Safeguarding migratory fish via strategic planning of future small hydropower in Brazil

Small hydropower plants (SHPs) are proliferating globally, but their cumulative threat to blocking migratory fish and the fisheries that these fish sustain has been underappreciated when compared with large hydropower plants (LHPs). Here, we quantified the trade-offs between hydroelectric generation capacity and the impacts on river connectivity for thousands of current and projected future dams across Brazil. SHPs are the main source of river fragmentation, resulting in average connectivity losses of fourfold greater than LHPs. Fragmentation by SHPs is projected to increase by 21% in the future, and two-thirds of the 191 migratory species assessed occupy basins that will experience greater connectivity losses due to SHPs than LHPs. A Pareto frontier analysis identified future dam portfolios that could halve the number of hydropower plants that are required to deliver the same energy-generation capacity compared with the least-favourable solutions, while simultaneously resulting in lower river fragmentation and protecting numerous undammed basins. Our results highlight the need for strategic planning that considers the unprecedented growth and cumulative effects of SHPs.

Automated summary

This study quantified the trade-offs between hydroelectric generation capacity and the impacts on river connectivity for thousands of current and projected future dams across Brazil, revealing that SHPs cause fourfold greater average connectivity losses compared to LHPs. The fragmentation by SHPs is projected to increase by 21% in the future, affecting two-thirds of the 191 migratory species assessed. Pareto frontier analysis identified future dam portfolios that could halve the number of hydropower plants required to deliver the same energy-generation capacity, while reducing river fragmentation and protecting undammed basins.