LOS ANGELES -- Every year for almost half a century, California snow surveyor Pat Armstrong has trekked the rugged Sierra Nevada with three simple tools: a snow core tube, a scale and a notebook.
For as long as he can remember, state water officials have relied on the accuracy of those tools to deliver crucial data on the size of the Sierra snowpack and its ability to sustain a growing population.
"It hasn't changed in 100 years," Armstrong said of the survey.
But there is a growing belief that this low-tech process alone is becoming too unreliable to accurately manage California's water needs.
A warming climate, experts and officials argue, has ushered in a new age of unpredictable rainy seasons and has caused the Sierra snowpack -- the state's largest naturally occurring reservoir -- to melt faster than ever before. Knowing how much snow is available is essential to maintaining California's water supply and minimizing flooding when the snow melts.
NASA now wants to take snow measuring into the digital age with SnowEx, a multiyear airborne snow study that uses a combination of high-tech tools to obtain precise estimates of how much water is contained in the snowpack, or the snow water equivalent.
The research will use airborne lasers and radar to measure the snowpack on a scale and elevation impossible to reach by foot. The data will reduce the need for water managers to generalize data over thousands of square miles of land.
Project partners, which include the European Space Agency and NASA's Jet Propulsion Laboratory and Goddard Space Flight Center, hope one day to measure worldwide snowpack by satellite.
"It's going to be a number of years ... but that is the dream," said Dave Rizzardo, water supply forecasting chief for the California Department of Water Resources.
For as long as Armstrong can remember, snow surveyors have trekked, skied and snowmobiled to spots thousands of feet high and miles apart, and carried with them what's known as a Mount Rose Sampler and a scale.
The sampler is recognizable in the hands of the state's chief snow surveyor, Frank Gehrke, who strides into a white meadow at Phillips Station near Lake Tahoe every April 1 and plunges the sampler deep into the powder.
The sampler is marked like a ruler on the outside to measure snow depth, while its hollow center digs out a "core" of snow. That snow is then weighed to determine how much water it contains.
"Manual measurements are still the backbone of the program and will be for the foreseeable future," Gehrke said.
The technique has worked for more than a century, state water managers say, but it's not 100 percent accurate. Since the surveyor must force the tube into the powder, the snow is compressed and oversampled by about 10 percent, said Ned Bair, a University of California, Santa Barbara hydrologist.
The sampler is used on some 250 "snow courses," or areas where folks like Gehrke and Armstrong will dip it into the snow 10 to 15 times over a 328-yard area.
The snow courses sometimes overlap with decades-old snow telemetry stations. These sites use ultrasonic sensors to measure snow depth and large, antifreeze-filled bladders, or "snow pillows," to measure the weight of snow gathered on top of them.
Snow telemetry stations aren't foolproof, though. They can be smashed by falling trees or avalanches, or damaged by curious bears. The stations also generate inaccurate data when ice forms over a pillow and causes inaccurate weight readings, Armstrong said.
Estimation errors have also become more frequent in recent years, because none of California's snow courses or snow telemetry sites are located above 12,000 feet -- a zone that is increasingly experiencing late-season snowmelt because of climate change.
Roughly 1.2 billion people worldwide -- 60 million of them on the West Coast of the U.S. -- depend on melted snow for water. Nearly a third of the world's surface is at one time or another blanketed in seasonal snow, and in California, the Sierra Nevada snowpack accounts for a third of the state's water supply.
Accurate forecasting gives the state's multibillion-dollar agriculture industry an idea of how much water farmers can anticipate in a growing season and lets water agencies know if they need to conserve water or release it from reservoirs. Ski resorts, white-water rafting companies and river fisheries all look to forecasts for hints on what conditions could be like later in the year.
But scientists and state officials say snow survey methods have failed to keep pace with a changing world. Extreme variations in precipitation tend to skew results, and climate change has altered the rate at which snow melts.
In a typical year, California's snow water equivalent estimates are accurate to within 10 percent, according to Rizzardo. In outlier years such as this one, however, that margin of error can reach as high as 20 percent to 25 percent.
SnowEx researchers chose a high-elevation, snowy plateau in Grand Mesa, Colo., and the Senator Beck Basin in the western San Juan Mountains to conduct their study.
By mounting various tools that measure snow depth, density and light reflection onto land-based equipment and aircraft, the study aims to find what combination gives the most comprehensive and accurate measurement of snow water equivalent.
Researchers used five aircraft to fly over the basins in tightly plotted, back-and-forth flight paths while zapping the snowpack with different wavelengths of radar and lasers to measure density, depth and ability to reflect light, said Thomas Painter, principal scientist of NASA's Airborne Snow Observatory.
Once the data are calculated, researchers will create estimates on the snow water equivalent.
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