January 2018 was a month of extremes. Not only was it by far the warmest January on record across the Western Alps, but also one of the wettest in systematic weather measurements, with widespread landslides at low elevations and massive snowfall in mountains. The weather of January 2018 was unusual, freakish in fact, at the upper extreme of the historical distribution of storminess, temperatures and precipitation in the Western Alps – breaking many weather records. Not only was January 2018 unprecedentedly warm, but also was it extremely wet and with unusual snowfall at higher elevations. As Regional Climate Models do not only predict substantial warming in the European Alps but also a slight increase in precipitation totals, we hypothesize that the extreme weather conditions observed during January 2018 and its ensuing impacts could yield valuable insights into typical winter conditions to be expected by the end of the 21st century.
At higher elevations, the January 2018 calamities started with the passage of winter storm Burglind (Eleanor) and new all-time wind gust records on summits as well as hefty snowfall in the Northern French and Western Swiss Alps. During the first three weeks of January, subsequent, stormy low-pressure systems transported further warm-wet air masses from the Atlantic and the Mediterranean to the Alps, leaving snow accumulations exceeding five meters (and even eight meters in regions affected by massive snowdrift, like Grand St. Bernard; Fig. 1b). These immense snow burdens pushed avalanche risk to extreme levels in the Alps, threatening many villages and communication routes, and leaving thousands of tourists stranded in mountain resorts. Indeed, several of the major ski destinations of the Alps, including Chamonix, Saas Fee, Val d’Isère, or Zermatt, had to shut their ski runs and to put helicopter shuttles in place to evacuate tourists from resorts during the major snowfall episodes.
Local residents and authorities were, however, not equally well prepared for the widespread, shallow landsliding, debris flows and rain-on-snow floods in smaller, low-elevation catchments in January 2018. This can at least in part be credited to a lack of experience with comparable events during other winter seasons, for which there is virtually no historical evidence of rainfall-induced mass movements, despite scientific surmise that ongoing climate warming could indeed promote landslides and debris flows, even at higher elevations and in winter.
For further information, https://www.nature.com/articles/s41561-018-0177-6?WT.feed_name=subjects_climate-change