Estimation of methane emission from rice paddies in mainland China

Methane emission from rice paddies in mainland China is estimated by the method of regional classification. Rice paddies in mainland China were classified into five major ecoclimatic regions and seven subregions according to regional ecological and agricultural parameters. The direct statistical agricultural data based on the 2484 county level records and climatic parameters of 160 meteorological stations in 1991 were employed for the classification and estimation. Methane emission rates obtained from six experimental sites representing 10 eco-agricultural conditions were taken into consideration for the estimation. Using this method, the total methane emission from mainland China turned out to be 15.3 Tg/yr. Seasonally, methane was found to be emitted mainly (up to 95%) between April and October with an emission peak in June. Geographically, methane emission was intensively (up to 80%) concentrated in the central part of China and in the middle and lower reaches of the Yangtze River. The three counties with highest methane emission are all located in Sichuan province, they are Daxian (0.105 Tg/yr, 107 degrees 24'E, 31 degrees 12'N), Yuechi (0.091 Tg/yr, 106 degrees 24'E, 30 degrees 30'N), and Guangan (0.089 Tg/yr, 106 degrees 36'E, 30 degrees 24'E), altogether accounting for 2% of the total methane emission from rice paddies of the country. Single-season rice (midrice in this paper) which was found mainly distributed in the southwest and southeast parts of the country plays the most important role in rice paddy methane compared with other rice methane sources. For comparison, several other known estimation methods employed by other authors were also used to make a comparison with the method of our data source. The estimated emissions from these studies are in the range of 7.7-24.6 Tg/yr. Trend analysis showed that methane emission in rice paddies from mainland China would remain at the present level in the near future.