Seasonally distinct runoff–recharge partitioning in an alpine tundra catchment

Abstract

Hydrological processes within the alpine tundra of the Taiga Cordillera ecozone in northwestern Canada are poorly understood, yet these areas receive more precipitation per unit area than lowlands and sustain late summer and winter flow in large river systems when contributions from other areas are reduced. The objective of this study was to quantify the spatial and temporal variability in streamflow and groundwater recharge within an alpine tundra basin with discontinuous permafrost and explore the potential impacts of climate change on the timing and intensity of these hydrological processes. Hydrometric and remote sensing methods were used to complete a water balance assessment of the study basin and compare spatial and seasonal differences in inputs, outputs, runoff ratio, and runoff–recharge partitioning during the 2019 open water season. During the freshet, the basin received large daily melt volumes and responded with highly efficient runoff. Evapotranspiration became the primary means of water loss in the early summer but declined as the summer progressed. During the summer, groundwater discharge exceeded precipitation inputs and sustained headwater subbasin streamflow. Groundwater recharge occurred primarily via glaciofluvial upland infiltration during the freshet and channel bed infiltration during the summer. The partitioning of basin outputs between runoff and groundwater recharge was highly seasonal, with a freshet ratio favoring runoff (0.83) while the early and late summer favored recharge (0.28 and 0.17, respectively). As climate change continues, higher air temperatures and greater precipitation are expected for the study basin. Longer open water seasons and declining permafrost extent within the study basin will result in a greater proportion of input water routed to storage and/or groundwater recharge instead of runoff. Shrubification and treeline expansion may also increase evaporative losses from alpine tundra areas, reducing both rapid runoff and delayed aquifer recharge contributions important for larger rivers at lower elevation.