Humans are the ultimate artisans, using the world around us as our toolkit for all kinds of inventions, towers, and devices. But sometimes our penchant for fashioning new constructions can damage the very world we live in. This is particularly true when it comes to dams – just over one-third of the world’s longest rivers are still free-flowing.
Healthy, free-flowing rivers are those unimpeded by human barriers. The 37 percent of unobstructed rivers that remain provide hundreds of millions of people with improved food security, as well as delivering sediment for agriculture, lessening the likelihood of extreme floods and droughts, and helping support a robust ecosystem.
"Rivers are the lifeblood of our planet," said Michele Thieme, lead freshwater scientist at the World Wildlife Fund, in a statement. "They provide diverse benefits that are often overlooked and undervalued. This first-ever map of the world's remaining free-flowing rivers will help decision makers prioritize and protect the full value rivers give to people and nature."
The international team of researchers spent more than a decade analyzing 12 million kilometers (7.5 million miles) of Earth’s rivers to provide the first-ever global assessment of their flow. Publishing their results in the journal Nature, the team found that 77 percent of the world’s rivers longer than 1,000 kilometers (~600 miles) have been severed from source to sea. These rivers are mainly found in remote regions like the Arctic, the Amazon Basin, and the Congo Basin. Dams are the primary reason for this loss of connection, although water extraction and sediment trapping are also involved.
"For millennia, rivers have provided food, contributed water for domestic use and agriculture, sustained transportation corridors and, more recently, enabled power generation and industrial production," write the authors. "These goods and services generally require built infrastructure, and society has addressed this demand by constructing an estimated 2.8 million dams."
To top it off, more than 3,700 hydropower dams are currently in the planning or construction phase. The team's results also suggest that river connectivity increases with decreasing river length. Around 97 percent of rivers between 10 and 100 kilometers (6 and 62 miles) long are free-flowing, but that amount decreases the longer they become.
"Renewable energy is like a recipe – you have to find the right mix of ingredients to have both a sustainable energy grid and a thriving natural world," said Thieme. "While hydropower inevitably has a role to play in the renewable energy landscape, well-planned wind and solar energy can be more viable options for rivers and the communities, cities, and biodiversity that rely on them."
Climate and land use change is likely only going to make matters worse. Given the current status and future prospects of our planet’s rivers, the team say action is needed to protect and restore our threatened water systems, many of which provide for diverse and dynamic environments across the globe.