Effects of Gridcell Inundated Fraction Parameterization on CH4 Dynamics in the Community Land Model

Abstract:

Production and oxidation of methane (CH₄) in the Community Land Model (CLM) largely depends on the gridcell inundated fraction within the model. The functioning version of the CH₄ model parameterizes gridcell inundated fraction using water table depth and surface runoff. Unfortunately, this method contains problems in representing dynamic seasonality of the gridcell inundated fraction and is not compatible with some of the recent model developments to represent permafrost thaw related processes. The future model development plan is to parameterize inundated fraction based on precipitation and river channeling to capture seasonal dynamics of hydrological cycles. Here, we investigate how different model parameterization of inundated fraction affect Arctic hydrological cycles. In addition, we quantify the rate of CH₄ production and oxidation under changes in inundated fraction using different parameterization methods. We used CLM4.5BGC to understand the behavior of hydrology as well as CH₄ production and oxidation. The results show that using water table depth and surface runoff to parameterize inundated fraction result in unrealistic seasonality especially in the high latitude region. For instance, winter freezing, spring thaw, and summer increase in inundated fraction were not manifested using water table depth and surface runoff to parameterize inundated fraction. The two other methods simulated these processes more realistically throughout the season except that precipitation based parameterization underestimated and river channeling based parameterization overestimated the overall high latitude inundated fraction compared to satellite based estimation. Despite the large difference in inundated fraction estimation, total CH₄ production and oxidation simulated in the high latitude region were similar across the three different parameterization of inundated fraction.