80% of Brazil’s electricity is generated by hydropower. David Holt

Much of the controversy over hydropower plants in tropical nations is focused on what dam construction and flooding will do to people and the environment. But what about what forests do for dams?

A team of US and Brazilian scientists presents a unique perspective on the relationship between forests and hydropower in an article recently published in the Proceedings of the National Academy of Sciences.

Stickler et al.’s study focuses on the polemic Belo Monte hydropower complex, situated in the Xingu River basin of the Brazilian Amazon. Upon its projected completion in 2015, Belo Monte will be the third largest hydropower dam in the world. Its construction has been the subject of local, national and international protests, especially because of the harm predicted for aquatic ecosystems and local people (including high-profile indigenous groups), along with its questionable economic viability.

Despite the heavy controversy, the Brazilian government moved ahead with the project; hydropower is just too appealing, especially in a country with enormous rivers and where about 80% of electrical energy consumption comes from this source. Belo Monte alone is expected to supply 40% of Brazil’s growing energy demand until 2019. But what happens when forests, and the rainfall they generate, are considered in these energy production estimates?

In this study, Stickler et al. integrate vegetation, hydrological and climate models at local and regional scales to create possible scenarios for energy generation from Belo Monte as it relates to Amazon forest cover. The novelty of this study is that the authors include the potential indirect effects of deforestation on river water flow in their analysis – namely regional decreases in rainfall – in addition to the direct effects of reduced evapotranspiration when forests are replaced with crops and pasture.

The construction of Belo Monte Dam has been the subject of local, national and international protests, especially because of the harm predicted for aquatic ecosystems and local people. Atossa Soltani/Amazon Watch/Spectral Q.

Without the inclusion of these indirect effects, they could have stopped at the finding that simulated future deforestation in the Xingu River basin (40% by 2050 under a ‘business-as-usual’ scenario) would increase river flow and energy generation by 10%, which supports previous Amazonian studies and the conventional wisdom about the relationship between forest clearing and streamflow.

By including the effect of forest cover on rainfall throughout the Amazon Basin, the study showed that declines in rainfall associated with future Amazonian deforestation on a larger scale would likely reverse that outcome: reduced rainfall in the in the Xingu River basin would counterbalance local evapotranspiration declines, ultimately decreasing river flow and energy generation by 30–36%. So, standing forests actually help secure hydropower potential, especially in places where rainfall seasonality is extreme.

These findings are key for policy makers and for the hydropower industry itself.

Only by continuing to keep Amazon-wide deforestation in check, would Brazil be able to fulfill its promises for energy generation from Belo Monte.

Stickler et al. conclude that under the business-as-usual deforestation scenario, Belo Monte would fall short of its assured energy target by one third. Only by continuing to keep Amazon-wide deforestation in check, would Brazil be able to fulfill its promises for energy generation from Belo Monte. And this, as the authors acknowledge, is without taking into account the additional contribution of climate change through greenhouse gas emissions to possible future droughts and a longer dry season in the Amazon. Could this information be enough to motivate the energy sector to become a proponent of forest conservation?

This article is timely, since the expansion of hydropower to meet electrical energy needs is at the top of the development agenda for many tropical nations with billions of dollars being invested in this energy source. Since the energy benefits may be less than initially imagined, the authors conclude that the viability of Belo Monte and similar projects as a reliable energy source still requires critical examination, especially given the already heavy costs on local society.

While measures to minimize the social and environmental costs associated with dam construction must continue, the dependence of hydropower on forests should also be taken into account. Brazil has gained international recognition for its reduction in Amazonian deforestation since 2005. This article provides compelling evidence that its hopes for national energy security through hydropower depend on continuing this trend.

For more information on issues discussed in this article, please contact Amy Duchelle at a.duchelle@cgiar.org