ATMOSPHERIC METHANE CONCENTRATION PATTERN OVER INDIA IN RELATION TO VEGETATION DYNAMICS- AN ANALYSIS USING ENVISAT-SCIAMACHY AND SPOT-VEGETATION NDVI DATA

摘要

This paper highlights the spatial and temporal variability of atmospheric columnar methane (CH4) concentration in the Kharif season over India and its correlation with the terrestrial vegetation dynamics. ENVISAT-SCIAMACHY product (0.5 deg X 0.5 deg) was used to analyse the atmospheric methane concentration. Weekly data covering the Kharif season (May to October) for two consecutive years (2004 and 2005) were used to compute monthly and seasonal concentration. SPOT-VEGETATION NDVI product for the same period was used to correlate the NDVI with CH4 concentration. Analysis showed that mean monthly methane concentration during the Kharif season varied from 1704 ppbv to 1780 ppbv with the lowest value in May and the highest value in September month. Correspondingly, mean NDVI varied from 0.31 (May) to 0.53 (September). Analysis of correlation between methane concentration and NDVI values at 0.5 deg X 0.5 deg grid level over India showed significant positive correlation (r velence 0.76). Further analysis using land cover information showed characteristic low correlation in natural vegetation region and high correlation in agricultural area. Grids, particularly falling in the Indo- Gangetic plain contributed significantly to the positive correlation. This was attributed to the rice which is grown as a predominant crop during this period. The CH4 concentration pattern matched well with growth pattern of rice with the highest concentration coinciding with the peak growth of the crop in September. Characteristically low correlation was observed (r < 0.2) in deserts of Rajasthan and forested Himalayan ecosystem. This paper highlights the synergistic use of different satellite based data in understanding the dynamics of atmospheric methane concentration in relation to vegetation as a source of emission.