Water for Food

Great Plains Megadroughts: Could it happen again?

March 27, 2014

The Nebraska Sandhills are a unique landscape, covering more than 20,000 square miles.

The Nebraska Sandhills are a unique landscape, covering more than 20,000 square miles. Photo by Michael Forsberg Photography/www.michaelforsberg.com

A visit to Nebraska’s little known Sandhills reveals a landscape of gently rolling sand dunes blanketed with prairie grasses and wetlands. With its rich diversity of plants and wildlife, wide-open views and glorious sunsets, the Sandhills are a unique ecosystem covering a quarter of the state. Beyond its charms, the region serves critically important environmental and economic functions for the entire nation.

It’s hard to imagine this lush, tranquil landscape was once a barren wasteland of swirling sand and obscured sun. About 1,000 years ago, while the Crusades were getting underway in Europe and the Vikings were discovering the New World, the Sandhills – and much of western North America – experienced a megadrought.

Defined more by persistence than severity, a megadrought lasts decades or even centuries. The medieval megadrought in North America dwarfs anything seen in modern times, including the Dust Bowl of the 1930s.

Drowned trees in California were the first clue that much drier times once existed. Additional research into tree rings, lake salinity and dating sand dunes provide further evidence. But other indications suggest that climatic anomalies were occurring elsewhere in the world, including agricultural records, abandoned archeological sites and evidence of cultural changes.

The reasons for this climatic anomaly, first identified in Europe as the Medieval Warm Period, are unknown. The Sandhills owe its current grassland lushness to winds that bring moisture up from the Gulf of Mexico during the spring. The grasslands lock down the dunes, preventing them from blowing and providing a critical recharge service for the High Plains Aquifer. Researchers at the University of Nebraska-Lincoln say they believe the winds shifted during the medieval megadrought, coming from the dry southwest instead. Though the Sandhills grasslands are resilient, able to survive the small droughts experienced by ranchers of the last few centuries, decades- or centuries-long megadroughts kill off the underground root system that bind the soil together, said UNL geologist Paul Hanson.

Climate scientists are investigating the role oceans play in causing shifting wind fields and droughts. Many suggest unusual, persistent conditions in the Atlantic Ocean may have affected the jet stream and storm tracks across North America.

“So far models can’t completely reproduce the geologic data, so we’re still exploring the mechanisms that lead to these persistent droughts,” said Sherilyn Fritz, DWFI fellow and UNL paleoclimatologist.

Could it happen again? It’s sobering to consider that if the conditions that existed the last time the Sandhill dunes were blowing were to return, the region could once more turn into a barren desert landscape and the verdant agricultural lands of North America could dry up. “It’s happened several times in the last 5,000 years, so it’s likely that it will happen again,” Hanson said.

But there’s no indication that’s happening now, he added. So while the media may refer to California’s current drought or the Great Plain’s extreme drought of 2012 as “megadroughts,” these modern events are still relatively short-term.

Studying the paleorecord provides a longer yardstick to evaluate natural variability and to put current droughts into perspective, Fritz said. In fact, many years of the last few centuries have been extremely wet, she added, particularly the first decades of the 20th century when water laws were largely put into place, an important consideration for current policymaking.

North America may not be headed toward a true apocalyptic megadrought like that experienced a thousand years ago anytime soon, but researchers warn that current water laws don’t reflect the severe, short-term droughts that are a common and natural feature of the Great Plains.

Drought in the Life, Cultures and Landscapes of the Great Plains, the 40th annual Center for the Great Plains Studies symposium, takes place April 1-4, 2014, at the University of Nebraska-Lincoln in collaboration with DWFI and the National Drought Mitigation Center.

Sherilyn Fritz is a DWFI fellow and a George Holmes university professor of paleoclimatology in the Earth and Atmospheric Sciences Department.

Paul Hanson is an associate professor in the Nebraska Geological Survey and associate director of the School of Natural Resources.

For more information on droughts in the Great Plains, see The Proceedings of the 2013 Water for Food Conference: Too Hot, Too Wet, Too Dry: Building Resilient Ecosystems

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