A recent report reveals that the Lake Tahoe Basin and the northern Sierra Nevada are currently experiencing a condition known as snow drought, according to new research and data from scientists at the Desert Research Institute (DRI). Snow droughts, or periods of below-normal snowpack, occur when abnormally warm storms or abnormally dry climate conditions prevent mountain snowpack from accumulating.
“As of early January, the snowpack in the Lake Tahoe Basin was only 28 percent of normal,” said Benjamin Hatchett, Ph.D., a postdoctoral researcher with DRI’s Division of Atmospheric Sciences. “We experienced warm wet and dry periods in November and a dry period in December that has created snow drought conditions throughout the region, followed by warm, rainy weather so far in January that has caused snowpack levels to decline further, especially at low elevation sites.”
Snow droughts have become increasingly common in the Sierra Nevada and Cascade mountains in recent years, as warming temperatures push snow lines higher up mountainsides and cause more precipitation to fall as rain.
Hatchett, an avid backcountry skier, and friend of SnowBrains began to notice the trend several years ago and recently published research outlining an approximately 1,200-foot rise in the winter snow levels over the last ten years across the northern Sierra Nevada.
“There has always been an occasional snow drought year in the mountains, but that was typically the ‘dry’ type of snow drought caused by lack of precipitation,” Hatchett said. “As the climate grows warmer and more precipitation falls as rain instead of snow, we are seeing that we can have an average or above-average precipitation year and still have a well below-average snowpack.”
The implications of snow drought have not yet been studied extensively, but may include impacts to water resources, snowmelt runoff, flooding, soil moisture, tree mortality, ecological system health, fuel moisture levels that drive fire danger, human recreation, and much more. In regions such as the Lake Tahoe Basin, where mountain snowpack sustains wildlife, ecosystems, local economies, and provides crucial water resources to downstream communities throughout the year, the impacts of snow droughts could be enormous.
The last four winters, Hatchett and fellow DRI climate researcher Daniel McEvoy, Ph.D., an assistant research professor of climatology and regional climatologist at DRI’s Western Regional Climate Center (WRCC) noted, have all exhibited some degree of snow drought in the northern Sierra Nevada. Even the recent huge winter of 2016/17, which ended with far-above-average snowpack levels (205% of the long-term median on April 1, 2017, in the Lake Tahoe Basin), began with a period of early-season snow drought during a dry November. This winter has been no exception, with snow drought taking hold over low elevation areas in November, and moving to higher elevation sites in December.
“We spend a lot of time going out and skiing, climbing, and hiking in the mountains, which is what inspired us to study these things,” Hatchett said. “We’re seeing and experiencing snow drought first-hand, and we have to quantify it and understand it because these are changing patterns on the landscape that will have massive implications for the mountain environments that we experience each day and the mountain communities that we live in.”
Only time will tell how the 2017/2018 winter season will end, but in the meantime, snow drought is affecting the region in ways that have not yet been fully quantified.