Modeling ice rich permafrost landscapes with CLM5 using dynamically coupled tiles

Abstract. Thawing of extended amount of ground ice in permafrost regions can lead to rapid, large-scale landscape changes known as thermokarst, which significantly alter the thermal, hydrological and biogeochemistry state of the soil and the land surface. These thermokarst processes are driven by excess ground ice and permafrost microtopography. However, large-scale land surface models, used in coupled earth system models for climate predictions, do not represent such small-scale processes, and may therefore miss important mechanism that could contribute to underestimation of current greenhouses emission predictions from the permafrost regions. In this study we implement a new tiling approach in the Community Land Model, version 5.0, which is used in several Earth System Models, which already includes representation of excess ground ice, to resolve permafrost. The approach divides the vegetated land unit of a grid cell in two interacting tiles, that exchange snow, heat, and water, enabling simulation of rapid thaw processes under permafrost degradation. We evaluate this model configurations at two contrasting sites: a palsa mire landscape in northern Norway, and an ice-wedge polygon landscape in northeastern Siberia. The new implementation significantly improves the representation of soil temperature and soil moisture dynamics. It successfully captures the coexistence of two contrasting landscapes, a cold dry elevated higher tile and a warm, saturated lower tile. At the palsa sites, the tiling approach proves to be necessary to maintain stable Palsa conditions until 2014. These results demonstrate that explicitly representing excess ice and landscape dynamics in land surface models improves simulation of permafrost dynamics and may help reduce uncertainty in projections of permafrost-carbon feedbacks.