Scientists link record drought in Mexico to global warming, human activity

April 13, 1:45 PMEnvironmental News ExaminerJ McMahon

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Researchers believe the causes of drought in Mexico may have effects across the border.
Here, a stock tank in Texas shows the effects of that state's severe drought.
(AP Photo/Texas Farm Bureau, Matt Felder)

U.S. and Mexican researchers have linked a severe, 15-year drought in Mexico to human activity, especially the clearing of land for grazing and the expansion of cities, University of Arkansas officials announced today. President Obama travels to Mexico on Thursday, where he is expected to discuss climate change and the economy with Mexican President Felipe Calderon.

Researchers used the tree-ring record and other data to reconstruct Mexico's climate for the past 500 years. They determined that the decade from 1994 to 2003 was the driest period except for two prior droughts, in the 1950s and 1560s.

"Droughts come and go, but the researchers believe that this drought in particular may have a human-generated component on both a regional and global scale," said Melissa Lutz Blouin, director of science and research communications for the university.

"Well-covered land surfaces conserve moisture more effectively than bare land surfaces, with more moisture retention and less heating. As land is cleared for grazing and urban expansion, it is laid bare to evaporation and therefore becomes warmer. Warmer temperatures bring less rain, contributing to drought."

The study concluded with data from 2008, but researchers believe the drought may be continuing, despite an increase of rain in some areas. By emphasizing land use, the study stresses that greenhouse gases are not the only contributor to global warming.

“Those are pathways by which humans are changing the natural systems globally and regionally,” said David Stahle, professor of geosciences at Arkansas and the study's lead scientist. “And these natural processes don’t necessarily conform to international borders. Those mechanisms may be in operation in the United States Southwest as well.”

Global warming models produced by scientists suggest that wet areas will become wetter, and subtropical arid areas will get drier. Therefore dry spells such as the one experienced in Mexico may persist longer and be more severe.

“This is one of the worst droughts in Mexico in the instrumental record,” Stahle said.

The scientists reported their findings in EOS, a publication of the American Geophysical Union. They include Stahle, professor Falco Fye and graduate student Dorian J. Burnette of the University of Arkansas; Edward R. Cook and Richard Seager of the Lamont-Doherty Earth Observatory; Jose Villanueva Díaz of the Instituto Nacional de Investigaciones Forestales, Agricolas y Pecuarias; Gómez Palacio of Durango, Mexico; R. Daniel Griffin of the University of Arizona; Rodolfo Acuña Soto of the Universidad Autonoma de Mexico; and Richard R. Heim Jr. of the National Oceanic and Atmospheric Administration.