Climate Change Could Cause Water Shortages in Many States, Says Report

Over 1,100 U.S. counties — more than one-third of all counties in the lower 48 states — could face higher risks of water shortages by mid-century as the result of global warming, and more than 400 of these counties will be at extremely high risk for water shortages, based on estimates from a new report by Tetra Tech for the Natural Resources Defense Council.

Over 1,100 U.S. counties — more than one-third of all counties in the lower 48 states — could face higher risks of water shortages by mid-century as the result of global warming, and more than 400 of these counties will be at extremely high risk for water shortages, based on estimates from a new report by Tetra Tech for the Natural Resources Defense Council.

The report uses publicly available water use data across the U.S. and climate projections from a set of models used in recent Intergovernmental Panel on Climate Change work to evaluate withdrawals related to renewable water supply.

The report finds that 14 states face an extreme or high risk to water sustainability, or are likely to see limitations on water availability as demand exceeds supply by 2050. These areas include parts of Arizona , Arkansas , California , Colorado , Florida , Idaho , Kansas , Mississippi , Montana , Nebraska , Nevada , New Mexico , Oklahoma , and Texas . In particular, in the Great Plains and Southwest United States , water sustainability is at extreme risk.

The more than 400 counties identified as being at greatest risk in the report reflects a 14-times increase from previous estimates.

"While detailed modeling of climate change impacts on crop production was beyond the scope of the Tetra Tech analysis, the potential scale of disruption is reflected based on the value of the crops produced in the 1,100 at-risk counties," says NRDC in a statement. In 2007, the value of the crops produced in the at-risk counties identified in the report exceeded $105 billion.

Sujoy Roy, principal engineer and lead report author for Tetra Tech, says his team used publicly available data on current water withdrawals for different sectors of the economy, such as irrigation, cooling for power generation, and municipal supply, and estimated future demands using business-as-usual scenarios of growth. "We then compared these future withdrawals to a measure of renewable water supply in 2050, based on a set of 16 global climate model projections of temperature and precipitation, to identify regions that may be stressed by water availability," said Roy . "These future stresses are related to changes in precipitation as well as the likelihood of increased demand in some regions."

The report forecasts that water withdrawal will grow by 25 percent in many areas of the U.S. including the arid Arizona/New Mexico area, the populated areas in the South Atlantic region, Florida , the Mississippi River basin , and Washington , D.C. , and surrounding regions.

Tetra Tech provides consulting, engineering, and technical services worldwide. According to its Web site, its employees include individuals with expertise in science, research, engineering, construction and information technology. The company's headquarters are in Pasadena , Calif. A summary of the report and related links are available at this Web site.

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