PHOENIX -- A new study by The University of Arizona, Cornell University and the U.S. Geological Survey says the chances of a "megadrought" that runs 35 years or more ranges from 30 to 40 percent over the next century in the Grand Canyon State.
Arizona State University climate expert Randy Cerveny said the region has been in a megadrought before -- the last happening about 400 years ago.
"It was incredibly destructive to the Native American population that was here at that time," Cerveny said. "But we haven't experienced anything since modern settlement."
"Lake Mead is not only responding to drought, but demand," Cerveny said.
The impacts of a megadrought would be far worse now because tens of millions of people now call the Southwest home.
"Places like Los Angeles are taking a lot more water out of Lake Mead than they used to," the climatologist said. "Lake Mead is not only responding to drought, but demand."
The northwestern Arizona-southeastern Nevada lake is currently at its lowest level since Hoover Dam was built in the 1930s.
"If we don't come out of the drought in the next 20 to 30 years, then we are in a megadrought," Cerveny said.
Cerveny said Arizona has been in drought since 1997 and that there's no way to know if we're entering another megadrought.
"We don't have the good precursors or indicators to tell us we would be entering one now," he said. "The only way to tell if we're in a megadrought is to keep watching, and if we don't come out of the drought in the next 20 to 30, years then we are in a megadrought."
The Arizona Daily Star reports that the southern part of the state is still behind in summer moisture this year, despite August being a very rain-heavy month.
Tucson has received more than 3 inches of rain since the season began June 15, but the summer average is 4.79 inches.
Still, rain has fallen in above-normal amounts in Nogales, Douglas, Bisbee, Safford, Willcox and Sierra Vista. In fact, parts of Sierra Vista near the Huachuca Mountains recorded up to 7 inches of rain in August alone.
University of Arizona climate scientist Mike Crimmins said patterns are favoring more moisture in September. Tucson averages 1.29 inches of rain in September, but he said tropical storms can boost that tremendously.
The Associate Press contributed to this report.