Abstract: Spring snow melt run-off in high latitude and snow-dominated drainage basins is generally the most significant annual hydrological event. Melt timing, duration, and flow magnitude are highly variable. and influence regional climate, geomorphology, and hydrology. Arctic and sub-arctic regions have sparse long-term ground observations and these snow-dominated hydrologic regimes are sensitive to the rapidly warming climate trends that characterize much of the northern latitudes. Passive microwave brightness temperatures are sensitive to changes in the liquid water content of the snow pack and make it possible to detect incipient melt, diurnal melt-refreeze cycles, and the approximate end of snow cover on the ground over large regions. Special Sensor Microwave Imager (SSM/I) and Advanced Microwave Scanning Radiometer for EOS (AMSR-E) passive microwave brightness temperatures (T-b) and diurnal amplitude variations (DAV) are used to investigate the spatial variability of snowmelt onset timing (in two stages, 'DAV onset' and 'melt onset') and duration for a complex sub-arctic landscape during 2005. The satellites are sensitive to small percentages of liquid water, and therefore represent 'incipient melt', a condition somewhat earlier than a traditional definition of a melting snowpack. Incipient melt dates and duration are compared to topography, land cover, and hydrology to investigate the strength and significance of melt timing in heterogeneous landscapes in the Pelly River, a major tributary to the Yukon River. Microwave-derived melt onset in this region in 2005 occurred from late February to late April. Upland areas melt 1-2 weeks later than lowland areas and have shorter transition periods. Melt timing and duration appear to be influenced by pixel elevation, aspect, and uniformity as well as other factors such as weather and snow mass distribution. The end of the transition season is uniform across sensors and across the basin in spite of a wide variety of pixel characteristics. Copyright (C) 2007 John Wiley & Sons, Ltd.

Authors: Ramage, J.M., Apgar, J. D., McKenney, R. A., and Hanna, W.,Ramage, J.M. (reprint author), Lehigh Univ, 31 Williams Dr, Bethlehem, PA 18015 USA Lehigh Univ, Bethlehem, PA 18015 USA

Map Scale: 1 : 0

Citation: Ramage, J.M., Apgar, J. D., McKenney, R. A., and Hanna, W.,Ramage, J.M. (reprint author), Lehigh Univ, 31 Williams Dr, Bethlehem, PA 18015 USA Lehigh Univ, Bethlehem, PA 18015 USA, 2007. Spatial variability of snowmelt timing from AMSR-E and SSNM passive microwave sensors, Pelly River, Yukon Territory, Canada.