Avalanches and Climate Change, Part II

Avalanche debris above Innsbruck, Austria in Spring 2019. 

This is the second of two posts exploring how climate change will affect avalanches, based in part on a recent paper by Strapazzon et al. (2021) in Frontiers in Physiology.  In the previous post, we examined the influence of climate change on the weather and snow characteristics of mountainous regions, emphasizing elevational- and seasonal-dependent trends.  Let's begin with a summary of some of the most relevant for avalanche dynamics and severity:

• Declines in snow cover duration and depth are likely and could be large at lower elevations (for high-emissions scenarios), but trends for upper elevations are smaller or in some areas less clear (especially for low-emissions scenarios)

• Snowfall intensity may increase, especially in colder upper-elevation areas that serve as the starting zones for major avalanches.

• Temperatures will increase, resulting in higher snowfall densities, more mid-season melt events, and more rain-on-snow events.   

Ignoring human-triggered avalanched by recreationists which is a very complex issue, the first bullet suggests a decline in avalanche activity, especially at lower elevations.  The second bullet, however, suggests an increase in avalanche activity, especially major avalanche cycles that are typically associated with extreme winter storms.  These represent two competing effects, but current thinking is that in a warming climate the overall frequency of avalanches will likely decrease in the lower elevations due to a decrease in snow cover and the areas and situations in which avalanches can occur.  At upper-elevations, frequency trends are less clear.  Note that we should still expect a lot of variability, so these are trends that will emerge from the natural year-to-year variability as we move through the 21st century.  For instance, in a given region there could have a year with a lot of low-elevation avalanches even as the overall trend in low-elevation avalanches is downward.  

The third bullet is an interesting one as it suggests that a greater fraction of future avalanches will be wet-snow rather than dry-snow avalanches.  I see this as a likely outcome of climate change and it would likely yield an increase in the ratio of wet-snow to dry-snow avalanches.  Utah's transitional snow climate with a mixture of maritime and continental characteristics could be especially vulnerable to such as shift, which would have implications for avalanche survival.  

As discussed by Strapazzon et al. (2021), dense snow in avalanche debris is more likely to interfere with respiration and the oxygenation of buried victims.  This is consistent with studies showing that the probability of survival in avalanches drops faster with time in denser, maritime snow climates.  Thus, in a warming world, there could be a more rapid decrease with time in the likelihood of survival for buried victims, with lower survival rates in avalanche burials.  

Studies also indicate that as snow depth and cover decline, terrain "roughness" is expected to increase.  In other words, there will be more rocks and other obstacles to injure or kill victims caught in avalanches.  

Year-to-year and decade-to-decade variations in weather, snow, and avalanches are very large, so what happens in Utah the rest of this year and even for the next decade or two is difficult to anticipate.  Trends in backcountry human-triggered avalanches and fatalities are also strongly affected by education and technology.  However, in the long run it seems likely that we will see a greater percentage of wet-snow avalanches.  Given that such avalanches are already prevalent in the spring, the increase as a percentage will probably be greater in the late fall, winter, and early spring.