Is Snowmelt Initiation Independent of Elevation?

Recent studies (Peterson et al, Dettinger and Cayan) have shown that the Western rivers routinely monitored by the USGS all rise together each spring, suggesting an organized signal of snowmelt initiation across the region. These are all large basins (over 100 km2), spanning similar ranges of aspect and elevation. However, within a given basin, should we expect the spring pulse of snowmelt to occur at the same time in a 470 km2 basin gauged at 1200 m as in a 2 km2 glacial cirque gauged at 3200 m? Should streamflow from a north-facing cirque rise and peak at the same time as that from a south-facing cirque? Data from sub-basins of the Tuolumne and Merced Rivers within Yosemite National Park, from small lake basins throughout the Sierra Nevada Mountains, and from CDWR snow pillow stations throughout the central Sierra Nevada suggest that the answer to both of these questions is yes. Elevation and aspect exert strong influences on air temperature and solar radiation, which are important factors in controlling snowmelt. Why, then, does melt appear uniform across the Sierra Nevada each spring? Do air temperature and solar radiation differ less than previously supposed? Do snowpack properties create some kind of buffer or limit on melt rates that make small-scale meteorological differences less important? If initial melt rates are uniform throughout the basin, why do high-altitude, north-facing cirques retain their snow-cover the longest? Do they start out with more snow, or do the dominant factors influencing melt rates and supply change as the season progresses? This study uses the available data to examine these hypotheses.