Global reduction of snow cover in ski areas under climate change

Kruskal-Wallis test and a Pairwise Wilcoxon test with Bonferroni correction was implemented to detect differences in annual scd between periods [28] and the results were visualized using underlying data distributions. The percent change of future annual scd relative to a historic baseline of annual scd was depicted via change maps (% change in annual scd) within all seven mountain regions. To assess the potential concentration of future ski areas towards less popu- lated areas in high altitudes, we plotted annual scd for all ski areas combined and separated into regions with low (<25% percentile), medium (>25% and <75% percentile) and high (>75% percentile) population density. Percentiles were based on single regions. We calculated the percent change in annual scd for future periods relative to historic numbers and differenti- ated between low, medium, and high population density in the ski areas to evaluate the con- centration effect of future reliable ski areas into less populated areas. Analysis and figures were implemented for all emissions scenarios (SSP1-2.6, SSP3.-7.0, SSP5.-8.5), since there is contrasting evidence which scenario best tracks current emissions trajectories [29, 30]. While we compare the three scenarios in our results, we focus on outlin- ing the results based on the high emissions scenario (SSP3-7.0) as warming is more pro- nounced in terrestrial systems compared to the Earth’s average, and mountain systems are particularly sensitive [31]. Detailed results on the low and very high emissions scenarios are

reported in the supplementary information (S1–S5 Tables and S1–S5 Figs). All analysis and visualisation were conducted via R version 4.0.5 (R Core Team 2021) using the package raster [32] and elevatr [33]. Results Annual snow cover days in the seven major mountain areas with downhill skiing will signifi- cantly decrease worldwide with climate change under a very high, high, and low emissions sce- nario (Fig 1, S1 and S2 Figs). For all currently recorded ski areas, annual scd will decrease substantially under a high emissions scenario (Fig 1; S1 Table). Mean annual scd will decline by 43% (Andes), 37% (Appalachian), 78% (Australian Alps), 42% (European Alps), 50% (Japa- nese Alps), 23% (Rocky Mountains) and 51% (Southern Alps) by 2071–2100 relative to historic times (S2 Table). On average, annual scd in many ski areas of the main global mountain regions will approach the threshold of 100 annual scd by the end of this century (Andes: 153 (-97.6) scd, European Alps: 137 (-80.3) scd, Southern Alps: 128 (-112.3) scd) and the Appala- chian Mountains: 116 (-57.3). In the Japanese Alps snow cover duration is projected to cross this threshold with 86 (-64.4) annual scd by 2071–2100. With 81 (-69.2) annual scd by 2041– 270 and 38 (-111.5) by 2071–2100, the average annual scd in the Australian Alps will reach this threshold sooner (S1 and S3 Tables). Despite similar losses in scd (-56.4), the Rocky Mountains will remain relatively snow reliable with on average 202 annual scd by the end of this century.

Annual scd in global ski areas will similarly decrease under a low and substantially decrease under a very high emissions scenario by the end of this century (S4 and S5 Tables, S1 and S2 Figs). In the Andes and the Southern Alps, however, annual scd will decrease more slowly in a low emissions scenario. In addition, in a low emissions scenario, no regions will on average fall below 100 annual scd, whereas the Australian Alps, the Appalachian Mountains and the Japa- nese Alps will fall beneath this threshold under a very high emissions scenario (S4 and S5 Tables). In general, all projections show an overall reduction of ski areas and a substantial increase in present ski areas with zero annual scd for future periods. Globally, 13% of current ski areas will experience a 100% decrease in annual snow cover days by 2071–2100 and 20% will decrease between 50 and 100% (Fig 2). Under a high emis- sions scenario, ski areas in the Southern Hemisphere (Andes, Australian Alps, Southern Alps) as well as the Japanese Alps and the Appalachians will be most severely affected by climate 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 4 / 15