Thursday, June 15, 2017

New Ways to Look at the Old Problem Measuring Snowpacks

This is a superb article about new methods to measure the water content of snowpacks. There are lots of variables and current snowpack surveys don't always capture them:
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% accurate. Since the surveyor must force the tube into the powder, the snow is compressed and over-sampled by about 10%, said Ned Bair, a UC 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 along a 300-meter path.

The snow courses sometimes overlap with decades-old snow telemetry, or SNOTEL, 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.

SNOTEL 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 SNOTEL sites are located above 12,000 feet altitude — a zone that is increasingly experiencing late-season snowmelt because of climate change.

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