It is well known that the grid cell size of a raster digital elevation model has significant effects on derived terrain variables such as slope, aspect, plan and profile curvature or the wetness index. In this paper the quality of DEMs derived from the interpolation of photogrammetrically derived elevation points in Alberta, Canada, is tested. DEMs with grid cell sizes ranging from 100 to 5 m were interpolated from 100 m regularly spaced elevation points and numerous surface-specific point elevations using the ANUDEM interpolation method. In order to identify the grid resolution that matches the information content of the source data, three approaches were applied: density analysis of point elevations, an analysis of cumulative frequency distributions using the Kolmogorov-Smirnov test and the root mean square slope measure. Results reveal that the optimum grid cell size is between 5 and 20 m, depending on terrain complexity and terrain derivative. Terrain variables based on 100 m regularly sampled elevation points are compared to an independent high-resolution DEM used as a benchmark. Subsequent correlation analysis reveals that only elevation and local slope have a strong positive relationship while all other terrain derivatives are not represented realistically when derived from a coarse DEM. Calculations of root mean square errors and relative root mean square errors further quantify the quality of terrain derivatives.

Abstract:This paper presents the development and testing of a new method to estimate daily snowfall from precipitation and associated temperature records. The new method requires two variables; the threshold mean daily air temperature at which 50% of precipitation is considered snow, and the temperature range within which mixed precipitation can occur. Sensitivity analyses using 15 climate stations across south-western Alberta, Canada, and ranging from prairie to alpine regions investigates the sensitivity of those two variables on mean annual snowfall (MAS), the coefficient of determination, and the MAS-weighted coefficient of determination. Existing methods, including the static threshold method, one linear transition method used by Quick and Pipes, and the Leavesley method employed in the PRMS hydrological modelling system are compared with the new method, using a total of 963 years of daily data from the 15 climate stations used for the sensitivity analyses. Four different approaches to using the two input variables (threshold temperature and range) were tested and statistically compared: mean annual variables based on the 15 stations, mean annual variables for each station, mean monthly variables for each station, and a sine curve representing seasonal variation of the variables. In almost all cases the proposed new method resulted in higher MAS-weighted coefficients of determination, and, on average, they were significantly different from those of other methods. The paper concludes with a decision tree to help decide which method and approach to apply under a variety of data availabilities.

This paper combines a wide-area assessment of forecast changes in wintertime synoptic conditions over western North America with a meso-scale alpine hydrometeorology model to evaluate the impacts of forecast climate change on snowpack conditions in an alpine watershed. The synoptic analysis was used to generate long-term climate time series scenarios using the Canadian Centre for Climate Modelling and Analysis first-generation coupled general circulation model (GCM). The alpine hydrometeorology model SIMGRID is used to predict changes in wintertime precipitation at the watershed scale. The SNOPAC model is a simple snow model that predicts the overall snow accumulation throughout a watershed based on the output from SIMGRID. A vapour transfer model has been incorporated into the SNOPAC model to estimate snow volumes more accurately. The model is applied to a small alpine watershed in the southern Canadian Rockies. The synoptic analysis and GCM output forecasts a modest increase in both winter precipitation and temperatures in the study area. The hypothesis herein is that the increase in winter precipitation due to synoptic conditions will not compensate for regional changes in the rain-to-snow ratios. The net result will be a decline in winter accumulations of precipitation as snow, and hence an expected decline in spring runoff.

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Narrow riparian woodlands along non-perennial streams have made it possible for vervet monkeys to penetrate the semi-arid karoo ecosystem of South Africa, whilst artificial water points have more recently allowed these populations to colonize much more marginal habitat away from natural water sources. In order to better understand the sequelae of life in these narrow, linear woodlands for historically ‘natural’ populations and to test the prediction that they are ecologically stressed, we determined the size of troops in relation to their reliance on natural and artificial water sources and collected detailed data from two river-centred troops on activity, diet and ranging behaviour over an annual cycle. In comparison to other populations, our data indicate that river-centred troops in the karoo were distinctive primarily both for their large group sizes and, consequently, their large adult cohorts, and in the extent of home range overlap in what is regarded as a territorial species. Whilst large group size carried the corollary of increased day journey length and longer estimated interbirth intervals, there was little other indication of the effects of ecological stress on factors such as body weight and foraging effort. We argue that this was a consequence of the high density of Acacia karroo, which accounted for a third of annual foraging effort in what was a relatively depauperate floristic habitat. We ascribed the large group size and home range overlap to constraints on group fission.Conservation implications: The distribution of group sizes, sampled appropriately across habitats within a conservation area, will be of more relevance to management than average values, which may be nothing more than a statistical artefact, especially when troop sizes are bimodally distributed.