Global Climate Change Impacts in the United States 2009 Report Legacy site

We evaluated how climate change resulting from increased greenhouse gas (GHG) emissions may affect the timing of wet avalanches and snow quality at Aspen Mountain in the years 2030 and 2100. Snow quantity was evaluated using the Snowmelt Runoff Model and snow quality was evaluated using SNTHERM. We determined the timing of wet avalanche activity by examining changes to historical average temperatures and snow quality by calculating the bulk density of the top 10 cm of the snowpack. Climate changes were evaluated using MAGICC/SCENGEN and the output from five General Circulation Models (GCMs). The climate change estimates were run using the relatively low, mid-range, and high GHG emissions scenarios: B1, A1B, and A1FI. To get higher resolution estimates of changes in climate, we used output from a regional climate model (RCM, MM5), which is nested in the Parallel Climate Model (PCM).|We defined wet avalanches as likely to occur when average daily temperature exceeds 0 degrees C and investigated three scenarios: first day when daily average temperature exceeds 0 degrees C, first three consecutive day period when average temperature exceeds 0 degrees C, and the day after which average temperature remains greater than 0 degrees C. By 2030 at the top of Aspen Mountain, wet avalanches are likely to occur between 2 and 19 days earlier than historical averages, with little difference across the GCMs. In 2100, the occurrence of wet avalanches at the top of the mountain varies strongly by CO2 emissions scenario. The low and mid-range emissions scenarios show that wet avalanches at the top of the mountain start 16 to 27 days earlier than historical averages. In contrast, the high emissions scenario shows wet avalanches occurring 41 to 45 days earlier. In spite of earlier melt initiation and the reduction in snowpack, snow density in the top 10 cm increased by less than 20% by 2030. (C) 2007 Elsevier B.V. All rights reserved.