by Katy Yan for International Rivers

Rivers are the planet’s lifelines, but the double threat of human interventions combined with climate change is already seriously compromising their health – and, by extension, ours. A major study last year found an overall decline in total discharge of most of the world’s major rivers – changes that could affect up to a billion people. Here we interview Dr. Margaret Palmer, director of the Chesapeake Biological Laboratory at the University of Maryland and a leading expert on how climate change impacts rivers.

What are your biggest concerns for the world’s major rivers?

MP: Over the past 50 years, the amount of runoff has changed substantially for many rivers due to the combined effects of withdrawals, dams, and climate change. The impacts of human alteration of the land around rivers are harming rivers at a far higher rate now and over the next 50 years than is climate change. But if climate change is added as an additional stressor on top of immediate anthropogenic impacts, rivers may not be able to supply the ecosystem services – like clean drinking water – that people depend on.

The effects of climate change on rivers are manifest through increases in temperature and changes in river discharge. Some parts of the world will experience higher flows and others lower flows, but all will experience warming. The impacts will be dramatically worse in basins that are otherwise impacted either by flow modification (e.g., by excessive water withdrawals) or development. In particular, urbanized watersheds in regions that are expected to experience less precipitation may have more severe and longer droughts. Urban areas that have substantially higher rainfall or that will have more intense storms may have more flooding. The reason is that urban areas typically have less riparian wetland and in general less wildland along rivers, which act to store water that can be released later.

Your research shows that areas impacted by dams would require more management interventions to mitigate the impacts of climate change than free-flowing rivers. Why are free-flowing rivers more resilient to climate change? What kinds of interventions will be needed?

MP: Free-flowing streams in wild areas have tremendous capacity to adjust to changes in discharge and sediment inputs (both of which are expected to change in many areas under future climate scenarios). But they need room to do this. When a channel changes shape or migrates across the landscape, it’s because the river is adjusting to a new flow or sediment regime. When you try to lock it in place or cut off its supply of sediment (due to dams), the ability of the stream to adjust and reach a new equilibrium is lost. We need to “free” rivers so they can move across the landscape and have some degree of buffering capacity which intact riparian corridors and wetlands (and floodplains) provide.

On the other hand, streams can do little about an increase in air temperature. If river water warms too quickly – say 3-4 degrees C in the next 25 years – then the organisms living in the stream are unlikely to be able to adapt fast enough to cope with this. At first, we will see declines in reproductive output or survival of young and over time, populations of some species will decline, while those species able to withstand warmer water (often nonnative species) will increase. However, keep in mind that if deforestation has occurred in a watershed, temperature increases (above historic levels) will be far greater and more harmful ecologically

To sum up, to manage for global change, we need to manage in a way that makes streams more resilient. It will be far cheaper and save more lives if we act now to protect rivers and the people they support.

Your study looked at both dam-impacted and non-dam impacted basins. Which basins are key hotspots that will require extensive management? How many people do these basins approximately impact?

MP: Basins that require major management decisions include for example the Nile in Africa which is already experiencing significant reductions in flow by the time the river reaches Egypt. The Nile Basin supports more than 180 million people and poverty is high. Its water is critical to irrigation in Egypt, Sudan, Uganda, and Ethiopia, yet given growth in water extractions and hydropower needs in the upper portions of the basin, climate change poses a major concern for the river and the people it supports.

The water that feeds the Indus River is from glaciers in the Himalayas and with increasing temperatures, glacial melting with significant increases in river discharge will occur. But a rapid reduction in glaciers could mean future water supplies may become increasingly limited, yet millions of people in northwestern India and Pakistan depend on the river.

How should river basin management change to reflect a changing climate?

MP: Current practices in river basin management should move aggressively toward restoring or preserving those natural features that contribute to a river ecosystems resilience. Most of these also benefit humans. For example, riparian wetlands and floodplains help store water so they reduce flooding and also help recharge the groundwater, which means more water will be available in the river (and for people) during dry periods. To accomplish this, river management will have to include moving people and infrastructure out of floodplains, removing levees, and allowing vegetation to grow back.

This interview was published in: World Rivers Review: Focus on Rivers, Water and Climate – September 2010

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