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

甲烷是一种强大的京都议定书规定的温室气体，具有仅次于二氧化碳的第二大辐射强迫。在全球范围内，很大一部分甲烷排放是自然产生的，如湿地和白蚁。在南亚，与稻田、反刍动物、化石燃料排放和生物质燃烧等较大的人为来源相比，自然湿地是较小但仍然重要的甲烷来源。甲烷的全球平均排放量一般受到很好的限制，但为了具体量化南亚的排放量，需要在南亚排放源附近进行测量。为了实现这一目标，2011年在印度大吉岭建立了一个测量站，现场测量甲烷，每天收集70多个测量数据。在该项目中，将利用地面、飞机和卫星对南亚甲烷浓度的观测，对每个来源部门（化石燃料、湿地、牲畜等）的甲烷排放量进行量化，卫星监测仪目前测量全球地球仪的甲烷浓度，由于其覆盖全球，是一种强有力的工具，而地面站点只测量一个地点。卫星的主要局限性是因为它们在云层和灰尘可能掩盖甲烷信号的地区容易出错。本建议中将开展的研究途径之一是将所有地面、航空器和卫星测量结果联合收割机结合在一起，并利用合并后的数据提供关于南亚卫星观测质量的信息。这将有助于更好地了解今后如何在该区域使用这些卫星观测。印度大气甲烷的主要来源之一来自稻田，也被称为人为湿地。控制这些排放的过程类似于自然湿地中发生的过程。当水覆盖土壤表面时，土壤下层的氧气被剥夺。在这些“缺氧”区域，细菌通过导致甲烷产生的途径代谢土壤中的有机物质。然而，人类对水管理、肥料使用和其他农业实践的影响使稻田甲烷的产生与自然驱动的湿地过程有很大不同。例如，人类通过灌溉人为地改变地下水位。农民还向土壤中添加额外的营养物质，为细菌提供比自然湿地更多的有机物质和氮。此外，稻田通常是在不含湿地的地区种植的，因此是人工引进的。这项研究的主要目标之一是提高我们对印度湿地来源（天然湿地和稻田）甲烷排放过程的理解。我将采用一个“湿地”模型，经过修改以包括农业实践，以模拟来自地面的排放，以及一个大气传输模型，将土壤中产生甲烷的过程与我们在大气中进行的测量联系起来。这些大气观测结果将用于改进湿地模型中的过程。使用这个工具，我将从印度次大陆的所有来源产生最准确和最新的甲烷排放量估计。最后，我将使用预测的水稻生长和未来气候情景，如政府间气候变化专门委员会第五次评估报告（IPCC AR5）中使用的情景，预测印度水稻农业到2100年的甲烷排放量。

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).