Thaw processes in ice-rich permafrost landscapes represented with laterally coupled tiles in a Land Surface Model

Abstract

Abstract. Earth System Models (ESMs) are our primary tool for projecting future climate change, but are currently limited in their ability to represent small-scale land-surface processes. This is especially the case for permafrost landscapes, where melting of excess ground ice and subsequent subsidence affect lateral processes which can substantially alter soil conditions and fluxes of heat, water and carbon to the atmosphere. Here we demonstrate how dynamically changing microtopography and related lateral fluxes of snow, water and heat can be represented with a tiling approach suitable for implementation in large-scale models, and investigate which of these lateral processes are important to reproduce observed landscape evolution. Combining existing methods for representing excess ground ice, snow redistribution and lateral water and energy fluxes in two coupled tiles, we show how the same model approach can simulate known degradation processes in two very different kinds of permafrost landscapes. Applied to polygonal tundra in the cold, continuous permafrost zone, we are able to simulate the transition from low-centered to high-centered polygons, and show how this results in i) more realistic representation of soil conditions through drying of elevated features and wetting of lowered features with related changes in energy fluxes, ii) reduced average permafrost temperatures at 13 m depth with up to 2 °C in current (2000–2009) climate, iii) delayed permafrost degradation in the future RCP4.5 scenario by several decades, and iv) more rapid degradation through snow and soil water feedback mechanisms once subsidence starts. Applied to warm, sporadic permafrost features, this two-tile system can represent an elevated peat plateau underlain by permafrost in a surrounding permafrost-free fen, and how it degrades in the future following a moderate warming scenario. These results show the importance of representing lateral fluxes to realistically simulate both the current permafrost state and its degradation trajectories as the climate continues to warm; both of which are likely to have important implications for simulations of the magnitude and timing of the permafrost carbon feedback.

Stability Conditions of Peat Plateaus and Palsas in Northern Norway

“…Therefore, a spatially distributed representation of microtopography and the resulting lateral heat and water fluxes holds significant potential to improve the model representation of peat plateaus. While such a scheme was presented in Aas et al (), more work is needed to reproduce the thresholds of peat plateau stability and the dynamic response to climate change in models. In this study, we have presented a detailed observational data set, as well as one‐dimensional modeling for the end‐members of permafrost conditions, that is, stable permafrost and permafrost‐free sites.…”

“…These results confirmed the crucial role of lateral erosion in permafrost degradation and the importance of the lateral fluxes (snow, water, and heat) and geometric relationship between the plateaus and surrounding mires in this processes. In order to improve the representation of permafrost degradation processes the land surface models used in the Earth system models, Aas et al () presents an implementation of the lateral fluxes of snow, water, and heat in the Noah MP land surface model. Based on the coupled modeling of two interacting tiles, this model is used to simulate the degradation of the Northern Norway peat plateaus during the coming century and provide a first‐order reproduction of the main related processes such as subsidence and soil moisture modification.…”

Mechanistic Modeling of Microtopographic Impacts on CO2 and CH4 Fluxes in an Alaskan Tundra Ecosystem Using the CLM‐Microbe Model

“…The spatial variability in soil moisture and soil temperature can be overpredicted if the lateral subsurface hydrologic and thermal processes are excluded (Bisht et al, ), and the same is true for the spatial variability in CH 4 emissions in Arctic polygonal landscapes. By incorporating these surface processes, the CH 4 models can improve the representation of lateral hydrologic and thermal transport, and thereby improve the accuracy of estimations (Aas et al, ).…”

Surface displacement revealed by L-band InSAR analysis in the Mayya area, Central Yakutia, underlain by continuous permafrost

“…This irreversible subsidence leads to the formation of thermokarst lakes and changes the entire landscape. Thermokarst-induced geomorphological and hydro-ecological changes have been reported in several studies through in situ observations, satellite images, and model simulations (e.g., Zakharova et al 2015;Ulrich et al 2017;Aas et al 2019). Thermokarst has also been found to damage or destroy infrastructure (Shiklomanov et al 2017;Hjort et al 2018).…”