Effects of Climate Change on Avalanche Accidents and Survival

Abstract

Avalanches are major natural hazards in snow-covered mountains, threatening people and infrastructure. With ongoing climate change, the frequency and types of snow avalanches may change, affecting the rates of avalanche burial and survival. With a wetter and warmer snow climate, consequences of burial may become more severe. In this review, we assess the potential effects of climate change on the frequency and characteristics of avalanches. We then discuss how these changes might affect the survival rates of subjects buried by avalanches and might influence the responses of search and rescue (SAR) teams and health care providers. While climate change is inevitable, the effects on avalanches remain elusive. The frequency of human triggered avalanches may not change, because this depends largely on the number and behavior of winter recreationists. Blunt trauma and secondary injuries will likely become more frequent as terrain roughness is expected to rise and snow cover to become thinner. Higher snow densities in avalanche debris will likely interfere with the respiration of completely buried victims. Asphyxia and trauma, as causes of avalanche death, may increase. It is unlikely that SAR and health care providers involved in avalanche rescue will have to change their strategies in areas where they are already established. The effects of climate change might foster the expansion of mitigation strategies and the establishment of mountain rescue services in areas subject to increased avalanche hazards caused by changes in snow cover and land use.

Keywords: avalanche; climate change; hypoxia; search and rescue; snow; trauma.

Figure 1

Avalanche fatalities in the Swiss Alps for the period of 1936–1937 to 2019–2020 (84 years). In recent decades, most victims were caught during recreational activities such as skiing (“Backcountry”)—illustrating the emergence and growth of winter tourism. Victims on roads including ski runs are counted in “Transportation.” Victims in villages (“Buildings”) became far less frequent due to extensive mitigation works (updated from Schweizer et al., 2021).

Figure 2

Snowpack structure in relation to snow depth for the Weissfluhjoch study site 2,540 m (Davos, Switzerland) for the 30-year period 1990–1991 to 2019–2020. (A) Snow depth in mid-January with full blue circles indicating poor snowpack structure, and red open circles indicating good snowpack structure. Snowpack structure is classified based on snow profile type as described by Schweizer and Wiesinger (2001): “poor” corresponds to profiles types 1–5, (with weak basal layers), “good” to profile types 6–10, (with well-consolidated basal layers). (B) Snow depth by snowpack structure class. With poor snowpack structure snow depth is significantly lower than with good structure (median: 117 vs. 141 cm; Mann-Whitney U-Test, p = 0.012). Boxes span the interquartile range from 1st to 3rd quartile with a horizontal line showing the median. Whiskers show the range of observed values that fall within 1.5 times the interquartile range above the 3rd and below the 1st quartile.

Figure 3

Avalanche fatalities in the Swiss Alps for the 40-year period 1978–1979 to 2017–2018 in relation to snow cover duration, expressed as snow day anomaly. Snow day anomaly refers to the deviation from the mean number of snow days. Snow days are days with snow depth >50 cm for a group of seven measurement stations in the Swiss Alps at 1,300–1,800 m. The 30-year mean (1961–1990) is 89 days (Marty, 2008). Open circles show individual values, in blue for years with low snow and in red for years with high snow. Box plots to left and right show the distribution characteristics. The median numbers of fatalities were 24 in low snow years and 22 in high snow years. The difference between the two groups is not statistically significant (U-Test, p = 0.28). Same presentation of box plots as described in Figure 2; asterisks show outliers.

Figure 4

Survival curves for Austria (solid black line: 2005–2013), Canada (solid gray line: 1981–2005), and Switzerland (dashed gray line: 1981–1991; black dashed line: 2005–2013) for completely buried victims (modified from Falk et al., 1994; Haegeli et al. 2011; Procter et al., 2016).

Figure 5

Breathing into an artificial snow avalanche. The porosity of the snow allows diffusion of O₂ from snow debris into the air pocket and diffusion of exhaled CO₂ into the surrounding snow. CO₂, carbon dioxide; O₂, oxygen (Illustration by Dalila Rovazzani. All rights reserved, used with permission).