Setting Up Methane Mitigation Measures for Indian Rice Fields: Representative Emissions and New Interpretations

Abstract

Rice cultivation produces methane (CH₄) due to anaerobic conditions induced by flood irrigation, significantly contributing to global warming. While most studies use national emission factors (EFs), our study synthesized 726 published measurements across India (the second largest methane emitter after China) to develop district-level water regime-specific EFs for estimating district-scale emissions and warming potential. CH₄ emissions from Indian rice fields increased from 3.7 (3.4–4.1) Tg to 4.8 (4.4–5.3) Tg during 1966–2017, driven by rice area and water-regime variations. Meanwhile, district-level emissions increased by ∼930%, influenced by management practices such as animal manure, fertilizer application, and water input, accurately reflecting regional variations compared to previous estimates. Employing a novel muti-output random forest mitigation model (R² ∼ 0.9), we found that a 25% warming reduction at the district-level requires curtailing animal manure, nitrogen fertilizer, and water input by 8.5%, 12.9%, and 10.9%, respectively. These curtailments nearly double for a 50% mitigation scenario. Comparing our emissions with previous bottom-up studies (used as inputs in global climate models) revealed discrepancies in prior national figures. With top-down estimates, our emissions correlated positively, suggesting higher reliability. Including our new regionally validated data in global climate models may provide more accurate climate projections at the Indian and global scales.