REMOTE SENSING OF INTERANNUAL SNOWMELT VARIABILITY, YUKON RIVER BASIN, YUKON TERRITORY, CANADA

Spring snow melt runoff in high latitude and snow-dominated drainage basins is often the most significant hydrological event annually. Timing, size, and duration can be highly variable and influence regional climate, geomorphology, and hydrology. Arctic and sub-arctic regions have sparse long term ground observations and are at risk of shifts in the snowmelt-dominated hydrology as high latitudes respond rapidly to climate change. Changes may occur in the volume or type of winter precipitation, timing of spring runoff and water storage, and growing season length. Passive microwave remote sensing data from the Special Sensor Microwave Imager (SSM/I) are used to investigate the interannual variability of recent snowmelt onset timing and duration for a complex landscape in northwestern North America. SSM/I 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, snow saturation, and the approximate end of snow cover on the ground over large regions. SSM/I-derived melt dates and duration are compared to topography and hydrology to investigate the interannual variability of melt timing in both uniform and heterogeneous landscapes in the upper Yukon River basin. Observations emphasize the Wheaton River (875 km²) in the southwest Yukon and the Ross (7250 km²) and Pelly (49000 km²) Rivers in the eastern Yukon, all of which are gauged basins. The terrain varies from fault-controlled lowlands to mountains with and without modern glaciers. Elevations range from 500 m to 2200 m. The climate is primarily semi-arid continental with temperature extremes in both summer and winter and the majority of precipitation falling as snow. SSM/I-derived melt onset varies annually by several weeks and occurs between late March and mid April. Snowmelt timing in upland regions precedes streamflow response by days to weeks, depending on basin size and characteristics. Melt timing and duration appear to be influenced by absolute pixel elevation, the spread of pixel elevations, weather, snow mass, and proportion of snow covered area, and both are highly variable during the period of record (1987 – 2004).