Snow Depth Variability at the Forest Edge in Multiple Climates in the Western United States

Snow depth variability between different sides of the forest edge was analyzed using airborne lidar in the Olympic Mountains, WA; Tuolumne River Watershed, CA; Jemez Caldera, NM; and the Boulder Creek Watershed, CO. At Boulder Creek there were statistically significant snow depth differences between leeward and windward forest edges (mean: 38%), which were likely the result of cold winter temperatures (-5 to -10 degrees C), substantial wind speeds (>10-12m/s), and the forest architecture. In the Olympic Mountains, wind speeds were similar to Boulder Creek, but snow depth differences between forest edges were not significantly different, likely due to winter temperatures near 0 degrees C and a more continuous forest distribution. At Jemez, forest shading likely caused significant snow depth differences between north and south facing forest edges (mean: 32%). Tuolumne had similar incoming solar radiation to Jemez, but only two of the four sites contained significant snow depth differences between north and south facing forest edges (14% and 31%). The Tuolumne sites without significant edge differences received less direct solar radiation due to shading by surrounding topography. At Jemez, Boulder Creek, and Tuolumne, snow depth differences between forest edges were greater than or equal to differences between exposed and under canopy areas. Furthermore, at Jemez and Tuolumne, forest-edge snow depth differences were similar to snow depth differences between different aspects in exposed areas. Therefore, snow depth differences between forest-edge classifications are of similar magnitude to classifications currently used to represent subelement heterogeneity within hydrologic models. Therefore, representation of forest-edge variability within models should be explored.