Satellite Quantification of Methane Emissions from Individual Countries in Southeast Asia: Roles of Dry and Wet Seasons

Chen Xu, Zichong Chen , Sarah Hancock, Xiaolin Wang, Xueying Yu, Mengyao Liu, Sion Chiew, Shrijwal Adhikari, Beau Damen

Southeast Asia is a global methane (CH4) hotspot, yet its emissions remain highly uncertain particularly regarding seasonal variability. Here we quantify methane emissions over ten Southeast Asian countries using TROPOMI satellite observations and analytical inversions at up to 0.25°×0.3125° resolution (~25km×25km), separately for the dry (October 2021-April 2022) and wet (May-September 2022) seasons. We find despite limited local retrievals during cloud-limited wet season, observations from downwind regions provide effective constraints, yielding considerable information. Our best estimates of annual total, anthropogenic, and natural emissions are 47.9(44.5-51.4), 27.8(26.4-29.2), and 20.1(18.1-22.3) Tg a-1 respectively; parentheses indicate uncertainty ranges from the inversion ensemble. Anthropogenic emissions show a clear seasonal contrast not adequately represented in current inventories, increasing from 24.2 Tg a-1 in the dry season to 32.8 Tg a-1 in the wet season, largely due to rice, livestock, and previously-overlooked oil and waste emissions. Annual rice and livestock emissions (10.8 and 5.8 Tg a-1) exceed UNFCCC reports by 64% and 53%, with large discrepancies in Thailand, Viet Nam, Myanmar, and Indonesia, reflecting the use of outdated activity data and low emission factors. Our separate dry- and wet-season satellite inversions provide an improved basis for mitigation efforts in Southeast Asia under the Global Methane Pledge.