Water & Drought

Rain, snow making a dent in California’s historic drought

Water at last rushes down to the Brown’s Ravine Recreation Area marina on Folsom Lake on Tuesday as a storm moved through the area.
Water at last rushes down to the Brown’s Ravine Recreation Area marina on Folsom Lake on Tuesday as a storm moved through the area. aseng@sacbee.com

The rain and snow falling across Northern California in recent days is by no means extraordinary. In the Sacramento region, precipitation remains below normal for the season. But inch by inch, forecasters say, it’s doing the work necessary if California is to reverse years of epic drought.

Since Friday, a series of storms have dropped close to 2.5 inches of rain in Sacramento, helping replenish reservoirs drained to historic lows last summer. More importantly, the storms have added to the snowpack blanketing the Sierra, a stark contrast to last year, which dawned with the state’s driest January in more than 100 years.

The last few days have brought more than 2 feet of snow to the high Sierra, even as warmer-than-average temperatures are resulting in rainfall at lower elevations.

January marks the beginning of storms associated with the powerful El Niño conditions in the Pacific Ocean, a phenomenon linked to above-average water temperatures along a stretch of the equatorial Pacific roughly twice the size of the United States. The warming leads to a shift in weather patterns that typically brings heavy rains, particularly to Southern California.

El Niño patterns also are associated with warmer temperatures, which can be a problem when it comes to breaking the state’s drought. While more than 75 percent of the demand for irrigation and drinking water is in the south state, the backbone of California’s water supply and delivery system – and most of its reservoir capacity – is in the north.

The infrastructure was built to take advantage of historic weather patterns, relying on ample spring runoff from Sierra snowpack to buoy the state’s arid interior through summer and fall. In a normal year, the snowpack provides 30 percent of the state’s freshwater supply.

The state’s drought crisis stems from a change in that pattern over the past four years. Last spring, Sierra snowpack was the lowest it had been in more than 500 years. State officials say the 2015 “water year” that ended Sept. 30 recorded the warmest high-elevation temperatures in the 120 years people have been keeping track.

This winter, by contrast, so far has brought more typical snowfall. State sensor readings Monday showed a range of snow water content across the Sierra, from 121 percent of normal in the northern range to around 90 percent of normal in the southern Sierra.

Much of the precipitation from Tuesday’s storm fell as rain in the lower mountains, as temperatures in the Sierra remain above historical averages. In Truckee, for example, low temperatures were about 15 degrees above normal on Monday and Tuesday, according to Weather Underground.

Even with some snowfall, experts were quick to note that it will be months before California knows whether the winter’s been a drought-buster.

“We made quite a dent, but the drought, it’s not over,” said Jim Mathews, a forecaster with the National Weather Service in Sacramento. “Most of the reservoir levels are still miserably low.”

Though water levels have risen in most state reservoirs in the past six weeks, lake levels remain far below historical averages, according to the Department of Water Resources. Folsom Lake had about 310,000 acre-feet of water Monday, more than double what it had in late 2015. But the lake is still at just 63 percent of normal for this time of year.

Among other large reservoirs, Lake Oroville is at 52 percent of normal; Lake Shasta is at 58 percent; and Trinity Lake is at 33 percent.

Reservoir levels are among the factors state officials consider when determining when to declare an end to drought. Mountain snowpack is another.

State officials say at least one of three things would need to happen for the drought to be at an end: Statewide reservoir storage would need to be at 90 percent of average levels; runoff forecasts for the state’s water year, which runs from October to September, would need to be 110 percent of average; or reservoirs on the four major rivers in the Sacramento River basin would have to reach flood control stage.

In the lower elevations, so much rain fell Tuesday that forecasters briefly issued a flood advisory for much of the Sacramento region. As of Tuesday, about 8.5 inches of rain had fallen since October. That’s about 90 percent of normal.

The return of heavy rains has meant a busy couple days for Sacramento tree service technician Matt Morgan. He’s responded to calls of toppled trees whose roots failed in the suddenly soggy soil.

“I’ve been from Lodi up to Yuba City out to Folsom the past two days and everywhere in between,” said Morgan, an assistant manager for Davey Tree Expert Co. “It’s been a hectic two days, I tell you what.”

Morgan may have an equally busy weekend ahead. Forecasters say another inch of rain could fall in the region when a storm hits Friday. The same storm could bring up to a foot of snow in the Sierra.

Ryan Sabalow: 916-321-1264, @ryansabalow

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