Improving soil temperature simulation accuracy in Arctic permafrost regions by incorporation surface organic layer in CLM5.0

The thermal insulation properties of the surface organic layer (moss, lichens, and litter; SOL) regulate energy exchange between the ground surface and atmosphere in Arctic permafrost regions. However, the default Community Land Model version 5.0 (CLM5.0) does not explicitly represent the SOL, potentially contributing to biases in simulated soil temperature and active layer thickness (ALT). In this study, we developed a simplified SOL thermal parameterization in CLM5.0 based on equivalent thermal resistance and heat capacity and evaluated it at nine Arctic permafrost sites using soil temperature observations from four sites and ALT observations from five sites. Compared with the control simulation (CTL), incorporating the SOL reduced soil temperature errors relative to in situ observations by an average of approximately 24% and reduced ALT errors by 47.6–81.3%. The SOL generally limited or delayed active layer deepening, although its effects varied among sites and emission scenarios. The proposed scheme provides a simplified site-scale framework for representing the thermal effects of the SOL in CLM5.0, but its regional application remains limited by the lack of spatially continuous SOL thickness data across the pan-Arctic region.