ALBERT

Description: Much of the snowmelt season is characterized by a patchy surface; differential heating of the snow and snow-free surfaces results in a significant horizontal transport of energy that affects and contributes to the snowmelt. The calculation of the rate of energy advection requires some knowledge of the behaviour of the thermal boundary layer over the patches of snow and snow-free surfaces. We present the results from a series of field observations of the rate of growth of the thermal boundary layer over snow and snow-free patches. The results confirm that the boundary-layer growth can be described by a power function of the distance from the leading edge of the patch. For the case of the thermal boundary layer over a snow patch within a bare field, the boundary-layer growth is affected by the upwind surface roughness; the thermal boundary layer over a snow patch within a 'rough' field grows much more quickly than that in a 'smooth' field. Relationships are derived and presented for the parameterization of the boundary-layer growth as a function of distance and upwind surface roughness. Copyright © 2006 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.

Description: Estimates of shortwave irradiance energy beneath needle-leaf forests over complex terrain are needed to drive energy balance snowmelt models and to evaluate the potential hydrological impacts of forest-cover change in mountain regions. This paper outlines and evaluates a physically-based model designed to estimate sub-canopy shortwave irradiance to snowcover under needle-leaf forest-cover with respect to surface slope and azimuth. Transmission of above-canopy irradiance was estimated using forest-surveys and hemispherical photographs to determine the fractions of forest-cover occupied by non-transmitting trunks, partially-transmitting crowns and fully-transmitting gaps with respect to above-canopy diffuse and direct beam shortwave irradiance. Simulations were conducted for continuous, uniform lodgepole pine forests on level site and a north facing slope and a discontinuous, non-uniform forest on a southeast facing slope during snowmelt at the Marmot Creek Research Basin, Alberta, Canada. Mean observed daily transmissivity values of inadiance were 0.09 at the north-facing forest, 0.21 at the level forest and 0.36 at the southeast-facing forest. Modelled and observed results indicate that potential snowmelt energy from sub-canopy shortwave irradiance is likely to exhibit the greatest variation with change in cloudiness and forest-cover density under south-facing forests and the least variation under north-facing forests. Comparisons of simulations to observations indicate that the model can explain much of the difference in daily shortwave transmission amongst sites, performing relatively poorest at the north-facing forest where fluxes were small and relatively best at the south-east facing forest where fluxes were large. However, simulation errors in terms of absolute irradiance were greatest at the southeast-facing forest, having a root mean square error (RMSE) 0.64 MJ m-2 d-1 compared to 0.44 MJ m-2 d-1 at the level forest and 0.27 MJ m-2 d-1 at the north-facing forest. Copyright © 2007 John Wiley & Sons, Ltd.

Description: Spatial and temporal patterns of areal snowcover depletion (SCD) were studied over a small (〈0.6 km2) alpine cirque within the Canadian Rocky Mountains using a combined approach of daily acquisition of remotely sensed imagery, together with meteorological observations and snowmelt modelling. Digital terrestrial photographs were georeferenced using a novel software tool together with a high-resolution digital elevation model and used to derive measurements of fractional snowcovered area (SCA) over the cirque. Manual snow surveys carried out in the pre-melt period were used to describe the initial frequency distribution of snow water equivalent (SWE) values over the cirque, and indicated a lognormal distribution of SWE when surveys were stratified by terrain features. Rates of snowmelt were simulated using a physically based snowmelt energy balance model, Snobal, driven by observed meteorological conditions at a nearby station, which were adjusted for slope orientation and exposure by making corrections to observed incoming shortwave and longwave radiation components in the cold regions hydrological model platform. Simulated melt rates were then applied to the approximated SWE distributions to model the decline in SCA over the spring. The model was found to perform well for the simulation of snowmelt based on point observations of SWE at the meteorological station, and produced a close correspondence between simulated and observed SCD curves representing two opposing slopes within the cirque. The results show that both the pre-melt distributions of SWE and the spring melt rates exhibit considerable spatial variability between distinct slope units within the cirque, and that this variability has a significant impact on simulated SCD. Assuming a unimodal pre-melt frequency distribution and conditions of spatially uniform snowmelt over complex terrain such as this can lead to large errors in the simulation results. It is suggested that modelling applications intended to represent snowmelt dynamics and areal SCD in similar alpine environments consider the effects of spatial variation in SWE distribution and melt energetics between slopes. Copyright © 2009 John Wiley & Sons, Ltd.

Description: To illustrate the hydrological impact of climate and land use change on an unregulated basin, the agriculture- and wetland-dominated Smith Creek Research Basin (SCRB) was examined in detail. Streamflows (1975-1994) show behaviour typical of the Canadian Prairies - generation primarily by snowmelt and cessation in May due to lack of runoff or groundwater contributions. Depressional storage has been drained for decades, reducing the extent of ponds by 58% and increasing drainage channel length 780%. Climate has also changed; increasing temperatures since 1942 have brought on a gradual increase in the rainfall fraction of precipitation (no trends in total precipitation) and an earlier snowmelt by 2weeks. The number of multiple-day rainfall events has increased by half, which may make rainfall-runoff generation mechanisms more efficient. Annual streamflow volume and runoff ratio have increased 14-fold and 12-fold, respectively, since 1975, with dramatically increasing contributions from rainfall and mixed runoff regimes. Snowmelt runoff has declined from 86% in the 1970s to 47% recently while rainfall runoff has increased from 7% to 34% of discharge. Peak discharge has tripled since 1975, with a major shift in 1994. Recent flood volumes in SCRB have been abnormally large, and high flows in June 2012 and flooding in June 2014 were caused solely by rainfall, something never before recorded at the basin. Changes to the observed character of precipitation, runoff generation mechanisms and depressional storage are substantial, but it is unlikely that any single change can explain the dramatic shift in SCRB surface hydrology. Further diagnostic investigation using process hydrology simulations is needed to explain the observed regime changes. © 2015 John Wiley & Sons, Ltd.

Description: The hydrography of the Prairies of western Canada and the north-central United States is characterized by drainage into small depressions, forming wetlands rather than being connected to a large-scale drainage system. In droughts, many of these water bodies completely dry up, while in wet periods, their expansion can cause infrastructure damage. As wetlands expand and contract with changing water levels, connections among them are formed and broken. The change in hydrographic connectivity dynamically changes the hydrological response of basins by controlling the area of the basin which contributes discharge to local streams.The objective of this research was to determine the behaviour of prairie basins dominated by wetlands through two sets of simulations. The first consisted of application and removal of water (simulating runoff and evaporation) from a LiDAR digital elevation model (DEM) of a small basin in the south-east of the Canadian Province of Saskatchewan. Plots of water surface area and of contributing area against depressional storage showed evidence of hysteresis, in that filling and emptying curves followed differing paths, indicating the existence of memory of prior conditions. It was demonstrated that the processes of filling and emptying produced differing changes in the frequency distributions of wetland areas, resulting in the observed hysteresis.Because the first model was computationally intensive, a second model was built to test the use of simpler wetland representations. The second model used a set of interconnected wetlands, whose frequency distribution and connectivity were derived from the original LiDAR DEM. When subjected to simple applications and removal of simulated water, the second model displayed hysteresis loops similar to those of the first model. The implications for modelling prairie basins are discussed. © 2011 John Wiley & Sons, Ltd.