Tropical wetland methane emissions and trends (2004–2023) inferred from Landsat-based inundated vegetation data

The role of tropical wetlands in the rise of atmospheric methane over the past two decades remains unclear. Current models define wetlands by surface water coverage, not making the distinction between high-emitting inundated vegetation and much weaker-emitting open water areas of wetlands. Here we use 30-m Landsat satellite data to identify tropical inundated vegetation, and combine it with chamber- and flux tower-derived emission intensities per unit wetland area to produce a Wetland Methane Emission Inventory (WMEI) at 0.1o ×0.1o spatial resolution and quarterly temporal resolution for 2004-2023. We find that tropical wetland emissions increased steadily by 16.3 Tg a-1 or 18% over the 2004-2023 period, with contributions from Africa (11.3 Tg a-1) and Asia (5.0 Tg a-1) and no net increase from South America. Tropical wetlands thus account for 21% of the global methane rise over that period though they do not appear to have contributed significantly to the 2020-2022 methane surge. The long-term trend and interannual variability of wetland emissions correlates strongly with vegetation activity as measured by solar-induced fluorescence (SIF) but not with temperature or precipitation.