Trends in Snowpack Chemistry and Comparison to National Atmospheric Deposition Program Results for the Rocky Mountains, U.S.A. 1993-2004

Seasonal snowpack chemistry data from the Rocky Mountain region for 1993-2004 was examined to identify long-term trends in concentration and chemical deposition in snow, and in snow-water equivalent. Comparisons of trends were made between snowpack data and National Atmospheric Deposition Program wetfall data from nearby sites in the region. We used an innovative, non-parametric correlation method known as the Regional Kendall Test. This technique expressed the slope, direction, and probability of trend for several sites at once in each of the Northern, Central, and Southern Rockies subregions. Seasonal Kendall tests were used to evaluate trends at individual sites. Sulfate deposition decreased with moderate to high significance in all three subregions in both wetfall and snowpack. Precipitation trends consistently were downward for wetfall-, snowpack-, and SNOTEL data for the Central and Southern Rockies subregions (p<0.02), while no trends were noted for the Northern Rockies subregion.