Flooding-Driven Greenhouse Gas Emissions From Global Upland Croplands

Greenhouse gas emissions from temporarily flooded upland croplands remain poorly characterized in the global greenhouse gas budget. We combined field measurements from 11 maize-field sites temporarily flooded across the North China Plain with a global synthesis of 23 flooded upland cropland sites to quantify diffusive emissions. Flooded croplands release high fluxes of nitrous oxide, carbon dioxide, and methane, with emission factors exceeding relevant Intergovernmental Panel on Climate Change (IPCC) defaults for rice paddies and newly flooded lands. Extrapolating site-level fluxes from limited observations over the estimated global area of flooded upland cropland and mean flooding duration yields a mean of 63.3 teragrams (Tg) of carbon dioxide-equivalent (CO₂-eq) emissions per year during the standing-water flooding periods, comprising 7.2 (1.7-17.2), 34.6 (9.0-83.7), and 21.5 (6.2-45.6) Tg from nitrous oxide, carbon dioxide, and methane, respectively. Temporarily flooded upland croplands are therefore identified as a previously overlooked component of the global greenhouse gas budget, providing an empirical basis for incorporating flood-driven emissions into future agricultural inventories.