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Risk of Southwest Megadrought Higher than Thought

A 21st century dustbowl?Employing a new scientific method for better assessing the risk of prolonged drought, researchers from Cornell, the University of Arizona and the U.S. Geological Survey determined that the risk of a decades-long megadrought in the arid U.S. Southwest is much higher than current assessments indicate – as high as 80-90 percent or more in certain areas.

The likelihood of longer duration megadrought – over 35 years – during the coming century is between 20 percent and 50 percent, while “the risk of an unprecedented 50-year megadrought” isn’t negligible under the most severe warming scenario, on the order of 5-10 percent, the scientists concluded.

As the researchers state in the abstract of a research paper to be published in the American Meteorological Society’s Journal of Climate, “These findings are important to consider as adaptation and mitigation strategies are developed to cope with regional impacts of climate change, where population growth is high and multidecadal megadrought—worse than anything seen during the last 2000 years—would pose unprecedented challenges to water resources in the region.”

Assessing the risks of megadrought

U.S. Drought Monitor for August 2014

A warming climate is projected to trigger changes in rainfall patterns, water supplies and ecosystems in semi-arid regions the world over, the scientists note in the abstract to their paper, entitled, Assessing the risk of persistent drought using climate model simulations and paleoclimate data.

Current, state-of-the-art global climate models underestimate and fail to fully take account of variability in the earth’s hydroclimate system, according to the researchers. More specifically, hydroclimate fluctuations “tend to be more energetic at low (multi-decadal to multi-century) than at high (inter-annual) frequencies,” they state. That suggests “the models underestimate the risk of future persistent drought.”

Aiming to improve the accuracy of hydroclimate projections at regional scales, the researchers developed a scientific method that combines the use of climate model projections as well as observational paleoclimate information. As they explain, “Where instrumental and paleoclimate data are reliable, these methods may provide a more complete view of prolonged drought risk.

“In the US Southwest, for instance, state-of-the-art climate model projections suggest the risk of a decade-scale megadrought in the coming century is less than 50 percent; our analysis suggests that the risk is at least 80 percent, and may be higher than 90 percent in certain areas.”

Megadrought risk assessment and adaptation

In an interview for the Cornell Chronicle, Toby Ault, lead report author and Cornell assistant professor earth and atmospheric sciences, stated:

“For the southwestern U.S., I’m not optimistic about avoiding real megadroughts.. As we add greenhouse gases into the atmosphere – and we haven’t put the brakes on stopping this – we are weighting the dice for megadrought.”

Most of California is in the midst of an “exceptional drought,” while Arizona, New Mexico, Oklahoma, Oregon and Texas are experiencing “moderate drought.” The results of the scientists’ study suggest worse may be yet to come.

“With ongoing climate change, this is a glimpse of things to come. It’s a preview of our future,” Ault told the Cornell Chronicle.

The scope of the scientists’ study extends to arid and semi-arid regions worldwide. Reservoirs providing water to Sao Paolo – the hub of Brazilian commerce and industry – are running dry, leading to accusations of poor water resource planning and management and controversy as to whether or not to ration water supplies.

Similarly, Australia, southern Africa and the Amazon Basin are vulnerable to megadrought. As temperatures continue to rise, moreover, the severity of droughts is likely to intensify, “implying that our results should be viewed as conservative,” the researchers state in their report.

It’s incumbent on government, community and business leaders , as well as planners, to identify mitigation strategies to cope with prolonged megadroughts, Ault said. “This will be worse than anything seen during the last 2,000 years and would pose unprecedented challenges to water resources in the region.”

Images credit: 1) Main image  NASA Earth Observatory; 2) U.S. Drought Monitor 3) Featured image Alan Stark, courtesy flickr

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