Tropical forests act as a major sink of atmospheric carbon dioxide, and store large amounts of carbon in biomass. India is a tropical country with regions of dense vegetation and high biodiversity. However due to the paucity of observations, the carbon sequestration potential of these forests could not be assessed in detail so far. To address this gap, several flux towers were erected over different ecosystems in India by Indian Institute of Tropical Meteorology as part of the MetFlux India project funded by MoES (Ministry of Earth Sciences, Government of India). A 50 m tall tower was set up over a semi-evergreen moist deciduous forest named Kaziranga National Park in northeastern part of India which houses a significant stretch of local forest cover. Climatically this region is identified to be humid subtropical. Here we report first generation of the in situ meteorological observations and leaf area index (LAI) measurements from this site. LAI obtained from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) is compared with the in situ measured LAI. We use these in situ measurements to calculate the total gross photosynthesis (or gross primary productivity, GPP) of the forest using a calibrated model. LAI and GPP show prominent seasonal variation. LAI ranges between 0.75 in winter to 3.25 in summer. Annual GPP is estimated to be 2.11 kg C m −2 year −1 .

The eddy covariance method is a powerful technique for quantification of CO 2 , H 2 O and energy fluxes in natural ecosystems. Leaf area index (LAI) and its changes are significant drivers of CO 2 and H 2 O exchange in a forest ecosystem due to their role in photosynthesis. The present study reports the seasonal variation of CO 2 and energy fluxes and their relationship with other meteorological parameters of a semievergreen primary forest of Kaziranga National Park, Assam, India during February 2016-January 2017. The diurnal pattern of half hourly average CO 2 fluxes over the forest was found to be mostly dominated by the incident photosynthetically active radiation. During the period of study, diurnal variations of CO 2 flux showed a maximum value of −9.97 µmol m −2 s −1 in the month of June during summer which is also the beginning of the monsoon season. The monthly averaged diurnal CO 2 flux and variation in LAI of the forest canopy closely followed each other. The annual net ecosystem exchange of the forest estimated from the CO 2 flux data above the canopy is 84.21 g C m −2 yr −1. Further studies are in progress to confirm these findings. The estimated average annual evapotranspiration of the semi-evergreen forest is 2.8 ± 0.19 mm day −1. The study of partitioning of energy fluxes showed the dominance of latent heat fluxes over sensible heat fluxes. The energy balance closure was found to increase with an increase in instability and the highest closure of around 83% was noted under neutral conditions.

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Amongst all the anthropogenically produced greenhouse gases (GHGs), carbon dioxide (CO2) and methane (CH4) are the most important, owing to their maximum contribution to the net radiative forcing of the Earth. India is undergoing rapid economic development, where fossil fuel emissions have increased drastically in the last three decades. Apart from the anthropogenic activities, the GHGs dynamics in India are governed by the biospheric process and monsoon circulation; however, these aspects are not well addressed yet. Towards this, we have measured CO2 and CH4 concentration at Sinhagad, located on the Western Ghats in peninsular India. The average concentrations of CO2 and CH4 observed during the study period are 406.05 ± 6.36 and 1.97 ± 0.07 ppm (µ ± 1σ), respectively. They also exhibit significant seasonal variabilities at this site. CH4 (CO2) attains its minimum concentration during monsoon (post-monsoon), whereas CO2 (CH4) reaches its maximum concentration during pre-monsoon (post-monsoon). CO2 poses significant diurnal variations in monsoon and post-monsoon. However, CH4 exhibits a dual-peak like pattern in pre-monsoon. The study suggests that the GHG dynamics in the western region of India are significantly influenced by monsoon circulation, especially during the summer season.

This study uses 1 yr of eddy covariance (EC) flux observations to investigate seasonal variations in evapotranspiration (ET) and surface energy budget (SEB) closure at a tropical semi-deciduous forest located in northeast India. The annual cycle is divided into four seasons, namely, pre-monsoon, monsoon, post-monsoon and winter. The highest energy balance closure (76%) is observed during pre-monsoon, whereas the lowest level of closure (62%) is observed during winter. Intermediate closure of 68% and 72% is observed during the monsoon and post-monsoon seasons, respectively. Maximum latent heat flux during winter (150 W m −2) is half of the maximum latent heat (300 W m −2) flux during the monsoon. ET is a controlling factor of SEB closure, with the highest rates of closure corresponding to the periods of the highest ET. The Bowen ratio ranges from 0.93 in winter to 0.27 during the monsoon. This is the first time the role of ET in the seasonal variation of SEB closure has been reported for any ecosystem in northeast India using EC measurements.