A World of Hurt

Wednesday, June 15, 2005

New Research Reveals Massive Impacts of Damming on World’s Large Rivers

World Rivers Review, June 2005

The extent to which dams affect the world’s large river systems is the focus of a major new study by a research team from the Landscape Ecology Group at Umeå University, Sweden. The rivers studied drain 54% of the world's land area and carry 60% of the planet's river-water. The researchers found that of 292 large river systems, 172 are affected by dams. WRR interviewed the researchers – Mats Dynesius and Christer Nilsson and Cathy Reidy – to discuss the significance of their findings.

Q: Your research reveals that more than half of the world's large rivers are fragmented and regulated by dams. Can you sum up the significance of these findings?

A: The damming of great rivers is among the most dramatic, deliberate impacts that humans have had on the natural environment. Most big river systems, including the 20 largest and eight of the most biologically diverse, now have dams on them. Damming has been particularly hard on specific biomes*: for example, most large river basins in deserts (82%) and in Mediterranean-type ecosystems (99%) are impacted by dams. If you consider that 83% of the discharge of the 292 large rivers studied is impacted, and that only minor portions of some biomes include hydrologically untouched river systems, our findings are a call for action. If we want to sustain the world’s biodiversity and riverine goods and services, then we need to replace large dam building with alternate solutions. Substitute energy sources include solar and wind, and regional energy needs can be met with smaller reservoirs or run-of-the-river dams. Further action should include removing some of the existing dams in the more heavily impacted parts of the world, and an international attempt to save some of the last wild rivers.

Q: You found that dams now hold back 15% of the world’s annual freshwater runoff. Many rivers have "staircases" of dams that can hold more than their whole annual flow – or more than four years' worth, in the case of the VoltaRiver in West Africa. Sediment, too, is held back behind reservoirs, affecting coastlines around the world. To what extent can “environmental flows” (more natural flows) from existing dams and “artificial floods” help restore some of the environmental damage done by these two phenomena?

A: The experiments in artificial flooding made so far – for example, in the Grand Canyon – suggest that some ecological processes might be restored to varying degrees. For example, sediment redistribution and fish migration will recover partly, and the downstream invasion of exotic species can be held back. However, the effects will vary by flow prescription. There needs to be some regularity of flooding, and some (infrequent) floods need to be larger than the others. Single floods will have only short-term importance. Full recovery (or close to) cannot be achieved unless dams are removed, especially in cases where rapids are permanently impounded or when most of the water passes underground and only a “minimum flow” is directed through the old river channel.

Q: There are clear “cumulative impacts” of various kinds of environmental degradation – for example, climate change and air pollution may start small, through individual acts, but the effect has become global. Is there a similar cumulative effect on global environmental health from the 45,000 dams now blocking Earth’s rivers?

A: There are surely cumulative effects, but we do not have quantitative data on this. However, a general example can be seen in the hydrologic alteration of biomes and subsequent disruption of global processes. As a biome’s hydrology becomes totally altered by dams (there are several approaching this state, including temperate forests and savannahs), inducing dramatic changes in land cover and flora and fauna, that biome’s biological and physical role in the planet will change and affect global environmental health. Also, the overall reduction in freshwater and sediment input to the seas may have unexpected consequences. The fact that floods that cause upwelling in seas are heavily restricted by dams is another impact which might have cumulative effects, for example on the nutrient balance of seas.

Q: Do you think the common practice of having a project environmental assessment for large dams is an effective way to assess whether or not a project should be built, based on environmental concerns?

A: It is better than nothing, but not very effective because environmental concerns are difficult to value properly. A big problem is that dams are treated individually, which means that decisions are based on established practice (“we have built similar dams before”) rather than on the fact that very few free-flowing rivers remain, or that regional and even global ecosystems are declining from the preponderance of dammed rivers. If every individual project would be evaluated at a larger scale where factors such as number of adjacent dams, total effects on the actual biome, etc. were included, better decisions could hopefully be made.

Q: Your research shows that the biodiversity supported by free-flowing rivers has a better chance of adapting to climate change than that associated with dammed rivers. Can you explain this? What should this mean for policy makers, and water managers in dry countries?

A: Every species has a climatic optimum, so when climate changes, populations will have to redistribute to accommodate to the new conditions. River and riparian corridors are major conduits for dispersal for both aquatic and terrestrial organisms, but when these are blocked by large dams, opportunities for redistribution will be obstructed. For dry countries, the focus needs to be shifted to alternative water harvesting and irrigation methods. For example, two types of water efficiency come immediately to mind that could be replicated: India’s recent successes with small-scale rainwater harvesting, and Israel’s incredibly efficient drip irrigation methods. Integrating these sorts of water management practices at the national level could have dramatic improvements on watershed sustainability.

Q: As your report notes, two of the most-dammed countries in the world – China and India – are planning many more dams for some of their most fragmented rivers. For example, China wants to build 49 more dams on the Yangtze alone, and India hopes to link 37 of its rivers in a vast scheme to move water from one region to another. What do you think it will take to change this picture? What are some next steps that could help decision-makers in developing countries balance the political and economic pressures that lead them to over-develop rivers and instead help preserve healthy rivers as a public good?

A: We are not socio-economists, and even researchers in that field are having a tough time to help developing nations meet their populations’ needs with minimal human and environmental costs. Human populations tend to only consider environmental needs once their own needs are met, and then it might be too late. That said, reducing global population growth – e.g., by means of fighting poverty and improving the status of women – would be the most important step. This would increase the possibilities of sharing resources between humans and nature in a more sustainable way. Another very important step would be to use water resources more efficiently. In dry regions, much could be improved by better balancing irrigation and crop choices (as mentioned above). In regions using rivers mainly for power generation, more efficient use of electricity is important.

Q: What motivated your team to undertake this study?

A: In the 1980s, there was a very heated debate in Sweden about the last free-flowing rivers. We (Christer Nilsson and Mats Dynesius) got involved as researchers because we had information about the natural qualities of these rivers. We were once told by a spokesman for the power industry that we should not be concerned if the last free-flowing rivers in Sweden got impounded, because “in the rest of the world, most rivers are free-flowing.” The skepticism we felt toward this argument triggered the start of the study.

*A biome is a major ecological community type (such as tropical rain forest, grassland or desert)


For More Information

The team’s report on their findings, “Fragmentation and Flow Regulation of the World's Large River Systems,” appears in the April 15, 2005 edition of the journal Science.

The team says its next step is to investigate how the world’s dams have affected the vulnerability of freshwater fish. For this project, the scientists will investigate extinctions caused by habitat losses. The upcoming research will predict the global distribution of freshwater fish that are threatened by extinction. In addition, the team will attempt to determine the global distribution of river systems that are affected by habitat loss because of dams.