Modelling methane emissions from Arctic tundra wetlands : effects of fractional wetland maps

Abstract: The Arctic tundra has been considered as one of the most sensitive areas to global climate change. One impact of global warming is that permafrost thawing could result in more waterlogged and anaerobic conditions, and consequently an increasing release of methane (CH4) to the atmosphere. These potential CH4 emissions can further amplify global warming. Therefore, it is important to assess the quantity of CH4 emissions from Arctic tundra wetlands and their sensitivity to climate change. Process-based CH4 modelling is commonly used to estimate CH4 emissions using single-source fractional wetland maps; however, it is not clear how the difference among multisource of fractional wetland maps affects CH4 estimations. In this study LPJ-GUESS WHyMe was applied to simulate CH4 emissions of Arctic tundra between 1961 and 2009 by using multisource fractional wetland maps, and their quantitative and qualitative differences in estimating CH4 emissions from these fractional wetland maps was compared. Parameter sensitivity tests and a parameter optimization for the model were performed before the model was applied to Arctic tundra. The CH4/CO2 production ratio under anaerobic conditions (CH4/CO2) and fraction of available oxygen used for methane oxidation (foxid) were identified as the most important model parameters in estimating total CH4 fluxes of Arctic tundra in the period 1961-2009. The regional simulation using multisource fractional wetland maps showed that the uncertainties of CH4 emissions in Arctic tundra caused by fractional wetland maps were larger than that due to parameter uncertainty. However, the temporal variability of CH4 emissions in Arctic tundra is not significantly different when using different fractional wetland maps. For different transport pathways of CH4 emissions, diffusion was determined as the dominant pathway for methane transport from wetland to the atmosphere in Arctic tundra. CH4 fluxes in Arctic tundra are more sensitive to soil temperature at 25 cm if the water table position is above the soil surface.