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NASA Study Predicts Megadrought in Southwest and Central Plains

According to a new study conducted by NASA, the United States could be faced with a decades-long megadrought in the second half of the 21st century. Their findings revealed that droughts in the Southwest and Central Plains of the United States between the years 2050 and 2099 could be the most severe in the last 1,000 years. The study, published on Feb 12, 2015 in the Journal Science Advances, is based on projections from several climate models. The scientists analyzed a drought severity index and two soil moisture data sets from 17 climate models that were run for both moderate and high emissions scenarios, surpassing drought conditions of the last millennium. The research found that continued increases in human-produced greenhouse gas emissions would drastically increase the likelihood of a megadrought, or a drought lasting more than three decades.

While the current likelihood of a megadrought is only 12%, the study warns of increased risk in our future. If greenhouse gas emissions stop increasing in the mid-21st century, the projected likelihood of megadrought is more than 60 percent, and if greenhouse gas emissions continue to increase along current trajectories throughout the 21st century, the risk increases to 80%. However, the risk of a megadrought could be minimized reduced by substantially reducing carbon emissions. Currently, the atmosphere contains 400 ppm of CO2. NASA scientists warn that if this number is not diminished, the megadrought is likely to occur.

With the country already facing large challenges in regards to its water supply, the implications of this study are severe. Droughts often have significant impacts on agriculture, ecosystems, city water supplies, and economic prosperity—as can be seen in California with an estimated $2.2 billion in lost revenue and 17,100 lost water dependent jobs in 2014 (see “UC Davis Report Analyzes Economic Impact of California’s Drought” JOW, February 2015 for insight on the economic impacts of drought).

Rising temperatures spurred by the greenhouse effect result in more evaporation and less precipitation for the region, which is already relatively dry. In fact, 11 of the past 14 years have seen drought in much of the American West—from California across to Texas and Oklahoma, according to the U.S. Drought Monitor.  In addition, many Southwestern areas that are currently drought-stricken are filling up with more people, creating a larger demand for water while reservoirs are already strained. Compared with the last millennium, the predicted dryness will be unprecedented, adding increased pressures to the U.S. water situation.  In fact, Rodney T. Smith, Ph.D. pointed out in a 2013 post on the Hydrowonk Blog that the Colorado River Basin received 15 maf of water flow last century, which is above the historic average of 13.4 maf (see “Increasing Hydrologic Risk in the Colorado River Basin” Hydrowonk Blog, January 28, 2013 for more hydrologic cycle information).

“The real challenge,” explains Ben Cook, a climate scientist at NASA and lead author of the study, “is whether we can take strategies we have now and apply them to the more severe droughts that are likely in the future. These droughts really represent events that nobody in the history of the United States has ever had to deal with.”

Many scientists and political leaders are worried that current water policies will not be sufficient enough to combat worsened drought conditions. Toby Ault, assistant professor of earth and atmospheric scientists at Cornell University, is among one of the many professionals of the field discontented with current policies. “The time to act is now,” Ault warns. “The time to start planning for adaptation is now. These future droughts could be minimized, but carbon emissions need to be lowered immediately.”

The predicted megadrought holds profound ramifications for future societies living in North America. The findings of the NASA study require citizens, scientists, and policy makers to consider how behaviors and policies must be adapted in preparation for more severe droughts in the future.

Written by Stratecon Staff