Monsoon failure key to dry times in Southwest.

PositionDrought - Brief article

Long-term droughts in southwestern North America often mean failure of both summer and winter rains, according to a study appearing in Geophysical Research Letters. The finding contradicts the commonly held belief that a dry winter rainy season generally is followed by a wet monsoon season, and vice versa. The research shows that, for the severe, multidecadal 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," says lead author Daniel Griffin, an Environmental Protection Agency researcher. "This gives us some indication that the monsoon and its failure is involved in drought persistence in the Southwest. Monsoon droughts of the past were more severe and persistent than any of the last 100 years. These major monsoon droughts coincided with decadal winter droughts."

Those droughts had major environmental and social effects. For instance, the late 16th-century mega-drought caused landscape-scale vegetation changes; a drought in the 17th century has been implicated...

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