Large-ensemble climate simulations to assess changes in snow stability over northern Japan

Abstract

To examine the influence of global warming including increased heavy snowfall frequency on the potential of natural dry snow avalanche frequency and magnitude, we estimated the frequency of weak layer formation and the associated slab overload above the weak layer over northern Japan. The estimation was numerically performed using climate models' output for 1800 winter simulations in each of the historical (1951–2010) and +4°C experiments by forcing a physical-based snowpack model with the result of the climate models. Here the +4°C experiment was defined as a climate when the global mean air temperature had increased by 4°C from the preindustrial level. The estimation results showed that the probability of weak layer formation, identified by the natural stability index, would decrease all over the area because of the shorter age of the weak layers caused by a warmer climate, indirectly indicating a potential decrease in avalanche frequency. However, because of increased heavy snowfall frequency, slab overload would increase by 10–15% in inland areas for weak layers of decomposing fragments/precipitation particles and the mountainous area facing the Sea of Japan for weak layers of facets/depth hoar, thereby potentially indicating an increased magnitude of avalanches.

Changes in snow avalanche activity in response to climate warming in the Swiss Alps

“…Enhanced temperatures hinder the formation of weak layers by directly affecting the temperature gradient across the snowpack (Richter et al, 2020). Interestingly, Katsuyama et al (2022) also found a decline in the proportion of persistent weak layers based on climate projections for Northern Japan.…”

“…Unlike previous studies relying on bulk snow cover properties or simple snow instability metrics (Lazar and Williams, 2008;Castebrunet et al, 2014;Katsuyama et al, 2022), we used machine learning models to classify dry-and wet-snow AvDs from simulated snow stratigraphy and meteorological variables. This enabled us to comprehensively evaluate the impact of different climate scenarios on snow avalanche activity, investigate changes in seasonality, and highlight causes of projected changes beyond a mere decrease in snow depth or shortening of the snow season.…”

“…To evaluate changes in snow avalanche activity for future decades, climate projections can be coupled with physics-based snow cover models that resolve the temporal evolution of snow stratigraphy required to assess snow instability. The few existing assessments of future snow stability based on simulated snow cover data (Lazar and Williams, 2008;Castebrunet et al, 2014;Katsuyama et al, 2022) relied either on bulk snowpack or meteorological parameters without accounting for the detailed snow stratigraphy, or employed a stability index that is a poor predictor of avalanche activity (Jamieson et al, 2007;Mayer et al, 2023). Thus, there is insufficient understanding of potential changes in avalanche activity within the current century and whether avalanche risk mitigation measures need to be adapted.…”