Forests Fuel Hydropowerby Bill Chameides | May 28th, 2013
posted by Wendy Graber (Researcher)
In the Amazon you don’t need to burn wood for a forest to contribute to energy production.
Once Upon a Time…
People thought the worth of a forest was determined by the value of its timber. We now know that leads to a gross undervaluation. Forests, like most ecosystems, provide a host of services whose value can far exceed the simple worth of the trees. Services like clean water and air, soil retention, stormwater control, habitat, and even increasing groundwater supply. Cut down a forest and you need to replace all the things the forest provides, and that can be quite expensive.
New York’s Water Story
A case in point – the riparian forests in upstate New York provide clean drinking water to the residents of the Big Apple. In the early 1990s the U.S. EPA mandated that the city build a filtration plant at a cost of ~$7 billion. But New York came up with a better plan at a savings of about $6 billion: rehabilitate the riparian forests in the Catskills where the water comes from and allow the trees, at a greatly reduced cost, to provide the needed filtration. The system works so well that New York City is one of the few major metropolitan areas in the U.S. that gets away with minimal filtering for its drinking water.
Is There an Energy Story?
Ok, forests providing clean water – that’s easy to understand. But what about energy? One way to generate energy from a forest is to cut it down and burn the wood – but that destroys most of the other services as well.
Is there a way to use forests to enhance energy production without burning them? Yes, say Claudia Stickler of the Amazon Environmental Research Institute and co-authors in a paper published May 13 in the Proceedings of the National Academy of Sciences. Interestingly like the New York story this one involves water as well.
Hydropower Reigns Supreme in Brazil
You’ve heard of king coal? Well, in Brazil, hydropower is king. According to the U.S. Energy Information Administration a whopping 79 percent of Brazil’s electricity came from hydropower in 2010. (In the U.S. that drops to about 7 percent.)
But Brazil wants even more hydropower, which brings us to the next chapter in our story.
Way Down Upon the Xingu River
You can find the Xingu River on a map in the northeastern corner of Brazil. It runs south to north for about 1200 miles and drains into the Amazon River.
Brazil has big plans for the Xingu River — more specifically, on the Xingu about 100 miles south of where it meets up with the Amazon. That is the construction site of the Belo Monte Dam, slated to be the third largest hydropower facility in the world behind China’s Three Gorges Dam and the Itaipu Dam operated jointly by Brazil and Paraguay. When completed the Belo Monte Dam will have the capacity to produce up to 11 million kilowatts.
Environmentalists Cheer… and Hiss
If you’re a fan of the environment, all that hydropower can seem like a good thing – energy without burning fossil fuels and so no air pollution, no greenhouse gas emissions. Right? Not quite.
First of all it’s not clear that “no greenhouse gas emissions” holds for hydropower in all settings, especially tropical rainforests. The carbon that is liberated from the forests to make way for the dam and the methane generated from the submerged organic matter can significantly tip the carbon footprint scale for hydroelectric facilities in the direction of new global warming.
And then there’s deforestation. Building a dam in the Amazon almost invariably means cutting down large swaths of trees. And there’s no way for an environmentalist to feel good about all that forest clearing. Blocking up the river with a dam is not so great either.
But that’s a problem for environmentalists. If you’re someone in the Brazilian government looking for a dependable and domestic source of energy, hydropower probably still looks like a good thing despite the environmental drawbacks. And if you’re in business to sell energy, hydropower also looks like a good investment. Right? Again, not quite. That’s where the Stickler et al paper comes in. But first…
An Aside on Hydropower 101
If you want to generate power from a river you have to have flowing water to drive the turbines. How much electricity you can generate depends upon the amount of water flowing. You can have the largest (or the third largest) dam in the world, but if the river is dry you’re not going to generate any power. If the river is raging, you’ll probably be able to operate the facility at or near to capacity. And as the river flow drops so does electricity generation. For example, take the two largest dams in the world. The Three Gorges Dam has a 22.5 million kilowatt operating capacity and dwarfs the second largest dam (Itaipu Dam) by almost 40 percent, and yet due to differences in seasonal river flow they generated the same amount of power—about 98 billion kilowatthours–in 2012.
Ok, now back to the story.
The Two Faces of Deforestation
The Stickler et al connection starts with cutting down trees. Cutting down trees, clearing forests, can change the rate of river flow as well as electricity generation.
The accepted wisdom has been that cutting down forests increases the river flow. With the trees gone, there is far less evapotranspiration and that leaves more water to flow off and out of the land into the river; hence more electricity generation – chalk one up for the dam builders.
But when you cut down a forest, you also alter the local hydrological cycle. There is, for example, less water vapor put into the atmosphere, and that can lead to less rainfall. Less rainfall means less water in the river and thus less electricity generation – the dam builders lose on that one.
So Which Is It?
The net result of deforestation on electricity generation depends upon the relative strength of these two competing effects. To determine which one would dominate for the case of the Belo Monte Dam, Stickler et al. carried out a series of model calculations simulating the hydrologic cycle over the Xingu River Basin for various scenarios of net deforestation in the region. Their results indicated that the effect from reduced precipitation would outweigh the effect of decreased evapotranspiration and as a result deforestation is expected to decrease the dam’s ability to generate electricity. If forest destruction proceeds as currently projected (with 40 percent less forests in the region by 2050) the authors estimate that the Belo Monte Dam will produce about 40% less electricity than the industry projects.*
There is a school of thought that you can’t think of energy devoid of the environment; that energy issues are really about energy and the environment. If Stickler et al are correct; the folks building the massive dam along the Xingu River are about to learn that lesson.
*Stickler et al’s result are location dependent and almost certainly do not apply everywhere. A study out last week in the Proceedings of the National Academy of Sciences by Silvio Simonit and Charles Perrings of Arizona State University found that for the region surrounding the Panama Canal retaining forest and reforesting other lands near the canal would not increase precipitation sufficiently to compensate for increased water needs from widening the canal.filed under: deforestation, energy, faculty, rain forest
and: Amazon, ecosystem services, hydropower, Xingu River