Global reduction of snow cover in ski areas under climate change

snow depth and duration negatively [38]. Consequently, a substantial decrease in snow cover duration is projected by the end of this century, for instance, in Europe [7, 39]. Likewise, our results show that this substantial reduction in annual scd is not restricted to regions but can be detected globally. However, regarding the long-term effect of climate change on snow reliabil- ity in ski areas, high altitude ski areas of the European Alps and the Rocky Mountains are pro- jected to be on average less affected than all other mountain skiing regions targeted in this study. These results are supported by existing regional literature, although projections vary within regions in dependence of local climatic conditions and elevation [1, 3, 7, 10, 40–42]. Since this study focuses on natural snow cover, the projections are only partly applicable for ski areas implementing technical snow management such as grooming, slope preparation or snowmaking [43]. Nevertheless, technical snowmaking in ski areas will have to be dramatically increased to compensate natural snow scarcity and to ensure economic profitability. The lack of snow is already problematic in many regions, with technical snowmaking increasing in importance for decades [14]. Predicted increases in the crucial amount of additional snow- making under future conditions varies depending on regional conditions and elevation [40, 42]. However, this measure is limited by the availability of fresh-water resources and by ambi- ent temperature and costly due to high energy consumption [44, 45]. Particularly low altitude

ski areas are more affected by climate change [6, 46] and artificial snow production will not compensate for the missing snow due to high economic costs, high resource demands and a lack of cold temperatures in the future [6, 40, 41, 47]. In addition, technical snow production can also have considerable ecological implications, like nutrient increase [48], change of soil properties [49] or impacts on plant phenology [50]. We project a considerable increase in ski areas completely lacking snow in the future. Thir- teen percent of all current ski areas will have a 100% decrease in annual snow cover days and one fifth will experience a reduction of 50% to 100% scd in 2071–2100 relative to a historic baseline under a high emissions scenario. In accordance, 80% snow reduction is projected globally under SSP5-8.5, although reductions are smaller in higher altitudes [51]. Moreover, we illustrate in this study that outward parts of mountainous areas and coastal ski areas are most affected by global warming. Hence, in the future, present ski areas will concentrate towards continental regions and central parts of the mountain ranges in higher elevations. The highest climate sensitivity was found for midlatitudinal coastal mountains in western North America with maritime climates, whereas areas with continental interior climates were less sensitive to climate change in regard of snow cover reliability [52]. In the Northeast of the US, viable ski areas are projected to contract northwards [53], which is supported by our results.

Accordingly, in the European Alps, a substantial reduction of snow water equivalent [9] is resulting in an upward shift of snow reliability [37]. Furthermore, the probability of optimal ski days is higher in the inner Alps and higher regions in the immediate future [11]. Besides the number of optimal ski days, the 100-day-rule [13] is used as an indicator for snow reliabil- ity and hence, the economic profitability of ski resorts. Our results indicate that a substantial proportion of present ski areas will globally fall below this threshold (Fig 2B). Another impor- tant skiing market, which was recently growing tremendously, is China. This country has not been included in this study as data on Chinese ski areas is lacking in OpenStreetMap. How- ever, a considerable shortening of the ski season length in most low altitude ski areas is simi- larly projected for China and the 100-day-rule will only be reached by 65% of Chinese ski resorts by the mid-century [40]. In this study, we used annual natural scd to identify global patterns of snow reliability in ski areas. Hence, while enabling the comparison of scd in mountain regions between future time periods and historic values, this study is limited in showing differences in spatial or temporal dynamics on a finer scale. Ski areas are characterized by extreme climate conditions [54], PLOS ONE Global reduction of snow cover in ski areas under climate change PLOS ONE | https://doi.org/10.1371/journal.pone.0299735 March 13, 2024 8 / 15