Tracking the snowpack
GIN FLAT, CALIF. -- — In deep winter, water scientist Frank Gehrke straps on his cross-country skis and trudges uphill in the thin, cold air to one of the most closely monitored frozen meadows on the continent, 7,200 feet above sea level in the Sierra Nevada.
To understand why his arduous, breath-sucking hike is important, stand still and listen to the snow. In the pale morning sun, the forest of pine and cedar comes alive with sound. Clumps of fresh powder fall with a thud or drip-drop from tree tops, quickening with the staccato of popping corn.
This place is like a Rosetta Stone for California’s water supply. It’s where the convergence of snow, sun and temperature enables scientists to predict floods or drought. It’s where they have installed sophisticated equipment to help understand how climate change is altering snow melt in the Sierra, a source of water for millions of Californians.
“Gin Flat’s always been the place where we try things and invest first,” said Michael D. Dettinger, a U.S. Geological Survey hydrologist based at Scripps Institution of Oceanography in La Jolla.
Although the state oversees more than 300 survey sites, what makes Gin Flat unique is its location, an elevation in Yosemite National Park just above the point where rain commonly turns to snow. That makes it an ideal spot to test the premise that a warming climate will produce more rain at higher elevations -- a shift that would bring more flooding and less snowpack to fill California reservoirs in mid-summer.
These days, with water woes plaguing the state, readings at Gin Flat will ultimately help determine how much more it could cost Californians to drink a glass of water or take a shower, or if they can water lawns without restrictions.
That is why Gehrke, 60, didn’t hesitate to ski three miles up the mountain last week, hauling a sled loaded with 60 pounds of fuel cells and tools. He is California’s snow survey chief, a man respected as the don of the Sierra snowpack. As caretaker of Gin Flat, he needed more power to fuel all the equipment at the site he helped develop.
Last week, his agency, the state Department of Water Resources, reported that Sierra snowpack was at 118% of normal for this date, compared with 63% of normal at this time last year, the driest year on record for Los Angeles.
But Gehrke is a cautious man, and never more so than when explaining snowpack surveys.
“We could slide back to below average. A March without snow could do it,” he said. “A lot of the reservoirs are pretty low from last year.”
That would be bad news for Southern California, which depends heavily on imported water, about half from northern mountains and the rest from the drought-stressed Colorado River. Further straining supplies, a court decision protecting a rare fish in the Sacramento-San Joaquin River Delta has reduced deliveries to the south by 30%. To comply with court stipulations, state officials last week cut southward flow for seven days by 75% of normal.
Amid fears of shortages, water rates probably will rise. Directors of the region’s water wholesaler, the Metropolitan Water District, will vote March 10 and 11 on a proposed 14.3% rate increase starting Jan. 1, 2009, in part to buy extra water. More rate increases are expected in 2010 and 2011.
Worried state and local officials look to data from locations like Gin Flat for assurances that the Sierra will continue to provide a steady stream of water to keep the economy growing and water rates low.
Gehrke cannot offer the certainty they crave, he said one morning last week over a hearty eggs-and-hash-browns breakfast at a restaurant en route to Gin Flat. He is not one to speak in sweeping terms. His tone is matter-of-fact.
“When it’s wet or dry, people go out and get into hyperbole about how much snow they’ve seen,” he said
“We always think it’s good to keep things grounded and not get carried away by the moment.”
He is more cautious about climate change predictions. Yet, he is concerned about how snowpack levels have become erratic during his 27 years of measuring. It was thick in 2005-06, extra-thin last year and is slightly above normal so far this winter.
“A lot of people I really respect say you’re going to see a lot more of this,” he said.
Gehrke and other scientists have equipped 11 sites in Yosemite with high-tech monitors, turning one of America’s most famous parks into an electronic snow laboratory.
Gin Flat, east of the park’s Big Oat Flat entrance, is named for a long-gone speak-easy. It provides a snowpack record dating back to 1930 that makes today’s data even more valuable.
In this outpost, devices measure the weight and temperature of snow, the strength of the sun rays heating the snow and the moisture in soil under the snow. Sonar-like sensors test the depth of the snow. Results from Gin Flat are reported hourly and transmitted every three hours to Virginia and then back to Sacramento.
Those results are reshaping how scientists look at snow.
Research scientist Bob Rice, for instance, is preparing a paper based on Gin Flat data that shows conventional measuring methods are overestimating the water content of snow by 20%.
For water managers, that’s like overdrawing a savings account by 20%.
“That 20% can make you or break you in a given year,” said Rice, of the Sierra Nevada Research Institute, part of UC Merced. “If we overestimate by 20%, then we have given out more water than we actually have.”
At Scripps, Dettinger used Gin Flat data to discover that snowmelt is penetrating Sierra Nevada granite and seeping deep into the ground, work that helped to track where the water goes.
As the earth warms, “It will be there in the summer when we and the fisheries and the forests need it,” Dettinger said.
But last week, all this high-tech, far-reaching science came down to a man and his sled.
Because this is a federal wilderness area, snowmobiles are banned.
To reach Gin Flat, scientists must make the 800-foot ascent on skis or snowshoes.
Gehrke stripped off his fleece jacket as he trudged upward with the sled-harness around his waist, breaking trail in fresh powder for more than three hours.
Time raced by, and with each strenuous step, pine shadows grew longer. Gehrke decided to stash the generator and fuel cells at midafternoon and, unburdened, skied the rest of the way to inspect Gin Flat.
He had underestimated how hard it would be to haul 60-pounds of technology by himself. He’ll be back this week to retrieve the generator and install it. He’ll return in early April to help UC Merced students use probes to make hundreds of depth measurements of the snowpack.
And when the snow disappears, he will hike up to mend a wood-shingled instrument hut mangled by bears.
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