Submitted to: Trans American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: 11/20/2005
Publication Date: 12/20/2005
Citation: Marks, D., Pomeroy, J., Winstral, Link, T., Seyfried, M. and Essery, R. 2005. Snowcover and climate, topography and vegetation in semi-aris mountain catchments. Abstract C21A-1072, Eos, Transactions of the American Geophysical Union, 86(52):F432.
Technical Abstract: Mountainous regions in the semi-arid Northwestern US are snow-dominated with sparse summer precipitation. Vegetation at high altitudes in this environment is dominated by dry grass and sagebrush with small deciduous and evergreen forest patches in mid-point and lower hillslope locations of north-facing slopes. Wind direction and variations in near-surface wind fields due to topography and vegetation control snow deposition, causing tremendous spatial heterogeneity in the distribution of the snowcover and the delivery of melt water. Snow is scoured from exposed areas during and shortly after storms and deposited in drifts that develop in the lee of exposed ridges, and inward from forest edges. Vegetation cover and soil development is associated with topography and topographic effects on the wind field, in that only sites with sufficient melt-water delivery from drifts and soil moisture storage potential can sustain forests. Forests are typically found down slope from the deepest sections of snowdrifts, where a melt-water supply can replenish soil moisture but where the persistence of snowcover into summer does not impede forest growth. Forest canopies diminish the energy available for melt by reducing turbulent transfer, increasing incoming longwave and reducing incoming shortwave. Hence, snowcover persistence is greatly increased by forest cover - this reduces the growing season and potential evapotranspiration demand over non-forested sites. In contrast, sparsely-vegetated, exposed areas of mountain catchments accumulate less snow, and that snow melts earlier and faster than in forested areas. These hydro-ecological characteristics are very dependent on the snow regime, for instance snow transport is substantial and primarily from one direction resulting in persistent locations for large snow drifts and a relatively reliable water supply for soil development and plant growth. Transport of snow primarily to the north-facing slopes delivers melt-water to sites that have lower potential evapotranspiration demand in summer, permitting more luxuriant forest growth. To better manage forest and water resources in mountain regions, it is important to understand and model the coupling between forest structure, climate, and snowcover.