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Study: Southwest U.S. In Midst Of Megadrought Like No Other

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Southern Nevada has been in a drought for about 20 years.

But now, we’re learning this isn’t just drought – it’s a megadrought. That’s a one in 500 years drought.

A study published in the journal "Science" concluded it’s not like megadroughts of the past.

A. Park Williams is the lead researcher on the project. He's a professor with Lamont-Doherty Earth Observatory of Columbia University. He explained that scientists can track droughts easily through the growth rings in trees. 

“Because trees live for hundreds of years or even over a thousand years we can use these tree ring records as proxies for past soil moisture and that’s how we see the megadrought,” he said.

He said there isn't an exact definition of a megadrought but scientists know it when they see it.

“When you see it in the tree ring record, you know it," Williams said, "It looks very different from anything modern society experienced during its period of rapid growth in the 1800s and 1900s. These megadroughts were far more severe than anything we saw during that time and much longer-lasting.”

Megadroughts are distinctive because of how much of a region they cover and how long they last. 

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Williams explained megadroughts are usually caused by a cluster of climate events from the Pacific Ocean known as La Nina, which makes the Southwestern U.S. drier.

The megadrought we're currently experiencing started the same way but climate change is making it worse.

“However, climate change is having a really important role here," he said, "The temperature in the western U.S. is somewhere between 2.5 and 3.0 degrees Fahrenheit warmer today than it would be without human-caused climate change. Those warmer temperatures dry things out.”

Williams said because of human-caused climate change what would have been a "garden variety" drought, “has been amplified into a drought that is as strong as the worst droughts of the last millennium because of this extra heat from human-caused climate change.”

While Southern Nevada, California and Arizona experienced a slightly wetter than usual winter, Williams said that doesn't take away from the fact that the region as a whole is in a drought that is on pace with other known megadroughts.

“The last 20 years are on average about as dry as the worst 20 year periods of the worst megadroughts, including that most recent 1500’s drought," he said, "The difference is those megadroughts had an opportunity to end, and as a result, those megadroughts lasted longer. This drought has not yet ended. It is still in its infancy.”

Megadroughts lasted anywhere from 30 to 100 years and only time will tell how long this one will last in the Southwest, Williams said.

With that in mind, Williams thinks it is important to be mindful of water, which is the limiting resource for living in the West. 

He pointed out that since the 1930s more water from the Colorado River has been promised to states than flows through it on an average year.

“One thing that should happen in the West is we need to get more realistic about how much water is available today and how much is going to available in the future,” he said.

Over the centuries, water, or the lack of it, has been the biggest factor to shape where life can flourish and where it can't. Williams pointed out that 6,000 years ago the Sahara Desert was green and littered with water holes and the American Southwest was bone dry - drier than it is today.

“Earth has the capability to really turn on us when it comes to water and being able to anticipate those changes is really, really important,” he said.

Guests

A. Park Williams, researcher, Lamont-Doherty Earth Observatory of Columbia University 

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