Forest impacts on snow accumulation and ablation across an elevation gradient in a temperate montane environment
Travis R. Roth and Anne W. Nolin
Water Resource Sciences, Oregon State University, Corvallis, OR, 97331, USA
Received: 05 Oct 2016 – Accepted for review: 22 Oct 2016 – Discussion started: 01 Nov 2016
Abstract. Forest cover modifies snow accumulation and ablation rates via canopy interception and changes in sub-canopy energy balance processes. However, the ways in which snowpacks are affected by forest canopy processes vary depending on climatic, topographic and forest characteristics. Here we present results from a 4 year study of snow-forest interactions in the Oregon Cascades. We continuously monitored snow and meteorological variables at paired forested and open sites at three elevations representing the Low, Mid, and High seasonal snow zones in the study region. On a monthly to bi-weekly basis, we surveyed snow depth and snow water equivalent across 900 m transects connecting the forested and open pairs of sites. Our results show that the dense, relatively warm on forests at Low and Mid sites impede snow accumulation through increased canopy snow interception and increase energy inputs to the sub-canopy snowpack. Compared with the Forest sites, snowpacks are deeper and last longer in the Open site at the Low and Mid sites (4 – 26 days and 11 – 33 days, respectively). However, we see the opposite relationship at the relatively colder High sites with the Forest site maintaining snow longer into the spring by 15 – 29 days relative to the nearby Open site. Over a 4 year study, canopy interception efficiency (CIE) values in the Low- and Mid-Forest sites, were 79 % and 76 % of the total event snowfall, whereas CIE was 31 % at the lower density High-Forest site. At all elevations, longwave radiation in forested environments appears to be the primary energy component due to the maritime climate and forest presence, accounting for 82 %, 88 %, and 59 % of total energy inputs to the snowpack at the Low-, Mid-, and High-Forest sites, respectively. Higher wind speeds in the High-Open site significantly increase turbulent energy exchanges and snow sublimation. Lower wind speeds in the High-Forest site create preferential snowfall deposition. These results show the importance of understanding the effects of forest cover on sub-canopy snowpack evolution and highlight the need for improved forest cover model representation to accurately predict water resources in maritime forests.
Roth, T. R. and Nolin, A. W.: Forest impacts on snow accumulation and ablation across an elevation gradient in a temperate montane environment, Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-529, in review, 2016.