India's dams major contributor to global warming

New Delhi, May 20: 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 told sources 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 (plants, plankton, algae, etc.) 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 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.

The methane emission from India 's dams is estimated at 27.86 per cent of the methane emission from all the large dams of the world, which is more than the share of any other country of the world.

Brazil comes second with 21.8 MT per annum, which is 18.13 per cent of the global figure.

Lima and his co-authors propose capturing methane in reservoirs and using it to fuel power plants. Lima says, "If we can generate electricity from the huge amounts of methane produced by existing tropical dams we can avoid the need to build new dams with their associated human and environmental costs." "It is unfortunate that Lima 's study has come too late to be included in the recent reports from the Intergovernmental Panel on Climate Change (IPCC)," says Patrick McCully, Director of the International Rivers Network.

"Climate policy-makers have largely overlooked the importance of dam-generated methane. The IPCC urgently needs to address this issue." The IPCC should initiate an independent study to assess the GHG potential of reservoirs in different parts of the world, including India. Emission of CO2 from reservoirs is already part of the mandatory reporting formats of IPCC. Reporting of methane emissions is suggested, but not mandated. The IPCC should make reporting of emission of methane from large dams mandatory.

Mr Thakkar said a study should be undertaken to assess as to what extent methane emitted from reservoirs and hydropower projects could be recovered for beneficial use, in the process also reducing the global warming impact of the reservoirs.

According to 2002 Central Water Commission Register of dams, India had 4525 large dams, including 475 under construction dams.

UNI