HR: 11:20h
AN: GC32A-05 INVITED     [Abstracts]
TI: The Sensitivity of Snowmelt Processes to Meteorological Conditions and Forest Cover During Rain-on-Snow
AU: * Marks, D
EM: danny@nwrc.ars.usda.gov
AF: USDA Agricultural Research Service, Northwest Watershed Research Center, Boise, ID 83712-7716 United States
AB: Devastating floods in the intermountain western US can result from rapid snowmelt during mid-winter rain-on-snow (ROS) events. Key components of snowmelt flooding during ROS are conditions prior to the storm, the combination of temperature, humidity and wind during the event, and the extent to which the snowcover is exposed to the wind. The critical antecedent condition is extension of the snowcover to lower elevations spanning the rain/snow transition zone. In the intermountain west this significantly increases the snow-covered area (SCA) and the volume of water stored in the snowcover. During ROS events warm storm conditions cause the elevation of the rain/snow transition to rise causing rain to occur over large areas with snowfall only in the highest elevations. In the intermountain west the snowcover is generally cooled by evaporation (latent heat flux) and warmed by sensible heat flux, such that turbulent fluxes have little effect on the energy state of the snowcover. However, during ROS condensation occurs on the snow such that most of the energy for snowmelt comes from the combination of sensible and latent heat exchange. If the SCA is extensive and exposed to the wind, the surface water input (SWI) may be more than doubled by the addition of snowmelt to the rain. Vegetation shelters the snowcover from the wind reducing turbulent exchange and causing significant differences between forested and open slopes. Examples of these effects are illustrated using data from recent ROS storms in early February, 1996, and January, 1997, which caused extensive damage across the western US.
DE: 0736 Snow (1827, 1863)
DE: 0740 Snowmelt
DE: 0764 Energy balance
DE: 1816 Estimation and forecasting
DE: 1817 Extreme events
SC: Global Climate Change [GC]
MN: Fall Meeting 2005