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The frost table depth is a critical state variable for hydrological modelling in cold regions as frozen ground controls runoff generation, subsurface water storage and the permafrost regime. Calculation of the frost table depth is typically performed using a modified version of the Stefan equation, which is driven with the ground surface temperature. Ground surface temperatures have usually been estimated as linear functions of air temperature, referred to as ‘n-factors’ in permafrost studies. However, these linear functions perform poorly early in the thaw season and vary widely with slope, aspect and vegetation cover, requiring site-specific calibration. In order to improve estimation of the ground surface temperature and avoid site-specific calibration, an empirical radiative–conductive–convective (RCC) approach is proposed that uses air temperature, net radiation and antecedent frost table position as driving variables. The RCC algorithm was developed from forested and open sites on the eastern slope of the Coastal Mountains in southern Yukon, Canada, and tested at a high-altitude site in the Canadian Rockies, and a peatland in the southern Northwest Territories. The RCC approach performed well in a variety of land types without any local calibration and particularly improved estimation of ground temperature compared with linear functions during the first month of the thaw season, with mean absolute errors

The hydrological sensitivity of a northern Canadian mountain basin to change in temperature and precipitation was examined. A physically based hydrological model was created and included important snow and frozen soil infiltration processes. The model was discretized into hydrological response units in order to simulate snow accumulation and melt regimes and basin discharge. Model parameters were drawn from scientific studies in the basin except for calibration of routing and drainage. The model was able to simulate snow surveys and discharge measurements with very good accuracy. The forcing inputs of the hourly air temperatures and daily precipitation were scaled linearly to examine the model sensitivity to conditions included in a range of climate change scenarios: warming of up to 5 °C and change in precipitation of +/− 20%. The results show that peak seasonal snow accumulation, snow season length, evapotranspiration, runoff, peak runoff, and the timing of peak runoff have a pronounced sensitivity to both warming and precipitation change, where the impact of warming is partly compensated for by increased precipitation and dramatically enhanced by decreased precipitation. The snow regime, including peak snow accumulation, snow-free period, intercepted snow sublimation, and blowing snow transport, was most sensitive to temperature, and the impact of a warming of 5 °C could not be compensated for by a precipitation increase of 20%. However, basin discharge was more sensitive to precipitation, and the impact of warming could be compensated for by a slight increase in precipitation. The impacts of 5 °C warming with a +/−20% change in precipitation resulted in snow accumulation, runoff, and peak streamflow decreasing by from one half to one fifth and the snow-free period lengthening by from 46 to 60 days; in both cases, the smaller change is associated with increased precipitation and the larger change with decreased precipitation. These results show that mountain hydrology in Northern Canada is extremely sensitive to warming, that snow regime is more sensitive to warming than streamflow and that changes in precipitation can partly modulate this response. Copyright © 2014 John Wiley & Sons, Ltd.

Yukon air temperature trends have been observed to change over the last several decades with an increase in annual, summer and winter air temperatures, while changes in precipitation have not been consistent. An assessment of freeze-up and break-up dates indicates that the ice cover season is becoming shorter with delays in freeze-up and advances in break-up timing. Mid-winter break-up events and associated flooding have been observed for the first time. Break-up water level trends suggest that break-up severity is increasing. These changes cannot be definitely attributed to climate change as there is some evidence suggesting that teleconnections may be a factor. The observed changes have significant implications pertaining to public safety, and economic impacts on property and infrastructure, transportation networks and hydroelectric operations. Ice jams and associated backwater and surges also affect aquatic ecosystems through impacts on biological and chemical processes.

Yukon air temperature trends have been observed to change over the last several decades with an increase in both summer and winter air temperatures. An assessment of streamflow response was carried out to determine if there are apparent trends in permafrost regions as a result of the observed temperature changes. Degrading permafrost places a greater reliance on the interaction between surface and subsurface processes. Annual mean, maximum and minimum flows were assessed using the Mann–Kendall test to statistically validate observed trends. Annual mean flows are observed to have slight positive trends over the last three decades within continuous and discontinuous permafrost zones, with variable results within sporadic permafrost regions. These results are generally in keeping with similar trends in annual precipitation, which has increased slightly. Though not generally statistically significant, annual peak flows have largely decreased within continuous permafrost regions, and lesser so within discontinuous regions. Results are variable within sporadic permafrost zones. These trends are likely associated with increased annual precipitation; however, it is conceivable that there may be increased infiltration amounts as a result of degrading permafrost. Winter low flows have experienced significant apparent changes over the last three decades. The greatest changes in winter low flows appear to be occurring within the continuous permafrost zone, where flows from the majority of sampled streams have increased. Winter low flows trends in streams within the discontinuous permafrost zone generally exhibit positive significant trends, but are more variable. Winter streamflow trends within the sporadic permafrost zone are not consistent.