Renew On Line (UK) 29a

Extracts from the Jan-Feb 2001 edition of Renew
These extracts only represent about 25% of it

10. Hydro Damned

The World Commission on Dams, an organisation of scientists, engineers and environmentalists, supported by the World Bank, recently warned that hydro projects could be a larger contributor to climate change than coal fired plants. It told the UN Climate Change Secretariat that greenhouse gasses were produced from ‘all 30 reservoirs for which measurements have been made’ and concluded that ‘there is no justification for claiming that hydroelectricity does not contribute significantly to global warming.’

The problem is that reservoirs behind the dams built to feed hydroelectric power plants, and also of course reservoirs built to store water, are a source of methane gas. It is produced by the decay of the biomass that is trapped when the reservoir is created, and also by biomass that comes down stream into the reservoir from the rivers or streams feeding it. Normally, without a reservoir in place, much of this biomass material would rot in open air or in well oxygenated rivers, and generate carbon dioxide gas. But when trapped in fetid sumps under water, anaerobic processes mean that, as well as producing carbon dioxide, methane is produced and bubbles up to the surface - the fetid water is less effective at absorbing it. Given that methane is 20 times more potent as a greenhouse gas than carbon dioxide, the result is that hydro plants can contribute much more to climate change than a coal fired plant of the same capacity. As Fred Pearce put it in an article in the Independent (13 Oct) ‘reservoirs magnify the greenhouse effect of the rotting of the Earth's vegetation’

The problem would presumably be worse in areas with heavy vegetation and high temperatures. Certainly, studies quoted by Pearce of the 112MW Balbina hydro plant in the Amazon rainforrest in Brazil have suggested that the greenhouse effect due to emissions from its reservoir were three times more than that which would be produced by an equivalent sized coal plant. And, he said, a similar figure has been suggested for the Petit-Suat dam in nearby French Guiana - which provides power to Europe's Ariane rocket launch site. The result is that, according to a calculation by Robert Delmas of the Aerology Observatory in Telouse, French Guiana now emits three times more greenhouse gas per capita than France - and more per capita than the USA.

Not all sites may be as bad, but research by the Cidade University of Rio de Janeiro suggests that up to half of Brazils hydro reservoirs have a climate change capacity equal to the equivalent coal fired plants. Meanwhile, Ghana, which Pearce says has ‘flooded a twentieth of its land area to create the giant Akosombo hydro project’ would, on the basis of St Louis's figures, emit ‘five times as much greenhouse gas as all the country's fossil fuel burning’

Pearce adds that, while only a third of the world's reservoirs are in the tropics, they appear to produce around 80% of the greenhouse emissions. And overall, an estimate of the total global impact of the words hydro projects and reservoirs by Vincenty St Louis from the University of Alberta, based on a modelling approach rather than measurements, has suggested that they could produce one fifth of the man-made methane emissions. If the carbon dioxide also produced is added in, then in total, Vincenty St Louis suggests that they might be responsible for around 7% of the man-made greenhouse effect - more than from aircraft.

Of course some of this carbon dioxide would be produced anyway, as the biomass rotted, and reservoirs often flood marsh land, which would have produced some methane in any case. But this marshland would also have absorbed some greenhouse gasses. And it is possible that there could also be some outgassing of dissolved carbon dioxide from reservoir waters - or at least reduced absorption.

Clearly, there are complex site specific interactions involved with local ecosystems when major hydro projects are installed - and we need detailed studies to identify the exact impacts in a variety of locations, including those in colder climates. But the initial studies certainly look worrying, and could spell the end for hydro projects in developing countries, given that these have increasingly being financed by agencies like the World Bank on the basis of their emission avoiding capacity.

Of course we have to set all this in context. In order to eliminate malaria, we have drained many swamps and marshlands around the world, so that methane emissions will be halted. In addition, with demand for water for irrigation rising, many lakes have been reduced in size. For example, the Aral Sea, in the S. Russian province of Uzbek, was once 150 miles across, but has been reduced in area by 50% and volume by 73%, due to use of its water for irrigation for cotton crops since the 1960's. The result of this has been the creation of a desert - the top soil has been blown away, and what was once a small fishing port is now twenty miles from the remaining lake.

Obviously, that's not something to advocate, it’s a local environmental and social disaster, but it does presumably mean that methane production has been reduced.

Overall then, it's possible that the emissions from hydro reservoirs will be cancelled out by the removal of marshland and swamps and by the loss of lake areas.

However, in order to slow climate change, we need to actually reduce emissions. No one is suggesting that we set about eliminating lakes to make room for the emissions from new hydro reservoirs, but it might be possible in some locations to reduce emissions from lakes by carefully management of the local biomass. Similarly in the case of new and existing hydro reservoirs - by removing as much biomass as possible before the reservoirs are formed and cutting back on growths upstream once they are established. But that could be expensive and environmentally disruptive.

Although it depends on the location, overall, it seems increasingly unlikely that major new hydro projects will be included as one of the options for support under the Clean Development Mechanism. That would clearly be a blow to the hydropower industry, which has, over the years, installed huge projects in developing countries. More importantly, it will mean that developing countries will have to look at other technologies to help them achieve emission reductions. If big projects are still seen as necessary, then Blue Energy (see earlier) may yet find its tidal fence technology in demand - that would not involve creating reservoirs. But it's a very site specific option. As we noted in Renew 125, smaller scale options like wind, solar and biomass seem much more likely to be relevant to most developing countries. And small hydro projects may also be suited - especially run of the river schemes, which do not rely on dams and reservoirs.

No one is talking yet of closing existing hydro projects. Even so, if hydro, which currently supplies around 20% of the worlds electricity, is seen as contributor to Climate Change rather than a solution, that will make it harder to meet the Kyoto emission reduction targets. While plants in cold climates like Norway and Canada are probably unaffected, the situation for those in northern and central Europe is less clear. And, for most other countries, hydro dam construction is going to be problematic. The only good outcome would be that money that would otherwise have gone to new large capital intensive hydro projects in developing countries might support smaller scale renewable technologies, better suited to local needs.