Hydrological and energy budget processes of the subarctic Canadian shield

There has been only infrequent research of the hydrology and energy budget of the subarctic Canadian Shield even though it is the third largest ecozone in Canada. In order to investigate important and largely unknown processes, two study sites near Yellowknife, Northwest Territories were instrumented to measure the components of the energy and water budgets. This was done to determine the predominant water and energy flux processes acting on subarctic Canadian Shield hillslopes and to understand runoff generation processes in the region. Results indicate that the magnitude of the spring snowmelt and its potential to flood exposed bedrock portions of the landscape controls the energy budget in the early part of the summer. In wet years high latent heat fluxes early in the summer deplete moisture storage by the end of July, after which latent heat fluxes decrease until the end of the growing season. In drier years, sensible heat dominates the early summer energy budget to a much larger degree than observed elsewhere in the subarctic. It then becomes a very arid landscape. High evaporation to precipitation ratios throughout the summer are an important feature of the western Canadian Shield subarctic region and this is important to its hydrology. Soil offers high available storage relative to adjacent exposed bedrock because evapotranspiration exceeds precipitation and soil filled areas dry. These differences in available storage result in a spatially heterogeneous runoff response within the basin because landscape elements spill runoff only where available storage is filled. Lateral inflows can be the primary source for filling soil zones to their storage capacity. The dependence of downslope landscape units on lateral inflows from upslope results in a cascading pattern of surface runoff generation. This is significantly different enough from the variable source area concept to indicate that another process must be operating. The element threshold concept is presented to generalize the suite of hydrological processes acting on subarctic Canadian Shield headwater basins. The new concept has the following attributes. It more accurately defines the important processes contributing to variable headwater subarctic Canadian Shield landscape runoff. It accounts for the different hydrological processes that occur in headwater basins. It recognizes that saturation thresholds vary extensively across headwater basins and that this affects subsequent runoff generation, such creates a disjointed contributing area that expands downslope depending on slope, soils, and vegetation. This thesis shows that hydrological and soil-vegetation-atmosphere modeling must account for dynamic small scale landscape elements and hydrological linkages in order to accurately represent the runoff generation processes on the subarctic Canadian Shield.

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