These images captured by NASA’s Aqua satellite show the difference between snow cover in 2010—the last year with average winter snowfall in the region—and 2015 across the Sierra Nevada Mountains. Credit: NASA/MODIS

The 2015 record low snowpack level in California’s Sierra Nevada mountain range is unprecedented in comparison to the past 500 years, according to a new paper published in Nature Climate Change(link is external). In their examination of paleoclimate tree-ring based records dating back to 1500, scientists from the University of Arizona, University of Arkansas, and NCEI’s Paleoclimatology Program expect that the current snowpack low has a strong likelihood of occurring only once every 500 years and only once every 1,000 years below 7,000 feet. Such an exceptional low level poses significant challenges to California, which receives over 30% of its yearly water supply from Sierra Nevada snowpack.