South Asian methane emissions, inferred from surface, aircraft and satellite observations

Methane is a powerful Kyoto Protocol regulated greenhouse gas and has the second largest radiative forcing after carbon dioxide. Globally, a large fraction of methane emissions are naturally occurring from sources such as wetlands and termites. In South Asia, natural wetlands are a smaller but still significant source of methane compared to the larger anthropogenic sources such as rice paddies, ruminants, fossil fuel emissions and biomass burning. Global average emissions of methane are generally well constrained but in order to specifically quantify emissions from South Asia, measurements taken in close proximity of South Asian sources are required. To fulfill this objective, a measurement site in Darjeeling, India was established in 2011 to measure methane on-site and collects over 70 measurements per day. In this project, methane emissions from each source sector (fossil fuel, wetlands, cattle, etc) will be quantified using surface, aircraft and satellite observations of methane concentration over South Asia.

Satellites currently measure methane concentrations around the globe and are powerful tools because of their global coverage, while surface sites only measure at one location. The main limitation with satellites is because they can be prone to errors in areas where clouds and dust can mask the methane signal. One of the avenues of research that will be done in this proposal is to combine all of the surface, aircraft and satellite measurements together and use the combined data to provide information on the quality of the satellite observations over South Asia. This will help to better understand how these satellite observations can be used over this region in the future.

One of the main sources of atmospheric methane in India comes from rice paddies, also known as anthropogenic wetlands. The process that governs these emissions is similar to that occurring in natural wetlands. When water covers the surface of the soil, oxygen is deprived to lower layers of the soil. In these "anoxic" zones, bacteria metabolize organic matter in the soil through a pathway that leads to methane production. However, the human influence on water management, fertilizer use and other agricultural practices makes rice paddy methane production a very different problem from a naturally driven wetland process. For example, humans artificially alter the water table level through the use of irrigation. Farmers also add additional nutrients into the soil, providing more organic matter and nitrogen for bacteria to utilize than would be found in a natural wetland. Furthermore, rice paddies are often created in areas that wouldn't otherwise contain wetland and thus are artificially introduced.

One of the main objectives of this research is to improve our understanding of the processes that drive methane emissions from wetland sources in India (from both natural wetlands and rice paddies). I will employ a "wetland" model, modified to include agricultural practices, to simulate emissions from the ground as well as a model of atmospheric transport to link the processes producing methane in the soil to the measurements that we make in the atmosphere. These atmospheric observations will be used to improve the processes in the wetland model. Using this tool, I will produce the most accurate and up-to-date methane emissions estimates, from all sources, from the Indian subcontinent. Finally, I will project emissions of methane from rice agriculture in India to the year 2100 using projected rice-growth and future climate scenarios such as those used in the Intergovernmental Panel on Climate Change Fifth Assessment Report (IPCC AR5).

Who Will Benefit?

Several academic and societal groups have been identified as beneficiaries of the proposed research. (1) The multidisciplinary research proposed here will benefit and link groups in atmospheric science, climate science, biogeochemistry and statistics. (2) The scientific community benefits from long-term operation of the Darjeeling station and in the collection of long-term data. (3) This project benefits NERC, which recently funded a large multi-institute project to quantify UK emissions, the Greenhouse gAs Uk and Global Emissions (GAUGE) project using terrestrial models and atmospheric data. (4) Students in India will benefit from proposed educational activities (5) The UK Department of Energy and Climate Change (DECC) will benefit through the incorporation of the new inverse method used in this project into the software used for UK emissions estimation and reporting to the United Nations Framework Convention on Climate Change. (6) Students in the UK will directly benefit from the proposed outreach activities (7) The public will benefit from research results disseminated to a general audience via the University of Bristol and my personal website.

How will they benefit?

This research has several important academic and economic/societal impacts, as outlined by the Research Councils UK (RCUK).

Academic Impacts:
(1) Enhancing the knowledge economy through scientific advancement - The proposed research uses a novel modeling framework and data from multiple sources to advance the state-of-the-art knowledge about methane emissions from South Asia. This framework could potentially be applied to other regions and globally. (2) Worldwide academic advancement to address issues of importance in other countries or globally - This research is critical for quantifying emissions of a potent greenhouse gas, methane, from a rapidly growing developing country and has wide ranging implications for global and Indian climate policies. A multinational and multidisciplinary team of scientists has been selected to target South Asian methane emissions in greater detail than has been done before. (3) Development of new and innovative methodologies, and cross-disciplinary approaches - I propose to develop a new and innovative method to deduce 'top-down' constraints on methane production in South Asia, using a novel "inverse" methodology and data from a variety of sources around South Asia. The project is fundamentally inter-disciplinary as it bridges atmospheric modeling, terrestrial wetland modeling and climate science and explores the synergies between the fields.

Economic and Societal Impact:
(1) Contributing towards evidence based policy-making - As evidenced by top-down emissions estimates of other gases, most bottom-up inventories, from which many policies are based, are often underestimated and have large uncertainties. The ultimate goal of this research is to provide the most up-to-date 'top-down' emissions estimates for methane, from various source sectors in South Asia, using all of the atmospheric observations available from the region. The results will be used to inform policy-makers in the UK and in India through the proposed impact activities. (2) Contributing toward environmental, sustainability, protection and impact reduction - The effect of wetland and rice paddy emissions on climate will be investigated to the year 2100. This will help to inform policymakers of the effect that these emissions will have on global climate. Furthermore, one of the goals of this research is to better understand the effect of agricultural practices on methane emissions from rice paddies in India. This improved understanding will help to inform where research should be targeted.