Spatiotemporal Variations Of Natural Wetland Methane Emission Over China Under Climate Change

Methane(CH4) is a powerful greenhouse gas with a global warming potential 28 times that of carbon dioxide(CO2). CH4 is responsible for approximately 20% of the Earth’s warming since pre-industrial times. The interplay between sources and sinks determines the global atmospheric CH4 abundance. The atmospheric concentration of CH4 has nearly tripled since pre-industrial times, but this increasing trend did not continue during the past three decades. However, after slowing to nearly zero over the past twenty years, the global CH4 concentration has shown a sustained increase since 2006. Knowledge of the sources of CH4 is crucial due to the recent substantial interannual variability of growth rates and uncertainties regarding individual sources.Along with global warming, revealing the past, current and future spatiotemporal patterns of CH4 emissions from natural wetlands over China is of great research significance given the fact that wetland systems play an important role in global CH4 cycle. Several studies have discussed the impacts of future climate change on CH4 emissions from wetlands on a global scale, but to the best of authors’ knowledge, there is no study investigating future spatiotemporal variations of natural wetland CH4 emissions over China.A new process-based model, TRIPLEX-GHG, is developed based on the legacy of a well-established dynamic global vegetation model, the Integrated Biosphere Simulator(IBIS), into which a new CH4 biogeochemistry module and a water table module were integrated to investigate dynamics of natural wetland CH4 emissions. The model performs well in the aspect of simulating magnitude and capturing temporal patterns of natural wetland CH4 emissions; therefore, it can be used as a reliable tool to stimulate spatiotemporal patterns of CH4 emissions from various natural wetlands under varying conditions..Based on this new model, this paper analyzed the spatiotemporal patterns of natural wetland CH4 emissions over China under three Representative Concentration Pathways(RCPs) scenarios, RCP2.6, RCP4.5 and RCP8.5, with fixed China’s natural wetland extents. Monthly anomalies of climate were taken from the outputs of Coupled Model Intercomparison Project Phase 5(CMIP5) and CO2 concentrations were prescribed from the RCP database. Results suggest that:When natural wetland extents were fixed, the amount of CH4 emissions from natural wetland systems over China would have risen by 32.0%, 55.3% and 90.8% by the end of 21 st century under RCP2.6, RCP4.5 and RCP8.5, respectively, compared with the current CH4 level. Southern China would have higher CH4 emissions compared to the lower CH4 release from central and northern China. Besides, there would be relatively low emission fluxes in western China while relatively high emission fluxes in eastern China. Spatially, the areas with relatively high CH4 emission fluxes would be concentrated in the Middle-Lower Reaches of the Yangtze River, the Northeast and the coasts of the Pearl River and Yarlung Zangbo River. In the future, most natural wetlands would emit more CH4 for RCP4.5 and RCP8.5 than that of 2005. However, under RCP2.6, the increasing trend would be curbed and CH4 emissions(especially from the Qinghai-Tibet Plateau) begin to decrease in the late 21 st century. Results of this research may provide references and suggestions for making China’s emission inventories of greenhouse gases and managing wetlands in scientific ways.