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article imageStudy shows southwestern U.S. on verge of a 'megadrought'

By Karen Graham     Aug 28, 2014 in Environment
Due to human-caused climate change, the very real possibility of the southwestern region of the United States experiencing a prolonged drought has been estimated at 50 percent. The chance of the region having a "megadrought" lasting 30 years is also high.
The study, "Assessing the risk of persistent drought using climate model simulations and paleoclimate data" was conducted by researchers from Cornell, University of Arizona and the U.S. Geological Survey, and will be published in the upcoming issue of the American Meteorological Society's Journal of Climate. Co-authors of the study included Julia E. Cole, David M. Meko and Jonathan T. Overpeck of University of Arizona; and Gregory T. Pederson of the U.S. Geological Survey.
Toby Ault, Cornell assistant professor of earth and atmospheric sciences and lead author of the paper says, "For the southwestern U.S., I'm not optimistic about avoiding real megadroughts. As we add greenhouse gases into the atmosphere – and we haven't put the brakes on stopping this – we are weighting the dice for megadrought."
U.S. Drought Monitor 
(Released Thursday  Aug. 21  2014)
U.S. Drought Monitor (Released Thursday, Aug. 21, 2014)
Richard Tinker
Greenhouse gases are gases in the atmosphere that absorb and emit thermal radiation within the infrared range. This is basically the way that greenhouse gases are formed. Without these gases, the earth's surface temperature would hover around 59 degrees Fahrenheit colder than our present temperatures. Since around 1750 and the start of the Industrial Revolution, human activity has increased the levels of greenhouse gases in the atmosphere.
Since August 12, most of the state of California has been experiencing a D4 "exceptional drought," which is the severest category. Oregon, Arizona, New Mexico, Oklahoma and Texas are suffering categories of drought ranging from D1 to D4. Climatologists really can't give a long-range prediction on how long the drought conditions will last in the southwestern states, but Ault says, "With ongoing climate change, this is a glimpse of things to come. It's a preview of our future."
Dust storm approaching Stratford  Texas. Dust bowl surveying in Texas.
Photo Date: April 18  1935
Dust storm approaching Stratford, Texas. Dust bowl surveying in Texas. Photo Date: April 18, 1935
NOAA George E. Marsh Album
The reality of severe drought is not lost on the few remaining survivors of the Dust Bowl of the 1930s. For seven long years, the Great Plains of America endured unspeakable misery and a devastating drought covering a 150,000-square-mile area, including the Oklahoma and Texas panhandles and neighboring sections of Kansas, Colorado, and New Mexico.
Ault says a megadrought lasting for 30 years could lead to a population migration on a scale never before seen in the United States. This possible scenario points to having strategies worked out ahead of time to deal with mass migration. "This will be worse than anything seen during the last 2,000 years and would pose unprecedented challenges to water resources in the region," he said.
Using computer models, the researchers found that California, Arizona and New Mexico would likely continue to suffer long periods of drought, while in northwestern states like Washington, Montana and Idaho, the chances of drought would actually decrease.
Long periods of drought have occurred throughout history. Ault points to the last "Big Dry" in Australia that lasted nine very parched and dry years, ending in April 2012. There is also the recent studies done on a region of sub-Saharan Africa detailing a series of "megadroughts," some lasting for centuries occurring over the past 3,000 years. That study was published in the April 17, 2009 issue of the journal Science.
There is also evidence based on a study of tree rings that a "megadrought" occurred in the 1150s along the Colorado River. Ault says that in natural history, these huge droughts occur every 400 to 600 years. But with greenhouse gases accumulating at a faster rate in the atmosphere, drought models and any underlying statistics would be put into a state of flux.
Besides the United States, southern Africa, Australia and the Amazon basin are also at risk for the possibility of a "megadrought." As long as there are increasing temperatures, the likelihood of severe drought conditions will worsen, "implying that our results should be viewed as conservative," the study reports.
More about drought conditions, southwest US, megadrought, dust bowl, D4 drought
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