TY - JOUR

T1 - Explicitly modelling microtopography in permafrost landscapes in a land surface model (JULES vn5.4_microtopography)

AU - Smith, Noah D.

AU - Burke, Eleanor J.

AU - Aas, Kjetil Schanke

AU - Althuizen, Inge H. J.

AU - Boike, Julia

AU - Christiansen, Casper Tai

AU - Etzelmüller, Bernd

AU - Friborg, Thomas

AU - Lee, Hanna

AU - Rumbold, Heather

AU - Turton, Rachael H.

AU - Westermann, Sebastian

AU - Chadburn, Sarah E.

N1 - CENPERMOA[2022] Publisher Copyright: © 2022 Noah D. Smith et al.

PY - 2022

Y1 - 2022

N2 - Microtopography can be a key driver of heterogeneity in the ground thermal and hydrological regime of permafrost landscapes. In turn, this heterogeneity can influence plant communities, methane fluxes, and the initiation of abrupt thaw processes. Here we have implemented a two-tile representation of microtopography in JULES (the Joint UK Land Environment Simulator), where tiles are representative of repeating patterns of elevation difference. Tiles are coupled by lateral flows of water, heat, and redistribution of snow, and a surface water store is added to represent ponding. Simulations are performed of two Siberian polygon sites, (Samoylov and Kytalyk) and two Scandinavian palsa sites (Stordalen and Iškoras). The model represents the observed differences between greater snow depth in hollows vs. raised areas well. The model also improves soil moisture for hollows vs. the non-tiled configuration ("standard JULES") though the raised tile remains drier than observed. The modelled differences in snow depths and soil moisture between tiles result in the lower tile soil temperatures being warmer for palsa sites, as in reality. However, when comparing the soil temperatures for July at 20ĝ€¯cm depth, the difference in temperature between tiles, or "temperature splitting", is smaller than observed (3.2 vs. 5.5ĝ€¯ĝ C). Polygons display small (0.2ĝ€¯ĝ C) to zero temperature splitting, in agreement with observations. Consequently, methane fluxes are near identical (+0ĝ€¯% to 9ĝ€¯%) to those for standard JULES for polygons, although they can be greater than standard JULES for palsa sites (+10ĝ€¯% to 49ĝ€¯%). Through a sensitivity analysis we quantify the relative importance of model processes with respect to soil moisture and temperatures, identifying which parameters result in the greatest uncertainty in modelled temperature. Varying the palsa elevation between 0.5 and 3ĝ€¯m has little effect on modelled soil temperatures, showing that using only two tiles can still be a valid representation of sites with a range of palsa elevations. Mire saturation is heavily dependent on landscape-scale drainage. Lateral conductive fluxes, while small, reduce the temperature splitting by ĝ1/4ĝ€¯1ĝ€¯ĝ C and correspond to the order of observed lateral degradation rates in peat plateau regions, indicating possible application in an area-based thaw model.

AB - Microtopography can be a key driver of heterogeneity in the ground thermal and hydrological regime of permafrost landscapes. In turn, this heterogeneity can influence plant communities, methane fluxes, and the initiation of abrupt thaw processes. Here we have implemented a two-tile representation of microtopography in JULES (the Joint UK Land Environment Simulator), where tiles are representative of repeating patterns of elevation difference. Tiles are coupled by lateral flows of water, heat, and redistribution of snow, and a surface water store is added to represent ponding. Simulations are performed of two Siberian polygon sites, (Samoylov and Kytalyk) and two Scandinavian palsa sites (Stordalen and Iškoras). The model represents the observed differences between greater snow depth in hollows vs. raised areas well. The model also improves soil moisture for hollows vs. the non-tiled configuration ("standard JULES") though the raised tile remains drier than observed. The modelled differences in snow depths and soil moisture between tiles result in the lower tile soil temperatures being warmer for palsa sites, as in reality. However, when comparing the soil temperatures for July at 20ĝ€¯cm depth, the difference in temperature between tiles, or "temperature splitting", is smaller than observed (3.2 vs. 5.5ĝ€¯ĝ C). Polygons display small (0.2ĝ€¯ĝ C) to zero temperature splitting, in agreement with observations. Consequently, methane fluxes are near identical (+0ĝ€¯% to 9ĝ€¯%) to those for standard JULES for polygons, although they can be greater than standard JULES for palsa sites (+10ĝ€¯% to 49ĝ€¯%). Through a sensitivity analysis we quantify the relative importance of model processes with respect to soil moisture and temperatures, identifying which parameters result in the greatest uncertainty in modelled temperature. Varying the palsa elevation between 0.5 and 3ĝ€¯m has little effect on modelled soil temperatures, showing that using only two tiles can still be a valid representation of sites with a range of palsa elevations. Mire saturation is heavily dependent on landscape-scale drainage. Lateral conductive fluxes, while small, reduce the temperature splitting by ĝ1/4ĝ€¯1ĝ€¯ĝ C and correspond to the order of observed lateral degradation rates in peat plateau regions, indicating possible application in an area-based thaw model.

U2 - 10.5194/gmd-15-3603-2022

DO - 10.5194/gmd-15-3603-2022

M3 - Journal article

AN - SCOPUS:85129821161

VL - 15

SP - 3603

EP - 3639

JO - Geoscientific Model Development

JF - Geoscientific Model Development

SN - 1991-959X

IS - 9

ER -