News•October 23, 2014

What Will Winter Hold for Drought-Plagued California?

California really needs this winter to be a wet one.

The state is now at the beginning of the fourth year of one if its worst droughts on record. The drought has been fueled by a spate of disappointing winter rainy seasons that have left meager snowpacks and diminished reservoir levels, combined with record-warm temperatures that have driven demand for the increasingly precious resource, and spurred a series of conservation measures around the state.

Shasta Lake, the largest manmade lake in California, was at 36 percent of capacity when this photo was taken in January 2014. As of Sept. 28, it was at 26 percent of capacity.
Credit: USGS/Angela Smith

Hopes that the coming winter could finally bring some relief were raised when the first murmurs of an impending El Niño began to emerge in March. The climate phenomenon can be associated with amped up rains in the southern part of the state, and so the words “El Niño” became something of a mantra across the parched lands.

“People have latched on to the notion that El Niño will bring about relief,” California state climatologist Michael Anderson told Climate Central. “That seems to be something they’ve grasped onto quite firmly.”

But this winter likely won’t be the one Californians so desperately need, as the budding El Niño is expected to only be a weak event and unlikely to do much to bolster those dwindling water reserves.RELATEDCalif. Heads for Warmest Year As Drought Hangs On
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However, that news doesn’t necessarily mean that this winter will be as dire as those of recent years past — though that’s a possibility. By virtue of not being under the drying influence of El Niño’s counterpart, La Niña, it’s also possible that California will at least see a wetter winter than they have in the past few years, the first step on the path out of the drought.

“We can’t rule anything out,” said Michelle L’Heureux, a meteorologist with the Climate Prediction Center, part of the National Oceanic and Atmospheric Administration, who helps put together monthly El Niño outlooks.

California’s predicament

The drought that now has California in its iron grip didn’t happen overnight, and no matter what happens this winter, it won’t end overnight either, experts say.

The dry conditions have accumulated over the past three years, but really began to metastasize across the state this past winter. Coming in to the season, California had just seen its driest year on record, with some cities measuring precipitation deficits of 30 to 40 inches.

California generally gets about half of its precipitation (in the form of both snow and rain) from December to February. Most of it falls as snow in the Sierra Nevada range, and this portion is critically important, as it provides a sustained flow into reservoirs for much of the state when it gradually melts in late spring and early summer.

But the 2014 water year, which ran from Oct. 1, 2013, to Sept. 30, 2014, “has been one of the driest in decades and follows two consecutive dry years throughout the state,” according to the California Department of Water Resources. The past three years are the driest such stretch on record in the state, Kevin Werner, the western regional climate services director at NOAA’s National Climatic Data Center, said during a NOAA teleconference earlier this month.

The 3-year precipitation record for California for 2011-2014 compared to the 30-year average.
Click image to enlarge. Credit: NOAA

As the rain and snow failed to fall this past winter, the drought spread its tendrils. At the beginning of December 2013, while almost the entire state was in some stage of drought, none of it was in the worst stage recognized by the U.S. Drought Monitor, exceptional. By April 1, 2014, one quarter of the state was in exceptional drought, and two-thirds was mired in the two highest categories, thanks to the tremendous precipitation deficit.

While late spring and summer are typically dry in California, drought can still spread in those months as the heat increases water usage among the state’s large population and ramps up evaporation. And spread it did, as the state experienced heat wave after heat wave in what is shaping up to be its warmest year on record. Currently, a stunning 58 percent of California is in exceptional drought, and more than 80 percent is in the worst two categories.

That is why the possibility of an El Niño-fueled wet winter is gripping California’s collective imagination.

Hopes hard to quash

The El Niño phenomenon is marked by unusually warm waters in the eastern and central tropical Pacific Ocean. The warm ocean in turn impacts the circulation of the atmosphere, and can alter weather and climate patterns around the globe. El Niños, for example, typically quash the Atlantic hurricane season, while boosting global temperatures.

Not long after the CPC and their partners at Columbia University’s International Research Institute for Climate and Society declared an El Niño watch in March, a plume of very warm water worked its way across the tropical Pacific, drawing comparisons to the monster El Niño of 1998, which brought a series of February storms streaming across California, causing flooding and mudslides and breaking precipitation records.

That comparison — coming at a time when it was actually far too early to reliably say anything about the likely strength of the coming El Niño — still buoyed the spirits of Californians.

But in the intervening months, that surge of heat hasn’t been sustained and it has become increasingly clear that this El Niño, if and when it forms, is unlikely to be a strong one, let alone come close to the record-breaking 1998 event.

Alan Haynes, a service coordination hydrologist at NOAA's California-Nevada River Forecast Center, said during a September press briefing that looking at all of the El Niño years on record and the precipitation associated with them, “it really takes a strong El Niño” to get “drought busting” rains. “Weak and moderate El Niños end up not getting you the precipitation you need to end the drought,” he said during last month’s briefing.

Still, residents have clung to the possibility that El Niño might change their precipitation fortunes, Anderson said.

When he goes out into communities to do outreach work and encounters people who say they’re just waiting for the El Niño, Anderson, the state climatologist, tries to set them straight. He explains that both California’s wettest and driest years in the past six decades have been associated with an El Niño, so “just saying it’s an El Niño year doesn’t really tell you anything,” he said. But still El Niño has stayed on people’s minds as winter approaches.

Wet winter?

So, what can California expect this winter? Good question, and one even forecasters can’t yet definitively answer, as seasonal forecasts are notoriously tricky.

With no strong El Niño or other climate signals to help guide them, forecasters don’t know what to expect for precipitation. In its recently released winter outlook, NOAA gave most of the state equal chances of above- or below-average rainfall. (A small part of Southern California does have increased odds of above-average rains.)

“We don’t know if it’s going to be a wet year or not,” Haynes said.

If it does turn out to be a strong El Niño, that only has a significant relationship to Southern California precipitation — not the snows that fall in the north and that are so critical to recharging depleted reservoirs.

To completely make up for the missing rains of last season, the state would need two winter’s worth of rain over this wet season, which is unlikely. It will most likely take years for California’s reservoirs to reset, making the mandatory water restrictions that many cities have adopted all the more necessary to ensure that there is enough water to get the state through the next few years of recovery.

Right now, with the expected weak El Niño, the best California can hope for this winter is that some storms materialize in November “that kind of wet the watershed up a bit,” Anderson said. Those storms would provide a base to support later rains and snows by moistening the underlying soils. (A system is expected to bring rains and snows to the Pacific Northwest this weekend, including parts of Northern California, especially near the coast.)

Expected trends in precipitation during the 2014-15 winter.
Click image to enlarge. Credit: NOAA

Then regular storms throughout the winter could bring further moisture — but you don’t want too much at once, as torrential rains falling on drought-hardened soils tends to run off and cause significant flash flooding.

The difference such storms can make can be seen when looking back at one of the few bright spots of last winter, when “atmospheric rivers” brought rains late in the season “and you can see the temporary improvement that they noted” on the Drought Monitor map, Anderson said. Of course once the rains stopped, those areas fell back into the drought’s clutches.

There is some hope that these atmospheric rivers could be more frequent this winter than they have been in recent ones, as warmer Pacific waters will likely cause a high pressure system that hangs out over the subtropics to be weaker than normal, said climatologist Kevin Trenberth, of the National Center for Atmospheric Research in Boulder, Colo. That weakening lets storm systems wander farther south than they have been lately, meaning precipitation for California.

Because of that potential setup, “I think that some relief is likely,” Trenberth said in an email.

And, of course, the situation could turn out to be better than expected, because “El Niño is not the only game in town,” said Mike Halpert, the CPC’s acting director, during the winter outlook briefing.

Other climate forces could play a larger role in California’s winter precipitation than forecasters currently think, allowing for rains up and down the coast. “An above-average rain season . . . is not out of the cards,” he said.

It’s not the favored outcome this winter, but it’s one of the best the state can hope for, Halpert said.

Even if climate forces align and bring about these best-case scenarios, the state is still in for a long recovery. Given the sheer magnitude of the drought, as Halpert said, “there’s still going to be large parts of drought in California when the winter’s over.”