The Changing Role of Forests in Controlling Snowpack
J. A. Biederman1, A. A. Harpold1,2, P. Broxton1, P. D. Brooks1,2
1 University of Arizona, 2 INSTAAR, Boulder, CO
In the Southwest, precipitation is concentrated in the mountains, and snowfall represents a large fraction of water available for ecosystem function, aquifer recharge, and runoff. The controls on peak seasonal snowpack are known to shift between forested and open environments as well as with slope and aspect.
We present a new distributed model to investigate how forests control snowpack at a resolution capturing forest structure. We examine how the role of forests in controlling snowpack varies over a range of slope and aspect, and we evaluate the energy balance under forest canopy and gap environments. The model is informed by airborne LiDAR and ground-based observations of climate, vegetation and snowpack. It represents interception, snow distribution by wind, latent and sensible heat fluxes, and radiative fluxes at a scale of 1 m on an hourly time step. We find that northerly aspects accumulate greater snowpack than southerly aspects but show lower spatial variability. On northerly aspects, most of the snowpack remains shaded by vegetation, whereas on southerly aspects the northern portions of gaps and southern forest edges receive direct insolation during late winter, when solar angles are greater. This difference in net radiation makes peak SWE in forest gaps and adjacent forest edges more sensitive to topography than SWE in areas under dense canopy. In ongoing work we are testing the changing role of forests across gradients of climate and forest disturbances such as fire, insect infestation and harvest or thinning.