Effects of Roads and Linear Forest Disturbances on the Snow Mass and Energy Balance

English Abstract:

Linear disturbances for infrastructure such as roads, power transmission and pipelines are commonplace and rapidly expanding across the seasonally snow-covered needle-leaf forest zone in North America. Compared to other disturbance practices (e.g., clearings for timber harvest), the relatively narrow extent and permanence of linear disturbances uniquely modifies surface-atmosphere exchanges, largely due to changes to longwave and shortwave radiation and greatly reduced snow interception capacity due to the reduction in needleleaf canopy. The sign and magnitude of these modifications are determined by how hydrometeorological processes such as snow interception, wind redistribution, radiation transfer and turbulent transfer of heat and water vapour are controlled by climate, forest structure, and slope-aspect. Results are presented from a modelling study of snow mass and energy balance dynamics in and around conceptual linear forest clearings. A solar ray trace model developed and tested against extensive measurements made at the Marmot Creek Research Basin is coupled to a snow energy and mass balance calculation scheme and applied to a range of latitude, slope-aspect, and disturbance and forest characteristics. The results are shown to resolve shading effects necessary to simulate the fine-scale variability in the snow surface energy balance that characterize these environments. A comparison of simulation results from a sensitivity experiment showed that the orientation of the disturbances (i.e., N-S vs. E-W), the latitude, and the width-to-tree-height ratio were three dominant factors determining the net impact of the linear disturbances on the timing and duration of snowmelt. The disparity in energy and mass balance over short distances highlights the importance of understanding the variability of hydrological inputs over forested regions that are fragmented by linear disturbances.