If you're still alive in Tucson through 2050 and beyond, you may well experience the longest, driest drought the Southwest has experienced in at least 1,000 years.
That's the message of a new study written by scientists at Columbia and Cornell universities and released Thursday.
Thanks to human-caused global warming, this region and the Great Plains are likely to experience droughts from 2050 to 2100 that are worse than the "megadroughts" that lasted up to 60 years in the Southwest in pre-Medieval times, the study said.
By 2100, this area will be not only be drier than during today's drought, but the future drought will probably last much longer than the current 20-year-long drought, said Jason Smerdon, one of the authors.
The study authors found an "overwhelming consensus" about future Sothwestern drought prospects in 17 climate models they looked at that project 21st century conditions, added Benjamin Cook, the study's lead author, who works at Columbia's Lamont-Doherty Earth Observatory for NASA's Goddard Institute for Space Studies.
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"This drying (that they're forecasting) is very robust," Cook said.
The current drought in the Colorado River Basin is the worst and longest-lasting since historical records have been kept starting in the early 20th century. It's caused Lake Mead at the Nevada border to drop to its lowest level on record, threatening future Central Arizona Project shortages to farmers and ultimately cities. Looking at the Southwest and Southern Great Plains, the current drought directly affects more than 64 million people, a news release accompanying the study said.
The risk of one of these major droughts will rise from 12 percent in the 2050s to more than 80 percent at the end of the 21st century, said Smerdon. That's the risk if climate change goes goes relatively unmitigated by reductions in greenhouse gas emissions, said a third author, Toby Ault, an assistant professor at Cornell.
"Consider the analogy of a golf course. The average golfer goes on and swings and some percentage of the course is covered in sand pits," said Ault, who earned his doctorate at the University of Arizona. "The likelihood you'll hit it is 10 percent. The likelihood of any one century in the past of hitting a megadrought level is 5 or 10 percent, maybe once or twice per milennium."
With climate change, the likelihood of a megadrought goes up considerably, "and the golf course is almost entirely covered by sand pits," Ault added.
The impacts of such a future drought could be devastating for this region, given its much larger population and use of resources today than 1,000 years ago, the authors said in a news release.
"We are the first to do this kind of comparison (with past megadroughts). . . and the story is a bit bleak," said Smerdon, a climate scientist at the observatory. "Even when selecting for the worst megadrought-dominated period, the 21st century projections make the megadroughts seem like quaint walks through the Garden of Eden."
The study is being published in the inaugural edition of the new online journal Science Advances, produced by the American Association for the Advancement of Science. The association also publishes the journal Science. Here's a link to the article.
Based on tree ring records, the longest megadrought in the Colorado River Basin lasted about 60 years, from 1118 to 1179 A.D., said Connie Woodhouse, a professor at the University of Arizona's Laboratory of Tree-Ring Research and its Geosciences and Geography departments.
Reconstruction of river flows using tree ring data found that the Colorado's lowest 25-year period was from 1130 to 1154, when it carried 84 percent of its average flow from 1906-2004. There's been no similar average made of the river's flows in the last 25 years, during the major drought, added Woodhouse, who didn't participate in the new study.
While the new study didn't make forecasts for the Colorado River, "it is likely that any related water resources in the region will be further stressed and reduced as the area continues to dry into the future," Smerdon said.
Daniel Cayan, a San Diego-based climate scientist who didn't work on this study, said "I'm not sure I endorse a real sensational statement" about future Southwestern droughts. But he believes that droughts that society has weathered in recent history will be exacerbated in the future by a warmer climate, he said in an interview.
"This latest drought situation we're seeing along the West Coast, into Nevada and parts of the Southwest, they've been aggravated by the fact that we've had record warm temperatures," said Cayan of the Scripps Institution of Oceanography. "The amount of snowpack that's built up has been disproportionately low because of the very warm temperatures that have been relentless in the last two years."
The question of global warming's impact on the drought isn't a black and white issue, it's a shades of gray issue, he added.
