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.

Increased attention directed at the permafrost region has been prompted by resource development and climate change. This review surveys advances in permafrost hydrology since 2000. Data shortage and data quality remain serious concerns. Yet, there has been much progress in understanding fundamental hydrologic processes operating in a wide range of environments, from steep mountainous catchments, to the Precambrian Shield with moderate relief, to the low‐gradient terrain of plains, plateaus and wetlands. Much of the recent research has focused on surface water, although springs and groundwater contribution to streamflow have also been studied. A compendium of water‐balance research from 39 high‐latitude catchments reveals the strengths and limitations of the available results, most of which are restricted to only a few years of study at the small watershed scale. The response of streamflow to climate receives continued if not increasing attention, from the occurrence of extreme hydrologic events to the changing regimes of river flow at a regional scale. The effect of climate change and the role of permafrost on the changing discharge of large boreal rivers are major topics for further investigation. Extended field and modelling research on physical processes will improve knowledge of permafrost hydrology and enhance its relevance to societal needs. Copyright © 2008 John Wiley & Sons, Ltd.

As the permafrost region warms, its large organic carbon pool will be increasingly vulnerable to decomposition, combustion, and hydrologic export. Models predict that some portion of this release will be offset by increased production of Arctic and boreal biomass; however, the lack of robust estimates of net carbon balance increases the risk of further overshooting international emissions targets. Precise empirical or model-based assessments of the critical factors driving carbon balance are unlikely in the near future, so to address this gap, we present estimates from 98 permafrost-region experts of the response of biomass, wildfire, and hydrologic carbon flux to climate change. Results suggest that contrary to model projections, total permafrost-region biomass could decrease due to water stress and disturbance, factors that are not adequately incorporated in current models. Assessments indicate that end-of-the-century organic carbon release from Arctic rivers and collapsing coastlines could increase by 75% while carbon loss via burning could increase four-fold. Experts identified water balance, shifts in vegetation community, and permafrost degradation as the key sources of uncertainty in predicting future system response. In combination with previous findings, results suggest the permafrost region will become a carbon source to the atmosphere by 2100 regardless of warming scenario but that 65%-85% of permafrost carbon release can still be avoided if human emissions are actively reduced.

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Abstract:Subsurface flow through peat plays a critical role in the hydrology of organic-covered, permafrost terrains, which occupy a large part the continental arctic, sub-arctic, and boreal regions. Hillslope drainage in these terrains occurs predominantly through the active flow zone between the relatively impermeable frost table and the water table above it. The hydraulic conductivity profile within this zone controls the subsurface drainage of snowmelt and storm water. Peat hydraulic conductivity profiles were examined at three sites in north-western Canada, each representing a widely occurring organic-covered, permafrost terrain type. Three independent measures of saturated hydraulic conductivity were used-tracer tests, constant-head wellpermeameter tests, and laboratory measurements of undisturbed samples. At all three sites, the conductivity profiles contained very high values (10-1000 m d 1 ) within the top ca 0Ð1 m where the peat is only lightly decomposed, a large reduction with increasing depth below the ground surface in the transition zone, and relatively low values in a narrow range (0Ð5-5 m d 1 ) below ca 0Ð2 m depth, where the peat is in an advanced state of decomposition. Digital image analysis of resin-impregnated peat samples showed that hydraulic conductivity is essentially controlled by pore hydraulic radius. The strong dependence of hydraulic conductivity on hydraulic radius implies that peat soils subjected to similar degrees of decomposition and compaction have a similar hydraulic conductivity regardless of the location. This explains the similarity of the depth-conductivity profiles among all three terrain types.