Methane emissions from global rice fields: Magnitude, spatiotemporal patterns, and environmental controls

Given the importance of the potential positive feedback between methane (CH₄) emissions and climate change, it is critical to accurately estimate the magnitude and spatiotemporal patterns of CH₄ emissions from global rice fields and better understand the underlying determinants governing the emissions. Here we used a coupled biogeochemical model in combination with satellite-derived contemporary inundation area to quantify the magnitude and spatiotemporal variation of CH₄ emissions from global rice fields and attribute the environmental controls of CH₄ emissions during 1901–2010. Our study estimated that CH₄ emissions from global rice fields varied from 18.3 ± 0.1 Tg CH₄/yr (Avg. ±1 SD) under intermittent irrigation to 38.8 ± 1.0 Tg CH₄/yr under continuous flooding in the 2000s, indicating that the magnitude of CH₄ emissions from global rice fields is largely dependent on different water schemes. Over the past 110 years, our simulated results showed that global CH₄ emissions from rice cultivation increased by 85%. The expansion of rice fields was the dominant factor for the increasing trends of CH₄ emissions, followed by elevated CO₂ concentration, and nitrogen fertilizer use. On the contrary, climate variability had reduced the cumulative CH₄ emissions for most of the years over the study period. Our results imply that CH₄ emissions from global rice fields could be reduced through optimizing irrigation practices. Therefore, the future magnitude of CH₄ emissions from rice fields will be determined by the human demand for rice production as well as the implementation of optimized water management practices.