By Claire Salisbury

Mega-dam construction is booming around the world, with promoters hyping hydropower as a green, renewable source of energy and a means of curbing climate change.

But as these dams are built in the Amazon, Mekong and elsewhere, they're doing great environmental and social damage and their green credentials are no longer adding up.

For example, high quantities of greenhouse gases are released from submerged soil and rotting vegetation, and from turbines and spillways, especially in the tropics, meaning that dam projects are often not the environmentally-friendly option they seem. But assessing the various impacts of dams, alongside their economic viability, is a complex task, and the decision-making process behind a dam is rarely transparent.

Now, a new tool has been developed with the aim of making this kind of assessment more open and available to all. The free HydroCalculator tool, developed by the NGO Conservation Strategy Fund (CSF), is accessible online and is easy to use. The tool's developers, CSF founder John Reid and CSF researcher Thaís Vilela, hope it will allow "a broad group of citizens, researchers and policymakers, to foresee and monitor the economic and environmental consequences of hydropower projects."

The HydroCalculator's end output offers a clear presentation of the net economic value of the dam under consideration, with and without the cost of greenhouse gas emissions factored in; the number of years required before the project generates a profit; and the number of years until net carbon emissions become negative.

Thousand Island Lake in China, the result of a dam built in the 1950s on the Xin'an River.Bryan Ong / Flickr

Reid was inspired to develop the HydroCalculator tool after carrying out numerous cost-benefit analyses of dams, and finding that many such projects "threatened ecosystems and didn't deliver much economic benefit," he said. "I wanted to make it easy for other people to do this sort of analysis.

"For too long, environmentalists had tacitly accepted that it was none of their business to weigh in on the economic merits of big construction projects. That's nonsense," he continued. "The tool is part of a bigger effort to make nature's advocates real players in large public investment decisions."

Vilela said the number of projects which aren't financially feasible "is surprising," and that "transparency in the decision-making process is our main goal."

To use the tool, accessed via CSF's website, the user inputs key project data, including the size of the area to be flooded, the vegetation types that will be submerged, projected costs, dam generating capacity and the price at which the electricity will be sold.

Default values for several factors, such as vegetation carbon content, the wholesale price of energy, and the energy discount rate, are available online if specific details are unknown. All of the dam project analyses that have previously been carried out can also be consulted on the website.

A graphic depiction of major factors influencing greenhouse gas emissions from hydroelectric dams.Vilela and Reid (2017) under a CC BY 4.0 license

Reid and Vilela validated the tool against in-depth, peer-reviewed studies of Amazonian dam impacts, and found that their simplified methodology produced comparable results. Although the precise results varied, the relative costs and benefits of different existing Amazon dams, and their economic feasibility, was similar. The inclusion of the cost of greenhouse gas emissions had both positive and negative effects on the economic feasibility of different dams, they found, but did not change the overall feasibility for any of them.

Recent scientific studies have shown how important hydropower dams are as a source of methane, something largely overlooked in dam impact assessments. Methane is far more potent than CO2, but it also degrades more quickly: over 100 years, methane has an effect more than 30 times stronger than CO2, but this increases to 86 times stronger when considered over a period of 20 years. This shorter timeframe is what really counts, scientists say, given the urgency with which CO2 emissions need to be curbed to prevent catastrophic global warming.

As a result, the incorporation of accurate greenhouse gas emissions estimates was key to the creation of the HyroCalculator. That "required installing a global map of carbon density, figuring out the emissions from each country's electricity mix, and finding a formula for reservoir-based emissions that can work for any project," said Reid. "The difficulty with emissions points to the central challenge with any web-based analytical tool: precision versus practicality."

The Tucuruí dam spillway on Brazil's Tocantins River. International Rivers / Flickr

In the name of practicality and ease of use, the Hydrocalculator does make some minor concessions to accuracy. Emissions from turbines and spillways, for example, were excluded from this version of the tool, because there's greater uncertainty around these sources, said Vilela. As a result, the calculator's emission estimates will be conservative, for now, but CSF is planning to add these additional sources into future versions.

The HydroCalculator has been well tested. It has been used by CSF for some time, and other organizations, including a development bank and International Rivers, an environmental NGO, have also employed the tool in their research.

Sarah Bardeen, of International Rivers, said their staff has "found the HydroCalculator to be useful in assessing a [dam's] economic viability when we have limited information about a project."

"The HydroCalculator shows that hydropower is far from carbon-neutral, and helps users calculate a ballpark estimate of greenhouse gas emissions from a dam's reservoir," Bardeen added. "This is important, because it puts information about reservoir emissions into the hands of affected communities, who are often shut out of the opaque planning processes around hydropower projects."

The Santo Antônio dam on the Madeira River in Brazil, part of the Madeira Hydroelectric Complex.Brazil's Growth Acceleration Program / Flickr

Both Bardeen and the CSF team emphasize that the tool should not be used in isolation, but as part of a broader assessment process. "Hydropower is a notoriously complex and risky power source to build, and there really isn't a tool that can capture and show all the environmental, social and economic consequences of building a dam," Bardeen explained.

Assessing the tradeoffs of hydropower development should be done through "deep analysis of primary data and listening to the people who would be affected," agreed Reid. "The HydroCalculator just lets you take a first step along that path."

Major environmental risks of dams—such as the direct and indirect impacts to biodiversity, effects on aquatic and terrestrial wildlife connectivity, and reduction in a waterway's nutrient and sediment flow—along with the consequences to local communities, must all be carefully weighed against the benefits of a proposed dam. Though, at present, none of these risks are tallied by the Hydrocalculator. Still, the tool goes a long way toward empowering dam project-impacted communities, the experts said.

Belo Monte dam under construction in 2015.Pascalg622 under a CC BY 3.0 license

In the Amazon, where mega-dam projects are slated for many of the basin's rivers, scientists fear that harm from dams will be irreversible. There, Indigenous people and traditional river communities are fighting to protect their sacred lands and livelihoods. And untold numbers of species still not described by science are at risk.

"Communities protecting their lands and waters need all the help they can get to evaluate the impacts of proposed hydropower projects. In the Amazonian context, this tool is another arrow in their quiver," Bardeen said. "But bad hydropower projects go forward for many reasons—and in Brazil, corruption, graft and authoritarianism have the tendency to steamroll reason and science."

The global debate around hydropower "is likely to intensify as pressure grows to meet expanding electricity demand and rein in greenhouse gas emissions," Reid and Vilela concluded in their paper. Tools such as the HydroCalculator can help provide the knowledge needed to navigate that debate.

Reposted with permission from our media associate Mongabay.