Dams have altered 48% of all river flow worldwide. And if all dams planned for the next few decades are built, that proportion will nearly double.

Credit: Jorge Saenz/AP

Günther Grill of McGill University in Montreal, Canada, and his team developed two ways to analyse how dams break up and regulate river flow. They calculated how 6,374 existing dams and 3,377 proposed ones affected (or would affect) river volume worldwide between 1930 and 2030. The team found significant changes to existing water flow in rivers such as the Parana River in South America (pictured). The biggest future effects would arise from dams being planned for the Amazon basin.

The models could help engineers to reduce the environmental effects of new dams.

Environ. Res. Lett. 10, 015001 (2015)