Abstract:We quantified the effects of forest vegetation on snow accumulation and ablation in a mid-latitude montane environment in Northern New Mexico. Detailed observations of snow depth along transects extending radially from trees showed that snow depth was 25% greater on the northern versus southern side of trees. At maximum accumulation, canopy interception resulted in a 47% reduction of snow water equivalent (SWE) under canopy. An array of ultrasonic snow depth sensors showed that snow ablation rates were 54% greater in open locations compared to locations under canopy. Maximum accumulation of SWE occurred 21 days later on the north versus south side of the trees. Binary regression tree models indicated strong correlation (R 2 D 0Ð68) between micro-scale (i.e. 10-cm resolution) canopy structure indices and snow depth. The regression tree model adequately resolved general tree-well structure, suggesting that future remotely sensed vegetation data may improve snow distribution models.
We used co-located observations of snow depth, soil temperature, and moisture and energy fluxes to monitor variability in snowmelt infiltration and vegetation water use at mixed-conifer sub-alpine forest sites in the Valles Caldera, New Mexico (3020 m) and on Niwot Ridge, Colorado (3050 m). At both sites, vegetation structure largely controlled the distribution of snow accumulation with 29% greater accumulation in open versus under-canopy locations. Snow ablation rates were diminished by 39% in under-canopy locations, indicating increases in vegetation density act to extend the duration of the snowmelt season. Similarly, differences in climate altered snow-season duration, snowmelt infiltration and evapotranspiration. Commencement of the growing season was coincident with melt-water input to the soil and lagged behind springtime increases in air temperature by 12 days on average, ranging from 2 to 33 days under warmer and colder conditions, respectively. Similarly, the timing of peak soil moisture was highly variable, lagging behind springtime increases in air temperature by 42 and 31 days on average at the Colorado and New Mexico sites, respectively. Latent heat flux and associated evaporative loss to the atmosphere was 28% greater for the year with earlier onset of snowmelt infiltration. Given the large and variable fraction of precipitation that was partitioned into water vapour loss, the combined effects of changes in vegetation structure, climate and associated changes to the timing and magnitude of snowmelt may have large effects on the partitioning of snowmelt into evapotranspiration, surface runoff and ground water recharge.
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