Snowmelt hydrology of two subarctic slopes, southern Yukon, Canada

Large quantities of water are discharged from subarctic basins during snowm elt season. Runoff contributing areas as well as timing and magnitude of me ltwater generation from different slopes are highly variable. Two slopes in the lower Wolf Creek basin, southern Yukon, were studied in 1997. The sout h-facing slope has a dense aspen forest that is leafless in the melt period (April - May) and is underlain by seasonal frost. The north-facing slope h as open stands of spruce and an organic layer that rests on mineral soils w ith permafrost. In 1997, snowmelt is advanced by over 10 days on the south slope, which receives more solar radiation than the north aspect. All meltw ater on the south slope infiltrates the frozen silt without generating runo ff. By the time significant melt events occur on the north slope, the frost and snow are gone from the south. Meltwater is able to infiltrate the froz en organic soil but deep percolation is prevented by the ice-rich substrate . Lateral flow begins after the organic layer is saturated, with much runof f along intermittent rills fed by diffuse and pipe flows. Rills and pipes a re interconnected but the drainage network and runoff contributing area cha nge depending on the disposition of the snow as well as water and frost tab le positions relative to local topography. Contrasts between the north and south slopes have important implications on direct runoff generation during the melt period. Situations similar to the study site can be found elsewhe re in subarctic North America and the observed processes have a bearing upo n hydrological modelling for the subarctic environment.