Will We Experience Snow This Winter?

Snow is a major component of our mountains. Snow cover results from the accumulation of snowfall on the ground during winter, and gradually melts in spring or transforms into firn, then glacier, at high altitude.

[Article issu de The Conversation, écrit par Marie Dumont, Chercheuse, directrice du Centre d’études de la neige, Centre National de Recherches Météorologiques, Météo France, CNRS, Université Grenoble Alpes (UGA)]

In the Alps, snow covers the ground for at least six and a half months per year above 2,000 meters above sea level.

Snow, a key element for the Earth

Snow has unique properties that make its presence on the ground essential in nature.

Snow has a white color, which means it reflects most of the sunlight. Its presence therefore limits the absorption of solar energy and therefore the increase in temperature locally, but also on a global scale when snow covers large areas.

Second, snow is a reservoir of water for mountainous regions and the surrounding plains: it limits the flow of rivers in winter and provides a high flow when it melts in spring. This meltwater is important for mountain ecosystems, as well as for agriculture and hydroelectricity production, but also for the availability of drinking water in certain regions of the world.

Finally, snow often has a high air content and acts as an insulator — a sort of foam of ice and air. This allows it to protect the soil from variations in air temperature, whether from cold during the winter months or from heat in spring. The fact that the soil is protected, for example from the cold, is important for the plants which are therefore protected from severe frosts: the snow plays a bit the same role as the mulch of a vegetable garden which protects the bare earth from climatic hazards .

Snow cover is globally affected by increasing temperatures

In response to rising global temperatures, snow cover is becoming scarcer around the world. Overall, since 1970, the duration of snow cover in the European Alps has shortened by around one month below 2000 meters above sea level.

Several snow observation sites have existed in the Alps for several decades and provide unique insight into the climate change signal in mountainous regions.

For example, at the Col de Porte site, located at a medium altitude (1,325 meters) in the French Alps, winter air temperature increased by 1.05°C between the two 30-year periods studied. (1960-1990 and 1990-2020, from 1^er December to April 30), while total winter precipitation did not change significantly. As a result, the average snow depth decreased by 40% between the two periods due to the change induced by the increase in temperature, with more rain at the expense of snowfall at this mid-altitude site where the average temperature winter is close to 0°C.

At low and medium altitude, the modification of the limit between rain and snowfall is the primary cause of the scarcity of snow.

At higher altitudes, as illustrated by the site of Weissfluhjoch perched at 2536 meters in the Swiss Alps, the temperature increase for the same periods is approximately the same as for the Col de Porte. However, average snow depth did not change significantly between the two thirty-year periods (when calculated over the periods December through April), and no major changes in total precipitation were observed. detected.

This is because the average winter temperature at this altitude is very low (-7.35 °C at Weissfluhjoch) and the climate-related temperature increase is not sufficient to convert snowfall in rain for the period from December to April.

However, the duration of snow cover, even at this altitude, shortened at the end of spring: the date of snow disappearance advanced by 15 days on average between the two 30-year averages. This is due to the increase in temperature in spring, which leads to more melting. It is the second leading cause of snow loss due to climate change.

In summary, snow cover retreats in response to increasing air temperature, more rapidly at low and medium altitudes due to the change in phase of precipitation (rain instead of snow), but also at higher altitudes. , due to earlier melting.

The depletion of snow cover has numerous consequences and profoundly modifies the society and economy of mountain regions, through, among other things, winter sports activities, but not only that.

The decline in snow cover induces a change in the water cycle in mountain regions, with flows increasing in winter (more rain) and decreasing in spring and summer (less snow).

The decline in snow cover, combined with rising temperatures, is leading to a “greening” of the Alps, with plants colonizing places previously devoid of vegetation, as well as a change in the distribution of vegetation with altitude. .

Finally, the retreat of the snow modifies the associated natural hazards, such as avalanches or rockfalls.

But this winter specifically: will there be snow?

We know that the average snow depth in winter will continue to decrease in the coming decades if greenhouse gas emissions do not decrease; but the variability of snow cover from one year to the next remains very strong: there are winters with good snow and winters with little snow, like the difference between weather and climate (the weather changing rapidly from from one hour to the next and from one day to the next and the climate representing the average of the weather over several decades).

If Météo-France is able to predict an anticyclonic day followed by the arrival of a disturbance and potential snowfall at the end of the week in Isère, we cannot predict whether at Christmas 2025 or 2030 there will be snow. snow, nor how the winter of 2024-2025 will position itself precisely in terms of snow cover compared to previous years.

The possibility of a very snowy winter cannot be ruled out today, but global warming is greatly reducing the probability of such an event – especially at low and medium altitudes – in favor of that of winters with little snow. As long as the temperature continues to rise, the likelihood of snowy winters decreases, upsetting and endangering the beauty and fragile balance of our mountains and all its inhabitants.