U.S. Soon to Face Worst “Megadroughts” in a Millennium, Scientists Predict

U.S. Soon to Face Worst “Megadroughts” in a Millennium, Scientists Predict

BY ZOË SCHLANGER 2/13/15 / http://www.newsweek.com/coming-us-megadroughts-will-be-worse-any-drought-seen-past-1000-years-306585

The current California drought, the worst in modern U.S. history, has ravaged the Western U.S. for years, dwindling water supplies and withering crops. But scientists say that based on what’s to come, the United States hasn’t seen anything yet.

Welcome to our “remarkably drier future.”

Analysis released Thursday from scientists at NASA, Cornell University, and Columbia University predicts that climate change will cause droughts in the Southwest and Great Plains of the U.S. that exceed any experienced in the last 1,000 years.

These “megadroughts” are likely to begin between 2050 and 2099, and could each last between 10 years and several decades.

“Our results point to a remarkably drier future that falls far outside the contemporary experience of natural and human systems in Western North America, conditions that may present a substantial challenge to adaptation,” the paper reads.

Droughts of this severity would undeniably make human life harder. More severe and longer-lasting drought means less water to grow food. Perhaps most challenging would be the allocation of drinking water in the Great Plains and Southwest of the U.S., where drought will be worst, according to the researchers. Already, towns are running out of water during the current drought in the Western U.S.

“[R]ecent years have witnessed the widespread depletion of nonrenewable groundwater reservoirs, resources that have allowed people to mitigate the impacts of naturally occurring droughts," the paper's researchers said. "In some cases, these losses have even exceeded the capacity of Lake Mead and Lake Powell, the two major surface reservoirs in the region,”

Warming temperatures and reduced rainfall due to climate change mean greater evaporation of surface water. Drought-depleted reservoirs also threaten to spark a feedback loop of scarcity: Less water in reservoirs will make subsequent droughts worse. “Combined with the likelihood of a much drier future and increased demand, the loss of groundwater and higher temperatures will likely exacerbate the impacts of future droughts, presenting a major adaptation challenge for managing ecological and anthropogenic water needs in the region.”

Even modeled using “moderate” future emissions predictions, climate change will cause droughts that will “exceed even the driest centuries” seen during the Medieval Warm Period between 1100 and 1300 A.D., according to the paper. That's during the same time of the so-called "Anasazi collapse," when Native Americans migrated en masse away from the four corners region of the U.S.—which consists of the southwestern corner of Colorado, northwestern corner of New Mexico, northeastern corner of Arizona, and southeastern corner of Utah. Skeletal remains of Anasazi people show "signs of starvation, disease, infant mortality and violence, suggesting extreme hardship and competition for dwindling water and food resources," according to B. Lynn Ingram, a paleoclimatologist at the University of California, Berkeley, and author of the book The West Without Water.

Ingram, who was not involved with the newly released paper forecasting megadrought, had previously concluded that the current drought has left California at its driest since 1580, when tree rings indicate "it was so dry those trees failed to grow." She sees a connection between the Anasazi's struggle with drought and our current drought crisis: Prior to the medieval megadrought, there was a period of wetness, and the Anasazi’s population size  grew, much like ours has. This left them "more vulnerable when the climate changed," she told Newsweek last year.

To analyze the impact of dry and wet periods, the researchers behind the newly released paper used data from tree rings, whose variations in pattern leave imprints indicating the soil conditions in any given year over decades of growth. They also drew data from 17 different climate change models based on various greenhouse gas emissions scenarios, as well as 15 models of historical rainfall and evaporation patterns.