How will the hydropower boom affect global river ecosystems?

Itaipu Hydropower Project on the Paraná River located on the border between Brazil and Paraguay. Image: Wikipedia

There are currently around 3,700 major new hydropower dam projects planned or under construction across the world, many of them in developing countries which lack widespread, reliable and affordable electricity supplies.  However, many of these same countries support biodiverse and relatively ‘natural’ large river systems, which raises questions of how to balance the potential ‘green’ energy gains from hydropower projects with the potential harm – barriers to fish migration, siltation, habitat change amongst others – they can cause to river ecosystems.

A new study ‘A global boom in hydropower dam construction‘, has been carried out by Professor Christiane Zarfl from the University of Copenhagen and colleagues at the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB) in Berlin, including BioFresh head Klement Tockner. The research team compiled data on future major hydropower projects to predict how much energy would potentially be produced if all projects were completed; and the potential impacts they would have on currently free-flowing river ecosystems.

The team found that despite a global ‘boom’ in hydropower developments, the extra electricity production “will not close the energy gap“, because energy demands will increase, due to growing human populations globally.  So despite the growth in global hydropower capacity – if all 3,700 dam projects were completed, the capacity would double to 1700 gigawatts (GW) within the next 20 years – the study predicts that the proportional hydropower contribution to overall energy production would barely alter (16% in 2011, 18% in 2040).  In short, the ‘boom’ in hydropower projects across the world – and their negative impacts on river ecosystems – will only keep pace with global energy demands, as opposed to providing a higher share of ‘green’ energy to overall supply.

The study shows the geographical spread of where new hydropower projects are planned, and so provides a basis for understanding where and how the various trade-offs and conflicts between energy production, freshwater biodiversity and human livelihoods are likely to take place in the future.  The maps below show: (1) the distribution of future hydropower projects, under construction (blue dots) or planned (red dots); and (2) the number of hydropower projects for each major river basin.   The maps show how the majority of hydropower construction will take place in developing countries and emerging economies, particularly along the Amazon basin in Brazil, the Ganges–Brahmaputra basin in India and Nepal, and the Yangtze basin in China.

Map (1): Global distribution of future hydropower dams, either under construction (blue dots 17 %) or planned (red dots 83 %). Image: Zarfl et al (2014)

Map (2): Number of future hydropower dams per major river basin. Image Zarfl et al (2014)

Speaking to ECOS Magazine, Professor Zarfl said, “Hydropower is an integrated part of transitioning to renewable energy and currently the largest contributor of renewable electricity.  However, it is vital that hydropower dams do not create a new problem for the biodiversity in the world’s freshwater systems, due to fragmentation and the expected changes in the flow and sediment regime.  That is why we have compiled available data on future expected hydropower dams – to form a key foundation for evaluating where and how to build the dams and how to operate them sustainably.”

The study estimates that 25 of the 120 large river systems currently classified as ‘free-flowing’ would lose that status, as dam construction fragments and modifies their courses.  It suggests that “Worldwide, the number of remaining free-flowing large river systems will thus decrease by about 21 percent” – a decrease which is likely to be most prominent on South American rivers, which are some of the world’s most unique and diverse freshwater ecosystems.

The IUCN Freshwater Fish Specialist Group states that South America is the most diverse continent for freshwater fish species, globally, with an estimated 4,000 species (and roughly 100 new species found each year).  The Amazon, Mekong, and Congo basins, which will be heavily impacted by future hydropower dams, jointly contain 18 % of the global freshwater fish diversity, and the Balkans – a hot spot for future hydropower development – are an important region for freshwater biodiversity in Europe, as described by a recent IUCN report.

The dam wall on the Itaipu hydropower project. Image: International Hydropower Association, Flickr

Freshwaters are already amongst the most threatened ecosystems in the world.  Hydropower developments can have negative effects on freshwater species in a number of ways – blocking migration routes, changing river flows and habitat, and dropping loads of fine sediment in areas where the river flow is slowed, potentially causing eutrophication and covering fish breeding sites.  Biodiversity loss as a result of hydropower projects has potentially negative knock-on effects for communities around rivers which rely on fishing for food and freshwater for drinking, washing and sanitation.

Despite being a low-carbon, renewable energy source, hydropower can significantly alter and degrade the rivers where it is implemented.  So, what is the solution to growing global energy demands?  Professor Zarfl and colleagues state that, “Even if the entire technically feasible hydropower potential will be exploited, which would correspond to a dam construction boom almost five times that currently estimated, hydropower would contribute less than half of the global electricity demand projected until 2040.”  

Hydropower water release. Image: Global Water Partnership, Flickr

Given this inability to keep up with demand, and the related environmental costs, is hydropower the most suitable response to global energy needs?  On average, life-cycle greenhouse gas emissions from hydroelectricity are more than 30 times lower than that of coal – potentially providing a key tool in mitigating climate change.  However,  how can we reconcile the potential climate benefits of hydropower with the potential harm it does to freshwater biodiversity?

The authors suggest that one solution might be to concentrate new hydropower developments on river basins that have existing hydropower projects, and are fragmented already – a new and perhaps pragmatic take on the old conservationists’ mantra of ‘preserve the best, restore the rest’.  For example, hydropower projects on the Rufiji River in Tanzinia – the last remaining large free-flowing river network in East Africa – might be moved to the Nile and Zambezi Rivers, which are already heavily fragmented today.  Whether this approach can account for spatial variation in energy needs, economic investment and political will is another matter.

The database of future major hydropower projects compiled by Professor Zarfl and colleagues provides a comprehensive new resource for conservationists, environmental planners and policy makers to help guide how and where hydropower developments are planned in the future.  However, it remains to be seen whether the growing global demand for new hydropower supply can be reconciled with the threats developments pose to freshwater ecosystems in the future.