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Report: How Climate Change Could Impact Crops

Over 1,100 U.S. counties— more than one-third of all counties in the lower 48 states — now face higher risks of water shortages by mid-century as the result of global warming, according to a new study by Tetra Tech for the Natural Resources Defense Council (NRDC). More than 400 of these counties will be at extremely high risk for water shortages.

The report uses publicly available water use data across the United States and climate projections from a set of models used in recent Intergovernmental Panel on Climate Change (IPCC) 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.  

Potential food losses The potential scale of disruption from climate change is based on the value of crops produced in the 1,100 at-risk counties. In 2007, the value of the crops produced in these counties exceeded $105 billion.  A separate study compared the Tetra Tech data with county-level crop production data from USDA. To find out how ag production in your state may be impacted, go to http://agcarbonmarkets.com/Science.htm.

"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," says Dan Lashof, director of NRDC's Climate Center. "Water shortages can strangle economic development and agricultural production... 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."

Tetra Tech said the goal of the analysis was to identify regions where potential stresses, and the need to do something about them, may be the greatest. The research firm 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.  Tetra 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. 

Water withdrawal will grow by 25% 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.

Estimated water withdrawal as a percentage of available precipitation is generally less than 5% for the majority of the Eastern United States, and less than 30% for the majority of the Western United States. But in some arid regions (such as Texas, the Southwest, and California) and agricultural areas, water withdrawal is greater than 100% of the available precipitation. In other words, in many places, water is already used in quantities that exceed supply.