Numerical modelling of permafrost dynamics under climate change and evolving ground surface conditions: application to an instrumented permafrost mound at Umiujaq, Nunavik (Québec), Canada

Abstract

Numerical simulations were carried out based on a conceptual cryohydrogeological model of a permafrost mound near Umiujaq, Nunavik (Québec), Canada, to assess the impacts of climate warming and changes in surface conditions on permafrost degradation. The 2D model includes groundwater flow, advective-conductive heat transport, phase change and latent heat. Changes in surface conditions which are characteristic of the site were represented empirically in the model by applying spatially-and temporally-variable ground surface temperatures derived from linear regressions between monitored surface and air temperatures. After reaching a transient steadystate condition close to present-day conditions, the simulations were then extended to 2100 under hypothetical climate warming scenarios and using imposed changes in surface conditions consistent with observed on-site evolution. The simulations show that the development of a thermokarst pond and shrubification respectively induce ground warming of up to 0.5°C and 1.5°C, upward migration of the permafrost base by up to 2 and 4 m, and a decrease in the lateral permafrost extent of 1 and 7 m, relative to a reference case without changes in surface conditions. Feedback from permafrost degradation which drives changes in ground surface conditions should be included in future numerical modelling of permafrost dynamics. RÉSUMÉ

Three‐Dimensional Numerical Modeling of Cryo‐Hydrogeological Processes in a River‐Talik System in a Continuous Permafrost Environment

“…(2020), and Perreault et al. (2021). In the Kuuguluk River model, simulated summer recharge rates across the thawed active layer generally varied between 50 and 200 mm/year, depending on the topography‐constrained heads, the local hydraulic conductivities (Table 2), and depth to the permafrost table.…”

“…The top surface of the model was divided into three boundary classes, based on their thermal and topographic conditions, being (1) riverbed, (2) floodplain, and (3) plateau (Figures 4 and 6b). These three surfaces were each assigned with specified temperature boundary conditions determined as follows: $$${T}_{\mathrm{s}}^{k}={{m}^{k}}_{\text{thawing}}\cdot {T}_{\text{air}}\quad \text{for}\quad {T}_{\text{air}}\ge 0{}^{\circ}\mathrm{C}$$$ $$${T}_{\mathrm{s}}^{k}={{m}^{k}}_{\text{freezing}}\cdot {T}_{\text{air}}\quad \text{for}\quad {T}_{\text{air}}< 0{}^{\circ}\text{C}$$$ where $${T}_{s}^{k}$$ is the assigned surface temperature (°C) for a specific boundary class k , T air is the air temperature (°C), and $${{m}^{k}}_{thawing}$$ and $${{m}^{k}}_{freezing}$$ are the so‐called thawing and freezing slopes for each class k , respectively (Perreault et al., 2021). These slopes were determined from simple linear regressions forced to pass through the origin of the graph of mean daily ground surface temperatures as a function of mean daily air temperatures, for air temperatures above and below 0 °C for each specific boundary class (Figure 7 and Table 3).…”

“…These slopes were determined from simple linear regressions forced to pass through the origin of the graph of mean daily ground surface temperatures as a function of mean daily air temperatures, for air temperatures above and below 0 °C for each specific boundary class (Figure 7 and Table 3). A similar approach of imposing surface temperatures as a function of ground surface conditions and air temperature was taken by Fortier et al (2011) and Perreault et al (2021) to assess the impacts of climate warming and changes in surface conditions on permafrost beneath a road embankment and in a discontinuous permafrost environment, respectively. The mean daily surface temperature of the three classes shown in Figure 7 (plateau, floodplain, and riverbed) were collected using HOBO™ Pro v2 temperature 7 for the empirical relationships between surface and air temperatures for these three surface conditions).…”

“…It considers the effect of water‐ice phase change and latent heat, as well as the effect of temperature on water density and viscosity, thermal conductivity, heat capacity, unfrozen water content, and relative permeability. The code has been successfully tested and applied in a variety of field studies of coupled groundwater flow and heat transport including those in permafrost regions (Dagenais et al., 2020; Perreault et al., 2021; Shojae‐Ghias et al., 2017, 2019), and against benchmarks from the Interfrost modeling consortium (Grenier et al., 2018; Rühaak et al., 2015). The general groundwater flow and advection‐dispersion heat transport equations solved in HEATFLOW‐SMOKER are described in the following sections.…”

“…(2011) and Perreault et al. (2021) to assess the impacts of climate warming and changes in surface conditions on permafrost beneath a road embankment and in a discontinuous permafrost environment, respectively. The mean daily surface temperature of the three classes shown in Figure 7 (plateau, floodplain, and riverbed) were collected using HOBO™ Pro v2 temperature probes buried about 5‐cm deep below each ground surface condition, while the air temperature was monitored at a climatological station in the Salluit Valley.…”