Sub-canopy radiant energy during snowmelt in non-uniform forests spanning a latitudinal transect
In mountainous, forested environments, snowcover dynamics exert a strong control on hydrologic and atmospheric processes. Snowcover ablation patterns in forests are controlled by a complex combination of depositional patterns coupled with radiative and turbulent heat flux patterns related to topographic and canopy cover variations. Quantification of small-scale variations of radiant energy in forested environments is necessary to understand how canopy structure affects snowcover energetics to improve the representation of snowmelt processes in spatially-explicit physically-based snowmelt models. Incoming solar and thermal radiation were measured during the melt season within continuous and discontinuous forest stands, and at the interface between forest patches and small clearings along a transect spanning the North American Cordillera. Results indicate that reductions in solar radiation at the snow surface are partially balanced by increased thermal radiation from the forest canopy, relative to open locations. The differences between the transfer processes for solar and thermal radiation can produce two net incoming and net snowcover radiation paradoxes in heterogeneous environments. In discontinuous canopies, net radiation in forested areas may exceed radiation in open sites, whereas in other situations, net radiation may be less than net radiation in closed canopy forests. The empirical results coupled with theoretical modeling indicates that the effects of forest canopies on the radiative regimes at the snow surface are controlled by complex interactions of slope, aspect, gap sizes, canopy height, canopy density, canopy temperature, snow surface temperature and snowcover albedo. In higher latitude, closed canopy forests, radiative regimes may be characterized by relatively simple geometric optical radiation transfer methods, whereas at lower latitude and more non- uniform forests, other processes such as canopy and stem heating must be considered. These net radiation differences coupled with decreased turbulent fluxes due to lower wind velocities and reduced snow water equivalent values due to canopy interception losses help to explain small-scale patterns of snowmelt in non- uniform forested areas. Future investigations will use physically based models coupled with LiDAR derived topographic and vegetation data to assess how these small-scale processes integrate in both space and time to control the timing and rates of snowcover ablation in complex vegetated terrain.
Hydrological Modelling of a Small Alpine Watershed in the Canadian Rocky Mountains
Alpine environments form the headwaters of many large river systems that supply a significant proportion of the world's population with water. Human reliance on the seasonal melt of snow packs and glaciers, coupled with the threat of climate warming, calls for the ability to accurately predict the hydrology of these high elevation regions. However, these efforts are often complicated by extreme heterogeneity with regards to land cover, slope, aspect, and elevation. In this study, a land-surface hydrological model (MESH) is used to simulate the Opabin watershed, a 5 km2 area within the Lake O'Hara Research Basin in Yoho National Park, British Columbia. Ranging in elevation from 2,000 to 3,400 metres above sea level, the watershed consists of exposed bedrock, a large moraine, talus slopes, alpine tundra, and subalpine forest - as well as several small lakes and a glacier. A landscape-scale approach using a single grid cell and land class is initially employed; however, this basic model generates simulated variables that do not conform well to observed values. Performing simulations with an increased number of land class divisions helps to address land-surface heterogeneity while finer grid resolution allows for spatial variations in topography. Although these alterations lead to a more realistic model, both come at the expense of computational efficiency and therefore may not be feasible for larger areas. This presentation explores these methods and attempts to understand how the issues of heterogeneity and scale can be resolved in the mountainous terrain of the Canadian Rockies.
A Coupled Energy and Water Balance Model for Snow-Vegetation-Soil Systems
In mountainous and cold regions of the world snowmelt dominates the water balance, yet is quantified poorly despite the wealth of available remote sensing observations. Field measurements of snow cover and soil moisture are limited to experimental sites while the accuracy of soil moisture measurements from passive and active microwave sensors such as the upcoming SMOS and SMAP missions depends on a good physical understanding of the soil system. An improved approach to interpret remote sensing observations is to use a physically - based model in conjunction with the observations. However, many of the models currently available are either too complex for use across a range of scales, or lack elements that govern the energy and mass balance of the system (for example, snow, soil or vegetation). A new coupled energy and water balance model that integrates snow and soil moisture has been developed to simulate the evolution of the snow cover in addition to soil temperature and moisture profiles. The model was formed by coupling Snobal, a physically - based two-layer snow model, with a simplified version of SHAW, a multi-layer soil heat and water balance model that also simulates soil freezing. We present a point test of the model for a snow covered bare soil using hourly measurements of meteorological conditions, from an experimental site within the Reynolds Creek Experimental Watershed in Idaho, USA. These data were used to drive the model, which was then evaluated against hourly measured snow deposition and melt, as well as soil temperature and moisture profiles from the same site. Later research will focus on the vegetation component of the coupled system. The coupled model is computationally simple enough for regional simulations and could be used to form the basis of a data assimilation framework to retrieve snow and soil parameters from remote sensing measurements.
Determining Snowmelt Contributions to the Water Balance in a Heterogeneous Alpine Watershed: Lake O'Hara Research Basin
The rivers flowing from the Rocky Mountains are an important source of water for much of the population in western Canada. Small-scale hydrological studies in mountain headwater catchments are necessary to better understand the timing of source water contributions (glacier melt, snow, rain) and the surface and subsurface pathways by which these waters reach mountain rivers. A hydrological study in the 5-km2 Opabin watershed, within the Lake O'Hara Research Basin, Yoho National Park is addressing these research needs through comprehensive hydrological monitoring and geophysical investigations. A key component of this work is assessing the seasonal and daily contributions of snowmelt to the water balance through a combination of field data collection and snowmelt modeling. Field data includes snow-water-equivalent surveys at the peak of accumulation and bi-weekly during the melt season, meteorological data from automatic weather stations, and oblique-angle photographs for snow-cover-area depletion monitoring. A distributed meteorological dataset is derived for this high-relief watershed, including terrain effects on incoming solar radiation. This dataset is subsequently used to drive a one-dimensional snowmelt model that is run in a distributed fashion for the melt season only. The results and challenges of determining snowmelt inputs for the 2008 season will be presented.
Assessing the potential contribution of blowing snow to the mass balance of glaciers in the Cariboo Mountains of British Columbia, Canada
The difference between snow accumulation and ice ablation determines the mass balance of glaciers, with snowfall as the dominant input. However, blowing snow is another important term in glacier mass balance. Blowing snow occurs when loose particles of snow at the surface are entrained by winds exceeding a certain threshold for transport. The role of blowing snow in the surface mass balance of glaciers in the Cariboo Mountains (the northern extension of the Columbia Mountains) of British Columbia, Canada is assessed in this study. The regional atmospheric modeling system (RAMS) model is used to simulate several case studies of blowing snow in the region of interest. The simulations are validated with meteorological data from a mesoscale network (mesonet) of high-elevation automatic weather stations (AWSs) entitled the Cariboo Alpine Mesonet (CAMnet) that has been developed in the region since 2006. The mass divergence (convergence) fields from the RAMS simulations provide an indication of the blowing snow erosion (accumulation) areas. These are then compared with the spatial distribution of glaciers in the Cariboo Mountains. Our results suggest that snow drift may contribute significantly to the mass budget of glaciers in the region.
Controls on Groundwater Flow in an Alpine Talus-Moraine Complex
Since alpine watersheds are the headwaters of rivers acting as major sources of water, there is growing concern over water shortages in areas dependent on mountain runoff. Talus and moraine complexes, as well as fractured bedrock, are a dominant hydrologic response unit within the Lake O'Hara Research Basin (LORB) in Yoho National Park, British Columbia. In this alpine environment, previous studies have shown that groundwater plays an important hydrological role. Although little is known about groundwater storage in these media, they are likely a significant groundwater reservoir and an important control on groundwater flow. The goals of this study are to develop a conceptual model of the talus and moraine complex and the fractured bedrock. The approximately 0.3km2 Babylon drainage basin within the LORB was chosen as the study site as it contains a talus and moraine complex that drains into one gaugeable stream. The conceptual model of this basin has been developed using geophysical, hydrological and hydrogeological methods. Three Ground Penetrating Radar (GPR) and Electrical Resistivity Imaging (ERI) surveys were used to characterize the subsurface structure and water distribution within the talus and moraine complex. The bedrock surface is clearly defined in the GPR profiles and its elevation agrees with that in the ERI inversions. Highly resistive talus material is observable in the ERI results, and areas of low resistivity are found within the bedrock. Hydraulic conductivity estimates of the geologic media, calculated using tracer slug injection and baseflow recession analysis methods, fall within the ranges from gravel to fractured rock. Isotopic hydrograph separations indicate that groundwater is a significant contributor to stream discharge. Linear reservoir models show basin response times of up to 16 hours. The geophysical and hydrological evidence points toward two flow systems operating in the Babylon basin, those of flow through the fractured bedrock and flow through the talus and moraine complex. Understanding the hydrologic characteristics of alpine talus and moraine complexes and fractured bedrock is of great importance to increasing our knowledge of alpine hydrology. The results from this study will enable the estimation of hydrologic parameters of these geologic media and provide valuable information for the predictive modelling of mountain streams.
Application of a Coupled Multiscale Atmospheric-Land Surface Model to Simulate the Snow Circulation in a Mountain Basin
Snow cover spatial variability and snowmelt runoff are greatly influenced by the snow advected due to the wind- flow in the atmospheric boundary layer. Typically this has been accomplished by considering the snow as a subgrid scale problem in the atmospheric models. However, this subgrid scale approach can not be sufficient to explain the snow dynamics. Therefore a multiscale strategy where the hydrological, climatological, meteorological and physiographic conditions of a basin are related should improve the understanding of snow dynamics. This methodology was developed coupling the Global Environmental Multiscale Limited Area Model (GEM-LAM) with the Cold Regions Hydrological Model (CRHM). The GEM-LAM was used on a one-way nesting configuration to simulate the atmospheric-land fields at 100m of resolution with the Interactions between Soil, Biosphere, and Atmosphere (ISBA) soil scheme. The CRHM is used as a snow transport model at the hydrometeorological stations located in the basin. The case of study is the 4th November 2007 at Marmot Creek (50° 57' N, 115° 10' W), Alberta, Canada. This strategy has proved to be a physics based procedure to describe the snow dynamics without interpolation methods.