African hydropower expansion: energy-emissions-ecosystem trilemma

The article ‘Rethinking energy planning to mitigate the impacts of African hydropower,’ co-authored by Prof. Andrea Castelletti from the Department of Electronics, Information and Bioengineering, Politecnico di Milano, together with colleagues from Carnegie Institution for Science at Stanford and Stanford University, was published in Nature Sustainability. The study presents a new holistic framework to support a more sustainable dam planning in Africa.

African rivers are among the mightiest in the world, are part of and contribute to some of the most biodiverse ecosystems and have allowed human society to thrive and flourish for thousands of years supporting the coexistence of human and natural systems. However, this delicate balance might be in peril.

Africa’s hydropower contributes between 15% and 20% of the total electricity consumed in the continent representing the largest renewable power source, around 10 times as much as solar and 5 times as much as wind produced in 2021. Given the increasing power demand and reliability needs, hydropower, traditionally perceived as a cheap, reliable, and carbon-neutral option, has attracted the interest of governments and investors. However, given the rapid decline in costs of other renewable power sources and the effects of climate change on water availability, many proposed hydropower projects have seen their economic viability reduced.

That’s because hydropower projects have been evaluated against other renewable power sources based on purely techno-economic considerations, without considering environmental aspects: while some hydropower projects can improve the power outlook of a region, these can also substantially alter the ecosystem they contribute to. Furthermore, whenever new reservoirs are built, the biomass available in inundated land and brought to the reservoir can be digested to produce greenhouse gas emissions, especially methane. As previous research showed, the relevance of these emissions for global climate will increase as we decarbonize the energy sector.

Given these interconnections between energy for socioeconomic development, ecosystem conservation, and climate change mitigation, the problem urges a more holistic perspective. A team of scientists at Politecnico di Milano and Stanford University set out to build a computer simulation framework to explore the sensitivity of these trade-offs to support dam planning in a way that is beneficial to humans and less detrimental to nature.

The results of the study show that, while between 40% and 68% of proposed hydropower capacity is economically viable in Africa, it would increase average river fragmentation and reservoir emissions by around 50% and 30%, respectively. The challenge is to understand how much of this proposed hydropower can be replaced with other power sources to reduce these impacts. So, the study examines the trade-offs between these three objectives to strike the best trade-offs and substantially reduce these impacts at low cost. More specifically, the research, integrating techno-economic, environmental, and climatic considerations, found that reservoir emissions and river fragmentation impacts can be reduced by at least 50% with a negligible impact on electricity prices and total costs.