Hydrometeorological response to chinook winds in the South Saskatchewan River Basin.
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Date
27/06/2016Author
MacDonald, Matthew Kenneth
Metadata
Abstract
The South Saskatchewan River Basin (SSRB) is amongst the largest watersheds in
Canada. It is an ecologically diverse region, containing Montane Cordillera, Boreal
Plains and Prairie ecozones. The SSRB is subject to chinooks, which bring strong
winds, high temperatures and humidity deficits that alter the storage of water during
winter. Approximately 40% of winter days experience chinooks. Ablation during
chinooks has not been quantified; it is not known how much water evaporates,
infiltrates or runs off. The aim of this thesis is to characterise the spatial variability of
surface water fluxes as affected by chinooks over SSRB subbasins and ecozones. The
objectives are addressed using detailed field observations and physically based land
surface modelling. Eddy covariance was deployed at three prairie sites. During
winter chinooks, energy for large evaporative fluxes were provided by downward
sensible heat fluxes. There was no evidence of infiltration until March. The Canadian
Land Surface Scheme (CLASS) coupled to the Prairie Blowing Snow Model
(PBSM) was used as the modelling platform. A multi-physics version of CLASSPBSM
was developed, consisting of two parameterisation options each for sixteen
processes. Field observations were used to evaluate each of the configurations. Three
parameterisations provide both best snow and best soil water simulations: iterative
energy balance solution, air temperature and wind speed based fresh snow density
and de Vries’ soil thermal conductivity. The model evaluation highlighted difficulties
simulating evaporation and uncertainty in simulating infiltration into frozen soils at
large scales. A single model configuration is selected for modelling the SSRB.
Modelling showed that the SSRB generally experiences no net soil water storage
change until March, confirming field observations. Chinooks generally reduce net
terrestrial water storage, largely due to snowmelt and subsequent evaporation and
runoff. The Prairie ecozone is that which is most strongly affected by chinooks. The
Montane Cordillera ecozone is affected differently by chinooks; blowing snow
transport increases during winter and runoff increases during spring. The Lower
South Saskatchewan is the subbasin most affected by chinooks. The Red Deer is the
subbasin least affected by chinooks.