A process-based modeling of soil organic matter physical properties for land surface models – Part 2 : Global land surface simulations and mineral soil compaction adjustment

Abstract. In the companion paper, Decharme (2025) developed a process-based framework using soil mixture theory to represent the effects of soil organic matter on soil physical properties in land surface models. The present study extends this work by testing the framework in global land surface simulations with the ISBA-CTRIP land surface modeling system. The approach derives the volumetric organic matter fraction and phase-specific densities from soil organic carbon and bulk density using mass volume relationships, and computes hydraulic and thermal parameters using mixing rules consistent with the model physics. We also introduce an optional mineral soil compaction adjustment, under the assumption that texture-based pedotransfer functions are calibrated on weakly compacted samples, whereas gridded bulk density products mostly reflect in situ conditions that include varying degrees of compaction. We examine the effects of both developments in multidecadal global offline simulations forced by a standard meteorological dataset and driven by SoilGrids soil inputs. Four configurations are compared, a mineral-only control, a previous empirical scheme, the new process-based scheme, and its compaction-adjusted variant. The evaluation combines site-scale constraints on porosity and hydraulic behavior with large-scale benchmarks of the terrestrial water and energy cycles, including terrestrial water storage variations, river discharge, evapotranspiration, soil temperature, and active layer thickness. Overall, the global experiments suggest that the new process-based scheme produces more consistent large-scale hydrothermal responses than the previous empirical scheme, whereas the compaction adjustment plays a secondary role and mainly acts as a local modulator.