PNNL

Abstract

Snow depth significantly differs between north- and south-facing forest edges, and between areas directly underneath the canopy and in the open. To account for this variability, a tiling parameterization based on classifications from high-resolution (1-3 m) vegetation maps was incorporated into the Distributed Hydrology and Soil Vegetation Model (DHSVM). Within each grid cell (90-150 m), the tiling parameterization simulated forest-snow variability with four independently evolving snowpacks, each with unique radiation conditions at the forest edge, underneath the canopy, and in exposed areas. In Tuolumne, CA, the tiled model simulated little difference in grid cell average SWE and late-season streamflow decreased by 3-4% compared to the non-tiled model. In Jemez, NM, the tiled model decreased late-season streamflow by 18% due to increased sublimation caused by relatively dry air, different wind speed scaling, and relatively high amounts of incoming longwave radiation that triggered more prevalent unstable boundary conditions within the forest tile. In Chiwawa, WA, the tiled model increased late season streamflow 15% due to high radiation attenuation and slow melt rates in the forest tile. Furthermore, within the Chiwawa, a substantial silvicultural practice was implemented to increase the north-facing edge’s fractional area. This practice increased late-season streamflow by 50-52% compared to the non-tiled model and 36-38% compared to tiled model simulations that did not represent forest edges. We conclude that representing the existing forest-SWE variability had an effect on late-season streamflow in some watersheds but not in others based on the fractional area of the forest edges, forest characteristics, and climate conditions.