Decadal Analysis of Baseline Methane Emissions from Rice Cultivation: Identifying Spatiotemporal Hotspots for Mitigation Targeting

Rice paddies account for approximately 22% of global agricultural methane emissions, while South, East, and Southeast Asia together contribute nearly 90% of the global rice-cultivated area. Consequently, mitigation planning for agricultural methane frequently targets rice systems with little nuance across these vast geographies. Such assessments often assume stylized representative hydrologic environments, such as continuous flooding in irrigated regions, to estimate baseline emissions. However, recent studies have revealed much greater heterogeneity in hydrologic conditions within rice-growing regions including irrigated systems, leading to substantial spatial and temporal variability in methane emissions from rice paddies.

In this study, we used satellite-derived planting dates and soil moisture data in conjunction with the process-based ORYZA model to estimate methane emissions for the Indian states of Bihar, West Bengal, and Punjab. Our results indicate a relatively consistent pattern of methane emissions in Punjab, whereas emissions in Bihar exhibited pronounced spatial and temporal variability. For instance, southwestern and eastern Bihar showed higher average methane emissions, with relatively low temporal variability, averaging around 141 kg ha⁻¹ and coefficients of variation ranging from 29% to 59%. In contrast, the northwestern region of Bihar exhibited lower average emissions (approximately 95.5 kg ha⁻¹) but much higher temporal variability, with a coefficient of variation of 77%.

We further identified key drivers of methane emission variability, including total seasonal rainfall, evapotranspiration, and irrigation intensity. Seasonal rainfall exceeding 1000 mm was associated with higher methane emissions, whereas a greater number of irrigation events did not correspond to increased CH₄ emissions. These findings suggest that, for a state such as Bihar, there is limited potential for methane mitigation through improvements in irrigation management alone, and that alternative soil and crop management strategies may be required to reduce emissions from current baseline levels.