LAYERS OF COMPLEXITY: CLIMATE CHANGE AND THE FUTURE OF AVALANCHES
Simon Horton
Learning about avalanches is an important part of winter travel in the mountains. For those passionate about spending time in the backcountry, understanding how to avoid avalanches is a lifelong endeavour. And with that, many may be wondering what impacts climate change could have on winter snowpacks and avalanche conditions.
Investigating a large avalanche in the Purcell Mountains. Photo credit: Mike Conlan and ASARC.
Layers of complexity
Snow avalanches are caused by complex interactions between weather, snow, terrain, and sometimes people. While the basics of how avalanches occur are understood, the details are incredibly complex. Backcountry travellers recognize this complexity by factoring risk and uncertainty into their decisions. Snow scientists deal with this complexity in the form of messy data sets, weak correlations, and uncertain conclusions. Accordingly, when we look at scientific studies about climate change and avalanches, we do not yet see clear conclusive results.
Climate versus weather
The first important thing to acknowledge is the main driver of avalanches is weather, not climate.
Avalanches result from layers of snow with different properties. These properties constantly evolve in response to changes in precipitation, temperature, humidity, wind, cloud cover, and solar radiation. Over the course of the winter, weather patterns like storms, cold snaps, and warm spells result in a layered snowpack structure.
Avalanches occur when a structurally weak layer undergoes mechanical failure. Possible causes of failure are natural stresses caused by weather (e.g., snowfall, warming) or the added stress of a person, snowmobile, or explosion. When a weak layer fails on a sufficiently steep slope, the snow will begin to slide downhill and cause an avalanche.
Timescales of hours, days, and weeks are more meaningful to the layers and stresses in the snowpack than climatic timescales of years and decades. However, long-term atmospheric changes do impact basic snowpack properties, which can impact overall avalanche conditions and winter recreation.
My work with the SFU Avalanche Research Program uses numeric models to track how weather over the course of the winter results in a layered snowpack. This helps predict the location, timing, and size of potential avalanches.
Long-term avalanche studies
An additional challenge is long-term avalanche datasets are hard to find. Existing research investigating impacts of climate change focus on naturally occurring avalanches that affect highways and villages because these types of avalanches have the best long-term records. However, the vast majority of backcountry accidents involve human-triggered avalanches, and to date, no study has considered how they could change in the future. Records of human-triggered avalanches are less consistent due to changes in the number of people in the backcountry and their behaviour in avalanche terrain.
Okay, so what do existing studies say?
After acknowledging the complexity of predicting avalanches, the fact that weather is more important than climate, and that there are limited studies, existing research on avalanches and climate change is summarized in a 2019 IPCC report on high mountain areas. This report highlights two main results:
- There will be more avalanches involving wet snow. This is because surface melting and rain-on-snow events will become more common at all elevations throughout the winter.
- At lower elevations, there will be a decline in the number and size of avalanches. This is because overall snow cover is projected to decrease.
Wet snow avalanches behave differently than dry snow avalanches. The mechanical processes for triggering are different and then once in motion, they typically move slower. They can still be very destructive due to their high density. Photo credit: Raven Eye Photography.
What other factors could impact future avalanche conditions?
There has been some indication that climate change can affect extreme weather events such as atmospheric rivers and extended dry periods. Like any weather event, these have a short-term impact on avalanche conditions, but the sequence, intensity, and duration of weather events will be more important than individual events.
Going back to the idea that avalanches are caused by “weather, snow, terrain, and sometimes people”, there are some additional factors that could indirectly influence avalanches. One is terrain, for example changes in glaciation and forest cover will change the terrain where avalanches happen (e.g., retreating glaciers, vegetation growing at higher elevations, wildfire). Another is human behaviour. Increased tourism and development in mountainous regions could increase the exposure of people to avalanche hazards.
Conclusions
For backcountry travellers, future recreation opportunities will be impacted by reduced snow cover and more wet snow than dry powder. However, the avalanche trend is unclear, especially for human-triggered avalanches. Areas that receive precipitation in the form of snow will continue to experience avalanches, but the degree of danger will depend on the specific sequence of weather events over shorter periods of time.
Safe travels this and future winters!
Simon Horton
Resources
- Get avalanche training and daily forecasts at www.avalanche.ca
- Learn avalanche safety basics in this online tutorial: avysavvy.avalanche.ca
- Learn about avalanche research in Canada at www.avalancheresearch.ca
Bonus section - What about the bad snowpack in western Canada this year?
Over the last month, many people have heard about dangerous avalanche conditions in western Canada. The snowpack structure, particularly in the Columbia and Rocky Mountains, is very weak, which has made it challenging to travel safely in the backcountry. These conditions have been described as “once-in-a-decade”, with similarities to the bad avalanche winter of 2002-03. These conditions were caused by a specific sequence of weather events:
- Below average snowfall in October and early November. It wasn’t extremely below average, but many areas had 60% of normal snow water content by the end of October.
- Relatively long cold snaps in November and December formed large and weak snow grains. Again, not extreme cold (colder temperatures have been recorded in 10 of the last 30 winters in Canada), but the coldest temperature recorded since 2017.
- A series of warm storms at the end of December buried the weak snow with dense and heavy snow, creating a widespread structural weakness.
- Below average snowfall throughout January prevented the weak layers from strengthening and kept them within the prime depth for human triggering. As of Feb 1, many western mountain ranges have 60 to 80% of normal snow water content.
The current avalanche conditions are the result of this sequence of weather events, none of which are particularly extreme. The outlook is that these conditions will likely persist for much of the winter in many of the interior ranges, but what actually happens will depend on the localized weather events over the next few months.
The BC Snow Conditions and Water Supply Bulletin for Feb 1 shows most mountain ranges have 60 to 80% of normal snow water content for this time of year.
