Ученые определили феномен «снежных пожирателей»: тепловые волны, ускоряющие таяние ледников и повышающие риск пожаров

This story was originally published by  Grist. Sign up for Grist’s  weekly newsletter here. Matthew LaPlante doesn’t have to go to a lab to see his research in action. On some mornings, he can just look out his own window in the mountains high above Salt Lake City. After a warm night when the temperature stays above freezing, he’ll wake up and see that the snow level has dropped by inches, revealing more of the aspens he taps for syrup. “It feels like a monster came and just in the middle of the night, took a bite out of a snowpack,” said LaPlante, a journalist and climate scientist at Utah State University. So it’s fitting that scientists have started calling these kinds of heat waves, marked by unusually high temperatures in the spring and early summer, “snow eaters.”  LaPlante was part of  a recent study, published in the journal Science Advances, that attempted, for the first time, to identify what conditions exactly make for a “snow eater.” Compared to normal warm spells or heat waves, the researchers determined that these events happen when temperatures stay above freezing through both day and night for multiple days, typically three to five. These events can roughly double the rate at which snow melts, causing flooding and making it challenging to manage water resources.  “Snow eaters” appear to be occurring earlier in the year and becoming more widespread in the Western United States as the climate warms. Since the 1850s, the study found, the area affected by snow eaters has increased by an average of about 40,000 square miles per century, and the first snow eater of the season has been arriving about one month earlier per century.  The term “snow eater” has  a murky history. By at least the 1880s, people in the West were talking about “snow-eating” chinooks, warm mountain winds that make snow disappear quickly. More recently, the phrase “snow-eater heat wave” first made  headlines  in March, when an early heat wave  enveloped much of the West, quickly wiping away snowpack in  the Colorado Rockies and California’s Sierra Nevada. The scientists hope the catchy, evocative term can help draw more attention to this type of heat wave, since there’s still a lot to learn. The study only looked at the Western U.S., but snow eater heat waves almost assuredly occur elsewhere, LaPlante said. Solar radiation is a major, but sometimes overlooked, driver of snowmelt, said Noah Molotch, a professor of geography at the University of Colorado Boulder who was not involved in the new study. When it interacts with heat waves, those impacts are amplified. As snow crystals warm up, they  lose some of their structure and light-reflecting abilities, causing snowpacks to absorb more sunlight and melt faster. “It’s a little bit of a — no pun intended — a snowball effect,” he said. Much of the Western U.S. saw  record-low snowpack  this spring. What was really unusual about it, Molotch said, was how widespread it was. Colorado received less precipitation than normal this winter, while California got lots of precipitation, but in the form of rain instead of snow. But across the region, “the one thing in common was above-average air temperatures,” Molotch said. These conditions have likely helped fuel exceptionally severe wildfires in the West, from Utah to Spokane, Washington, where  hundreds of homes burned earlier this month. “Drought stress for mountain forests around the Western U.S. is heavily dictated by the snow that accumulates each winter and then melts through the spring and summer,” Molotch said. “There is a direct connection there in terms of the water availability and drought stress that can provide one of the important ingredients for increases in wildfire intensity and frequency.” If scientists are able to better predict what will happen to snowpack, it could help water managers plan for what’s coming. Early or rapid snowmelt poses problems for managing water resources in the West, where snowpack serves as a key source of fresh water in the drier summer months. “Water that would otherwise be stored as snow comes out early, and then we have to deal with it as a hazard instead of a resource at our reservoirs and along the rivers and streams,” said Ben Hatchett, a co-author on the study and a scientist at Colorado State University’s Cooperative Institute for Research in the Atmosphere. Snow-eater heat waves also may pose risks to skiers, hikers, and anyone else on or near mountains. They could be linked to hazards such as avalanches, glacial collapses, and permafrost melt, Hatchett said, though scientists are still investigating those connections. He lives in the Sierra Nevada, and he’s noticed one tangible change over his lifetime: The soundscape has changed. “At night, it used to be quiet,” he said. “And now it’s not quiet, because everything’s melting all the time.” This article originally appeared in Grist at https://grist.org/science/new-heat-wave-category-snow-eaters-study/. Grist is a nonprofit, independent media organization dedicated to reporting on climate change.