River deltas that support millions of people are threatened by climate change and hydropower
Rivers create hotspots for food production and livelihood support, but they are increasingly threatened by the impacts of climate change. As much as 90% of the Mekong River Delta could fall below sea level this century due to rising seas and loss of the critical sediment that maintains river beds. The implications of that shift are drastic — more than 17 million people live in the delta, where their livelihoods depend on its biodiverse rivers.
New research from the Natural Capital Project’s Rafael Schmitt and Gretchen Daily shows the important role that sediment plays in climate resilience for coastal delta communities worldwide and how poorly planned hydropower dams threaten the natural flow of sediment.
The paper, published in Proceedings of the National Academy of Sciences, is the latest in a series of publications from Schmitt on strategic hydropower planning for greener economies. Here, he discusses how hydropower, when planned with care, can be an important stepping-stone towards a more sustainable energy system.
This is an updated adaptation of this story from June 2021.
Why is the connectedness of rivers so important to hydropower planning?
Rafael Schmitt: People depend on river waters in so many ways. Rivers provide people with drinking water, irrigation for crops, aquatic habitat and fisheries, and many important cultural benefits. They also can provide a tremendous amount of energy through hydropower.
Hydropower dams can play an important role in helping developing economies transition to a cleaner energy system that also meets the needs of their people. But the environmental externalities — the side effects — of dams can be catastrophic.
The United States and Europe have many examples of the damaging side effects of dams, from the collapse of fisheries in the United States’ Pacific Northwest to loss of biodiversity and livelihoods in the Colorado River and Delta. These examples foreshadow what could happen in many developing countries, like those in the Greater Mekong region, if dams aren’t planned strategically.
The goal of my work is to build our understanding of the connectivity of river systems to show the benefits they provide to people. When we can highlight those benefits, we can help countries make hydropower development decisions that are smarter and more sustainable.
What is sediment and how does it provide benefits to people?
Sediment is the term we use for all kinds of solids that are transported by water — sand, silt, gravel and more. When water transports sediment, it defines the shape of a river channel, creating aquatic habitat and enabling people to access the water and other benefits that rivers provide.
Sediment has traditionally been framed as a problem, because too much sediment can smother stream beds and destroy fish habitats. Such an overload of sediment is often the result of poor land management practices like large-scale agriculture and deforestation. Sediment is beneficial to people — you just need the right amount of it.
How does hydropower hinder the climate change resiliency benefits that sediment provides to people?
When you install a new hydropower dam, it creates a cascade of impacts. Fish habitats are disrupted or destroyed, natural irrigation waters are blocked, and sediment stops flowing to downstream communities.
For coastal communities, sediment supply is especially critical in combatting climate change. Rising sea levels and extreme storm events are constantly and increasingly eroding shorelines. It’s estimated that 680 million people live less than 10 meters above sea level. By 2050, that number is expected to rise to one billion people. If a dam cuts off the sediment supply to those coastal communities, their shores will quickly erode into the sea. Keeping natural sediment supply flowing from river basins to coasts is crucial as a nature-based solution to combat climate change. When a delta has a natural supply of sediment, it can respond to external pressures like rising sea levels on its own.
Hydropower dams often disproportionally impact communities that are already overburdened. Those communities don’t have another way to replace the lost nutrition, the lost job, and the loss of traditional fishery-related culture.
How can countries strategically plan for hydropower development without increasing threats to communities and livelihoods?
First, the country or region needs to determine how much hydropower they require to meet the needs of their population. Thanks to the rapid development of photovoltaic solar energy in recent years, a country that may have required 50 hydropower dams a few years ago can now invest primarily in solar and only develop five dams. Rather than the main energy source, hydropower can act as a backup for the times the sun isn’t shining, like nights and cloudy days.
Second, we can apply our scientific models to determine the trade-offs for each combination of energy system (e.g., a specific mix of solar and hydropower). We know we need a certain amount of hydropower, so we use numerical methods to identify combinations of dam sites which would create the least cumulative negative impacts on the environment and people while also providing enough energy.
Sometimes, the answer might be not to develop new dams inside the country, but instead to import hydropower energy from somewhere else.
What’s next for your research?
Much research has looked at how dams influence downstream ecosystems and people, but hasn’t focused much on the upstream.
When you build a dam, you need to manage the land surrounding the reservoir in addition to the reservoir itself. If too much sediment is flowing down into a dam’s reservoir, that’s going to increase operation and maintenance costs because it’s constantly filling up. Deforestation and aggressive agricultural practices can contribute to increased sediment and decreased dam efficiency.
The more power you can generate from an existing dam, the less need there is for building more dams. So, how can we make current dams more effective by better managing the land around them?
Watch a short video explainer of Schmitt’s work here.
If you’re interested in learning more about Schmitt’s strategic hydropower work, read his papers:
- R. J. P. Schmitt, N. Kittner, G. M. Kondolf, D. M. Kammen, Joint strategic energy and river basin planning to reduce dam impacts on rivers in Myanmar. Environ. Res. Lett. 16, 054054 (2021).
- V. Barbarossa, R. J. P. Schmitt, M. A. J. Huijbregts, C. Zarfl, H. King, A. M. Schipper, Impacts of current and future large dams on the geographic range connectivity of freshwater fish worldwide. PNAS. 117, 3648–3655 (2020).
- R. J. P. Schmitt, S. Bizzi, A. Castelletti, J. J. Opperman, G. M. Kondolf, Planning dam portfolios for low sediment trapping shows limits for sustainable hydropower in the Mekong. Science Advances. 5, eaaw2175 (2019).
- R. J. P. Schmitt, N. Kittner, G. M. Kondolf, D. M. Kammen, Deploy diverse renewables to save tropical rivers. Nature. 569, 330 (2019).
- R. J. P. Schmitt, S. Bizzi, A. Castelletti, G. M. Kondolf, Improved trade-offs of hydropower and sand connectivity by strategic dam planning in the Mekong. Nature Sustainability. 1, 96–104 (2018).