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October 26, 2018

A small fence separates the densely populated Tijuana, Mexico (right) from the United States in the Border Patrol's San Diego sectorRed-tailed hawks can live to be up to 20 years old. If a fledging had caught a thermal in 1994 and spent the next two decades aloft above the U.S.-Mexico border, it would have witnessed some startling changes:

Mexican border cities like Ciudad Juarez and Tijuana ballooning as thousands streamed north to work in maquiladora factories, assembling products like garage door openers to be sold in the U.S. and Canada. Farmland around American cities morphing into suburbs. Mexican land being turned into agricultural fields.

What would not be visible from the air is the depletion of Mexican groundwater to grow the fruits and vegetables sent north.

The North American Free Trade Agreement was intended to erase barriers to trade and investment between Canada, Mexico and the United States, allowing goods to circulate freely.

However, 24 years after it came into force, the economics of the deal have had a profound effect on land use along the U.S.-Mexico border, according to a study by four Arizona State University professors published this month.

Between 1992 and 2011 — the period covered in the study — regional land and water use partially re-oriented around the needs of American cities, leading to crop-to-urban conversions and water savings in the U.S., while agricultural and urban expansion in Mexico resulted in aquifer exploitation and reduced river flows.

“There’s an incentive in the U.S. to convert irrigated cropland to cities to save water,” said Bohn, a research scientist in the School of Earth and Space Exploration. “Planners in Arizona counted on this to help them balance their water budget under the Groundwater Management Act. … Because the U.S. is more affluent … (it) can afford to lose some cropland. In all the different factors combined, the U.S. can outsource some of its agriculture to Mexico. That dynamic was interesting.”

Mexico is not really in a position to be taking on the burden of outsourcing fresh fruit and vegetable production, Bohn said. While it’s very profitable, it’s also groundwater-intensive.

“They’re already running out of natural capital,” he said. “It’s a time bomb waiting to go off.”

Senior sustainability scientist Enrique Vivoni, a professor in the School of Earth and Space Exploration, also worked on the study.

“We have taken our problems and shipped them across the border,” Vivoni said. “This was very surprising for us. It’s what we call illusory sustainability. It’s only sustainable if you think about your own little box. We’re doing a great job in Arizona, but we live in this broader context.”

Senior sustainability scientists Giuseppe Mascaro, assistant professor in the School of Sustainable Engineering and the Built Environment, and Dave White, director of the Decision Center for a Desert City, also contributed to the study, which was published in Environmental Research Letters this month.

Read the full story on ASU Now.

Top photo: A small fence separates the densely populated Tijuana, Mexico (right) from the United States in the Border Patrol's San Diego sector. Photo by Sgt. 1st Class Gordon Hyde. Public domain photo courtesy of Wikipedia

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