Researchers from the United States, Europe, and China have concluded that as the earth warms over the next 40 years and rainfall patterns change, increasing ethanol production to meet U.S. mandates could strain supplies of irrigation water, especially in the northern Great Plains. Relying on a sophisticated agro-ecological model, GEPIC, and the IPCC's A2 greenhouse gas emissions scenario, the four scholars found that reaching a target of 15 billion gallons of corn ethanol per year would imply a 19 percent increase in irrigation water consumption, from 10.22 to 12.18 teraliters per year.
Considering that the increase takes place over a 40 year period, perhaps it is not unmanageable as such. But, as earlier studies by some of the same researchers have shown, the clash between ethanol production and water needs raises serious questions about the wisdom of U.S. biofuels strategy. As a Rice University press release put it earlier this week: "It takes 50 gallons of water to grow enough Nebraska corn to produce the amount of ethanol needed to drive one mile"—or, put in different terms, "The production of one liter of corn ethanol requires between 350 and 1400 liters of water from irrigation, depending on location."
The earlier studies found that switching from standard gasoline to corn ethanol yields little or no decreases in greenhouse gas emissions. That's consistent with a conclusion Spectrum also reached on the basis of interviews with experts. With U.S. production of natural gas and oil rising quite sharply, and its dependence on foreign fuels decreasing, the strain that ethanol production is putting on already sorely stressed water systems—on top of adverse impacts on global food prices—suggests that the U.S. ethanol program may be due for a critical review.