Enhanced Prescription of Soil Organic and Mineral Content in the ORCHIDEE LSM to Better Simulate Soil Temperatures: Application at Nine High‐Latitude GEM and FLUXNET Sites

Over the past two decades, numerous studies have emphasized the importance of including organic matter (OM) in land surface models (LSMs) to accurately represent soil thermal and hydrological properties. This is particularly relevant in Arctic regions, where organic‐rich soils are widespread. Consequently, most LSMs incorporate parameterizations that account for OM effects, although these implementations are often simplified. Recent advancements in global soil data sets now enable more precise modeling of soil properties by providing detailed inputs for soil composition and physical characteristics. This study focuses on the refinement of the representation of soil organic and mineral content and the revision of the parameterizations of heat capacity, thermal conductivity, and porosity in the ORCHIDEE LSM, using data from the SoilGrids 250m v2.0 database. The updated model is evaluated across multiple Arctic and boreal sites and compared against two earlier versions: (a) a Bulk version that neglects OM effects on the thermal processes and (b) a simplified version with a basic OM prescription. Results show that incorporating OM into thermal processes modeling significantly improves soil temperature simulations, particularly under the soil surface in the critical zone. For some sites, root mean square errors (RMSE) are reduced by up to 50% compared to the Bulk version, especially during the snow‐free summer months. These findings highlight the value of high‐resolution soil data sets, such as SoilGrids, for improving simulations of thermal dynamics in carbon‐rich Arctic soils.