Biosphere-atmosphere exchange of methane in India as influenced by multiple environmental changes during 1901-2010

It is highly uncertain on how human and natural environmental factors have altered methane (CH4) emissions from terrestrial ecosystems in India. Using a process-based, Dynamic Land Ecosystem Model (DLEM) driven by climate, land cover and land use change (LCLUC), atmospheric nitrogen deposition (NDEP), atmospheric carbon dioxide (CO2) concentration, and tropospheric ozone (O3) pollution, we examined CH4 flux from terrestrial in India during 1901-2010. The DLEM simulations have shown that total CH4 flux over the country ranged from 2.9 Tg C year−1 to 6.5 Tg C year−1 with significant inter-annual variations driven by climate during 1901-2010. Contemporary CH4 emissions have primarily occurred from rice fields (3.9 ± 0.9 Tg C year−1) while wetlands contributed to 2.1 ± 0.6 Tg C year−1 in the 2000s. During 1901-2010, total CH4 emission from the terrestrial biosphere has increased by ∼2.1 Tg C year−1. LCLUC has increased CH4 emissions by 2.3 Tg C year−1 primarily due to increase in the rice-based cropping systems as well as irrigation expansion during the study period. Elevated CO2 concentration stimulated plant biomass production in both rice fields and wetlands that increased CH4 emissions by 0.7 Tg C year−1. On the contrary, climate change decreased net CH4 emissions by ∼1.2 Tg C year−1 due to negative effects of extreme high temperature as well as occurrences of extreme drought events on plant growth. Our study suggests that LCLUC and elevated CO2 concentration have significantly increased CH4 emissions from terrestrial ecosystems in India.