A modeling perspective on wetland methane production and emission

Abstract:

Methane (CH₄) is the third most important greenhouse gas after H₂O and CO₂. The effects of global warming on wetland hydrology have a strong impact on wetland CH₄ production and emission, via both hydrologic and biogeochemical processes, presenting a challenge to accurate projection of CH₄ responses to climate change. We are working on the development of CH₄ module—including CH₄ production, consumption and transport processes— in the Community Land Model (CLM4.5) in order to estimate CH₄ fluxes in a regional and global scale. However, high uncertainties are still present in sensitivity of CH₄ production to soil temperature, hydrology, pH and redox potential, rough treatment to vertical soil resolution and fractional inundation, and simplified parameterizing of CH₄ transport and emissions. Our research aims to (1) use tower eddy covariance and aircraft measurements of CH₄ concentration and surface flux to test the CH₄ processes in CLM model; (2) obtain a better understanding and parameterization of the biogeochemical and biogeophysical processes of high latitude wetland CH₄ production and emission; (3) assess impact of climate variability on wetland CH₄ emission. Our analysis of CLM shows that the modeled predictions of the seasonal cycle of CH₄ in high latitude wetlands is very sensitive to active layer hydrological cycle. The abrupt soil water increase in the period of soil thawing and snow melting leads to unrealistically large emissions of CH₄ during the spring season. We present improvements required to generate realistic seasonal cycles of high latitude CH₄ fluxes in the model.