Over 260,000 kilometers of rivers at risk due to proposed hydro dams

"We used a dataset of more than 3700 potential hydropower projects and calculated their impacts on rivers worldwide," says Prof. Bernhard Lehner from McGill University's Global HydroLab, who created the underpinning global river maps. "It was sobering to learn that many of today's remaining free-flowing rivers are at risk of being permanently transformed by new energy infrastructures."

Moreover, the study also finds that all the proposed dams on free-flowing rivers would collectively generate less than 2% of the renewable energy needed by 2050 to keep global temperature increase below 1.5? C -- a small contribution with potentially devastating consequences to the remaining free-flowing rivers, and the people and wildlife that depend on them.

The researchers suggest that, as global leaders convene for a critical round of UN climate and biodiversity summits this fall, policymakers must consider the tradeoffs between hydropower development and maintaining healthy freshwater ecosystems.

Looking at the tradeoffs -- Hydropower development vs. environmental costs

"It is true that hydropower is a source of renewable energy with relatively low carbon emissions," says Günther Grill, a post-doctoral fellow at McGill who crunched the numbers and developed the spatial environmental assessment model to estimate the effect of future dams. "However, hydropower projects can permanently and irreversibly impact river and floodplain dynamics and functions, often in tropical wilderness areas with high biodiversity."

The policy paper points to the fact that connected and healthy rivers deliver diverse benefits that are often overlooked: freshwater fish stocks that improve food security for hundreds of millions of people; delivery of sediments that nourish agriculture and keep deltas above rising seas; and floodplains that help mitigate the impact of floods and support a wealth of biodiversity.

"When it comes to river health, climate change and biodiversity loss, we can no longer afford to think of these as separate issues," says Michele Thieme, lead freshwater scientist at World Wildlife Fund (WWF) and lead author of the study. "Rivers are powerful agents for keeping wildlife and communities healthy, especially in a warming climate, yet their ability to support life is threatened by hydropower dams in many parts of the world. The best policy solutions will be those that balance renewable energy needs with the many benefits of thriving freshwater ecosystems."

Safeguarding free-flowing rivers while meeting climate targets and energy needs

In the paper, the researchers have compiled a list of science-based policy solutions to meeting climate targets and energy goals, while also safeguarding free-flowing rivers and their benefits to people and nature. These solutions include avoiding river fragmentation by exploring alternative development options, such as non-hydropower renewable energy, like solar and wind; minimizing impacts by siting dams in locations with fewer consequences on people and nature; restoring rivers through dam removal; or offsetting the negative impacts of dams on one river by formally protecting another, similar river.

"There has been a long history of conflicts, studies, and debate over how to both protect rivers and develop them sustainably," adds Lehner. "With a pause in new developments caused by the global pandemic, anticipated further implementation of the Paris Agreement and high-level global climate and biodiversity meetings in 2021, now is an opportune moment to consider the current trajectory of development and policy options for reconciling dams with freshwater system health."

The research was funded in part by WWF in Washington, DC and by McGill University in Montreal, Quebec, Canada.