ORCHIDEE-MICT (v8.4.1), a land surface model for the high latitudes: model description and validation

Abstract

Abstract. The high-latitude regions of the Northern Hemisphere are a nexus for the interaction between land surface physical properties and their exchange of carbon and energy with the atmosphere. At these latitudes, two carbon pools of planetary significance -those of the permanently frozen soils (permafrost), and of the great expanse of boreal forestare vulnerable to destabilization in the face of currently observed climatic warming, the speed and intensity of which are expected to increase with time. Improved projections of future Arctic and boreal ecosystem transformation require improved land surface models that integrate processes specific to these cold biomes. To this end, this study lays out relevant new parameterizations in the ORCHIDEE-MICT land surface model. These describe the interactions between soil carbon, soil temperature and hydrology, and their resulting feedbacks on water and CO 2 fluxes, in addition to a recently developed fire module. Outputs from ORCHIDEE-MICT, when forced by two climate input datasets, are extensively evaluated against (i) temperature gradients between the atmosphere and deep soils, (ii) the hydrological components comprising the water balance of the largest highlatitude basins, and (iii) CO 2 flux and carbon stock observations. The model performance is good with respect to empirical data, despite a simulated excessive plant water stress andPublished by Copernicus Publications on behalf of the European Geosciences Union. 122M. Guimberteau et al.: ORCHIDEE-MICT, a LSM for the high latitudes a positive land surface temperature bias. In addition, acute model sensitivity to the choice of input forcing data suggests that the calibration of model parameters is strongly forcingdependent. Overall, we suggest that this new model design is at the forefront of current efforts to reliably estimate future perturbations to the high-latitude terrestrial environment.

ORCHIDEE-SOM: modeling soil organic carbon (SOC) and dissolved organic carbon (DOC) dynamics along vertical soil profiles in Europe

“…However, models with depth-dependent diffusion coefficients have been tested, but did not yield substantial improvements relative to models with a fixed diffusion coefficient (Boudreau, 1986). In fact, most of the models of diffusion at the ecosystem level assume a constant diffusion parameter with depth (Bruun et al, 2007;Guimberteau et al, 2018;O'Brien and Stout, 1978;Wynn et al, 2005). Our results confirm that this assumption is valid for four temperate sites with different vegetation inputs and soil properties.…”

Recent Changes in the ISBA‐CTRIP Land Surface System for Use in the CNRM‐CM6 Climate Model and in Global Off‐Line Hydrological Applications

“…Elsewhere, over the continuous permafrost region or over the Himalayan plateau, the simulated ALD reproduces in situ measurements well. The resulting skill scores given in each scatter plot lead to two main conclusions: (1) errors in simulating ALD are small, or at least reasonable, considering the low resolution of the model and with regard to other model results (Dankers et al, ; Ekici et al, ; Gouttevin et al, ; Guimberteau et al, ; Guo et al, ; Koven et al, ; Paquin & Sushama, ); (2) the quality of the ALD simulation is independent of the atmospheric forcing used even though the sfxcm6_e2o simulation with ERA‐Interim‐based E2O forcing exhibits slightly better scores than the PGF‐driven simulation ( sfxcm6_pgf ).…”

The role of northern peatlands in the global carbon cycle for the 21st century

“…Soil water fluxes and storage are resolved by a multi‐layer physically based soil hydrology scheme (Guimberteau et al, 2018). Decomposition and accumulation of peatland soil C are also parameterized as a multi‐layer scheme (Qiu et al, 2019); soils are vertically discretizated into 32 layers (≤ 38 m, with exponentially coarser vertical resolution as depth increases).…”

“…Soil thermodynamics, energy exchanges between the soil and the atmosphere, are calculated based on a one‐dimensional Fourier equation. Soil water freeze–thaw processes and the latent heat exchanges involved in soil water phase change, in addition to its impacts on soil thermal and hydrological properties, are represented (Guimberteau et al, 2018). Permafrost processes, such as palsa formation and subsidence or collapse of the peat soil column in the event of ground ice thaw, are not modelled.…”