CLM-Wet-MS v1.0: A Community Land Model with Wetland-Adapted Plant Physiology and Microbial Soil Decomposition for Simulating Carbon Dioxide and Methane Fluxes at Temperate Riverine Wetlands

Abstract. Temperate inland riverine wetlands contribute meaningfully to regional carbon cycling, yet they remain poorly represented in land surface models. This study introduces CLM-Wet-MS, a modified version of the Community Land Model version 5 (CLM5) that incorporates a dedicated wetland landunit with wetland-adapted soil hydrology and a microbial soil decomposition scheme. The model was applied at Bibong wetland, a freshwater riverine wetland in South Korea, dominated by Phragmites australis. Hydrological representation is a dominant control on simulated carbon fluxes. The simulation configuration with observation-driven prescribed soil moisture is the only one that realistically reproduce the observed aerenchyma-dominated CH₄ transport. The microbial decomposition scheme reduces a persistent winter respiration bias that parameter optimization alone could not correct. Bayesian-based hierarchical parameter optimization was then performed against eddy covariance observations of gross primary productivity (GPP), ecosystem respiration (ER), and methane flux (FCH4). Optimization reduced root-mean-square error (RMSE) by 57.8 % (GPP), 37.1 % (ER), and 31.2 % (FCH4), with optimized parameters consistent with wetland-adapted C3 grass physiology and soil biogeochemistry. Comparison with plot-scale chamber measurements show that flux estimates diverge according to their spatial coverage, highlighting the influence of observation scale on model evaluation in heterogeneous wetlands. The CLM-Wet-MS model provides an optimized baseline for wetland modeling within CLM5 that can be extended to regional-scale simulations incorporating multiple land cover types.