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When rivers stop flowing, so do crucial natural benefits

The Mekong delta supports 17 million livelihoods in southeast Asia. As sea levels rise and development of hydropower continues unchecked, those who rely on the natural pace of the river are increasingly at risk.

Flowing more than 4,900 kilometers through six countries, the Mekong supports the largest freshwater fishery on earth. Its rich biodiversity rivals that of the much larger Amazon River Basin, but fish aren’t the only critical natural resource provided by the Mekong. Sediment, including sand and silt, is carried downstream and through the delta by the river’s powerful flowing waters. It’s full of important nutrients that enrich soils and create fertile land for agriculture in the lower regions of the Mekong and the Mekong Delta, where millions of subsistence farmers live. Besides providing nutrients, sediment also creates more climate-resilient communities. When sand and small rocks flow through the basin, they settle in lower-lying delta areas and become a crucial natural barrier against sea-level rise.

Even with all the benefits provided by free-flowing rivers, though, many countries are building more and more dams. “Countries in the Mekong and in other developing areas are facing a big energy challenge,” said Rafael Schmitt, a geomorphologist and hydrologist at the Stanford Natural Capital Project. “They’re trying to create energy options that support development but don’t have a big carbon footprint, which often means hydropower. But big hydropower can be very damaging to ecosystems.” Already, the hydropower dams that have been built in the Mekong Basin have reduced sediment flowing to the Delta, where the coastline is quickly shrinking under rising seas.

To explore this conflict between climate, development, and impact on rivers, Schmitt and his colleagues set out to understand if a different approach to investing in hydropower might help. The research, published in Science Advances, shows that more strategic planning—including the natural contributions that ecosystems are providing to people—integrated early on in the development process may have resulted in much more positive outcomes for the Delta without compromising hydropower generation. “The Mekong is a very good place to explore this idea of strategic hydropower planning because of the sheer number of people it supports. There are so many rice plantations, and the inland fisheries that support so many livelihoods are the most productive in the world,” said Schmitt. “What we know is that if you build dams based primarily on economic objectives, you’re not really accounting for the whole picture. If you take a strategic approach, you can consider the tradeoffs between human development and ecosystems that support livelihoods.” In the Mekong basin, hydropower development has been anything but strategic. Dams have been constructed on a project-by-project basis, with minimal coordination between the six countries and without considering the loss of natural benefits—like nutrient-rich farming soil and sea-level rise protection—that a free-flowing Mekong would provide. Schmitt and the team identified an optimal sequence for how and where dams could have been developed along the river to minimize stresses on the natural ecosystems. But, because of the amount of development that has already occurred in the Mekong, the optimal scenario isn’t an option any more. Even now, in the face of growing opposition, new dams are continuing to open. In October, the controversial Xayaburi Dam began operations in Laos, where it is the first of five major dams planned for the Mekong in the country.

Some groups advocate for the benefits of sustainable hydropower in the region, but the researchers say that opportunities for low-impact hydropower development in the Mekong Basin are limited, especially in the countries of the lower basin. “Many of the organizations working in this “sustainable” space in the Mekong should know that low-impact hydropower is a myth as long as it includes dams in the primary downstream portion of a river. Because there are already so many dams, additional major dams will invariably impact the lower basin, so you are going to see impacts on the lower areas of the basin,” said Schmitt. The team did identify areas where dams with less impact on the lower Mekong are still possible. These areas are upstream existing dams, primarily in China. Here, they say, applying a strategic approach now can still have positive socioeconomic impacts for the people downstream who rely on the Mekong’s waters and sediment Although the damage to ecosystems and livelihoods has already been done in many areas, the researchers hope the work will be used to guide future development decisions all around the world. “This conflict between development and impact on the ecosystem was pretty much unsolvable even ten years ago,” said Schmitt. “But now there are practical options for people to adopt—with cheap solar and other alternative energy choices, decision makers can look for different alternatives. We hope that this work will be applied beyond the Mekong basin, so that emerging countries can really optimize how and where to use hydropower without sacrificing all those benefits that their rivers are providing every day.”

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