Model-based evaluation of methane emissions from paddy fields in East Asia

Abstract

　Evaluating regional budgets of methane (CH₄), a potent greenhouse gas and short-lived climate forcer, is an important task for future climate management. This study estimated historical CH₄ emissions from paddy fields in East Asia by using a process-based terrestrial biogeochemical model driven by climate and land-use data. To capture the range of estimation uncertainty, this study used two CH₄ emission schemes, four paddy field maps, and two seasonal inundation methods for a total of 16 simulations. The mean CH₄ emission rate during 2000-2015 was estimated to be 5.7 Tg CH₄ yr^-1, which is similar to statistical inventories and other estimates. However, the large standard deviation (± 3.2 Tg CH₄ yr^-1) among the simulations implies that serious estimation uncertainties remain. Three factors - CH₄ emission scheme, paddy field map, and inundation seasonality - were responsible for the disparity of the estimates. Because of the lack of historical management data, the model simulation did not show a decreasing trend in the agricultural CH₄ emissions. A sensitivity analysis for temperature indicated that a 1-2 °C temperature rise (typical warming in mitigation-oriented scenarios) would substantially enhance CH₄ emissions. However, a sensitivity analysis for water management indicated that a lower water-table depth would largely mitigate the emission increase. Additional studies to improve agricultural datasets and models for better paddy field management are still needed.