Hydropower — often considered a renewable source of energy that is key to meeting global climate goals — is big business in the Amazon, Congo and Mekong river basins, where more than 450 dams are on the drawing board.
But dam building in tropical rainforests comes at a huge cost to biodiversity and the tropical rain forest ecosystems that provide humans with clean air and water, according to a Texas A&M University study published Thursday in the journal Science.
“Far too often in developing tropical countries, major hydropower projects have been approved and their construction begun before any serious assessments of environmental and socioeconomic impacts had been conducted,” study lead author Kirk Winemiller, an aquatic ecologist at Texas A&M University, said.
The tropics, the earth’s most biologically diverse and forested region, stores more carbon than any other region. Hydropower’s impact on biodiversity is an important factor because biodiversity loss may reduce the rain forest’s ability to withstand and help mitigate climate change, recent studies have shown.
Biodiversity is being threatened throughout the tropical forests of Asia, Africa and South America, according to the Texas A&M researchers.
The dam-building rush, especially in the Amazon, impedes tropical fish migration and vastly expands deforestation because of the construction of new roads. Brazil, for example, gets two-thirds of its electricity from hydropower, and 334 new dams are being proposed in its diverse tropical rainforests.
In Southeast Asia, the Mekong River Basin already has 370 dams, and there are plans for construction of nearly 100 more, including dams on the river mainstem, Winemiller said.
“The Lower Mekong River supports important inland fisheries, recently valued at about $17 billion a year,” he said.
Fishery losses in the wake of new dam construction poses a food security challenge in Thailand, where 99 new dams planned for the Mun River Basin would require up to a 63 percent expansion of agricultural land, which leads to further deforestation, the study says.
The study adds that economic projections often exclude or underestimate the costs of environmental improvement following the construction of major dams. China, for example, spent $26 billion to reduce the ecological impacts of the Three Gorges Dam — the world’s largest hydropower dam — on the Yangtze River.
“Long-term ripple effects on ecosystem services and biodiversity are rarely weighed appropriately during dam planning in the tropics,” the study says. “Institutions that permit and finance hydropower development should require basin-scale analyses that account for cumulative impacts and climate change.”
Scientists unaffiliated with the study say it illustrates the possibly outsized impact that dam building in the tropics has on biodiversity, and possibly the climate.
José Maria Cardoso da Silva, an environmental geography professor at the University of Miami, said the study shows that three of the most biologically diverse river basins on earth are under high pressure from dam building, and countries are doing too little to prevent significant environmental harm from such development.
New roads built for dam construction create new economic opportunities, or “economic frontiers,” such as logging in previously untouched rainforests, creating unregulated access and deforestation, which is a major source of carbon dioxide emissions fueling climate change, he said.
Methane emissions from newly-built reservoirs only increase hydropower’s impact on the climate, he said.
“Nothing is going to change if we do not propose feasible solutions so that megadiverse countries can produce the clean and renewable energy to sustain their development without damage to their extraordinary biodiversity,” Silva said.
Mauro Galetti, a Sao Paulo State University conservation biologist in Brazil who published a study in December showing that a decline in biodiversity in tropical forests reduces their ability to store carbon, said dam building is a “major disaster.”
“Many politicians and engineers proclaim that hydroelectric power dams is a ‘green energy,’ but this is a big mistake,” he said. “Hydroelectric dams create a huge impact on climate, biodiversity and people’s health. This study alerts us to the large-scale impact of dams in tropical forests, and if these projected dams are built, we will have a worse scenario for climate change than we would expect.”