Flows from river basins in northwestern Canada have been rising in the last two decades as a result of climate warming. In the wetland‐dominated basins that characterise the southern margin of permafrost, permafrost thaw and disappearance, and resulting land‐cover change, is occurring at an unprecedented rate. The impact of this thaw on runoff generation in headwater basins is poorly understood. Permafrost thaw has the potential to fundamentally alter the cycling and storage of moisture inputs in this region by altering the type and relative proportions of the major land‐cover types, such as peat plateaus, channel fens and flat bogs. This paper examines streamflow changes in the four Water Survey of Canada gauged river basins (152–2050 km2) in the lower Liard River valley, Northwest Territories, Canada, a region where permafrost thaw has produced widespread loss of forest and concomitant expansion of permafrost‐free wetlands. Annual runoff in the lower Liard Valley increased by between 112 and 160 mm over the period of 1996–2012. The Mann‐Kendall non‐parametric statistical test and the Kendall‐Theil robust line were used to ascertain changes in streamflow. Historical aerial photographs from 1977 and high‐resolution satellite imagery (WorldView 2) from 2010 were used to measure the rate and pattern of permafrost thaw in a representative 6 km2 area of Scotty Creek. Permafrost thaw‐induced land‐cover change is both increasing the adjacency between runoff producing and transmitting land cover types and transforming certain land covers that store water into ones that produce runoff. This land‐cover change was found to be the single most important factor (37–61 mm) contributing to the observed increase in river discharge. Other contributing factors include increases in plateau runoff contributing areas (20–32 mm), increases in annual effective precipitation depth (18–30 mm), contribution of water from the melt of ice within permafrost (9 mm) and increases in baseflow (0.9–6.8 mm). Although runoff has significantly (p < 0.05) increased in all four basins, the largest increases are in basins with a relatively high cover of flat bogs. Copyright © 2014 John Wiley & Sons, Ltd.

Measurements of active layer thickness (ALT) are typically taken at the end of summer, a time synonymous with maximum thaw depth. By definition, the active layer is the layer above permafrost that freezes and thaws annually. This study, conducted in peatlands of subarctic Canada, in the zone of thawing discontinuous permafrost, demonstrates that the entire thickness of ground atop permafrost does not always refreeze over winter. In these instances, a talik exists between the permafrost and active layer, and ALT must therefore be measured by the depth of refreeze at the end of winter. As talik thickness increases at the expense of the underlying permafrost, ALT is shown to simultaneously decrease. This suggests that the active layer has a maximum thickness that is controlled by the amount of energy lost from the ground to the atmosphere during winter. The taliks documented in this study are relatively thin (<2 m) and exist on forested peat plateaus. The presence of taliks greatly affects the stability of the underlying permafrost. Vertical permafrost thaw was found to be significantly greater in areas with taliks (0.07 m year−1) than without (0.01 m year−1). Furthermore, the spatial distribution of areas with taliks increased between 2011 and 2015 from 20% to 48%, a phenomenon likely caused by an anomalously large ground heat flux input in 2012. Rapid talik development and accelerated permafrost thaw indicates that permafrost loss may exhibit a nonlinear response to warming temperatures. Documentation of refreeze depths and talik development is needed across the circumpolar north.

In the zone of discontinuous permafrost, the cycling and storage of water within and between wetlands is poorly understood. The presence of intermittent permafrost bodies tends to impede and re‐direct the flow of water. In this region, the landscape is characterized by forested peat plateaus that are underlain by permafrost and are interspersed by permafrost‐free wetlands. These include channel fens which convey water to the basin outlet through wide, hydraulically rough channels and flat bogs which are typically thought to retain moisture inputs as storage. Field studies conducted at a peatland‐dominated landscape near Fort Simpson, Northwest Territories, Canada, indicate the presence of ephemeral drainage channels that form a cascade of connected bogs that ultimately discharges into a channel fen. Consequently, understanding bogs as dynamic transmitters of surface and subsurface flows, rather than simple storage regions, calls for further examination. Whether bogs act as either storage features or flow through features has a direct impact on the runoff contributing area in a basin. Here, two adjacent series of bog cascades were gauged over two consecutive years to determine spatial and temporal changes in effective runoff contributing areas. It was found that runoff varies significantly between two adjacent bog cascades with one cascade producing 125 mm of runoff over the 2‐year period, while the other yielded only 25 mm. The bog cascades are primarily active during the snowmelt season when moisture conditions are high; however flows can also be generated in response to large rain events. It is proposed that bog cascades operate under an ‘element threshold concept’ whereby in order for water to be transmitted through a bog, the depression storage capacity of that bog must first be satisfied. Our work indicates that whether bogs act as storage features or flow‐through features has a direct impact on the runoff contributing area in a basin. Neglecting to represent connected bogs as dynamic transmission features in the landscape is shown to underestimate water available for streamflow by between 5 and 15%, and these systems are therefore a key component of the water balance in discontinuous permafrost regions. Copyright © 2015 John Wiley & Sons, Ltd.

Taliks (perennially thawed soil in a permafrost environment) are generally found beneath water bodies or wetlands, and their development and evolution in other environments is poorly documented. Sustained isolated taliks between seasonally frozen surface soils and permafrost have been observed at the Scotty Creek Research Station in the discontinuous permafrost region of the Northwest Territories, Canada. These taliks have been expanding both vertically and laterally over the past decade of monitoring. The main controls on expansion are thought to be (1) the availability of energy, determined by incoming radiation and advective heat flux, (2) the ability to transfer this energy to the freezing/thawing front, determined by the thermal conductivity (soil properties and moisture content), and (3) the presence and thickness of the snowpack. These controls are investigated using data collected in the field to inform a 1‐D coupled thermodynamic freeze‐thaw and unsaturated flow model. The model was successfully used to represent observed thaw rates in different parts of the landscape. It is found that high soil moisture, deeper snowpacks, and warmer or faster advective flow rates all contribute to accelerated talik growth and subsequent permafrost degradation. Simulations show that slight perturbations of available energy or soil properties, such as an increase in average surface temperature of 0.5°C or a 1‐cm change in snow water equivalent, can lead to talik formation, highlighting the vulnerability of this landscape to changes in climate or land cover.

Northwestern Canada is one of the most rapidly warming regions on Earth. The scale and rapidity of recently observed warming-induced changes throughout this region indicate that it is particularly sensitive to climate warming and capable of rapid responses to perturbations. Unprecedented rates of permafrost thaw in the zone of discontinuous permafrost are transforming forests to wetlands, and changing the distribution and routing of water over the landscape as evidenced by recent increases in basin discharge. However, the impact of increasing basin discharge on basin water storage is not well understood. Water levels on a permafrost plateau, channel fen, and isolated and connected bogs were monitored from 2003-2017 in the Scotty Creek watershed, Northwest Territories. The water level in the channel fen did not significantly change over the period of study, sustained by inputs from the increasingly-connected network of bogs as permafrost barriers thawed. Bogs with varying levels of connection to the drainage network released from storage between 40 and 53 mm of water over the study period. The water level in the monitored isolated bog did not significantly change over this period. Estimates of moisture contributions derived directly from vertical permafrost thaw and from the lateral expansion of contributing areas account for 90% of the observed cumulative increase of 1043 mm in basin runoff between 1998-2012, leaving 109 mm of this increase unaccounted for. Increasing connectivity to the drainage network and transient wetland drainage at the landscape scale resulted from permafrost thaw-induced talik development. The similarity between the magnitude of wetland drainage and that of enhanced runoff suggests that increased connectivity of wetlands to the drainage network may contribute to increasing runoff from the Scotty Creek watershed. Permafrost thaw-induced land cover transition was found to have both short and long-term effects on runoff generation.