Southwest Megadroughts Are Coming Back Because of Climate Change, Scientists Say

The Weather Channel ^ | 7/25/19 | Ron Brackett

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By less than an hour agoweather.com

(Getty Image)

A dry landscape stands on Navajo Nation lands on June 7, 2019, in the town of Gallup, New Mexico. Rising temperatures associated with global warming have worsened drought conditions on their lands over recent decades leading to a worsening of water access.

At a Glance

• The U.S. Southwest experienced a dozen megadroughts from the years 800 to 1600.
• These droughts lasted for decades at a time.
• Researchers say they have discovered the cause of those droughts.
• Climate change could cause another megadrought soon, they say.

Scientists say they have pinpointed the cause of medieval megadroughts that stretched for decades at a time, and they warn climate change could soon cause them to return to the American Southwest.

From the 9th through the 16th centuries, the Southwest experienced about a dozen megadroughts. These extreme droughts were caused by a combination of three factors, according to a new study by researchers at Columbia University's Lamont-Doherty Earth Observatory.

Two of the factors were warming sea surface temperatures in the Atlantic Ocean and high radiative forcing, which occurs when the atmosphere traps more energy from the sun than it radiates back into space, according to the study published this week in Science Advances.

The third, and most important factor, was severe and frequent La Niña events, periods when tropical Pacific Ocean temperatures are cooler and storms are pushed toward the Northwest.

“Both a warm Atlantic and a cold Pacific change where storms go,” Nathan Steiger, the study's lead author, told Vice. “They both result in fewer storms going to the Southwest.”

(Ghetto Image)

Parched land stands along a dried river on Navajo Nation lands on June 7, 2019, near the town of Thoreau, New Mexico. Rising temperatures associated with global warming have worsened drought conditions on their lands over recent decades leading to a worsening of water access.

On top of having less rainfall because of fewer storms, the radiative forcing caused any moisture that was there to evaporate more quickly.

Beginning in 1600, volcanic eruptions that spewed particles into the atmosphere blocked some of the sun's energy and decreased the effect of radiative forcing, thereby greatly reducing the number of megadroughts.

However, the increased burning of fossil fuels that started with the Industrial Age pumped more carbon dioxide into the atmosphere, which is again trapping the sun's energy.

This makes the Southwest, parts of which have seen ongoing drought for years now, more vulnerable to megadroughts, according to the Earth Institute's State of the Planet blog.

“Because you increase the baseline aridity, in the future when you have a big La Niña, or several of them in a row, it could lead to megadroughts in the American West,” Steiger said.

Forecasting the effect of climate change on La Niña events remains tricky, the study says. The bigger worry may be "the possibility that radiative forcing could gradually come to dominate the hydroclimate of the Southwest, with the recurrence of megadroughts becoming almost assured."

[joe fonebone]

Perhaps I am just being nieve, but isn’t the southwest....... desert?

[Political Junkie Too]

How much of this "megadrought" is the result of a massive influx of people from Central America moving to the American southwest, and then drawing upon the water supply?

-PJ

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No idea, but it’s raining right now in the high desert...

[z3n]

There are some drought resistant species of trees. I am going off of memory from when I started reading about Acacia Tortilis quite a few years ago, and the plan to plant them in semi-arid parts of africa, with the theory being that if they get a good foothold over a large enough area, they help the soil get a biome back, as well as help the soils retain moisture both from that and their canopy, which then allows arid grasses and other plants to take hold, and various animals and insects to thrive (and aerate the new top soil layers) and so on.

That was quite a few years ago, but it appears they’ve had some success with that approach already.

Of course, Acacia Tortilis would be considered invasive in North America. But it just raises the question as to weather some semi-arid areas can be recovered.