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

Evaluating regional budgets of methane ( CH 4 ) , a potent greenhouse gas and short‑lived climate forcer, is an important task for future climate management. This study estimated historical CH 4 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 CH 4 emission schemes, four paddy field maps, and two seasonal inundation methods for a total of 16 simulations. The mean CH 4 emission rate during 2000 ‑ 2015 was estimated to be 5.7 Tg CH 4 yr ‑1 , which is similar to statistical inventories and other estimates. However, the large standard deviation ( ± 3.2 Tg CH 4 yr ‑1 ) among the simulations implies that serious estimation uncertainties remain. Three factors ‑ CH 4 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 CH 4 emissions. A sensitivity analysis for temperature indicated that a 1 ‑ 2 ° C temperature rise ( typical warming in mitigation‑oriented scenarios ) would substantially enhance CH 4 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.