Global Methane Emissions from Rice Paddies

Abstract Rice paddies are a major source of atmospheric methane (CH 4 ). However, the strength of this source is highly uncertain. To improve estimates of CH 4 emission at the regional and global scales requires process based models, integrating the environmental and biological factors that determine the rate of CH 4 emission. In this study, we used such a model to calculate the spatial and seasonal variations in CH 4 emission from rice paddies, with the support of an integrated GIS data set defining distribution of rice paddies, rice calendar, climate, and soil conditions. The calculated rates of CH 4 emission in a rice-growing season varied greatly, from 5 to 90 g CH 4 m −2 , for rice paddies across the globe. In most rice paddies daily mean CH 4 effluxes were from 50 to 400 mg CH 4 m −2 . Annual total emission was estimated to be 53 Tg; two thirds of this was emitted between 10°N and 30°N. Monthly CH, emissions ranged from 1.4 Tg in January to 8.7 Tg in August, and more than a half of the emission occurred between June and October. Our model suggests that, on average, 12% of the simple carbon substrate from decomposition of soil organic matter and rice plants was transformed into CH 4 , and the emitted CH 4 accounted for 6.5% of the rice net primary production.