June 19, 2013 | 06:52 AM (BD Time)
19 June, 2013 Wednesday
DCC elections after Eid-ul-Fitr : EC ; Hartal progressing peacefully in CHT ; Indefinite transport strike continues in Khulna ; 18-party to stage demo countrywide on June 22 ; Snowden claims online Obama expanded 'abusive' security programs
Wrong climate for big dams
Reducing climate pollution and eradicating poverty are two of the biggest challenges facing the world today. Large dams are the wrong response to both of these pressing problems for the following reasons:
River flows are increasingly unpredictable. Large dams have always been based on the assumption that future stream-flow patterns will mirror those of the past, but this is no longer true. Climate change has begun to significantly and unpredictably change precipitation patterns. On the one hand, more frequent droughts will make many hydropower projects uneconomic, while on the other, more extreme rainfall will increase siltation of dams (reducing their useful lifetimes) and increase the risk of dam failures and catastrophic flood releases.
Dam reservoirs emit greenhouse gases. In the tropics, dam reservoirs are a globally significant source of one of the most potent gases, methane. Even outside of the tropics, some dams can be significant sources of methane. Meanwhile, free-flowing rivers play a crucial role in helping trap carbon.
Healthy rivers are critical for supporting life on Earth. Big dams make it harder for people and ecosystems downstream of dams to adapt to climate change by reducing water quality and quantity, drying up forests and wetlands, flooding productive land, and destroying fisheries.
Due to widespread damming, healthy rivers are becoming an endangered species - just when we need them the most. Yet hundreds of new large dams are being proposed for key rivers, particularly in the Global South. A global dam boom poses huge risks to the natural support systems that we all depend on, and will make it harder for all life on Earth to adapt to a warming world. Instead of damming the world's rivers, it is both possible and practical to develop climate-safe energy and water supply systems that improve lives, share the development wealth, and help us weather the coming storm.
More than 50,000 large dams choke at least 60% of the world's rivers. The consequences of this massive engineering program have been devastating. Large dams have wiped out species; flooded huge areas of wetlands, forests and farmlands; displaced tens of millions of people, and affected at least half a billion people living downstream.
In addition to these serious impacts, large dams are a major source of emissions, particularly in the tropics (a hotspot for damming). Brazilian researchers have estimated that dams and reservoirs are responsible for almost a quarter of all human-caused methane emissions. These 104 million tonnes of methane are responsible for at least 4% of all human-caused warming.
Reservoirs emit greenhouse gases due to rotting organic matter from the vegetation and soils flooded when the reservoir is created; the plants that grow in the reservoir, and the detritus that flows into the reservoir. Gases are also emitted when water is discharged through turbines and spillways. Some reservoirs flood "carbon sinks" such as tropical forests, increasing their climate-change impact.
Scientists have studied more than 30 reservoirs, and found emissions at all of them. In the tropics, dam reservoirs are especially potent emitters of the very powerful greenhouse gas, methane. Balbina Dam in Brazil, for instance, is ten times dirtier than a coal-fired power plant generating an equivalent amount of electricity.1 Despite having some of the highest-emitting dams on the planet, Brazil is planning to build up to 60 dams in the Brazilian Amazon alone.
Outside of the tropics, the global warming impact of dams is significantly lower than that of fossil fuel-generated electricity but definitely not negligible. For instance, the Wohlen reservoir in Switzerland continues to emit well above the average natural lake in Europe, even after 90 years of operation. While temperate reservoirs emit less than tropical reservoirs, studies show that they should still be taken into account in global estimates of emissions.
Despite the strong evidence that dams are a significant source of climate pollution, reservoir emissions are rarely taken into account in national carbon registries or emissions targets.
Major rivers play a surprisingly large role in helping tropical oceans absorb carbon. The vast flow of major river basins delivers phosphorus , iron and other nutrients far offshore, where it is consumed by certain forms of sea life such as phytoplankton. These microorganisms "fix" carbon by taking it out of the atmosphere. The organisms eventually sink, taking carbon with them to the deep seafloor. Dams could change the delicate workings of this ecosystem service by holding back the river-borne and nutrient-rich sediment that feeds this cycle.
At least two major river basins slated for damming - the Amazon and the Congo - are important planetary sources of nutrient flows. A 2009 study2 on Africa's biggest proposed hydropower project, the Grand Inga Complex on the Congo, says that "plans to divert, store or otherwise intervene in Lower Congo River dynamics are truly alarming" and "ignore the river's significant influence on the equatorial Atlantic, which, in turn, is central to many climate change models." Despite its potentially huge impact on increasing greenhouse gas emissions, Grand Inga's proponents hope to garner carbon credits to offset some of its huge price tag.
Scientists predict that damming the Amazon, the Congo, the Mekong and other high flow rivers in warm-ocean areas could reduce their ability to mitigate climate change. Research on other rivers' carbon-sink capacity is underway.
The most serious consequence of climate change for human society will likely be the changes in rain and snowfall patterns that a warmer world will bring. We are already experiencing an unprecedented number and intensity of extreme floods and droughts, and the problem is expected to grow.
The future will bring extremes of drought and flood outside the historical record that will continue to worsen as the climate warms. Large dam developers do not currently take climate change into account in their plans. If they did, dams would need much greater capacities to safely pass high floods, and projections of power generation for hydropower projects would have to allow for the probability of new extremes of drought. These factors would increase the costs and reduce the benefits from dams, thus making the alternatives to them even more attactive.
Large hydropower projects are potentially highly vulnerable to changes in precipitation and streamflow. A 2011 World Bank report states: "Heavy reliance on hydropower creates significant vulnerability to climate change and is a feature that many low- and middle-income countries have in common." The report summarizes the impacts on the hydropower sector as "reduced firm energy, increased variability, increased uncertainty." In order to increase the flexibility of the system and its resilience to more variable climatic conditions, the report recommends an adaptation response that "may require a policy decision to diversify away from hydropower."
Dozens of countries are already over-dependent on hydropower, and most of them are poor. Yet it is in the already hydro-dependent countries where the bulk of new large hydro capacity is planned, such as Brazil, Ecuador, Ethiopia and Southern Africa. Even with our existing climate, many of the hydro-dependent countries are already experiencing energy shortages when droughts strike, and often with severe economic consequences. For example, Kenya (66% hydro-dependent) has regularly incurred significant costs of drought-induced energy shortages. In 2011, Kenya had a 90 MW shortfall in power due to drought, and had to replace lost hydropower with expensive emergency generators. Other East African nations also experience regular, c
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