Thursday, November 01, 2012, 4:30PM - 5:30PM
RL-1 room 269
Full title: "Beetles, dust, and snow: Projecting changes in snowmelt in forested subalpine areas in the Colorado River Basin"
The recent mountain pine beetle epidemic in the Colorado River Basin has resulted in widespread tree mortality in pine stands across the Colorado Plateau. Because of complex micro-scale (i.e. tree well scale) interactions between vegetation and snow processes, one of the most signiﬁcant issues resulting from this epidemic is the potential hydrologic impacts of the effects of changing forest structure. Using SNTHERM, we conducted a comparative modeling scenario analysis of the snowpack along a transect between two trees over the course of the snow ablation season (28 February–30 June) under four forest stand conditions to assess changes in snowpack characteristics because of loss of canopy biomass. We found that the red phase scenario (intermediate phase of tree death) exhibited a 4-day earlier snow disappearance date than the living stand scenario and grey phase scenario (advanced phase of tree death), although the timing of isothermal conditions at 0ºC was identical. A potentially important cause of earlier snowmelt timing in red-phase stands is due to increased needle-litter deposition, reducing snowpack albedo and increasing snowpack energy. Colorado subalpine-snowpack surface albedo is not only affected by needle deposition, but also by enhanced aeolian dust deposition. We examine the combined and comparative effects of dust and litter on snow surface albedo and temperature gradients through field modification of snow surface dust and litter concentrations. We suspect that dust deposition in forested environments will serve to significantly reduce subcanopy albedo, with relatively minor additional reductions from tree litter deposition associated with the mountain pine beetle. Albedo becomes a more significant factor in snowmelt processes in more open canopy conditions associated with tree death, and therefore our understanding of surface albedo will become increasingly important in snow-covered areas affected by both beetle-related mortality and dust deposition.