Historic drought in Mexico suggests human influence

University of Arkansas researchers and their colleagues have examined recent climate patterns in Mexico and determined that the country underwent severe drought conditions between 1994 and 2008, and that human changes related to land use and global warming may have aggravated the dry, warm conditions.

'This is one of the worst droughts in Mexico in the instrumental record,' said David Stahle, Distinguished Professor of geosciences at the University of Arkansas.

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 Diaz of the Instituto Nacional de Investigaciones Forestales, Agricolas y Pecuarias; Gomez Palacio of Durango, Mexico; R. Daniel Griffin of the University of Arizona; Rodolfo Acuna Soto of the Universidad Autonoma de Mexico; and Richard R. Heim Jr. of the National Oceanic and Atmospheric Administration reported their findings in EOS.

The researchers looked at data from the Drought Area Index in Mexico, which uses tree ring chronologies and instrumental data on temperature and precipitation to reconstruct climate patterns in that country for the past 500 years. They found that the 10 years from 1994 to 2003 were some of the driest in the climate record, falling only behind the historic drought of the 1950s and the early colonial drought of the 1560s. However, they also found that the temperatures reached record highs during the more recent drought.

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.

Global warming models produced by scientists for the Intergovernmental Panel on Climate Change 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.

In addition, land use practices in Mexico may contribute to its climate change. 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.

'Those are pathways by which humans are changing the natural systems globally and regionally,' Stahle said. 'And these natural processes don't necessarily conform to international borders. Those mechanisms may be in operation in the United States Southwest as well.'

Stahle is a faculty member in the J. William Fulbright College of Arts and Sciences.