3.9 SUMMARY Changes in New Snow & Upper Snowpack Density, 2030 Chnages in Snow Depth (%) Changes in Density (%) 20 Using the climate change scenarios and SRM and SNTHERM models, we estimate that 15 the date when snow starts to accumulate at 10 the base is pushed back by approximately 1 week by 2030 and anywhere from 1.5 to 4.5 5 weeks by 2100. This is caused by an increase 0 in air temperature. Earlier snowfall amounts -5 in the warm-wet scenario melted in October and caused a lag in peak snow depth at the -10 top of the mountain. In some scenarios, -15 this causes the maximum snow depths to -20 fall short of historical maximums. For midlow elevation (7,000-10,000 ft) winter snows, a 15% increase in snowfall -25 mid elevation (10,000-12,000 ft) compensates for a 1.5°C (2.7°F) increase -30 in air temperature such that there was little Nov. 15 Dec. 20 Feb. 15 Mar. 20 Apr. 01 change in snow depth. Snow depth in 2030 Date during spring break showed a 7 to 25% decline in the base area, with small decreases near the top of the mountain. However, the FIGURE 3.15: Changes in snow quality by elevation by 2030. Dates are approximate for a typical snow onset of the spring avalanche cycle (melt season by 2030. initiation) started earlier by 4 to 5 days in all model runs. All model runs show skiable snow for all elevations on Aspen Mountain Changes Snow Depth by Elevation, 2030 in 2030, but by 2100 this is only true for the B1 scenario. Results for the A1B scenario 40 for 2100 indicate that a persistent snowpack low elevation (7,000-10,000 ft) will only exist for the upper two-thirds of the mid elevation (10,000-12,000 ft) 30 mountain. For the A1FI scenario, persistent snow coverage is confined to only the top 20 third of the mountain. Snow depth goes to almost zero for the base area in 2100 under 10 the A1B emission scenario. In the A1FI scenario, snow depth goes to near zero for 0 the entire lower two-thirds of the mountain, with melt initiation beginning five weeks -10 earlier. The effect is substantially reduced under the low emissions B1 scenario. In the -20 A1B scenario, even in 2100 with a 7 to 9°F (4 to 5°C) increase in air temperature, there -30 Nov. 15 Dec. 20 Feb. 15 Mar. 20 Apr. 01 is little change in overall snow depth in the Date elevation bands from 9,500 feet (2,896 m) to the top of the mountain, compared to current levels. The level at which overall snow depth FIGURE 3.16: Changes in snow depth by elevation by 2030. Dates are approximate for a typical snow shows little change rises to 10,300 feet (3,139 season by 2030. m) under the high emissions A1FI scenario, which has a more substantial 11 to 12.5°F (6 to 7°C) ski season warming. In spite of the reduction in snowpack, snow quality has less than a 20% increase in the density of the top few inches of snow by 2030, which in our judgment, does not substantially reduce the quality of the snow. By 2100 densities could be substantially higher. 40 © 2006 Aspen Global Change Institute