News•December 18, 2014

Rain a ‘Start’ for Calif., But Drought Entrenched

So there’s good news and there’s bad news on the California drought.

The good news is that recent rain has finally started to chip away at the severe precipitation deficits the state is facing. The bad news is that most of California is still in a deep drought and it’s going to take a long time to fully recover.

Precipitation totals (in inches) for the western U.S., including California, over the past 60 days.
Click image to enlarge. Credit: NOAA

Or, to quote the summary from Thursday’s U.S. Drought Monitor update: “Cautious optimism, but still a long way to go.”

The drought has been one of the major weather and climate stories this year, as a disastrously dry winter wet season failed to recharge the state’s water system, and then record-high warmth quickly melted the meager snowpack while also driving up demand for water, drawing down reservoirs and sucking up precious groundwater.

Desperately needed rain finally began to spatter drought-baked soils this fall, as the Ridiculously Resilient Ridge of high pressure that had kept storms away slackened. A few respectable storms dropped modest rain and snow in October and around Thanksgiving. And then, last week, the taps turned on full-force.

Parts of Northern California were drenched by rain, with precipitation exceeding 10 inches as a “Pineapple Express” atmospheric river siphoned tropical moisture and dropped it over the region. More importantly, that atmospheric river — which, as its name suggests, is a stream of moisture-laden air — dumped significant snow on the Sierra Nevada Mountains.

The Sierra snowpack is critical to California’s water system — that snow gradually melts come spring and summer, with the water trickling into streams, rivers and reservoirs, upon which the state’s residents and agricultural industry depend.

After rains drench the state, California saw a one-category improvement in its drought across parts of the northern portion of the state.
Click image to enlarge. Credit: U.S. Drought Monitor

Overall, the spate of storms has resulted in about 30 inches of precipitation over parts of Northern California in the past two months, Kevin Werner, the western regional climate services director at NOAA's National Climatic Data Center, said during a NOAA teleconference Thursday.

He called that “a really healthy start to the water year.”

And that’s music to the ears of Californians.

With that influx of water, the Drought Monitor upgraded a large chunk of Northern California from “exceptional” drought (the highest of their five categories) to “extreme.” So that’s better, but still not good.

The reason conditions are still so stark is that this drought is historic in its proportions. According to a study published recently in the journal Geophysical Research Letters, which looked at the records of drought in the growth rings of California trees, this is the most severe drought there in the past 1,200 years.

The depth of the drought has been due to a combination of lack of precipitation and exceptionally warm temperatures. The driest year the state has ever recorded, 2013, has been followed by what will be its warmest year on record by a wide margin.

Like the globe as a whole, California has seen temperatures rise with the human-caused buildup of heat-trapping greenhouse gases in the Earth’s atmosphere. While warming has played a role in the heat aspect of this drought, its exact influence on other aspects of the drought — which is always a complex phenomenon — is an active area of research.

The change in groundwater levels across California during it's three-year historic drought, from September 2011 to September 2014.
Credit: NASA JPL

But what’s certain is that California is in a deep, deep precipitation hole — to the tune of a deficit of 30 to 50 inches in the Sierras, or about a year’s worth of precipitation, Werner said.

Without rain and snow, water levels in reservoirs have fallen dramatically. Lake Shasta, the state’s biggest reservoir, has seen a stunning decline over the past three years.

“Each year it’s gone down dramatically from the previous year,” Werner said. The recent rain has caused a small uptick in water levels, “so you can see that there’s been some healthy rises,” he said. “But it’s got a long, long way to go.”

With so little water in above-ground reservoirs, residents have turned to the water stored by nature underground. A new NASA satellite analysis presented at the annual meeting of the American Geophysical Union in San Francisco this week found that the state has lost 11 trillion gallons of groundwater since 2011. The Central Valley alone has lost enough groundwater to fill Lake Mead, the largest reservoir in the country, the scientists behind that work said.

That water has been building up for millennia, meaning it will take a long time to replenish, much longer than streams and lakes.

But, as some added good news, both January and the winter as a whole look to have better chances of above-normal precipitation for much of California, though one wet winter won’t erase the drought.

“The recent storms we’ve seen have been helpful, but again we’ve got a long, long way to go,” Werner said.