Nav: Home

Megadrought risks in Southwest soar as atmosphere warms

October 10, 2016

ITHACA, N.Y. - As a consequence of a warming Earth, the risk of a megadrought - one that lasts more than 35 years - in the American Southwest likely will rise from a low chance over the past thousand years to a 20- to 50-percent chance in this century. However, by slashing greenhouse gas emissions, these risks are nearly cut in half, according to a Cornell-led study in Science Advances, Oct. 5.

"Megadroughts are rare events, occurring only once or twice each millennium. In earlier work, we showed that climate change boosts the chances of a megadrought, but in this paper we investigated how cutting fossil fuel emissions reduces this risk," said lead author Toby Ault, Cornell professor of earth and atmospheric science.

If climate change goes unabated - and causes more than a 2-degree Celsius rise in atmospheric temperature - megadroughts will become very probable, Ault said.

"The increase in risk is not due to any particular change in the dynamic circulation of the atmosphere," Ault said. "It's because the projected increase in atmospheric demand for moisture from the land surface will shift the soil moisture balance. If this happens, megadroughts will be far more likely for the next millennium."

Ault explained a natural "tug-of-war" governing the surface moisture balance between the precipitation supply (rain) and evaporation (transpiration). But he cautions that increases in average regional temperatures could be so dramatic - more than 4 degrees Celsius (7.2 degrees Fahrenheit) - that evaporation wins out. This, in turn, dries out the land surface and makes megadroughts 70- to 99-percent likely.

"We found that megadrought risk depends strongly on temperature, which is somewhat good news," Ault said. "This means that an aggressive strategy for cutting greenhouse gas emissions could keep regional temperature changes from going beyond about 2 degrees Celsius (3.6 degrees Fahrenheit)."

This lower average warming figure cuts the megadrought risk almost in half, he said.

These tug-of-war scenarios could very well play out in the American Southwest, according to tree ring and geologic records. During sequences of exceptionally dry years, those rings tend to be relatively narrower than in wet years, he said.

"Tree rings from the American Southwest provides evidence of megadroughts, as there are multiple decades when growth is suppressed by dry conditions," Ault said, pointing to several megadroughts that occurred in North America between 1300 and 1100 B.C.

"We also know they have occurred in other parts of the world, and they have been linked to the demise of several pre-industrial civilizations," he said.

The tug of war between moisture supply and demand might play out differently in other parts of the world, Ault said.

"Nonetheless, even in the Southwest we found examples of plausible 21st-century climates where precipitation increases, but megadroughts still become more likely," said Ault, who noted the normally verdant Northeast is in the middle of drought. "This should serve as a cautionary note for areas like the Northeast expecting to see a more-average moisture supply.

"Megadrought risks are still likely to be higher in the future than they were in the past," he said. "Hence, efficient use of water resources in the drought-stricken American Southwest are likely to help that region thrive during a changing climate."

"I wouldn't ever bet against our ability to, under pressure, come up with solutions and ideas for surmounting these challenges," said co-author Jason Smerdon of Columbia University's Lamont-Doherty Earth Observatory," but the sooner we take this seriously and start planning for it, the more options we will have and the fewer serious risks we'll face."
-end-
On the paper, "Relative Impacts of Mitigation, Temperature, and Precipitation on 21st-Century Megadrought Risk in the American Southwest," Ault is joined by Justin S. Mankin and Benjamin Cook, both of the NASA Goddard Institute for Space Studies, and Smerdon. The National Science Foundation supported this research.

Cornell University

Related Climate Change Articles:

The black forest and climate change
Silver and Douglas firs could replace Norway spruce in the long run due to their greater resistance to droughts.
For some US counties, climate change will be particularly costly
A highly granular assessment of the impacts of climate change on the US economy suggests that each 1┬░Celsius increase in temperature will cost 1.2 percent of the country's gross domestic product, on average.
Climate change label leads to climate science acceptance
A new Cornell University study finds that labels matter when it comes to acceptance of climate science.
Was that climate change?
A new four-step 'framework' aims to test the contribution of climate change to record-setting extreme weather events.
It's more than just climate change
Accurately modeling climate change and interactive human factors -- including inequality, consumption, and population -- is essential for the effective science-based policies and measures needed to benefit and sustain current and future generations.
More Climate Change News and Climate Change Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Anthropomorphic
Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#534 Bacteria are Coming for Your OJ
What makes breakfast, breakfast? Well, according to every movie and TV show we've ever seen, a big glass of orange juice is basically required. But our morning grapefruit might be in danger. Why? Citrus greening, a bacteria carried by a bug, has infected 90% of the citrus groves in Florida. It's coming for your OJ. We'll talk with University of Maryland plant virologist Anne Simon about ways to stop the citrus killer, and with science writer and journalist Maryn McKenna about why throwing antibiotics at the problem is probably not the solution. Related links: A Review of the Citrus Greening...