<p>Drylands cover 40–50% of the Earth’s surface and make an important contribution to the terrestrial carbon sink and the global carbon cycle. However, in addition to extended dry periods, drylands also experience extreme flood events. Here we report carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) emissions from flooded drylands in central Australia (Kati-Thanda-Lake-Eyre basin; KTLE) in 2019. At the time of sampling the wet areas of the KTLE emitted 1.4 ± 0.6 Tg CO₂ d^− 1 and 0.31 ± 0.13 Gg CH₄ d^− 1 (24.6 ± 10.6 Gg CO₂e) and consumed 3.0 ± 1.3 Mg N₂O d^− 1 (0.8 ± 0.4 Gg CO₂e). The low basin slope resulted in a large area of inundation (up to 33,547 km²), that remained wet for an extended period. Up-scaling the daily fluxes for the changing wet surface area, for the wet period, has the potential to result in 127.1 ± 59.6 Tg of CO₂ and 22.2 ± 10.5 Gg of CH₄ (1.8 ± 0.8 Tg CO₂e) emitted, and 2.5 ± 1.3 Gg of N₂O (0.7 ± 0.3 Tg CO₂e) consumed (Total = 129.6 ± 59.2 Tg CO₂e). The low gradient and associated low volume of water transported and large wet area also resulted in the vertical flux of carbon being much more important than the river transported carbon. This first-order estimate of GHG emissions from the KTLE suggests that when flooded, dryland systems globally have the potential to make a significant (e.g. 2.8% of annual global inland river CO₂ emissions), but currently unaccounted for, contribution to global GHG emissions, and may need to be included as feedback in global climate models.</p>