Why Climate Change Matters to Rivers

Graphic courtesy Journal of Climate, modified by UCAR
Author: Bevan Griffiths-Sattenspiel

With all our focus on saving energy by saving water as a climate change strategy, its easy to forget that not everybody is convinced that global warming is occurring and that rivers are integral to the issue. A key concept to keep in mind when connecting rivers to climate change is that scientists predict rivers will be our canaries in the coal mine. In other words, the changes that occur as a result of our greenhouse gas emissions will be expressed through our rivers, lakes and streams--in fact, new evidence suggests that many rivers are already trying to tell us something.

Researchers from the National Center for Atmospheric Research (NCAR) in Boulder, CO believe that rivers around the world are already showing the signs of a changing climate. The study won't be released until mid-May but the center has already published a few details.

According to a press release on NCAR's website:

"Rivers in some of the world's most populous regions are losing water, according to a new comprehensive study of global stream flow. The study, led by scientists at the National Center for Atmospheric Research (NCAR), suggests that in many cases the reduced flows are associated with climate change. The process could potentially threaten future supplies of food and water.
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The scientists, who examined stream flow from 1948 to 2004, found significant changes in about one-third of the world's largest rivers. Of those, rivers with decreased flow outnumbered those with increased flow by a ratio of about 2.5 to 1.
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Many factors can affect river discharge, including dams and the diversion of water for agriculture and industry. The researchers found, however, that the reduced flows in many cases appear to be related to global climate change, which is altering precipitation patterns and increasing the rate of evaporation. The results are consistent with previous research by Dai and others showing widespread drying and increased drought over many land areas.

The study raises wider ecological and climate concerns. Discharge from the world's great rivers results in deposits of dissolved nutrients and minerals into the oceans. The freshwater flow also affects global ocean circulation patterns, which are driven by changes in salinity and temperature and which play a vital role in regulating the world's climate. Although the recent changes in the freshwater discharge are relatively small and may only have impacts around major river mouths, Dai said the freshwater balance in the global oceans needs to be monitored for any long-term changes."

The map above shows the change in runoff inferred from streamflow records worldwide between 1948 and 2004, with bluish colors indicating more streamflow and reddish colors less. In many heavily populated regions in the tropics and midlatitudes, rivers are discharging reduced amounts into the oceans. In parts of the United States and Europe, however, there is an upward trend in runoff. The white land areas indicate inland-draining basins or regions for which there are insufficient data to determine the runoff trends.

Although some rivers are experiencing increased flows, a much larger share have reduced flows. Not only do the decreased flows cause strains to a river's fragile ecosystem, but many of the rivers experiencing lower flows supply water regions with thriving populations, including the Yellow River in northern China, the Ganges in India, the Niger in West Africa, and the Colorado in the southwestern United States.

For these reasons and many others, saving water and saving energy is is a critical piece of the climate change puzzle. Reducing water consumption, implementing low impact development and reusing wastewater whenever possible can reduce energy use and carbon emissions, improve the flow and health of rivers and slow the rate of climate change. Since many changes resulting from global warming are seen as inevitable, water efficiency and other smart water management strategies will improve the resiliency of our rivers and help us adapt to climate change.