Spatial variability of hillslope water balance, wolf creek basin, subarctic yukon

A hydrological study was conducted between 1997 and 1999 in the subalpine o pen woodland of the Wolf Creek Basin, Yukon, to assess the interslope water balance variability. The water balance during the snowmelt and summer peri ods on four hillslopes revealed strong contrasts in process magnitudes and highlighted important factors including frost, vegetation, soils and microc limate that Controlled vertical and lateral fluxes of water. Snow accounted for approximately half the annual water input, while differences in accumu lation among hillslopes were related to interception properties of vegetati on. Available energy at the snow surface controlled the melt sequence and t he snow on some slopes disappeared up to two months earlier than others. Sn owmelt runoff was confined to slopes with ice-rich substrates that inhibite d deep percolation, with the runoff magnitude governed by the snow storage and the antecedent moisture of the desiccated organic soils prior to melt. During summer, evapotranspiration exceeded rainfall, largely sustained by w ater from the soil moisture reservoir recharged during the melt period. Dif ferences in net radiation on slopes controlled the potential evapotranspira tion. with the actual rates limited by the phenology of the deciduous fores ts and shrubs. Evapotranspiration was further suppressed on slopes where th e organic soils became dry in late summer. Summer runoff was confined to sl opes with porous organic layers overlying mineral soils to form a two-layer flow system: (1) quickflow in the surface organic layer and (2) slowflow i n the mineral soil. Differences in the rates of flow were related to the po sition of the water table which may rise into the organic layer to activate quickflow. The presence of ice-rich frost and permafrost impeded vertical drainage and indirectly regulated the position of the water table. The loca tion of the hillslope within a basin influenced recharge and discharge dyna mics. Slope segments with large inflows sustained discharge throughout the summer to enhance basin runoff. In this way, the present study provides ins ight into basin hydrology. Copyright (C) 2001 John Wiley & Sons, Ltd.