This current drought, Murphy said, will provide a “true test” of whether the mechanisms established then will work despite considerable population growth and agricultural sector expansion.

The proximate cause of the drought is a weather pattern that has been dominated by an unusually intense and persistent area of high pressure off the coast of British Columbia. This feature has acted like a traffic cop at an intersection, rerouting storms northward into Alaska and helping to direct several shots of extremely cold, Arctic air southward into the lower 48 states. Most pertinent to California, it has left the state unusually warm and dry.

Tomatoes are one of California's most valuable crops.
Credit: California Department of Water Resources.

The warmth is worsening the drought conditions, with several all-time monthly high temperature records broken, including in the state capital of Sacramento, which reached 79°F on Jan. 24, breaking the previous warmest January high temperature by 5°F. Such high temperatures dry soils faster and lead to steeper moisture deficits.

The high pressure area, known to meteorologists as a “resilient ridge” of high pressure, is likely to remain roughly in place through March, said Jon Gottschalk, the head of forecast operations at the Climate Prediction Center in College Park, Md., in an interview. Gottschalk said computer models show the high pressure area weakening and shifting for short time periods in the next two months, which could allow some storminess to reach California, but that overall the dry setup is likely to endure.

Elusive broader explanation for dry weather pattern

A mystery facing meteorologists and climate scientists, though, is why this resilient ridge of high pressure occurred in the first place.

Some of the suspects include the Pacific Decadal Oscillation, which is a natural climate cycle involving the ocean and atmosphere in the Central and Northern Pacific Ocean, and the current absence of La Niña and El Niño conditions in the Pacific as well. Some emerging research suggests that global warming may be making such blocking areas of high pressure stronger than they otherwise would be in some regions of the world, although other research has found a decrease in blocking events in areas like the North Atlantic, which makes for an unclear picture overall.

Kevin Anchukaitis, a scientist at the Woods Hole Oceanographic Institution in Massachusetts, said that high pressure areas lurking to the Northwest of California during the cold phase of the Pacific Decadal Oscillation have favored drought conditions there in the distant past.

“My impression is that’s not an uncommon configuration to result in California drought,” Anchukaitis said.

Scott Stine, a geography professor at California State University at East Bay, told Climate Central that the weather pattern during the wet season to date may be similar to what led to long-lasting drought conditions in California during medieval times.

Stine’s research has revealed a history of extreme and persistent drought in California, which, he said, should be a warning for water managers who think another back-to-back dry year is unlikely to happen. The first such drought period lasted from about CE 850 to CE 1090, Stine said, with the second one occurring from about CE 1140 to CE 1320.

Stine said there is some evidence that the moisture that did not make it to California during those extended droughts was instead re-routed to Alaska, much as it has been this winter. Record rainfall in parts of Alaska have led to large avalanches that cut off Valdez, Alaska, from its only road link.

“We may be seeing over the last year or so, the very synoptic (atmospheric) circulation setup that we saw during the medieval climatic anomaly,” he said.

But the key difference between the droughts that stood out from Stine’s research and the current event is the duration. The most severe period of the current drought has lasted 13 months so far, Stine said, whereas past “megadroughts” in the region lasted for seven decades or more. However, when looking at the West overall, the region has been in a drought for about 13 years, which could qualify as a megadrought, said Benjamin Cook, a climate scientist at Columbia University’s Lamont-Doherty Earth Observatory in Palisades, N.Y.

Drought had sudden origins, could it have a sudden end?

Although the forecasts don’t offer much hope for drought relief, a sudden end to the severe drought is possible. In fact, it may be normal for California droughts to end suddenly.

Research by Michael Dettinger, a hydrologist for the U.S. Geological Survey and the Scripps Institution of Oceanography shows that about 33 to 40 percent of California droughts were ended by intense storms known as “atmospheric river” events, which can produce copious amounts of precipitation across relatively narrow areas of the West.

Satellite image of Central California, showing the nearly barren Sierra Nevada Mountains, just barely exhibiting some snow cover (in white).
Click image to enlarge. Credit: NASA.

Atmospheric rivers are corridors of air laden with moisture that can stretch for thousands of miles long, and are only about 300 miles wide. A majority of the West’s heavy precipitation and flooding events have been associated with atmospheric rivers.

Dettinger’s research, which was published in the December issue of the Journal of Hydrometeorology, found that atmospheric river events can effectively end even major droughts in California within just one month. In fact, Dettinger found that most droughts in the West end abruptly, with one very wet month pulling the state from a significant precipitation deficit to a surplus.

That would seem to offer some hope for the Golden State, but the same study shows there is also reason for concern.

The study found that atmospheric river events are most common in California during the November-through-March period, with the probability dropping off considerably beyond that.

In other words, the study also found that the clock is ticking down to April 1.

Global warming’s impact

Anchukaitis said past megadroughts have occurred naturally, which indicates they can be triggered again simply by natural climate variability. “When we look back at the past and we see these megadroughts, they don’t necessarily respond to some kind of forced response of the climate system,” he said. “They just sort of happen.”

Manmade climate change, however, is likely adding to the problem of drought conditions by increasing temperatures, which increases the evaporation of water from plants, soils, and reservoirs, thereby worsening drought. Studies show that although global warming may not trigger drought conditions, it is likely already exacerbating them and is more likely to worsen them in the future.

Cook has a forthcoming study in the journal Climate Dynamics that quantifies the effects of global warming-related impacts on evaporation, which found that in Western North America, global warming will “almost certainly . . . amplify droughts in the future and amplify their impacts,” he said. He said this is likely already occurring in the West, but that it’s difficult to quantify.

What isn’t hard to quantify, however, is how desperate California’s plight is and just how critical the next two months are in determining the state’s fate in the face of increasingly bone dry conditions.