| Summary: | The oil sands industry in Canada routinely uses soil-vegetation-atmosphere-transfer (SVAT) models, calibrated against short-term (<~10 years) field monitoring data to generate a single set of optimized soil hydraulic parameters. These calibrated SVAT models are then used to evaluate long-term reclamation cover performance based on long-term (~60 years) historical climate data. This approach attempts to characterize variability in the long-term water balance of these covers using historical climate variability but does not incorporate the potential variability associated with soil hydraulic parameters. In addition, little attention has been given to date on the variability that might be associated with future climate change. The focus of this research was on the long-term water balance of reclamation covers used in the oil sands industry. The objectives of this research were to: (1) quantify parameter variability in the modelling of water balance; (2) characterize the impact that future projected climate change will have on the water balance; and (3) evaluate methods of downscaling global climate change projections to regional (local) scales to evaluate changes in future water balances. Parameter variability was characterized through Inverse Modelling (IM) of soil hydraulic parameters for 12 soil cover designs, replicated in triplicate, at Syncrude Canada Ltd’s Aurora North mine site. Global scale climate change projections were downscaled (using LARS-WG) from Coupled Model Intercomparison Project Phase 5 (CMIP5) for the baseline and future periods at Fort McMurray Airport Station, while regional scale climate projections were generated for the 4km grid covering the Fort McMurray Airport station using the Weather Research and Forecasting (WRF) model. The key findings include the following: (1) variability in the simulated actual evapotranspiration (AET) is controlled primarily by climate variability, while variability in the simulated net percolation (NP) is controlled equally by parameter and climate variability; (2) future AET and NP will increase relative to the historical baseline period regardless of the climate change projection, time period, or cover soil profile; and (3) relative increases in the future AET and NP from WRF are not significantly different from LARS-WG. Overall, the findings highlight that the relative increase in future NP is significantly higher than that for AET, particularly for the reclamation covers. Increases in the NP rates are likely to result in accelerated flushing of constituents contained within the mine waste but will also create larger water yields to surface waterbodies and downstream receptors. Here the water yield represents the total release of water from the covers that includes NP and runoff. These changes should be taken into account in the design of reclamation covers at oil sands mine sites.
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