Topics

Identifying Avalanche Terrain Avalanche Mitigation Structural Defenses Avalanche Zoning Acceptable Risks CGS Bulletin 49 Avalanche Dynamics & Modeling Publications

Wet avalanches might become more common in a warming climate.

How will Climate Change affect Avalanches

Overview of Climate Change effects

The Intergovernmental Panel on Climate Change (IPCC) has concluded that temperatures are rising worldwide. State of the Climate in 2017 published by the American Meteorological Society reported that "Accompanying the record-high greenhouse gas concentrations was nominally the highest annual global surface temperature in at least 135 years of modern record keeping." The rates and implications of warming are uncertain, but this trend deserves recognition for avalanche hazard and risk analyses. Land use planning and engineering designs for avalanche protection requires reliable estimates of design events and how these might change in future decades.

Warming vs. Precipitation

General warming would suggest that the avalanche season will become shorter, and thus the overall hazard might become less. If precipitation patterns do not change, this reasoning might hold. However, most major avalanche periods of importance in land-use planning and engineering result from periods of prolonged heavy precipitation often accompanied by high winds. Thus, it is possible that climate change could result in an increase in avalanche hazards if storms become longer and/or more intense. The probability of these changes is unknown.

Long-term Records from Switzerland

Avalanche records from Switzerland are among the longest and most complete in the world. A 1997 study by the Swiss Federal Institute for Snow and Avalanche Research (Schneebeli, Laternser and Ammann) looked at 100 years of Swiss weather data and 50 years of and avalanche records. The study concluded that, while a long-term warming trend was clear, the mean potential avalanche activity near Davos has remained unchanged for the past 96 years.

A more recent 2013 study looked at wet snow avalanches in the Swiss Alps. For the 50 year period prior to 2002, the proportion of mid-winter wet snow avalanches increased by 0.4% per year, and concluded that this trend is likely to continue.

Iceland

Iceland also has an extended historic record of avalanches impacting fishing villages. A 2003 study found a correlation between atmospheric circulation tied to the North Atlantic Oscillation index and the number of snow avalanche cycles. The study linked avalanche disasters in Iceland to a rise in this index and speculated that a continued rise in this index could result in more large avalanches.

Norway

Climate change is expected to affect arctic and high latitude areas more than low and mid-latitudes. The Norwegian Road Administration is pro-actively planning for climate change impacts, including snow avalanches. A 2009 Report Adapting to Climate Change states that avalanches and lower elevations have become less frequent, but expresses concern about increases in avalanche sizes and frequencies at higher elevations due to wetter and more intense storms. Also, the study forecasts an increase in the frequency of slush flows, a type of avalanche unique to high latitude snow climates.

North America

Snow climates in North America vary widely from maritime to continental and from temporate to arctic. Effects of climate change on avalanches will presumably also have wide variations. While weather and climate data cover relatively long periods, avalanche data is much more limited. Furthermore, avalanche records tend to vary over time, generally becoming more complete in recent years. Comparing avalanche activity is further complicated by the evolution of avalanche control frequencies and methods. A 2018 study surveyed avalanche professionals in the U.S. and Canada and presented observations and predictions of climate change effects in North America. The findings suggest that we should expect more wet avalanches, reduced avalanche activity at lower elevations and more activity at higher elevations.

Canada

Avalanche records at Rogers Pass on the trans-Canada highway provide one of the longest records for snow and avalanches in North America. A 2013 study examined weather and avalanche records between 1965-2011. The authors found an increase in the mean annual air temperature over three decades at two long-term weather stations ranging from +0.5 °C to +0.7 °C. More early season rain events were suspected of causing rain crusts in the lower snowpack. These crusts are known to cause persistent weak layers that may result in more frequent destructive deep slab avalanches. However, the data did not reveal an increase in the frequency of natural avalanches over the three decade period. The authors acknowledged the potential influence of an evolving avalanche control program.

Forest Conditions

Forests have long been recognized for their ability to prevent or reduce the size of avalanches. One of the earliest avalanche protection laws was instituted in Switzerland in 1876 that prevented forest removal above avalanche-prone villages. Large areas of forests in North America are experiencing high mortality rates due to drought and insect infestations. This phenomenon might be expected to continue if warming persists. When forest mortality occurs on steep slopes additional avalanche terrain could be created. Similarly, burned areas can become new or expanded avalanche terrain due to loss of vegetation in potential starting zones.

A 2009 study looked at the effects of climate change on forests in Europe and found that warming and increases in CO₂ are expected to increase growth of forests, especially in northern and western Europe. The study also concluded that drought risk will increase and outweigh the positive effects in southern and eastern Europe.