Biosphere-Atmosphere Exchanges of Carbon, Water, and Energy in India: Synthesis from Eddy Covariance Measurements for Enabling Socioeconomic Benefits

Hosting the largest population in the world and one of the major growing economies, the greenhouse gas emissions from India remain significant. This is also largely contributed to by the vast agricultural tracts in this country, which occupy more than half of its landmass. However, India is committed to the Paris Climate Accord, and the biodiverse forests, mangroves, and grasslands in this region occupy almost 40% of the landmass, which stores potentially a large amount of carbon. In the context of a changing climate, it is also crucial to understand the ecohydrology of these ecosystems, as it is intricately linked to their carbon cycle. The coupling between these two is a crucial factor in ensuring sustainable development, as land and water remain two resources constrained by various developmental and mitigation activities. However, the magnitude and spatiotemporal variabilities of carbon, water, and energy exchanges between terrestrial ecosystems and the atmosphere are not well understood in India, primarily due to a lack of coordinated efforts in measuring these using Eddy Covariance (EC) techniques. This lacuna has hindered the development of remote sensing-based biophysical products and ecosystem models, leading to uncertainties in the national, regional, and global carbon budgets. In this study, the EC flux observations in India, across the dominant land use and land cover types in 12 locations, are systematically reviewed using a standard methodology. The assessment shows that cropland absorbs the maximum carbon during the Indian monsoon, although this is not generally true for all agro-climatic regions. Some forests, croplands, and mangroves function as well-watered ecosystems, while others oscillate between well-watered and water-stressed conditions, depending on the temperature and moisture availability. Mangroves sequester a large amount of carbon; however, their ability to sequester carbon is restricted by the salinity of the surrounding basin. Water-limited ecosystems demonstrate the highest water-use efficiency (WUE); irrigated croplands exhibit the lowest. Indian forests, which are mainly tropical and subtropical, register a lower WUE than the temperate and boreal forests. The global and regional flux networks, such as FLUXNET, AmeriFlux, AsiaFlux, ICOS, and OzFlux, have greatly improved our understanding of terrestrial ecosystem functioning and ecosystem-atmosphere exchanges, whereas our data review and systematic analysis are the first of their kind in India. These will be useful to the research community, planners, and policymakers alike, aiding in improved decision-making and the just allocation of resources to benefit all stakeholders.