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India has the second largest population, one of fastest growing economies and is ranked third in greenhouse gas emissions by fossil-fuel burning in the world. However, there has been little monitoring of atmospheric CO2 concentration over India to date. Here we reanalyse pioneering atmospheric CO2 observations at Cape Rama, India (CRI) during the period from February 1993 to October 2002, using three forward transport models to simulate atmospheric CO2 and separate tracers of terrestrial and oceanic fluxes, and fossil-fuel emissions. The CO2 seasonal behaviour at this site has clear signals from monsoon-driven meteorology and terrestrial ecosystem activity, which are generally captured by all three models. The quality of the agreement between the simulations and the observations varies with season, with better results obtained during the southwest monsoon months when the CRI site observes the oceanic air of mostly southern hemispheric origin. Relatively poor model-data agreements in the other seasons, when air originating from the Indian subcontinent passes over the site, arise from the inability of coarse-resolution global models to represent CRI appropriately. In addition, limited atmospheric CO2 measurements in the South Asia region only provide poor constraint on inversion fluxes. Flux signal footprint analysis of the CRI station highlights the need of extending the observation network inland and to different parts of the country for better understanding of the carbon cycle of India. [ABSTRACT FROM AUTHOR]

• Calibration and validation of a process-based ecosystem model at an Indian forest. • Modelled and observed annual GPP are 2433 gC m−2 y−1 and 2399 gC m−2 y−1. • Mismatch exists between empirically derived and modelled photosynthetic parameters. • Model simulated sensible and latent heat fluxes concur with direct observations. The ecosystem-atmosphere exchanges of terrestrial ecosystems are key drivers of global carbon, water, and energy cycles which are crucial to be measured accurately and represented in bottom-up biogeochemically and biogeophysically coupled ecosystem, Earth system, and climate models for improving the model predictions and impact assessment of climate change on these ecosystems. The diverse natural ecosystems in India are poorly represented in these models due to the absence any of integrated data-model framework and intercomparison study so far. To partially address this, we have used flux-tower measurements in this study to simulate the gross primary productivity (GPP), sensible (H), and latent heat fluxes (LE) of a moist semi-evergreen deciduous forest in the Kaziranga National Park in subtropical Northeast India using a process-based model ISAM. The model is calibrated using two years of measurement which improves its performance when subsequently run to simulate these fluxes for a year. The model produced annual GPP, mean maximum H, and LE are 2432.26 gC m−2 y−1, 29 and 82 W m−2 respectively as compared to their measured values i.e. 2398.47 gC m−2 y−1, 26 and 73 W m−2 correspondingly. Additionally, we report the calibrated model biogeochemical and biogeophysical parameters which will be useful to simulate the fluxes in this forest using the aforementioned models. [Display omitted] [ABSTRACT FROM AUTHOR]