Contributions of extreme snowfall events to interannual snowfall variability
Heavy snowfall events may be the delight of skiers and snowboarders, but what do they mean for water resource managers?
We found that the single largest 3-day snowfall event each year contributes 6-35% of total annual snowfall at SNOTEL stations in the western United States (Lute and Abatzoglou, 2014). Considering that water availability in most of the West is contingent on snowmelt, the presence or absence of extreme snowfall events in a given year can mean the difference between a water surplus year and a drought year, respectively. Furthermore, these events were found to be pivotal in shaping the year-to-year variability in annual snowfall totals: the top decile of 3-day snowfall events accounts for more than 70% of interannual snowfall variability at SNOTEL sites. Extreme snowfall events were correlated with the phase of the El Nino Southern Oscillation, suggesting the potential to forecast the probability of these events months in advance.
Projected changes in extreme snowfall events
How will extreme snowfall events change with climate change?
While we have some idea of what changes to expect in extreme precipitation, very little study has been devoted to changes in extreme snowfall events. These events typically occur at near freezing temperatures, making them especially vulnerable to warming and introducing the possibility of heavy winter rain events. Using global climate model projections downscaled to western U.S. SNOTEL stations, we found that snowfall extremes are projected to decline less than small to moderate snowfall events and may even increase in size in the coldest regions (Lute et al., 2015). A warmer atmosphere can hold more water vapor, allowing larger snowfall events, especially in really cold areas. Given projected large decreases in total snowfall, this means that extreme snowfall events will contribute an even larger portion of total snowfall than they did historically. Fewer snow days and greater contributions from heavy events will help to increase year-to-year variability in annual snowfall. More frequent low snowfall years combined with increased year-to-year snowfall variability will present significant challenges to water management.