Western states face megadrought, experts warn

The United States’ drought-stricken Southwest and Great Plains should brace for the worst and most persistent drought in 1,000 years, according to a report out today by the Earth Institute at Columbia University.

The current extreme drought blanketing California and other parts of the West may be just the beginning. New research suggests that by 2050, the regions may enter the longest and driest period for a millennium — a product of natural weather cycles and man-made greenhouse gas emissions.

“The 21st century projections make [past] megadroughts seem like quaint walks through the Garden of Eden,” said Jason Smerdon, a co-author of the report and a climate scientist at the Lamont-Doherty Earth Observatory, part of Columbia’s Earth Institute.

Megadroughts last at least 10 years. Some researchers believe a megadrought contributed to the decline of the Anasazi, or ancient Pueblo people, in the Colorado Plateau in the late 13th century.

“The last time we’ve seen this kind of megadrought in these regions was in the 1400s. The projected conditions by the latter half of the 21st century will be as bad or worse than the severe megadrought periods of the past … worse than anything we’ve seen in the last 1,000 years,” Smerdon said.

This is the first study to conclude that the severity of this century’s drought could surpass even the worst megadroughts of the last millennium. Such a scenario would affect many more people because of the nation’s growing population. The current drought affects more than 64 million people, according to NASA.

“The report supports a growing body of evidence that links climate change to megadroughts,” said Juliet Christian-Smith, a climate scientist in the Oakland, California, office of the Union of Concerned Scientists, a group that works to develop solutions to global problems such as climate change. “Climate change and global warming will make bad droughts much worse.”

Lack of water, she said, is one of the effects of climate change that people feel the most.

Most information about past droughts comes from the study of tree rings from thousands of tree samples across the U.S., Mexico and parts of Canada.

The researchers combined drought history with several climate change projections. They applied 17 climate models to analyze the future impact of rising temperatures and compared two global warming scenarios. One projected continued increase in greenhouse gas emissions that contribute to global warming. The other assumed a peak in midcentury, followed by a decline in emissions.

Both scenarios concluded the same thing.

“The results … are extremely unfavorable for the continuation of agricultural and water resource management as they are currently practiced in the Great Plains and Southwestern United States,” said David Stahle, a professor in the department of geosciences at the University of Arkansas and the director of the tree ring laboratory there.

“In California we’re trying to cut our oil use by half by 2030,” Christian-Smith said. “That would change our emissions substantially by 2050.”

Eleven of the past 14 years have been drought years in much of the American West, including California, Nevada, New Mexico and Arizona and across the southern Plains to Texas and Oklahoma, according to the U.S. Drought Monitor.

Depleted water supplies have forced Western states to impose water restrictions, which are mandatory in some areas. In California’s Central Valley, some farmers are no longer getting water from state reservoirs.

“If the future looks like this study suggests, it might have enormous financial ramifications in terms of losing our agriculture,” Christian-Smith said.