Megadroughts Worse Than the Dust Bowl Could Hit the Southwest

[Buster's Uncle]

Megadroughts Worse Than the Dust Bowl Could Hit the Southwest
BusinessWeek
By Karen Weise  September 04, 2014 


       

A rancher in California's Central Valley delivers hay, which he now has to buy to feed his herd of beef cattle
Photograph by Frederic J. Brown/AFP via Getty Images



The drought in California has already devastated the environment and upended the state’s economy. Imagine if it were to last for a decade. Or four decades. Or longer. So-called megadroughts are increasingly likely as the earth warms, according to a new scientific paper that paired historic drought patterns with climate change models.

Toby Ault, an assistant professor at Cornell University and lead author of the study, said he and co-authors from the University of Arizona and the U.S. Geological Survey suspected that climate change would “load the dice” and make megadroughts more common, but they didn’t know by how much. So they took past drought patterns, documented through tree rings and other assessments, and then simulated the impact of global warming based on three scenarios for each of the 27 predictive models of climate change compiled by the Lawrence Livermore National Laboratory. The results will be published in the American Meteorological Society’s Journal of Climate.

Once or twice a century, the U.S. has seen a roughly decade-long drought, such as the one that created the Dust Bowl in the 1930s and another in the 1950s that severely parched the Midwest and Texas. Historically, there has been less than a 50 percent likelihood of a prolonged drought occurring in any given 10-year period. But when the researchers factored in the changes in precipitation that are anticipated by the climate change models, the likelihood of a decade-long drought jumped more than 90 percent in some areas.





Even more alarming, they found an increased risk of a megadrought lasting more than 35 years. The Sahel region of Africa faced a dry spell that long leading up to and through the 1980s, as did Northern Mexico about 400 years ago. A paper ominously titled “Megadrought and Megadeath in 16th Century Mexico,” written by Rodolfo Acuna-Soto of the Universidad Nacional Autonoma de Mexico, in Mexico City, and researchers from the University of Arkansas, describes how a prolonged drought likely aggravated disease epidemics. As a result, the region’s population was decimated, falling from almost 22 million to less than 2 million over the course of just three decades.

Under the modeling by Ault’s team, in the coming century the Southwest faces a 20 percent to 50 percent chance of a megadrought lasting longer than 35 years. They found a “non-negligible” risk of an even more severe scenario—a drought lasting longer than half a century, something they said hasn’t been seen in more than 2,000 years. Under their most adverse prediction for global warming, the researchers predict there is a 5 percent to 10 percent chance this could happen. “We know the greater Southwest and Mexico are vulnerable to this kind of slow-moving natural hazard,” Ault said.

As troubling as the predictions are for the U.S., parts of Africa, Australia, and South America are even more likely to see long droughts.





Ault said the U.S. can develop ways to manage long droughts, but “it does concern me that more vulnerable nation seems to be exposed to equal if not greater risks than we have.” Ault said he’s optimistic that the U.S. can create models to pare back water usage to survive the dry spells, “in the same way Los Angeles has been an example of how to be prepared for earthquakes.”


http://www.businessweek.com/articles/2014-09-04/megadroughts-worse-than-the-dust-bowl-could-hit-the-southwest?campaign_id=yhoo

[Buster's Uncle]

Southwest Could Face a Megadrought This Century
LiveScience.com
By Becky Oskin, Senior Writer  14 hours ago



Risk of a 10-year-long drought by 2100.



The Southwest faces a dry and dusty forecast, with a 90 percent chance of a decade-long drought searing southern regions of Arizona and New Mexico this century, if global greenhouse gas emissions stay the same.

The drought risk for southern portions of California and Nevada is nearly as great, with an 80 percent chance of a decade-long drought by 2100. California is already in the midst of an extreme drought. In 2014, the water shortage is expected to cost the state a total of $2.2 billion, including agricultural losses, according to a recent study from the University of California, Davis.

The U.S. Southwest has always suffered droughts. Tree rings and other historical records show one or two of these 10-year dry spells strike every century, such as in the 1950s. But computer models predict that climate change will tweak this historical drought pattern. Thanks to global warming, the Southwest is transitioning to a hotter and drier local climate, with less rain and snow, studies show.

"A drier Southwest is also a Southwest at risk of a megadrought," said Toby Ault, a climate scientist at Cornell University in Ithaca, New York, and lead author of the new study, published Aug. 28 in the Journal of Climate Science.

In the new study, Ault and researchers from the University of Arizona and the U.S. Geological Survey calculated the odds of future long-term droughts in the Southwest, accounting for the drying from global warming. They estimated the risk of consecutive dry years using climate models combined with historical drought records, such as tree rings and river flows.

Not only did the researchers find a high probability of a prolonged Southwest drought, they also discovered an increased risk of megadroughts, which parch the region for decades. The odds of a 35-year megadrought this century were between 20 and 50 percent, depending on whether or not emissions fall or continue at current levels.

A 35-year megadrought could sap the Colorado River of the water needed for the eight states and two countries that depend on its copper-colored flow.

The Southwest's drying climate will also boost the chances of an extraordinary 50-year megadrought from one or two per 1,000 years to between 5 and 10 percent this century, the study found.

The risks could be worse because the region's rising temperatures may add to drought conditions by increasing evaporation, the researchers said. The study only accounts for declining rain and snow

Ault said that knowing the future risks could help people prepare for the threats from megadroughts.

"I view a megadrought as another type of natural hazard, but it's a hazard that moves in slow motion," Ault said. "It unfolds over decades. Like many other hazards we face, we can adapt to it, prepare for it and plan for it."


http://news.yahoo.com/southwest-could-face-megadrought-century-114302224.html