For 412 of these counties the risk of water shortages will be "extremely high," according to the report, a 14-fold increase from previous estimates.
In the Great Plains and Southwest United States, water sustainability is at extreme risk finds the report, which is based on publicly available water use data from across the United States.
"This analysis shows climate change will take a serious toll on water supplies throughout the country in the coming decades, with over one out of three U.S. counties facing greater risks of water shortages," said Dan Lashof, director of the Climate Center at NRDC. "Water shortages can strangle economic development and agricultural production and affected communities."
"As a result," he said, "cities and states will bear real and significant costs if Congress fails to take the steps necessary to slow down and reverse the warming trend."
Counties shown in dark red are at greatest risk of water shortage by 2050. (Map courtesy Tetra Tech)
The report, issued Tuesday, 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.
Sujoy Roy, principal engineer and lead report author, Tetra Tech, said, "The goal of the analysis is to identify regions where potential stresses, and the need to do something about them, may be the greatest."
"We 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," Roy explained.
"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," Roy said. "These future stresses are related to changes in precipitation as well as the likelihood of increased demand in some regions."
The report also is based on climate projections from a set of models used in recent Intergovernmental Panel on Climate Change work to evaluate withdrawals related to renewable water supply.
Water withdrawal will grow by 25 percent in many areas of the United States, 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, the analysis projects.
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 given based on the value of the crops produced in the 1,100 counties at risk.
In 2007, the value of the crops produced in the at-risk counties identified in the report exceeded $105 billion.
A separate study compared the Tetra Tech data with county-level crop production data from the U.S. Department of Agriculture. Click here for state-specific fact sheets outlining the potential agricultural impacts. http://agcarbonmarkets.com/Science.htm.
The NRDC is using the report in its lobbying efforts to persuade Congress to pass legislation limiting the greenhouse gas emissions that drive climate change.
"Water management and climate change adaptation plans will be essential to lessen the impacts, but they cannot be expected to counter the effects of a warming climate," said Lashof. "The only way to truly manage the risks exposed by this report is for Congress to pass meaningful legislation that cuts global warming pollution and allows the U.S. to exercise global leadership on the issue."
Click here for a look at county-specific and state-specific maps detailing the report findings. and http://rd.tetratech.com/climatechange/projects/nrdc_climate.asp.
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