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Is Western U.S. experiencing a ‘megadrought’?

Posted on 16 August 2021 by greenman3610

This is a re-post from Yale Climate Connections

The Western U.S. is shattering drought records this summer. For the first time since the drought monitor was created, over 95% of the region is in drought. Near Las Vegas, Lake Mead – the largest reservoir in the U.S. – is at its lowest level since it was built.

“This is a bigger event than the 1950s drought in the Southwest or the Dust Bowl drought in the Central Plains,” says Benjamin Cook, a climate researcher at NASA, in this new video by independent videographer Peter Sinclair. “We have to go back at least 500 years before we find any event that’s even similar in magnitude.”

Scientists have found from clues in tree rings have that intense, prolonged droughts called “megadroughts” occurred regularly during the Middle Ages. Now the West may be in another megadrought period, this one made even worse by climate change.

Climate change makes historical drought patterns more intense by increasing temperatures and thus evaporation. This poses challenges to water supplies in the West as they come primarily from surface water like the Colorado River. Much of the population growth in the Southwest happened during the 1980s and 1990s, which were relatively wet decades.

Though there have been many improvements in water use efficiency in recent decades, they have not been able to match losses from drought.

“The Colorado River drains the entire Southwest – it’s about an eighth of the U.S. The river itself is actually not that big, it’s about the size of the Hudson and if you can imagine, it’s serving 40 million people,” says Brad Udall, a research scientist at Colorado State University’s Colorado Water Institute. “If it suffers, everyone suffers.”

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Comments 1 to 4:

  1. You should investigate your usual origin of humidity. Isn't it the Amazon? The tremendous destruction of the Amazon hinders water vapor escape to the north and the south, causing drought and fire. A hot evapotranspirating Amazon brings rain and lower temperatures from the higher layers of the troposphere. This year, the Amazon is cool itself and has no energy for maintaining the convectional water-export in the right height.

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    Moderator Response:

    [DB] This post is about megadroughts in the western US, not the Amazon.  For background on the effects of water vapor in the atmosphere (a feedback to temperature changes, not a driver of them), read both versions of this post and the comments section.  Please stay on-topic.

  2. A shorcut to understanding Western drought cycles can be found in William DeButs book "A Great Aridness", Oxford U., 2011. I think he reminds us that those cycles have been repeating about every 1,000 years since the end of the last ice age. The last "bad one" was around 1050 CE

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  3. William DeBuys...that pesky speller, sorry

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  4. I was curious what caused these megadrougts in the past, and found this:  "Civilization-Collapsing Megadroughts of Medieval Times Could Be in Store for a Warming Earth".

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