the evolution of snow conditions over the past 60 years

In Auvergne-Rhône-Alpes according to Météo France data, the average winter temperature (between December 20 and March 20) increased by + 1 ° C between the current climatic period (1991-2020) and the previous period (1961 -1990).

A drop in snow cover is observed at medium altitude (below 1500 m). This is the case everywhere in the Alps and the Massif Central.

Climate projections, reported and compiled by the Regional Climate Air Energy Observatory (ORCAE) indicate that, “under the assumption of an increase in the average temperature of + 2 ° C, the number of days with snow on the ground would decrease by one month at 1,500 m altitude, going from 5 to 4 months in the Northern Alps. The thickness of the snowpack would decrease by 40 cm.

At 1,200 m, the snow cover would be very low and the conditions for practicing winter sports would no longer be met.

Above 2,500 m, the snowfall would be slightly delayed, the melt a little faster (12 days less snowfall) and we would see a slight decrease in the thickness of the snowpack ”.

Evolution of snow cover: nuances

According to the readings made on the Météo France automated reference station for this parameter, located at an altitude of 1325m at Col-de-Porte in Chartreuse (Isère), the Regional Climate Air Energy Observatory, for example, recorded a decrease of 31% (-33 cm) over the winter season between 1961 and 2020, going from an average of 105 cm of snow depth between 1961-1990 to an average of 72 cm between 1991 and 2020.

However, be careful with the raw figures because here in Chartreuse the number of days with at least 30 cm of snow on the ground remains very important. We can even say that the snow cover is abundant since it has been calculated for 60 years that “97% of winters can be considered very snowy with more than 40 days with at least 30 cm of snow on the ground”.

In detail, it is over the period from December 20 to January 10 that the decrease in snow cover begins to be felt here. Between 1961-1990 and 1991-2020, it fell by an average of 14%. While the decrease in snow cover remains insignificant between January 11 and March 20 between these same 30-year periods.

A Chamonix, the loss of snow depth is on average 18 cm in 60 years. On this measuring station, winters with little snow are more numerous in the most recent climatic period and the snowiest winters are mostly in the previous climatic period. The decrease in the average number of snow days (> = 30cm of snow on the ground) is 40%.

In Haute-Maurienne at Bessans, if the measurement indicates -11 cm of snow, the number of days with snow decreased on average only by 5% between 196-1990 and 1991-2020, which is not significant. Same observation in the Vercors, in Autrans, which lost 9 cm of snow on average over the period and in the Massif Central for Mont-Dore / Sancy with 4 cm loss of average snowfall.

Climate change is a major issue for mountain areas since it leads to a decrease in natural snow cover, especially at low altitude and also acts on the production of artificial snow, which can only function in weather conditions. specific.

Avalanches higher in altitude

Two recent studies published in Scientific Reports (link in English) tend to show that artificial snow will help maintain the snow conditions necessary for the operation of winter sports resorts in the first half of the 21st century. These studies were carried out by the National Meteorological Research Center (CNRM, Météo-France / CNRS) and Irstea Grenoble, on the evolution of snow cover in 129 winter sports resorts in the Alps and the Pyrenees during the 21st century.

They conclude: “after 2050, the situation worsens sharply until the end of the century. The impact of warming on snow cover in the resorts is strong from 1.5 ° C of global warming and without artificial snow. With 45% artificial snow cover, snow cover remains comparable to the current situation for global warming below 2 ° C, but above 3 ° C, artificial snow will no longer be sufficient to compensate for the reduction in snow. ‘natural snow cover’.

By 2100, in the case of strong greenhouse gas emissions, the reduction in the average winter thickness could reach 80 to 90%, with a very limited duration of snow cover, and a snowpack regularly non-existent in middle Mountain.

This change in snow cover also induces changes in the risk of avalanches. Scientists have observed for several decades a reduction in the number of powder snow avalanches, an increase in the number of wet snow avalanches, including in winter, and a gradual increase in the altitude reached by avalanches.

Beyond the strict winter period, climate change will also have more and more repercussions on water resources in summer. The snow cover in the mountains has the function of a “water tower. By gradually melting during spring and summer, when precipitation is less and demand is greater, it maintains the flow of rivers.

Source: A la Une – Le Progrès | Le Progrès by

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