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Snow accumulation, re-distribution and melt are important hydrological considerations in the Arctic. This study presents a model of the late-winter snow cover and the ensuing snowmelt in a High Arctic environment at a scale of 1 km. Indexing is used to spread the snow data from a lowland weather station to various terrain units over a 16×13 km2 target area east of Resolute, Cornwallis Island, Canada. Meteorological variables measured at this base station are spatially extended by field derived empirical relationships for the computation of melt at various terrain units using the energy balance approach. These melt rates are weighted by the fractional coverage of various terrain unit within each 1×1 km2 cell. The snow distribution pattern is obtained daily and model performance was tested by comparing observed and computed dates of melt and the radiation balance over snow. The simulated snow pattern compared favourably with the snow cover imaged by LANDSAT. Daily changes in the probability distribution of snow water equivalent over the target area was examined and snow depletion curves were derived. They describe sub-grid variability over an area and our results point to several assumptions that should be scrutinized in sub-grid parameterization of snow distribution.

ABSTRACT. Semi-permanent snow is part of the continuum between seasonal snow and glacier ice. Although ubiquitous in the High Arctic, most late-lying snow banks and snow beds have lost their perennial status over the past decade as the summers have become progressively warmer. The loss over the past decade is the most unprecedented since aerial photography of the Canadian Arctic islands was first undertaken over half a century ago, and it has produced observable thermal, hydrological and ecological impacts. Where the ground has become exposed beneath the perennial snow cover, seasonal ground thaw has deepened. Tundra ponds and patchy wetlands fed principally by meltwater in the summer have suffered water-level decline or desiccation. The water balance of headwater basins is also affected, losing a buffering vehicle that accumulates storage surplus from the wet cool years to support streamflow and evaporation in the dry warm years. The tundra vegetation, already sparse, undergoes changes in the long term. As an essential source of water in the polar desert environment, the widespread distribution of semi-permanent snow magnifies its Arctic-wide importance.

AbStRACt. Arctic wetland environments are sensitive to ongoing climate change as seen by the recent loss of lakes and ponds in southern Alaska, Siberia, and northern Ellesmere island, Canada. A clearer picture of the mechanisms accounting for these losses or the persistence of ponds is presently required. to better understand and quantify the hydrologic processes that are leading to the sustainability or demise of High Arctic ponds, a detailed study was conducted during the summer seasons of 2006 at Somerset Island, Nunavut (72˚43' N, 94˚15' W). A water balance framework that quantifies water inputs, losses, and storage was employed on four ponds situated in three broad geomorphic areas (coastal, bedrock, and glacial terrain, which includes plateau and moraine). The initial snow cover amount influenced the water level pattern for the summer season. Large end-of-winter snow accumulations in the deep bedrock pond ensured large initial water storage and seasonal sustainability despite variable climatic conditions and a coarse substrate, which encouraged subsurface outflow. Connectivity to a stream draining an upland area and a melting late-lying snowbed nearby allowed the small Moraine pond to maintain stable water levels throughout both years. Sandy soils typical of the Coastal and Plateau ponds favored seepage and subsurface water losses, leading to desiccation of these ponds during dry periods. Lateral water losses from the Coastal pond were enhanced by the presence of a downslope frost crack that formed a steep hydraulic gradient with the pond. High initial snowfall and substantial rain maintain pond water levels, but in years with low snowfall and dry conditions, ponds are vulnerable to disappearance unless a range of dependable hydrological linkages exists.Key words: Arctic hydrology, climate change, connectivity, low-gradient wetland, sustainability RÉSuMÉ. Les milieux humides de l'Arctique sont sensibles aux changements climatiques continus, tel que l'atteste la perte récente de lacs et d'étangs du sud de l'Alaska, de la Sibérie et du nord de l'île d'Ellesmere, au Canada. À l'heure actuelle, il faut obtenir une meilleure idée des mécanismes à la source de ces pertes ou à la source de la persistance des étangs. Afin de mieux comprendre et de quantifier les processus hydrologiques qui entraînent la durabilité ou la disparition des étangs de l'Extrême arctique, une étude détaillée a été réalisée au cours des étés 2005 et 2006 à l'île Somerset, au Nunavut (72˚43' N, 94˚15' O). À quatre étangs situés dans trois grandes zones géomorphologiques (côtière, roche de fond et terrain glaciaire, ce qui comprend plateaux et moraines), on a utilisé un cadre de référence de bilan hydrique quantifiant les gains, les pertes et le stockage d'eau. La quantité de couverture de neige initiale exerçait une influence sur le modèle de niveau d'eau pendant la saison d'été. Les fortes accumulations de neige en fin d'hiver dans la profonde roche de fond des étangs donnaient lieu à un important stockage initial de l'eau et à la durabi...