Trends in Regional Large Magnitude Snow Avalanche Occurrence and Associated Climate Patterns in the U.S. Northern Rocky Mountains

Abstract:

Large magnitude snow avalanches pose a hazard to humans and infrastructure worldwide. Analyzing the spatiotemporal behavior of avalanches and the contributory climate factors is important for interpreting climate and historical avalanche variability as well as improving avalanche forecasting. Here, we attempt to identify and examine trends in regional avalanche activity, and specific climate variables that contribute to years with large magnitude avalanche events across the U.S. northern Rocky Mountains of northwest Montana. Using established dendrochronological methods, we developed a long-term (1867-2019) regional avalanche chronology using tree-rings from 647 trees exhibiting 2134 avalanche-related growth disturbances. We then used principal component analysis to examine avalanche-climate relationships that suggest large magnitude avalanche years are characterized by a deep snowpack represented by high seasonal maximum snow water equivalent. The major ocean-atmosphere teleconnections associated with these high snowpack and avalanche years were the Pacific Decadal Oscillation (PDO) and the Pacific North American (PNA) pattern. By using a generalized linear autoregressive moving average model that accounts for the past effect of avalanches on sample availability, we demonstrate that the first principal component is inversely proportional to avalanche probability suggesting a decrease in years with regional large magnitude avalanches as snowpack decreases. A decreasing trend in overall avalanche probability through time is coincident with snowpack losses across the region. Our results suggest potential future decreases in large magnitude avalanche frequency as climate warming drives snowpack losses across the study region, which is consistent with similar avalanche climate regions in Canada and Switzerland.