In China, midseason paddy drainage, which reduces growing season methane fluxes and enhances growing season nitrous oxide fluxes, was first implemented in the early 1980s, and has gradually replaced continuous flooding in much of the paddy rice area. We constructed a prediction rice paddy methane and nitrous oxide emissions in China using the DNDC biogeochemical model. Results of continuous flooding and midseason drainage simulations for all paddy fields in China (about 30 million ha) were combined with regional scenarios for the timing of the transition from continuous flooding to predominantly mid-season drainage to generate estimates of total methane (CH4) and nitrous oxide (N2O) flux for 1980-2000. By shifting from continuous flooding to midseason drainage management, we estimate that total N2O emissions from the rice paddies in China increased by about 0.17 Tg N2O-N yr−1 due to the stimulated nitri- fication and denitrification, while CH4 emissions decreased by about 4.5 Tg CH4-C yr−1 due to increased soil aeration. Simulated net carbon loss in paddy soils was about 0.65 Tg C yr−1 due to elevated decomposition. On a 100-year time frame, CH4 has a global warming potential (GWP) 23 times that of CO2, and N2O has a GWP 296 times that of CO2. The total GWP impact (2000 vs. 1980) of shifting to predominantly mid-season paddy drainage was -0.138 Pg CO2-equiv yr−1 from methane, +0.077 Pg CO2-equiv yr−1 from nitrous oxide and +0.0024 Pg CO2 yr−1 from soil C loss, for a total GWP impact of -0.059 Pg CO2-equiv yr−1 . The results imply that more than half of the GWP benefit of decreased CH4 emissions was offset, primarily by increases in N2O emissions, and to a small degree by soil C loss.
Joint Assembly Meeting, American Geophysical Union
European Geophysical Society
Li C, Qiu J, Frolking S, Xiao X, Salas W, Moore B, Boles S, Huang Y, Sass R. 2003. Greenhouse gas emission consequences of large-scale changes in water management of China’s rice paddies during 1980-2000. Spring 2003 AGU, Nice France.