On the configuration and initialization of a large-scale hydrological land surface model to represent permafrost

Abstract

Abstract. Permafrost is an important feature of cold-region hydrology, particularly in river basins such as the Mackenzie River basin (MRB), and it needs to be properly represented in hydrological and land surface models (H-LSMs) built into existing Earth system models (ESMs), especially under the unprecedented climate warming trends that have been observed. Higher rates of warming have been reported in high latitudes compared to the global average, resulting in permafrost thaw with wide-ranging implications for hydrology and feedbacks to climate. The current generation of H-LSMs is being improved to simulate permafrost dynamics by allowing deep soil profiles and incorporating organic soils explicitly. Deeper soil profiles have larger hydraulic and thermal memories that require more effort to initialize. This study aims to devise a robust, yet computationally efficient, initialization and parameterization approach applicable to regions where data are scarce and simulations typically require large computational resources. The study further demonstrates an upscaling approach to inform large-scale ESM simulations based on the insights gained by modelling at small scales. We used permafrost observations from three sites along the Mackenzie River valley spanning different permafrost classes to test the validity of the approach. Results show generally good performance in reproducing present-climate permafrost properties at the three sites. The results also emphasize the sensitivity of the simulations to the soil layering scheme used, the depth to bedrock, and the organic soil properties.

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

“…In permafrost lowlands of the Taiga Plain, soil thawing has led to subsidence and inundation of ground surfaces resulting in extensive forest loss, fragmentation, and concomitant wetland expansion and conversion mostly to sphagnum-dominated bogs (Baltzer et al, 2014;Helbig et al, 2016). In the southern Arctic, increased permafrost thawing is leading to changes in channel permafrost conditions, increasing winter groundwater flow in the channel, and increasing occurrence of aufeis formation (Ensom et al, 2020). Many northern ecosystems are underlain by ice-rich permafrost that is highly sensitive to thawing during warm summers (Segal et al, 2016;Lewkowicz and Way, 2019) or following other disturbances (Williams et al, 2013).…”

Hydrologic-land surface modelling of the Canadian sporadic-discontinuous permafrost: initialization and uncertainty propagation

“…The JMC and WH models were configured using the approach of Elshamy et al . (2020), where MESH was applied to three permafrost sites along the Mackenzie River valley.…”

“…Soil moisture memory was shown by Cosgrove et al (2003) and Rodell et al (2005) to be larger than thermal memory for shallow soil columns (2m and 3.5m), such that reaching a quasi-equilibrium state for moisture during spin-up requires more time than soil temperature, depending on soil characteristics. However, such conclusions may not be valid for deeper soil columns recommended for LSM simulation of permafrost, due to their larger thermal/hydraulic inertia (Sapriza-Azuri et al , 2018;Elshamy et al , 2020;Lamontagne-Hallé et al , 2020). For example, Elshamy et al (2020) showed that soil moisture stabilized faster than soil temperature in simulations for the Mackenzie River Basin using a 51.24m soil column.…”

“…However, such conclusions may not be valid for deeper soil columns recommended for LSM simulation of permafrost, due to their larger thermal/hydraulic inertia (Sapriza-Azuri et al , 2018;Elshamy et al , 2020;Lamontagne-Hallé et al , 2020). For example, Elshamy et al (2020) showed that soil moisture stabilized faster than soil temperature in simulations for the Mackenzie River Basin using a 51.24m soil column. Further, soil moisture data can be helpful.…”

“…For instance, Walker and Houser (2001) demonstrated added value from assimilating observed surface soil moisture to reduce the spin-up time of a global climate model, noting that different soil properties, e.g. soil texture, hydraulic/thermal conductivity, depth to bedrock, govern the memory of the soil system and hence the required spin-up (Rodell et al , 2005;Shrestha and Houser, 2010;Elshamy et al , 2020).…”