Modelling the effects of permafrost loss on discharge from a wetland‐dominated, discontinuous permafrost basin

Abstract

Permafrost degradation in the peat‐rich southern fringe of the discontinuous permafrost zone is catalysing substantial changes to land cover with expansion of permafrost‐free wetlands (bogs and fens) and shrinkage of forest‐dominated permafrost peat plateaux. Predicting discharge from headwater basins in this region depends upon understanding and numerically representing the interactions between storage and discharge within and between the major land cover types and how these interactions are changing. To better understand the implications of advanced permafrost thaw‐induced land cover change on wetland discharge, with all landscape features capable of contributing to drainage networks, the hydrological behaviour of a channel fen sub‐basin in the headwaters of Scotty Creek, Northwest Territories, Canada, dominated by peat plateau–bog complexes, was modelled using the Cold Regions Hydrological Modelling platform for the period of 2009 to 2015. The model construction was based on field water balance observations, and performance was deemed adequate when evaluated against measured water balance components. A sensitivity analysis was conducted to assess the impact of progressive permafrost loss on discharge from the sub‐basin, in which all units of the sub‐basin have the potential to contribute to the drainage network, by incrementally reducing the ratio of wetland to plateau in the modelled sub‐basin. Simulated reductions in permafrost extent decreased total annual discharge from the channel fen by 2.5% for every 10% decrease in permafrost area due to increased surface storage capacity, reduced run‐off efficiency, and increased landscape evapotranspiration. Runoff ratios for the fen hydrological response unit dropped from 0.54 to 0.48 after the simulated 50% permafrost area loss with a substantial reduction of 0.47 to 0.31 during the snowmelt season. The reduction in peat plateau area resulted in decreased seasonal variability in discharge due to changes in the flow path routing, with amplified low flows associated with small increases in subsurface discharge, and decreased peak discharge with large reductions in surface run‐off.

Summary and synthesis of Changing Cold Regions Network (CCRN) research in the interior of western Canada – Part 2: Future change in cryosphere, vegetation, and hydrology

“…Many areas within the Taiga Plain are highly susceptible to thaw through this process (e.g., Gibson et al, 2020) and widespread replacement of forest-covered peat plateaus by wetlands is expected over the coming decades. A caveat is that these ecosystems represent some of the strongest ecosystem-protected permafrost, so undoubtedly a portion of permafrost peatland will linger, but this will depend on the degree of warming and also fire (Stralberg et al, 2020).…”

Evaluating the suitability of three gridded‐datasets and their impacts on hydrological simulation at Scotty Creek in the southern Northwest Territories, Canada

“…The input forcing dataset, used to simulate discharge for the subcatchment, consisted of measured relative humidity, wind speed, incoming shortwave radiation, temperature, and precipitation at Scotty Creek from 2008 to 2013. Other model parameters for CRHM were transferred to similar basins or from field observations at Scotty Creek (Quinton & Baltzer, ; Stone et al, ). Because no discharge data exists at the subcatchment level, model performance was determined to be acceptable by comparing observed and simulated snow depth, snow water equivalent, evapotranspiration, and water level in multiple hydrological response units against model output (Stone et al, ).…”

“…Other model parameters for CRHM were transferred to similar basins or from field observations at Scotty Creek (Quinton & Baltzer, ; Stone et al, ). Because no discharge data exists at the subcatchment level, model performance was determined to be acceptable by comparing observed and simulated snow depth, snow water equivalent, evapotranspiration, and water level in multiple hydrological response units against model output (Stone et al, ). Here, the same model was used changing only the input forcings using daily temperature and precipitation from ANUSPLIN, ERA‐Interim, and MERRA‐2 for the grid point nearest to Scotty Creek for the period from 2008 to 2013.…”

Summary and synthesis of Changing Cold Regions Network (CCRN) research in the interior of western Canada – Part 2: Future change in cryosphere, vegetation, and hydrology

“…Talik expansion provides an additional drainage path for wetland dewatering-one that conducts water throughout the year (Connon et al, 2018;Devoie et al, 2019). While this may give rise to transient increases in basin discharge due to the increased connectivity and dewatering of wetlands (Quinton et al, 2019), the process is not sustainable and may result in eventual drying of the landscape with increasing ET (Stone et al, 2019). Regeneration of black spruce forest may ultimately occur in the absence of permafrost, as has been observed further south Northwest Territories-British Columbia border (Carpino et al, 2018).…”