The role of snow processes and hillslopes on runoff generation in present and future climates in a recently constructed watershed in the Athabasca oil sands region

Mine reclamation in the Athabasca oil sands region Canada, is required by law where companies must reconstruct disturbed landscapes into functioning ecosystems such as forests, wetlands, and lakes that existed in the Boreal landscape prior to mining. Winter is a major hydrological factor in this region as snow covers the landscape for 5–6 months and is ~25% of the annual precipitation, yet few studies have explored the influence of winter processes on the hydrology of constructed watersheds. One year (2017–2018) of intensive snow hydrology measurements are supplemented with 6 years (2013–2018) of meteorological measurements from the constructed Sandhill Fen watershed to: (a) understand snow accumulation and redistribution, snowmelt timing, rate, and partitioning, (b) apply a physically based model for simulating winter processes on hillslopes, and (c) evaluate the impact of soil prescriptions and climate change projections on winter processes in reclaimed systems. The 2017–2018 snow season was between November and April and snow water equivalent (SWE) ranged between 40 and 140 mm. Snow distribution was primarily influenced by topography with little influence of snow trapping from developing vegetation. Snow accumulation was most variable on hillslopes and redistribution was driven by slope position, with SWE greatest at the base of slopes and decreased toward crests. Snowmelt on hillslopes was controlled by slope aspect, as snow declined rapidly on west and south‐facing slopes, compared with east and north‐facing slopes. Unlike results previously reported on constructed uplands, snowmelt runoff from uplands was much less (~30%), highlighting the influence of different construction materials. Model simulations indicate that antecedent soil moisture and soil temperature have a large influence on partitioning snowmelt over a range of observed conditions. Under a warmer and wetter climate, average annual peak SWE, and snow season duration could decline up to 52% and up to 61 days, respectively, while snowmelt runoff ceases completely under the warmest scenarios. Results suggest considerable future variability in snowmelt runoff from hillslopes, yet soil properties can be used to enhance vertical or lateral flows.