WETMETH 1.0: A new wetland methane model for implementation in Earth system models

Abstract. Wetlands are the single largest natural source of methane (CH₄), a powerful greenhouse gas affecting the global climate. In turn, wetland CH₄ emissions are sensitive to changes in climate conditions such as temperature and precipitation shifts. However, biogeochemical processes regulating wetland CH₄ emissions (namely microbial production and oxidation of CH₄) are not routinely included in fully coupled Earth system models that simulate feedbacks between the physical climate, the carbon cycle, and other biogeochemical cycles. This paper introduces a process-based wetland CH₄ model (WETMETH) developed for implementation in Earth system models and currently embedded in an Earth system model of intermediate complexity. Here we: (i) describe the wetland CH₄ model; (ii) evaluate the model performance against available datasets and estimates from the literature; (iii) analyze the model sensitivity to perturbations of poorly constrained parameters. Historical simulations show that WETMETH is capable of reproducing mean annual emissions consistent with present-day estimates across spatial scales. For the 2008–2017 decade the model simulates global mean wetland emissions of 158.6 Tg CH₄ yr¹, of which 33.1 Tg CH₄ yr¹ are from wetlands north of 45° N. WETMETH is highly sensitive to parameters for the microbial oxidation of CH₄, which is the least constrained process in the literature.