News Section
Stories from Climate Central's Science Journalists and Content Partners

Is the West’s Dry Spell Really a Megadrought?

SAN FRANCISCO — The drought that has been afflicting most of the Western states for the past 13 years may be a “megadrought,” and the likelihood is high that this century could see a multi-decade dry spell like nothing else seen over the past 1,000 years, according to research presented at the American Geophysical Union Fall Meeting on Wednesday and Thursday.

Today, drought or abnormally dry conditions are affecting every state west of the Mississippi River and many on the East Coast, with much of the Southwest under long-term severe, extreme or exceptional drought conditions. While drought conditions nationwide are down this year, they remain entrenched in the West.

Lakeside homes, Lake Isabella, Calif. 
Click image to enlarge. Credit: Don Barrett/flickr

Since 2000, the West has seen landscape-level changes to its forests as giant wildfires have swept through the Rockies and the Sierra Nevada, bark beetles have altered the ecology of forests by killing countless trees and western cities have begun to come to terms with water shortages made worse by these changes as future snowpack and rainfall becomes less and less certain in a changing climate.

“The current drought could be classified as a megadrought — 13 years running,” paleoclimatologist Edward Cook, director of the Tree Ring Laboratory at Columbia University’s Lamont-Doherty Earth Observatory in Palisades, N.Y., said at an AGU presentation Wednesday night. “There’s no indication it’ll be getting any better in the near term.”

But the long period of drought the West is currently experiencing may not be a product of human-caused climate change, and could be natural, he said.

“It’s tempting to blame radiative forcing of climate as the cause of megadrought,” Cook said. “That would be premature. Why? There’s a lot of variability in the system that still can’t be separated cleanly from CO2 forcing on climate. Natural variability still has a tremendous impact on the climate system.”

Tree ring data show that decades-long droughts have occurred before humans started emitting greenhouse gases that fuel climate change. Long-lasting drought events have been tied to fluctuations in ocean conditions, which can alter large-scale weather patterns. For example, when the tropical Pacific Ocean is cooler than average, but the Atlantic Ocean is unusually mild — as has been the case during the past several years — there is a higher risk of drought in parts of the West and Central U.S. 

The area of the West that was affected by severe drought in the Medieval period was much higher and much longer than the current drought, tree ring data show.

It is “indeed pretty scary,” Cook said. “One lasted 29 years. One lasted 28 years. They span the entire continental United States.”

Click image to enlarge. 

Two megadroughts in the Sierra Nevada of California lasted between 100 and 200 years.

Cook is among the first to suggest that the current drought in the West is a megadrought, which is typically defined as a widespread drought lasting for two decades or longer, Cornell University assistant professor of earth and atmospheric sciences Toby Ault said during an AGU presentation Thursday.

But the idea that the current 13-year dry spell will be of similar magnitude of the megadroughts found in tree ring records is subject of debate.

“Are we in a megadrought? I guess we are,” Ault said. “They are a threat to civilization in the future.”

Ault is studying the probability that the U.S. will experience a megadrought this century on the order of no other dry period seen here at any time in the last millennium.

Data gleaned from tree rings and other sources show that the chance of a decade-long drought in the U.S. this century would be about 45 percent, and a multi-decade-long drought less than 10 percent, he said.  

“That’s not the whole picture because we’re going to see climate change in this century,” he said.

He said that the chances of a widespread multi-decade megadrought are high in the worst-case scenario, but he quoted University of Arizona geosciences professor Jonathan Overpeck to characterize the chances of megadrought in less severe scenarios: “It’s extremely non-negligible, the risk of prolonged multi-decadal megadrought.”

The bottom line: “The picture looks like we’re going to have to take this seriously,” Ault said.

Such dry spells would have severe implications for the nation’s water supply, and the U.S. is going to have to adapt and find smarter ways to cope, he said.

The current drought is occurring at a time of sweeping and abrupt changes in the nation’s forests as a result of both the extended dry period and human-caused climate change, said Lisa Graumlich, dean of the College of the Environment at the University of Washington.

Speaking at AGU on Wednesday, Graumlich said vast ecosystem changes are happening at an unprecedented scale across the country as tree mortality in Western forests is increasing dramatically, partly because bark beetles are spreading widely as summer warm seasons are longer than before.

“The time in which forests are burning in the West is much longer than it was in previous decades,” she said. “Forest insects are erupting across the West.”

Those changes and others including loss of sea ice, longer growing seasons in the Arctic, tundra being replaced by forests and shrubs, are occurring across an area scientists haven’t seen before, she said.

“We’re seeing right now ecosystem tipping points,” she said. “They’re at an unprecedented spatial scale. They’re related to timing of biological events that ecologists are finding surprising.”

Related Content 
Ongoing Coverage of Historic U.S. Drought 
Drought Has Ties to La Nina, with Global Warming Assist 
Wet Times are Masking New York's Real Drought Risk 
Epic Flooding Deals Colorado Drought Crippling Blow


By kermit
on December 12th, 2013

“It’s tempting to blame radiative forcing of climate as the cause of megadrought,” Cook said. “That would be premature.”

...seems an odd way of putting. albeit common. If a baseball player starts taking steroids and his homeruns etc. doubled the next year, it would be true that he would have only batted about half as many if he had not gone on the juice. But *all of his plays have to be seen in light of his athletic enhancement. So too, whether there would have been a 13 year megadrought or not with GW, it is nonetheless taking place in such a situation. Likely the bark beetles would have done only a fraction of the damage - how would the drought have looked under those conditions? And the higher heat increases the need of plants (and subsoil ecosystem, etc.) for water. And when it does rain, it is more likely to be a torrential downpour. Might there have been a drought without GW? Sure, but it wouldn’t have been the same.

Reply to this comment

By Eric Peterson (Front Royal, VA 22630)
on December 13th, 2013

Kermit, the megadrought has completely natural causes, namely La Nina.  The droughts in the 30’s and even the early 50’s were worse and had the same cause.  The only thing global warming does is add a degree or two to heat waves which exacerbates the drought in summer (with no effect in winter). 

There is a theory about enlargement of the Hadley cells that may have an impact on future drought.  The only manifestation of that so far is over the ocean and it is only slight.  On land geographic circulation trumps Hadley.

Reply to this comment

By john harkness
on December 13th, 2013

Abnormally dry or drought conditions now cover the West Coast of the contiguous US from border to border…

In the bigger picture:

“To have a good chance at staying under two degrees C, industrialised countries need to crash their CO2 emissions 10 percent per year starting in 2014, said Kevin Anderson of the Tyndall Centre for Climate Change Research at the University of Manchester.”

Our only choices now are:

1) dramatic, universal, coordinated action to drastically reduce mining and burning of naturally sequestered carbon; or

2) an essentially uninhabitable planet, probably within the lifetime of many living today.

Unfortunately, we seem to be picking #2.

Reply to this comment

By Sky McCain (Hartland, Devon, UK)
on December 14th, 2013

Surely it is fallacious to assume that weather conditions that have occurred in the past have a good chance of repeating.  This might be reasonable if most climate forcing and other conditions such as vegetation [millions of cattle wrecked the grasslands in the West and Southwest] and the Amazon rainforest [will be all but wiped out very soon] were still present.  Unfortunately, that is not the case.  Although three periods of drought in that region have been recorded over the last thousand years or so, the land recovered.  There is very little evidence that the necessary conditions are present or predicted which would bring back enough moisture to prevent the extreme desertification that the area is now headed for.  There is a saying –“What hath God wrought?”  We have no one to blame but ourselves.  We have squandered the gifts and assets of the very being we emerged from.  Surely we know not what we do.

Reply to this comment

By Fred Bauder (Crestone CO 81131)
on December 14th, 2013

I suppose my perspective is somewhat skewed by my location where we are having a wet year after about a decade of pretty dry years and one extremely dry year, 2002, the like of which has not seen since 1645. However, the pattern seems more or less normal; I should point out that I am 71. Looking in contemporary weather for signs of global warming or associated climate change is misguided. There is not a lot of difference between nightly lows of -15 and -18 in terms of life and ecology, but the statistical difference is huge. Look at statistics if you want to do serious analysis; for influencing public opinion, feel free to point out this or that unusual event, but keep in mind that that is political science, not climate science. See for a long range survey of flow in our local creek.

Reply to this comment

By Barn Cat (Neenah)
on December 14th, 2013

It’s pathetic that so many delusional people see weather facts through a false prism of man made global warming. The earth warms and cools on its own regardless of what mankind does.

Reply to this comment

By Mike Lince (Glendale, CA 91205)
on December 15th, 2013

The cause of the problem is less important than our response to the problem.  As the author points out, we will have to figure out how to allocate our water resources as they become more scarce.  One thing we will have to look at the impact of tourism, not only in the U.S., but around the world. 

For example, hotel patrons, no matter where they are in the world, typically will take luxurious showers and/or fill bathtubs the size of spa hot tubs, then drain them.  Think about the water table in Las Vegas and the waste of the precious water resources there being consumed in hotels and motels too numerous to mention.  The water from the Colorado River is insufficient to fill Lake Powell and Lake Mead reservoirs as water is funneled off to California and to water dozens of golf courses that have sprung up along the river in recent decades. 

When water becomes a scarce commodity, it will go to those willing to pay for it.  Metered water and the accompanying bill will likely become the new norm in the foreseeable future, especially in tourist spots, something that is probably past-due.

Reply to this comment

By Mitch (College Station TX 77840)
on December 15th, 2013

The earth does not warm and cool on its own—the earth warms and cools because of changes in its radiative budget. What causes the changes?
1) solar output
2) albedo
3) greenhouse gas heat trapping

Right now, solar energy reaching the earth is declining slightly from a peak in the 1960’s, albedo is declining because of warming-caused loss of sea ice and snow with little change in cloud, and greenhouse gases are increasing strongly because we burn fossil fuels. The lowered albedo and increase in greenhouse gases have caused significant increases in solar energy captured and retained by the earth.  Given those facts, would a rational person expect warming or not?

Reply to this comment

By Eric Peterson (Front Royal, VA 22630r)
on December 16th, 2013

“Right now, solar energy reaching the earth is declining slightly from a peak in the 1960’s, albedo is declining because of warming-caused loss of sea ice and snow with little change in cloud, and greenhouse gases are increasing strongly because we burn fossil fuels. “

Last one is definitely correct, although it should be pointed out that the added warming diminishes with each added amount of added CO2.  Albedo is basically flat, see for the outgoing (reflected) SW graph (dropping slightly but basically flat).  Clouds dictate albedo much more than ice (see same paper for tropical albedo changes.

Solar “energy” only declined recently.  The more pertinent measurement is solar activity.  Solar energy is reduced when solar activity is very high and also when it is very low.  But solar activity is also responsible for weather changes, for example high solar activity reducing the wintertime snow cover in Siberia.

Reply to this comment

By Phil Morris
on December 15th, 2013

Warming and cooling of the earth is well understood in terms of the Milankovitch cycles (changes of the Earth’s orbit around the sun) and unusual events such as the Pliocene Eocene Thermal Maximum (PETM) which occurred some 56 million years ago, and is thought to have been caused by massive outgassing of CO2 from volcanic activity.  The Earth’s temperature rose during the PETM by 6 Celsius over a period of 20,000 years.  Humans are now causing a massive outgassing of CO2 by burning fossil fuels, and with our current business as usual approach, we’re going to raising the Earth’s temperature by 6 Celsius in a span of 100 years!

Reply to this comment

By Atanacio Luna (Quail Valley, CA 92587)
on December 15th, 2013

The comments on this blog are well informed. There are a lot of errors in Pluvinergy, but it still seems to be a good solution for water and energy, or at least it the area for a short and long term solution for the US West, and subsequently for the world. It would be great to have people of the caliber on this website comment on the concept.
The current solution is RO desalination, and pricing to reduce use. This is not suitable, because RO takes a lot of energy, thus causes CO2, reduced use, is fine, but it can only go so far. Additional storage, and sub-ocean water reservoirs just seem too destructive; yet the alternative offered by the concept seems so appealing.

Reply to this comment

By Robert hansen
on December 16th, 2013

I just came onto your post and found it quite interesting. I am also associated with flood damage,water removal,and love to enjoy the stuff on the same as it’s rarely found on internet. Thanks again for writing such a good post.

Explore more about   water damage repair Las vegas

Reply to this comment

By Vincent (90274)
on December 17th, 2013

There is plenty of water in the world. It is simply unevenly distributed. Water sharing and water transfer are the solution, and at a fraction of the cost of desalination and other exotic Koch Brother-led schemes.

Reply to this comment

By Jim Steele (Californnia)
on January 2nd, 2014

The cool phase of the Pacific Decadal Oscillation (PDO) enables stronger high pressure systems in the Pacific that block moisture laden winds from reaching the American Southwest. The PDO’s 20 to 30 year cycles correlate well with past megadroughts. Too much hype has been given to CO2 caused climate change and the models that suggests drought will be caused by warmer summers. In contrast these recent droughts, and past megadroughts are due to drier winters. To build a more resilient environment, we should direct funding and research towards watershed restoration in order to hold the water on the land as long as possible. The current degradation of our streams and lost wetlands, as well as urbanization effects that try to run the water off the land as quickly as possible, dries the soils and reduces the soils heat capacity further, exacerbating droughts and heat waves. The overzealous focus on speculative human contributions has caused us to lose sight of these natural cycles of drought and funds have been misdrirected to create speculative future scenarios that MAY happen due to CO2 levels. The evidence is much stronger that we need to restore our watersheds! Controlling CO2 levels will never stop megadroughts.

Reply to this comment

By Robert hansen (nevada)
on February 15th, 2014

I just came onto your post and found it quite interesting. I am also associated with water removal san francisco,Water damage san francisco,and love to enjoy the stuff on the same as it’s rarely found on internet. Thanks again for writing such a good post.

Reply to this comment

By gerald mitchell (Gulfport, mississippi, 39503)
on August 30th, 2014

This may be hard for someone who is super educated to understand as it is so simple. The
Reason it has not rained out west is, we as a nation
Have not prayed to God and asked him for relief. I will begin to pray to Christ for rain, who will join me.
Though our Lord can and will help us maybe he has
Let this drought happen because of the way we all treat our environment causing such climate change.

Reply to this comment

Name (required):
Email (required):
Enter the word "climate" in the box below:

[+] View our comment guidelines.

Please note: Comment moderation is enabled. Your comment will not appear until reviewed by Climate Central staff. Thank you for your patience.