In the higher elevations of the western U.S., seasonal snow accumulation provides the primary source of water input to the terrestrial ecosystem. Recent changes in climate and vegetation cover (e.g. fire suppression, beetle infestation, fire) have potentially large, yet unrealized implications for water availability and ecosystem health. In this regard, we have developed a series of ecohydrological instrument clusters to measure snow depth, soil moisture and temperature, sap flow, and fluxes of carbon, water vapor, and energy. Clusters deployed across elevational transects in the Sierra Nevada and Rocky Mountains provide the measurements needed to understand the impacts of forest structure on snowmelt dynamics and broader ecohydrological feedbacks. These observations indicate that snow accumulation is greater in open versus under canopy locations (29% greater on average) but snow ablation rates (sublimation and melt) are also greater in open areas (39% greater on average). Therefore snow water equivalent differences between open versus under canopy locations were generally lower than snowfall differences. As a result of these competing factors, snow disappearance timing is more similar in open versus sub-canopy areas then would be expected based on snow accumulation differences alone. The time-space evolution of differences in snow water equivalent between under canopy and open areas, therefore, is a function of the magnitude of the differences between open and sub-canopy snow accumulation (i.e. input terms) versus differences between open and sub-canopy snowmelt and sublimation (i.e. loss terms). The magnitude of the differences in these two terms in open versus under canopy positions is dictated by several physiographic and climatic factors which vary across a variety of scales. This presentation will synthesize observations from diverse climatic and physiographic regimes to develop the conceptual models of snow-vegetation interactions needed for testing a variety of climate and land cover change hypotheses
Molotch, N.P., Musselman, K.N., Kirchner, P.B., Bales, R.C., and Brooks, P.D. (2012): Effects of forest structure on snow accumulation and melt derived from ecohydrological instrument clusters across the Western US (Invited). Fall Meeting, American Geophysical Union, December 2012. Abstract C33D-0684..