Large dams in the country may be the largely unnoticed culprits causing global warming. A latest study estimates that total emissions of methane, a greenhouse gas, from the country’s large dams could be 33.5 million tonnes (MT) per annum, which means Indian dams might be the largest global warming contributors compared to all other nations.
Environmentalist Himanshu Thakkar said that if the estimates are taken as very high and the methane emission is placed at half of it, even then the amount is very alarming as it is still equivalent to 425 MT of Co2.
The study by Ivan Lima and colleagues from Brazil ‘s National Institute for Space Research (INPE) was recently published in a peer-reviewed journal, South Asia Network on Dams, Rivers & People said here.
Mr Thakkar said the study had to make a number of assumptions in arriving at these estimates, as no measurements of the methane concentration or emission have been made for reservoirs in India. Most measurements of methane emission from reservoirs have been done in Canada, Brazil and French Guyana. But, still there was no doubt about the major role played by dams in the emission of greenhouse gases in tropical countries like India, he said. The “fuel” for emission of greenhouse gases from the dams is the rotting of the vegetation and soils flooded by reservoirs, and of the organic matter that flows into it. Methane is produced at the bottom of the reservoirs in the anaerobic conditions prevailing there, over the life-span of the reservoirs. The gases are released at the reservoir surface, at turbines (of hydropower projects) and spillways, and downstream of the dam.
The study estimates that the emission of methane from all the reservoirs of the world could be 120 MT per annum. This means that of the total global emissions of methane due to all human activities, contribution from large dams alone could be 24 per cent. The study does not include the emission of nitrous oxide and carbon dioxide from large dams. If all these are included, the global warming impact of large reservoirs would go up further.