A coupled hydrologic and snowpack stable water isotope model assesses
controls on isotopic inputs across a large, mountainous basin. The most
depleted isotope conditions occur in the upper subalpine where snow
accumulation is high and rainfall is low. Snowmelt evolution over time
indicates isotopic enrichment is not dictated by melt fractionation but
is determined by elevation which controls the amount, phase and isotopic
mass of spring precipitation coincident with the ablation period. With
respect to snowpack kinetic fractionation, its effect on snowmelt is a
balance between energy and snow-availability. It is highest above
treeline and in the shrub-dominated upper montane where vegetation
shading is low, while deep snowpack and conifer forests limit the
influence of kinetic fractionation in the subalpine. Wet years reduce
the effects of snowpack fraction on snowmelt across the basin, except in
the lower montane where added snowfall bolsters water-limited
conditions.