1 in 10 Watersheds in the Continental US Stressed with Number Likely to Grow

Nearly one in 10 watersheds in the United States face demands exceeding their natural supply -- a number that is likely to grow as a result of global warming, a new study suggests.

Published in the journal Environmental Research Letters, the study included a look at the demand on freshwater resources for each of the 2,103 watersheds located in the continental United States. In all, 193 are currently "stressed," meaning demand exceeds natural supplies.

Next, the researchers used existing climate projections to estimate future water stress for each watershed.

The results were ominous.

"By midcentury, we expect to see less reliable surface water supplies in several regions of the United States," said the study's lead author, Kristen Averyt, associate director for science at the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder. "This is likely to create growing challenges for agriculture, electrical suppliers and municipalities, as there may be more demand for water and less to go around."

Taking this one step further, the researchers investigated the causes of water stress for each region.

The West, the team discovered, is particularly vulnerable to stress for two reasons, one being that supply and demand are nearly equal. As a result, even the slightest shift can have significant impact. Second, the area has long relied on imported and stored water in order to supplement natural supplies.

Overall, the greatest contributor to water stress is agriculture. However, the study showed that the need for cooling water for electric power plants place the largest burden on the local water supply wherever they are found.

"A single power plant has the potential to stress surface supplies in a local area," said co-author James Meldrum, a researcher in the Western Water Assessment, a program of the National Oceanic and Atmospheric Administration (NOAA) and CIRES.

Furthermore, agricultural and municipal demands are spread among many users, allowing for a degree of flexibility in, for example, efficiency use.

"But because power plant decisions are so capital intensive, they tend to be locked in for a long time," Meldrum said. As a result, the researcher warns that "power plants -- and our access to electricity -- may be put at risk when water is not adequately considered in planning."