R. J. Granger

Variation in Surface Energetics during Snowmelt in a Subarctic Mountain Catchment

Surface energetics and snow ablation were examined during the 1999 snowmelt season in a mountain subarctic tundra valley in the Yukon Territory of Canada. Considerations of melt energetics at small scales were made with respect to the frame of reference of the sloping surface snowpack. During relatively warm and sunny conditions early in melt, snow ablation rates were dramatically higher on the south-facing slope and strongly reduced on the north-facing slope, compared to the valley bottom. Negative spatial covariances developed between maximum snow accumulation and ablation rate during early and middle melt, with the highest ablation rates occurring on slopes with the shallowest snowpacks. Atmospheric conditions were sufficiently well mixed across the valley that reference level air temperatures and humidity among the slopes were close to levels of measurement accuracy. However, under high levels of April insolation, notable differences in incoming solar radiation to varying slopes/aspects caused relatively larger differences in net radiation and surface temperature, which were progressively magnified as shrubs and soil became exposed during snow ablation. Under cloudier conditions later in melt, the south-facing snowpack had mostly ablated, vegetation was exposed at all sites, and ablation rates were virtually identical between the valley bottom and north-facing slope. Driven primarily by initial differences in insolation and snow accumulation, surface energy fluxes changed sign and magnitude over space, not only with insolation, vegetation cover, slope, and aspect, but also with the snow cover state and ground/ vegetation exposure. Melt rate was, hence, controlled by both incoming energy and evolving and initial snow states. For these reasons, and because of the slope-based frame of reference necessary to precisely define the snowmelt energy balance, simple aggregate representations of melt in subarctic mountain environments that are based on averaged energy flux, snow state, and flat-plane conceptions may require substantive corrections that should be explored in modeling studies.

Soil moisture storage in mature and replanted sub-humid boreal forest stands

Soil moisture profiles at two mature forest sites (Pine and Mixed-Wood) and two plantations (1981 Pine and 1992 Mixedwood) in central Saskatchewan were studied in conjunction with soil properties, precipitation, interception and evapotranspiration. Sampling locations within each stand were chosen to highlight differences in soil moisture due to interception, evapotranspiration and soil physical properties.Soil moisture storage to 1-m depth was greatest on the 92-Plantation where transpiration and interception of precipitation were less than the other sites. Moisture storage in the 81-Plantation was similar to that in the mixed-wood stand. The Pine stand had the lightest textured soils and stored least water to 1-m depth. Variability in moisture storage was also observed within stands and was associated with canopy structure and density, water extraction patterns and mechanical site preparation. In the furrows at the 92-Plantation, wet soils in combination with low infiltration rates and transpiration may ...

An extension of the force‐restore method to estimating soil temperature at depth and evaluation for frozen soils under snow

Hirota, T., Pomeroy, J. W., Granger, R. J., Maule, C. P. (2002). An extension of the force-restore method to estimating soil temperature at depth and evaluation for frozen soils under snow. Journal of Geophysical Research-Atmospheres, 107, Issue D4.

Estimation of Water Temperature of Large Lakes in Cold Climate Regions during the Period of Strong Coupling between Water and Air Temperature Fluctuations

Abstract Near-surface bulk water temperature measured in large northern lakes during the warm season with buoys can be characterized by three components: a slowly varying seasonal-/climate-related trend, fluctuations at the time scale of weather perturbations, and rapid daily fluctuations. When thermal infrared data are used to estimate surface water temperature, an additional term relating the differences between the skin and bulk temperatures is implied. Buoy data in this work serve to demonstrate the existence of a period of strong signal coupling between fluctuations of water temperature and air temperature. The period of strong signal coupling does not extend beyond the date of maximum temperature in the water temperature trend. During this period, a simple linear transformation of air temperature fluctuations can be used to simulate the buoy water temperature fluctuations. Attempts to simulate water temperature fluctuations from air temperature alone are not possible beyond this period. Water temper...

Evaporation/Evapotranspiration Estimates with Remote Sensing

Evaporation is the transfer of water from a surface to the atmosphere. The evaporative process is intimately linked to the energy balance. In northern environments, the interactions between energy, land, and water can be different from those for more temperate regions. The application of any evapotranspiration model, with or without the use of remotely sensed data, to the northern environment requires that due consideration be given to those factors that become increasingly significant as one moves northward. For methods based on some reformulation of the energy balance, the inclusion and correct parameterization of the soil heat flux term is essential. The effect of the vegetation cover on the partitioning of energy to soil heat flux has been recognized and is demonstrated. Remote sensing of evaporation from water surfaces in northern regions suffers from two major deficiencies: (1) Relatively little is known about the evaporation regime of northern lakes; and (2) relatively little effort has been directed towards the development of remote sensing techniques for estimating evaporation from open water in general. For the estimation of lake evaporation, an improved understanding of the advective boundary layer over water is required. With respect to remote sensing of lake evaporation, although water surface temperatures are easily obtained in the absence of cloud cover, improved parameterization of ice formation and decay is required.