Long-term droughts in the Southwestern North America often mean failure of both summer and winter rains, according to new tree-ring research from a University of Arizona-led team.
The finding contradicts the commonly held belief that a dry winter rainy season is generally followed by a wet monsoon season, and vice versa.
The new research shows that for the severe, multi-decadal droughts that occurred from 1539 to 2008, generally both winter and summer rains were sparse year after year.
"One of the big questions in drought studies is what prompts droughts to go on and on," said lead author Daniel Griffin, a doctoral candidate in the UA School of Geography and Development. "This gives us some indication that the monsoon and its failure is involved in drought persistence in the Southwest."
The new 470-year-long history of summer precipitation in the Southwest covers most of Arizona, western New Mexico and parts of northern Mexico.
"This is the first time researchers have used tree rings to take a closer look at the monsoon in a large and important area of the American Southwest," said Griffin, who also is an EPA STAR Research Fellow at the UA Laboratory of Tree-Ring Research.
"Monsoon droughts of the past were more severe and persistent than any of the last 100 years," he said. "These major monsoon droughts coincided with decadal winter droughts."
Those droughts had major environmental and social effects, Griffin said, pointing out that the late-16th-century megadrought caused landscape-scale vegetation changes, a 17th-century drought has been implicated in the Pueblo Revolt of 1680 and the 1882-1905 drought killed more than 50 percent of Arizona's cattle.
Co-author Connie A. Woodhouse, UA associate head and associate professor of geography and development, said, "The thing that's interesting about these droughts is that we've reconstructed the winter precipitation, but we've never know
|Contact: Mari N. Jensen|
University of Arizona