Unprecedented megadrought in US south-west and Great Plains

For some reason,when I see this, Guy McPherson comes to mind.

‘The dust bowl that never ends’

US faces worst droughts in 1,000 years, predict scientists

Climate change is likely to cause decade-long mega-droughts across US south-west and Great Plains, new study shows

the Guardian

12 February, 2014

The US south-west and the Great Plains will face decade-long droughts far worse than any experienced over the last 1,000 years because of climate change, researchers said on Thursday.

The coming drought age – caused by higher temperatures under climate change – will make it nearly impossible to carry on with current life-as-normal conditions across a vast swathe of the country.

The droughts will be far worse than the one in California – or those seen in ancient times, such as the calamity that led to the decline of the Anasazi civilizations in the 13th century, the researchers said.

“The 21st-century projections make the [previous] mega-droughts seem like quaint walks through the garden of Eden,” said Jason Smerdon, a co-author and climate scientist at Columbia University’s Lamont-Doherty Earth Observatory.

Researchers have long known that the south-west and Great Plains will dry out over the second half of the 21st century because of rising temperatures under climate change.

But this was the first time researchers found those droughts would be far worse even than those seen over the millennia.

The years since 2000 give only a small indication of the punishment ahead. In parts of Arizona, California, Nevada, New Mexico, Oklahoma and Texas, 11 of those years have been drought years.

As many as 64 million people were affected by those droughts, according to Nasa projections

Those conditions have produced lasting consequences. In California, now undergoing its fourth year of drought – and the worst dry spell in 1,200 years, farmers have sold off herds. Growers have abandoned fields. Cities have imposed water rationingч.

But future droughts could be even more disruptive, because they will likely drag on for decades, not years.

“We haven’t seen this kind of prolonged drought even certainly in modern US history,” Smerdon said. “What this study has shown is the likelihood that multi-decadal events comprising year after year after year of extreme dry events could be something in our future.”

The study, Unprecedented 21st-Century Drought Risk in the American Southwest and Central Plains, was published in a new online journal Science Advances.

The researchers said the effects of drought would likely be exacerbated by population growth in the south-west and rising demands for water.

Already current demands for water – for agriculture and for daily life – have drastically reduced groundwater sources in California and across the south-west.

Under the current warming trajectory, the south-west and Great Plains could expect to see chronic water shortages, making it impossible to carry out farming and ranching under current methods.

“Given the likelihood of a much drier future and increasing water resources demand, groundwater loss and higher temperatures will likely exacerbate the impacts of future droughts, presenting a major adaptation challenge,” the paper said.

The researchers used data derived from tree rings, whose growth patterns show the effects of dry and wet years, sampled across North America, and soil moisture, rainfall and evaporation records, and 17 climate models to study the effects of future temperature rise on the region.

Southwest, Central Plains Face ‘Unprecedented’ Drought

Climate Central

12 February, 2014

Climate change is creating an “unprecedented” risk of severe drought in the Southwest and Central Plains. Rising temperatures and decreasing rainfall mean that future drought could be more extreme than any drought seen in at least the past 1,000 years and the effects could reverberate for urban dwellers and farmers across the regions.

The 1930s Dust Bowl created post-apocalyptic conditions for the Central Plains, but Lisa Graumlich, who heads the University of Washington’s College of the Environment, said that the severe drought that plagued the Southwest from 1100-1300, ”makes the Dust Bowl look like a picnic.” That drought occurred during what researchers have called theMedieval Climate Anomaly and contributed to widespread ecosystem shifts and the collapse of civilizations across the Southwest.

Yet both those droughts pale in comparison to the severity of drought projected to befall those regions — which encompass all or part of 17 states from California to Louisiana to Minnesota — during the latter half of the 21st century if greenhouse gas emissions continue to rise according to a new study published in Science Advances. Both regions are all but guaranteed to experience a severe drought that would last at least a decade, with the odds of a drought lasting multiple decades at about 80 percent. In comparison, the chances of a multidecadal drought occurring during 1950-2000 was less than 10 percent.

Previous studies have looked forward at drought risks and also drawn comparisons to the Dust Bowl but none have drawn comparisons with tree ring records of the past. This one not only does that but uses a suite of 17 climate models and three drought measures to provide as much insight as possible.

Historical and future drought risk in the Southwest and Central Plains.
Credit: Cook, et al., 2014

"The surprising thing to us was really how consistent the response was over these regions, nearly regardless of what model we used or what soil moisture metric we looked at. It all showed this really, really significant drying" Benjamin Cook, a researcher at the NASA Goddard Institute for Space Studies and lead author of the study, said.

The significance isn’t lost on Graumlich, who wasn’t affiliated with the study.

“When they tell me we are headed to something like, or exceeding, the severity of the Medieval Climate Anomaly, the hair on my neck starts standing up. It’s very, very serious,” Graumlich said.

Graumlich said that the drought during that period essentially dried up rivers east of the Sierra Nevada mountains and caused water levels at Mono Lake, an expansive inland lake in California, to virtually disappear. Highly evolved societies collapsed and descended into warfare.

The Dust Bowl, though less severe in terms of drought and length, impacted a larger population. More 3.5 million people abandoned the Plains in the 1930s as massive dust storms rolled over houses and fields and heat baked the region.

Climate change is not only projected to dry out the western U.S. but also drive temperatures higher, which would help reinforce drought. That pattern is currently on display in California, where heat is helping keep dry conditions locked in place, according to research published late last year by Kevin Anchukaitis, a paleoclimatologist at Woods Hole Oceanographic Institute.

Anchukaitis said the new study shows, “the increasing importance that higher temperatures and increased evaporative demand will have in fueling severe and persistent droughts.”

The odds of drought lasting a decade and drought lasting longer than a decade in the Southwest and Central Plains.Click image to enlarge. Credit: Cook, et al., 2014

Technology and groundwater have helped insulate farmers from drought more than their Dust Bowl and Pueblo Indian counterparts. But the California drought has still cost the state at least $2.2 billion and thousands of jobs. And groundwater, which has been used to reduce the impacts somewhat, isn’t a renewable resource, at least not at the current rates of use.

That’s in part why future droughts in the Southwest and Central Plains could be even more costly. Agriculture in California, a nearly $43 billion industry, and grains produced in the Central Plains, including 40 percent of the world’s corn and about 10 percent of the world’s wheat, would both take big hits from any prolonged drought and could have a ripple effect felt beyond the region. Food supplies could be disrupted and price shocks could reverberate through global markets.

Growing populations in urban areas from Dallas to Minneapolis to Phoenix to Los Angeles could also face water shortages.

“The work is well laid out, but it’s a tough paper to read given the implications, especially for someone who calls the Southwest home,” Jonathan Overpeck, director of the Institute of the Environment, said. “Impacts on water supply and natural land cover could be especially large in the Southwest, where warming is already exacerbating a 15-year long drought, and reservoir levels are already at all-time lows on the Colorado River.”

The study outlines the risk of drought using a few methods including the Palmer Drought Severity Index, which decision makers use to access federal emergency funds. Graumlich said that familiarity helps make this study more accessible to urban planners, water managers and agricultural services who will have to deal with an unfamiliar and sobering future