10 Aug 2023
 | 10 Aug 2023

Potential of using CO2 observations over India in regional carbon budget estimation by improving the modelling system

Vishnu Thilakan, Dhanyalekshmi Pillai, Jithin Sukumaran, Christoph Gerbig, Haseeb Hakkim, Vinayak Sinha, Yukio Terao, Manish Naja, and Monish Vijay Deshpande

Abstract. Devising effective national-level climate action plans needs a more detailed understanding of the regional distribution of sources and sinks of greenhouse gases. Due to insufficient observations and modelling capabilities, India’s current carbon source-sink estimates are uncertain. This study uses a high-resolution transport model to examine the potential of CO2 observations over India for inverse estimation of regional carbon fluxes. We make use of four different sites in India that vary in measurement technique, frequency and spatial representation. These observations exhibit substantial seasonal (7.5 to 9.2 ppm) and intra-seasonal (2 to 12 ppm) variability. Our modelling approach, a high-resolution Weather Research and Forecasting Model combined with Stochastic Time Inverted Lagrangian Transport (WRF-STILT) model, performs better in simulating seasonal (R2 = 0.50 to 0.96) and diurnal (R2 = 0.96) variability of observed CO2 than the current generation global models analysed in the study. Representation of local flux variability like biomass burning in the model needs further refinement, depending on the site location. During the agricultural season, crop biospheric uptake in the Indo-Gangetic Plain region significantly modulates the CO2 variability in the northern Indian stations. Depending on the region and time of the year, the anthropogenic and biospheric emission components contribute differently to CO2 variability. The choice of emission inventory in the modelling framework alone leads to significant biases in simulations (5 to 10 ppm), endorsing the need for accounting emission fluxes, especially for non-background sites. By implementing a high-resolution model, our results emphasise that observations from Indian sites can be useful in deducing carbon flux information at regional (Nainital) and sub-urban to urban (Mohali, Shadnagar, Nagpur) scales. On accounting for observed variability, the global carbon data assimilation system can thus benefit from the measurements from the Indian subcontinent.

Vishnu Thilakan et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-1582', Sajeev Philip, 30 Sep 2023
    • AC1: 'Reply on RC1', Vishnu Thilakan, 22 Nov 2023
  • RC2: 'Comment on egusphere-2023-1582', Anonymous Referee #2, 08 Oct 2023
    • AC1: 'Reply on RC1', Vishnu Thilakan, 22 Nov 2023

Vishnu Thilakan et al.

Vishnu Thilakan et al.


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Short summary
This study investigates the usability of CO2 mixing ratio observations over India to infer the regional carbon sources and sinks. We demonstrate that a high-resolution modelling system can represent the observed CO2 variations reasonably well by improving the transport and flux variations at a fine scale. Future carbon data assimilation systems can thus be benefitted from these recently available CO2 observations when fine-scale variations are adequately represented in the models.