Estimating Trends and Variation of Net Biome Productivity in India for 1980-2012 Using a Land Surface Model

In this paper we explore the trend in net biome productivity (NBP) over India for the period 1980-2012 and quantify the impact of different environmental factors, including atmospheric CO2 concentrations ([CO2]), land use and land cover change, climate, and nitrogen deposition on carbon fluxes using a land surface model, Integrated Science Assessment Model. Results show that terrestrial ecosystems of India have been a carbon sink for this period. Driven by a strong CO2 fertilization effect, magnitude of NBP increased from 27.17 TgC/yr in the 1980s to 34.39 TgC/yr in the 1990s but decreased to 23.70 TgC/yr in the 2000s due to change in climate. Adoption of forest conservation, management, and reforestation policies in the past decade has promoted carbon sequestration in the ecosystems, but this effect has been offset by loss of carbon from ecosystems due to rising temperatures and decrease in precipitation. Plain Language Summary Our study presents the results for net biome productivity (NBP) for India on a country scale, which are estimated using a state-of-the-art land surface model. Environmental factors, such as elevated atmospheric CO2, climate change, nitrogen deposition, and land cover changes, have been identified as the major factors responsible for changes in terrestrial carbon fluxes. Broadly, the manuscript presents the relative contribution of these environmental factors to changes in NBP in India for the last three decades. Most of the published studies on this topic have focused on the NBP estimates at regional or global scale. To the best of our knowledge, this is the first attempt to quantify NBP at country scale. The results presented are timely because this manuscript adds to the knowledge of the carbon budget on a country level, identifies uncertainties in our understanding that can motivate further experiments, and aides in quantifying the regional and global carbon budget. These original research results presented in this study have implications for the ongoing international debate on climate treaty which calls for countries to apply the carbon stored in its forests and other ecosystems toward its budgeted reduction in carbon dioxide and other greenhouse gases.