Human activities impeding the flow of two-thirds of the world’s longest rivers


A recent Nature article that maps the world’s free-flowing rivers shows that the flow of most of the world’s longest rivers has been impeded by man-made constructions such as dams and reservoirs, leading to the rapid decline of some of the most diverse, complex and dynamic ecosystems on the planet.

Dams and reservoirs are drastically reducing the benefits that healthy rivers provide to people and nature worldwide.
©Adobe Stock, by Gary Sax

The study developed the first high-resolution and replicable global assessment of human impact on the planet's waterways, providing detailed maps of world rivers that show just how drastically man-made activity is impacting our rivers.

The estimated 2.8 million dams on the planet are overwhelming identified as the main culprits.

Using satellite data and computer-modelling software, an international team spent ten years analysing the connectivity of 12 million kilometres of rivers worldwide.

They found that just over a third (37%) of the 242 longest rivers had retained their free flow. Less than a quarter (23%) of very long rivers (longer than 1,000 km) and less than half of long rivers (500-1,000 km) have retained a direct connection between their source and the sea.

This is especially concerning, as these rivers are vital for the exchange of water, nutrients, sediments and species with deltas, estuaries and the ocean.

Most of the remaining free-flowing rivers are confined to the less populated remote parts of the planet, including the Arctic, the Amazon and the Congo basins. Only a few very long rivers remain free-flowing in densely populated areas, such as the Irrawaddy and Salween.

As rivers provide a vital link to land, groundwater and the atmosphere, this extreme disruption is having a profound effect on the Earth's biodiversity. According to Pasquale Borelli, the JRC scientist who was part of the international team behind the report, “by harnessing the natural flow of rivers for our own uses, we’re damaging the biodiversity on which life as we know it depends.”

The authors also warn that dams have already led to a significant fall in the numbers of river fish, which 158 million people rely on for their animal protein intake, particularly in poorer parts of the world.

The hydropower dilemma

In the global efforts to develop a carbon-neutral economy, hydropower has been much vaunted as a sustainable and environmentally friendly renewable source of energy.

However, this study shows that, while hydroelectric power sources are significantly cleaner in terms of emissions than oil, gas or coal, mega-power projects that involve dams and reservoirs could have unforeseen negative effects.

With global warming and consumer demand on the rise, sustainable solutions also need to be found to close the gap between irrigation demand and extreme water stress.

The authors hope that the new data, methods and results developed by this study will inform concerted action at the global and national level to restore and maintain the world’s rivers, helping to prioritise rivers with high conservation value for protection and informing the selection of low-impact infrastructure development.

The JRC's high-resolution (250 m) Global Soil Erosion Map was used in developing this study.

The JRC also tracks the extent of the world’s rivers and lakes through the Global Surface Water Explorer, the latest version of which it will present at next week’s Living Planet Symposium in Milan.

Further information