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Abstract:After a programme of integrated field and modelling research, hydrological processes of considerable uncertainty such as snow redistribution by wind, snow interception, sublimation, snowmelt, infiltration into frozen soils, hillslope water movement over permafrost, actual evaporation, and radiation exchange to complex surfaces have been described using physically based algorithms. The cold regions hydrological model (CRHM) platform, a flexible object-oriented modelling system was devised to incorporate these algorithms and others and to connect them for purposes of simulating the cold regions hydrological cycle over small to medium sized basins. Landscape elements in CRHM can be linked episodically in process-specific cascades via blowing snow transport, overland flow, organic layer subsurface flow, mineral interflow, groundwater flow, and streamflow. CRHM has a simple user interface but no provision for calibration; parameters and model structure are selected based on the understanding of the hydrological system; as such the model can be used both for prediction and for diagnosis of the adequacy of hydrological understanding. The model is described and demonstrated in basins from the semi-arid prairie to boreal forest, mountain and muskeg regions of Canada where traditional hydrological models have great difficulty in describing hydrological phenomena. Some success is shown in simulating various elements of the hydrological cycle without calibration; this is encouraging for predicting hydrology in ungauged basins.

Pomeroy, J. W., Gray, D. M., Hedstrom, N. R., Janowicz, J. R. (2002). Prediction of seasonal snow accumulation in cold climate forests. Hydrological Processes, 16(18), 3543-3558. 59th Eastern Snow Conference (ESC), Stowe, Vermont, 5-7 June 2002.Accumulation of snow under forest canopies is known to decline with increasing canopy density and leaf area because of snow interception and sublimation in the canopy. Seasonal snow accumulation measurements, collected over a decade from various forest stands in western Canada, were used to test and develop methods to relate forest snow accumulation to stand properties and observations of either small-clearing seasonal snow accumulation or seasonal snowfall. At sub-stand scales, the variability of seasonal snow accumulation was not well related to stand leaf area, seasonal interception or small-clearing seasonal snow accumulation. At the stand scale, physically based snow interception equations predicted seasonal snow accumulation from the stand leaf area and the seasonal snow accumulation or snowfall in adjacent clearings. A simple parametric form of these equations showed the sensitivity of seasonal snow accumulation to leaf area at the forest stand scale and suggested a relationship to extrapolate snow accumulation or snowfall measurements from clearings to forests. These relationships, developed from Canadian boreal forest observations, are consistent with Kuz'min's (1960. Formirovanie Snezhnogo Pokrova i Metody Opredeleniya Snegozapasov. Gidrometeoizdat: Leningrad) relationship between accumulation and canopy density derived from Russian observations, suggesting a good degree of transferability. Copyright 2002 Crown in the right of Canada. Published by John Wiley Sons, LtdNon peer reviewe

Abstract:A series of process-based algorithms has been developed to describe the accumulation, unloading and sublimation of intercepted snow in forest canopies. These algorithms are unique in that they scale up the physics of interception and sublimation from small scales, where they are well understood, to forest stand-scale calculations of intercepted snow sublimation. Evaluation of results from the set of algorithms against measured interception and sublimation, in a southern boreal forest jack pine stand during late winter, found that the coupled model provides reasonable approximations of both interception and sublimation losses on half-hourly, daily and event bases. Cumulative errors in the estimate of intercepted snow load over 23 days of test were 0 . 06 mm SWE, with a standard deviation of 0 . 46 mm SWE. Sublimation losses during the evaluation were high, approximately two-thirds of snowfall within this period. Seasonal intercepted snow sublimation as a portion of annual snowfall at the model test site was lower than sublimation during the tests, ranging from 13% for a mixed spruce±aspen, 31% for the mature pine and 40% for a mature spruce stand. The results indicate that sublimation can be a signi®cant abstraction of water from mature evergreen stands in northern forests and that the losses can be calculated by application of process-based algorithms. #