Snowpack warming questioned

While the Western United States is in a warming trend, an apparent error in sensors at SNOTEL sites has inflated those numbers, a University of Montana researcher has found.

Jared Oyler of the Montana Climate Office examined temperature data from SNOTEL sites from 1991-2012 and found they had a temperature bias of 1 degree Celsius per decade, indicating warmer temperatures than actually existed outside.

Oyler said that while the results aren’t completely conclusive, it appears temperature gauges at more than 700 SNOTEL sites indicated temperatures of 33.8 to 34.7 degrees Fahrenheit which should have been 32, or freezing.

The number is significant when examining snowmelt regimes, he noted. When compared with other data, temperature changes in the past 20 years have actually been fairly flat, he said.

The temperature errors apparently began about 20 years ago when SNOTEL site sensors were replaced with ones better at measuring extreme low temperatures, Oyler said last week.

“Observations from other station networks clearly show that the western U.S. has experienced regional warming,” Oyler said. “But to assess current and future climate change impacts to snowpack and important mountain ecosystem processes, we need accurate observations from the high elevation areas only covered by the SNOTEL network. The SNOTEL bias has likely compromised our ability to understand the unique drivers and impacts of climate change in western U.S. mountains.”

The SNOTEL (Snow Telemetry) sites are administered by the federal Natural Resources Conservation Service. They are designed to remotely measure mountain snowpack for water forecasting.

Oyler said a long-term solution might be to install a more accurate temperature sensor, which is expensive and time consuming, or to create a model to correct the temperature bias.