Characterizing the extreme 2015 snowpack deficit in the Sierra Nevada (USA) and the implications for drought recovery

“The main take-home is thinking about drought over longer time scales. The first wet year doesn’t necessarily solve the longer-term problem.”

Steve Margulis, principal investigator, UCLA’s Henry Samueli School of Engineering and Applied Science

• Uses a new spatially distributed snow reanalysis data set in combination with longer term in situ data to analyze the Sierra Nevada (USA) snowpack
• Analysis indicates that water year 2015 was a truly extreme (dry) year
• Finds the range-wide peak snow volume was characterized by a return period of over 600 years (95% confidence interval between 100 and 4400 years) having a strong elevational gradient with a return period at lower elevations over an order of magnitude larger than those at higher elevations
• Finds that the 2015 conditions, occurring on top of three previous drought years, led to an accumulated (multiyear) snowpack deficit of ~ 22 km3, the highest over the 65 years analyzed
• Early estimates based on 1 April snow course data indicate that the snowpack drought deficit will not be overcome in 2016, despite historically strong El Niño conditions
• Results based on a probabilistic Monte Carlo simulation show that recovery from the snowpack drought will likely take about 4 years