Seasonal variability of TROPOMI-derived methane over India: Contrasting fingerprints of anthropogenic sources and land-use controls.

Methane (CH₄) is a potent greenhouse gas whose rapidly increasing atmospheric concentration exerts a strong influence on near-term climate forcing. Understanding its spatial variability is particularly important over India, where diverse anthropogenic activities interact with monsoon-driven atmospheric processes. This study presents a geospatial assessment of atmospheric methane by integrating TROPOMI column observations with spatial datasets representing major environmental settings, including coal mining regions, petroleum refineries, landfill and municipal dump sites, cities under the National Clean Air Programme (NCAP), irrigation hydro-command systems, livestock-dominated environments and mangrove ecosystems. To distinguish localized atmospheric enhancement from regional background variability, a background-corrected methane metric (ΔXCH₄) was adopted. Analysis for 2019-2025 reveals a coherent seasonal cycle, with minimum atmospheric methane concentrations during the pre-monsoon period and maximum enhancement during the post-monsoon and winter seasons. Mean atmospheric methane increased by 7.96 ± 0.57 ppb yr-1, slightly lower than the global methane growth (∼9.9 ± 0.69 ppb yr-1) reported for the same period by NOAA. Seasonal comparison with the deseasonalized NOAA Northern Hemisphere methane trend shows close agreement during winter (DJF) and pre-monsoon (MAM), moderate enhancement during the southwest monsoon (JJAS), and substantially higher atmospheric methane during the post-monsoon (ON) season, indicating regional atmospheric influences superimposed on the global methane increase. Landfill and municipal dump sites exhibited the strongest and most persistent atmospheric enhancement, whereas coal mining regions and NCAP cities showed moderate but spatially variable signatures. Petroleum refinery environments remained close to the regional background, livestock-dominated environments displayed diffuse atmospheric behaviour, irrigation hydro-command systems exhibited characteristic seasonal responses, and mangrove ecosystems generally remained below the regional background. Independent evaluation using WDCGG observations, EDGAR emission inventories, seasonal wind climatology and representative HYSPLIT trajectories demonstrates that atmospheric methane over India is governed by the combined influence of natural and anthropogenic methane sources, land-use systems and atmospheric transport rather than emission strength alone.