Climate change could mean less avalanches


Climate change is worsening many types of natural disasters and dangers around the world, from fires to hurricanes. But there is one type of danger that could actually decrease as temperatures warm, according to an analysis of European avalanches spanning more than two centuries.

Scientists have examined climate records and historical documents describing more than 730 avalanches since the 1780s in the Vosges Mountains in France. They found that as winter temperatures rose between the mid-19th and early 20th centuries, the number and size of avalanches dropped and those that did appear to be moving upwards.

The findings could have implications for efforts to understand how climate change will affect these risks in the years to come. “If you look at what happened at such a low altitude in the past, you will be able to anticipate what will happen in the future at high altitude”, explains Nicolas Eckert, statistician at the National Research Institute. for agriculture, food and the environment and Grenoble Alpes University in France. He and his colleagues reported the results on October 25 in Proceedings of the National Academy of Sciences.

The amount, density, and other physical properties of snow in an area all affect avalanche risk. “This means that in theory snow avalanches should be very sensitive to climate change,” Eckert explains. But so far, he adds, there haven’t been many investigations into this link.

Records of past avalanches are often scarce and do not go far enough into the past for long-term trends to become apparent. The Vosges, a small chain in northeastern France, are an exception. People have inhabited the region, from valley bottoms to mountain ridges, for centuries.

Eckert and his colleagues were able to collect a multitude of historical documents referring to 734 avalanches that occurred between 1783 and 2013. These included photographs, diaries, administrative documents, postcards, travel guides, etc. Among them were a hand-drawn map from the mid-19th century showing the location of a house damaged by an avalanche, a photo of the aftermath of an avalanche that hit a valley in 1894, and a document mentioning a man who “died under the ruins of his house which a torrent of snow which rushed from the top of the ravine toppled from top to bottom” in 1783.

[Related: What to do if you get caught in an avalanche]

The researchers also looked at temperature and precipitation records and historical documents describing winter conditions in the region. They then analyzed how avalanche activity and climatic conditions have changed over time.

Initially, according to their study reports, the avalanches were “intense and widespread” at all altitudes. But that changed during the period from around 1850 to 1920, when the Little Ice Age (a cold period that affected Europe and North America from the 14th to the 19th century) ended. As winter temperatures warmed by about 1.35 degrees Celsius (2.43 degrees Fahrenheit), the region has experienced seven times fewer avalanches per year. At the same time, these events also decreased in size and occurred over a shorter season.

Perhaps most strikingly, avalanches have almost completely disappeared from low-lying sites and only persist today in the highest areas of the Vosges. “All this comes directly from the fact that the climate warmed up between the middle of the 19e century and early 20e century, ”Eckert says.

When temperatures rise, snow becomes scarcer. Other characteristics of the remaining cover, including cold and snow stratification, may also change to affect avalanche activity.

Today our climate is warming due to the use of fossil fuels, and scientists expect snowfall to decrease in many places. This could mean that the risk of avalanches is also decreasing, Eckert says. “However, of course, we know there is a lot of variability,” he adds, pointing out that warming temperatures are currently leading to more intense snowfall and avalanches at very high altitudes in the Alps and l ‘Himalayas. “So snow avalanches will also persist in many areas, although they decrease at lower elevations. “

Still, his team’s analysis suggests that low-level avalanche activity may be a glimpse of what to expect in high-altitude terrain. In a next step, he and his colleagues will examine whether similar patterns can occur in other chains beyond the Vosges. They are also working on predictions of how changes in avalanche activity might translate into changes in risk to people.

“We can easily calculate the risk to buildings or people inside buildings, but when it comes to risk to people doing backcountry activities, it’s more complicated because ‘they go where they want to go,’ Eckert explains. “The correlation between a decrease in avalanche activity and a real decrease in risk is not so obvious.”

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