Spatiotemporal methane emission from global reservoirs

Inland aquatic systems, such as reservoirs, contribute substantially to global methane (CH₄) emissions; yet are among the most uncertain components of the total CH₄ budget. Reservoirs have received recent attention as they may generate high CH₄ fluxes. Improved quantification of these CH₄ fluxes, particularly their spatiotemporal distribution, is key to realistically incorporating them in CH₄ modeling and budget studies. Here we report on a new global, gridded (0.25° lat × 0.25° lon) study of reservoir CH₄ emissions, accounting for new knowledge regarding reservoir areal extent and distribution, and spatiotemporal emission patterns influenced by diurnal variability, temperature-dependent seasonality, satellite-derived freeze-thaw dynamics, and eco-climatic zone. The results of this new data set comprise daily CH₄ emissions throughout the full annual cycle and show that reservoirs cover 297 × 10³ km² globally and emit 10.1 Tg CH₄ yr⁻¹ (1σ uncertainty range of 7.2–12.9 Tg CH₄ yr⁻¹) from diffusive (1.2 Tg CH₄ yr⁻¹) and ebullitive (8.9 Tg CH₄ yr⁻¹) emission pathways. This analysis of reservoir CH₄ emission addresses multiple gaps and uncertainties in previous studies and represents an important contribution to studies of the global CH₄ budget. The new data sets and methodologies from this study provide a framework to better understand and model the current and future role of reservoirs in the global CH₄ budget and to guide efforts to mitigate reservoir-related CH₄ emissions.