Understanding Forest-Snow Dynamics for Wenatchee Watershed in Canopy Gaps Scenario in a Distributed Hydrologic Model

Snowmelt is a significant source of runoff in the mid to high latitude mountainous areas. Several studies have found noticeable differences in snow-cover dynamics between forest gaps and open-continuous forested areas. Researchers have found that canopy gaps have the potential to alter the magnitude and timing of the snowmelt. Most of these studies are focused at the plot-scale. There are very few studies that have addressed that distinction in snow cover between forested and forest gaps areas at the watershed scale. In this study we evaluate the impact of canopy gaps on snow cover at a watershed level. To model the forest-snow interaction in canopy gaps, we use the canopy gap component of a widely used physics-based hydrologic model, the distributed hydrology soil vegetation model (DHSVM) that captures the physical processes for snowpack evolution in the forest gaps and forested areas separately at a sub-grid scale (within a resolution typically 10-150 m). The study focuses on the snow dominated Wenatchee basin, WA, USA at 30m spatial resolution. We use DHSVM to predict sub-hourly snow water equivalent (SWE) with and without forest gaps and compare how these two scenarios impact the magnitude and timing of maximum snow water equivalent (SWE) and the timing of snowmelt. The comparisons are at the yearly time scale and the variation of the discrepancies are presented spatially over the watershed area. This study will help to understand the influence of snow cover dynamics on flow hydrographs especially in mountainous regions under forest management.

Keywords: Forest, snow water equivalent, distributed hydrology, canopy gap, snowmelt, watershed.