Future Changes in Snowpack over North America from NARCCAP

As global temperatures rise, snow resources over North America are predicted to change in significant ways. Long-term changes in the timing of the snow season and amount of snow will negatively impact natural ecosystems and the human use of snow resources for water storage, hydroelectric power production, irrigation and recreation. Here we examine future changes in snowpack (snow water equivalent, SWE) using the North American Regional Climate Change Assessment Program (NARCCAP, Mearns et al. 2013) suite of regional climate models (RCMs). These models are intended for use in climate process studies as well as climate change impacts and adaptation studies. SWE from the current climate simulations of the NARCCAP models is compared against an ensemble of off-the-shelf, gridded "observation based" SWE products compiled from a number of sources (satellite, reanalysis, snow-pack models, gridded observations). During winter, the RCMs are found to overestimate SWE in the mountains of western North America. Also, simulated snow tends to stay on the ground for longer than observed in mountainous regions. By mid-Century, the NARCCAP RCMs predict that winter SWE amounts will decrease dramatically over most of North America. The only exception to this is in northern Canada, where warmer temperatures mean it is no longer "too cold to snow" and SWE amounts increase. In some regions, such as the Southern Rockies, the models suggest that decreases in SWE are linked to changes in both precipitation type (transition from snow to rain) and an increase in snowmelt. In other areas, such as New England, the processes driving changes in SWE are less clear. In addition to changes in winter snowpack amounts, the NARCCAP models show that the snow season (defined here as the time with measurable snow on the ground) will decrease substantially. In the future peak snow amounts are expected to occur earlier in the season, and significant snowmelt will happen earlier in spring. These changes will have significant repercussions for water, energy, agriculture, and recreation in the west.