Climate scientists study the odds of a US megadrought

December 14, 2017 by Blaine Friedlander, Cornell University

To help untangle fact from speculation, Cornell climate scientists and their colleagues have developed a "robust null hypothesis" to assess the odds of a megadrought - one that lasts more than 30 years - occurring in the western and southwestern United States. The research was published online in the Journal of Climate.

"We're establishing a baseline. We're looking for the normal pulse of a megadrought. How often do they occur? Do they happen more in periods of ?" asks Toby Ault, assistant professor of earth and atmospheric sciences and lead researcher. "We're examining things happening over the last 1,200 years - including the period known as the 'Medieval Climate Anomaly' from about 800 to 1300 A.D. - and we're applying that understanding to see what could happen in the next 100 years."

In the southwestern United States, water management is a top concern. If a megadrought occurs, large-scale decisions affecting millions of Americans must be made to protect agriculture, the ecosystem and potable water systems, said Ault. Thus, understanding the odds of a widespread megadrought becomes important for planning purposes.

To help understand the concept of a robust null hypothesis, think of tossing a coin. "It lands either heads or tails. Even though the toss is random, over several tries you can still get long runs of heads, heads, heads, heads, heads," said Ault. If this happens, it can fool you into thinking that other forces are in play and that it is more than just the randomness of the , he said: "We needed to rule out this possibility as an explanation for megadroughts in the past."

Using tree ring and other physical evidence, researchers determined that the American Southwest saw five megadroughts from 800 to 1300 A.D., a period almost as warm as it is today, though Ault explained that the causes were different, such as solar activity. Today, Ault and his colleagues want to know if an actively warming world can stimulate a megadrought.

"With a robust null hypothesis, we have a better understanding of how megadroughts are part of the natural variability and what drives the odds of its occurrence," Ault said. "It's surprising that even with this simple statistical model, we can get megadroughts that are as prolonged, as severe and as widespread as the worst droughts of the last 1,200 years in the west."

However, the simple model does not generate clusters of megadroughts. "Like those that occurred during the medieval period, those events were likely to have been caused by something other than chance alone," Ault said.

Explore further: Megadrought risks in Southwest soar as atmosphere warms

More information: Toby R. Ault et al, A Robust Null Hypothesis for the Potential Causes of Megadrought in Western North America, Journal of Climate (2017). DOI: 10.1175/JCLI-D-17-0154.1

Related Stories

Megadrought risks in Southwest soar as atmosphere warms

October 11, 2016

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 ...

Southwest may face 'megadrought' within century, study finds

August 26, 2014

(Phys.org) —Due to global warming, scientists say, the chances of the southwestern United States experiencing a decadelong drought is at least 50 percent, and the chances of a "megadrought" – one that lasts up to 35 years ...

Early-onset spring models may indicate 'nightmare' for ag

September 2, 2016

Warm springs in the Great Lakes and Northeast regions - which create havoc for agriculture - may start earlier by mid-century if greenhouse gas emissions are not reduced, according to a new Cornell University study published ...

Climate scientists create Caribbean drought atlas

July 19, 2017

Cornell atmospheric scientists have developed the first-of-its-kind, high-resolution Caribbean drought atlas, with data going back to 1950. Concurrently, the researchers confirmed the region's 2013-16 drought was the most ...

Recommended for you

Paleontologists report world's biggest Tyrannosaurus rex

March 22, 2019

University of Alberta paleontologists have just reported the world's biggest Tyrannosaurus rex and the largest dinosaur skeleton ever found in Canada. The 13-metre-long T. rex, nicknamed "Scotty," lived in prehistoric Saskatchewan ...

NASA instruments image fireball over Bering Sea

March 22, 2019

On Dec. 18, 2018, a large "fireball—the term used for exceptionally bright meteors that are visible over a wide area—exploded about 16 miles (26 kilometers) above the Bering Sea. The explosion unleashed an estimated 173 ...

2 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

aksdad
1.5 / 5 (2) Dec 14, 2017
If you don't understand the mechanisms that cause a drought, you can't make accurate predictions about possible future droughts. Even if you do understand the mechanisms, if they are chaotic or random, you still can't make accurate predictions. It sounds like they are a long way from understanding or predicting.
Shootist
1 / 5 (1) Dec 16, 2017
The glaciation cometh

https://wattsupwi...dimming/

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.