How Long Will the Naturally Caused Drought Persist in the U.S.?


Anthony Watts recently published a post about the current drought in the U.S. titled To NCDC: We Haven’t Seen an El Nino since 2009/10, What Do You Expect? It reminded me and other persons (see Don B’s comment here) of Roger Pielke, Sr.’s post last year Perspective On The Hot and Dry Continental USA For 2012 Based On The Research Of Judy Curry and Of McCabe Et Al 2004. Roger, Sr. initially referred to a presentation by Judith Curry (Climate Dimensions of the Water Cycle). Judith discussed the presentation in her blog post here. Her presentation included a group of drought maps from McCabe et al (2004).

McCABE ET AL (2004)

McCabe et al (2004) Pacific and Atlantic Ocean influences on multidecadal drought frequency in the United States is an examination of the impacts of the Atlantic Multidecadal Oscillation and Pacific Decadal Oscillation on drought in the United States. Full paper is here. The abstract reads:

More than half (52%) of the spatial and temporal variance in multidecadal drought frequency over the conterminous United States is attributable to the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO). An additional 22% of the variance in drought frequency is related to a complex spatial pattern of positive and negative trends in drought occurrence possibly related to increasing Northern Hemisphere temperatures or some other unidirectional climate trend. Recent droughts with broad impacts over the conterminous U.S. (1996, 1999-2002) were associated with North Atlantic warming (positive AMO) and northeastern and tropical Pacific cooling (negative PDO). Much of the long-term predictability of drought frequency may reside in the multidecadal behavior of the North Atlantic Ocean. Should the current positive AMO (warm North Atlantic) conditions persist into the upcoming decade, we suggest two possible drought scenarios that resemble the continental-scale patterns of the 1930s (positive PDO) and 1950s (negative PDO) drought.

My Figure 1 is Figure 5 from McCabe et al (2004). The two right-hand maps indicate drought conditions (in red) during positive AMO conditions. Map c is for positive AMO and positive PDO conditions, and map d indicates positive AMO with negative PDO conditions.

Figure 1

Figure 1

The AMO went positive in the mid-1990s, and it is still positive. Considering that its “cycle” varies from 50 to 80 years, it’s difficult to tell when an AMO cycle peaks and starts its decline, so we may easily have another couple of decades of positive AMO-induced drought in store. Refer to Figure 2, which is a comparison of the Atlantic Multidecadal Oscillation Index data from the NOAA ESRL (here), and the Pacific Decadal Oscillation Index (here). The AMO data has been standardized (divided by its standard deviation) to put it in the same format as the PDO index data. And both datasets have been smoothed with 121-month filters, which is one of the standard formats provided by the ESRL for their AMO data.

Figure 2

Figure 2

Looking at the two datasets since 1979 smoothed with 13-month filters, Figure 3, the PDO has cycled quite strongly between positive and negative values since 1998. I’ve also included standardized NINO3.4 sea surface temperature data in the graph. The NINO3.4 data are a commonly used index for the strength, frequency and duration of El Niños (positive spikes) and La Niñas (negative spikes). Much of the yearly variability in the PDO data are, of course, responses to El Niño and La Niña events, as are many of the AMO wiggles. The AMO rise may have slowed somewhat, again difficult to tell, but the PDO data has been trending toward cold PDO conditions. This additional long-term variation in the PDO data is caused by changes in wind patterns and the interdependent changes in sea level pressure in the North Pacific.

Figure 3

Figure 3

In their FAQ webpage here, NOAA answers in response to the question “Can we predict the AMO?” (my boldface):

We are not yet capable of predicting exactly when the AMO will switch, in any deterministic sense. Computer models, such as those that predict El Niño, are far from being able to do this. What is possible to do at present is to calculate the probability that a change in the AMO will occur within a given future time frame. Probabilistic projections of this kind may prove to be very useful for long-term planning in climate sensitive applications, such as water management.

Based on the results of McCabe et al (2004), drought conditions will likely cycle between maps c and d in their Figure 5 (my Figure 1) until the AMO decides to shift. Refer again to the closing sentence of the McCabe et al (2004) abstract:

Should the current positive AMO (warm North Atlantic) conditions persist into the upcoming decade, we suggest two possible drought scenarios that resemble the continental-scale patterns of the 1930s (positive PDO) and 1950s (negative PDO) drought.

McCabe et al (2004) has been cited more than 400 times by other peer-reviewed papers.


Another paper that describes the influence of the Atlantic Multidecadal Oscillation on precipitation in the United States is Enfield et al (2001) The Atlantic multidecadal oscillation and its relation to rainfall and river flows in the continental U.S. The abstract of Enfield et al (2001) reads (my boldface):

North Atlantic sea surface temperatures for 1856-1999 contain a 65-80 year cycle with a 0.4 _C range, referred to as the Atlantic Multidecadal Oscillation (AMO) by Kerr [2000]. AMO warm phases occurred during 1860- 1880 and 1940-1960, and cool phases during 1905-1925 and 1970-1990. The signal is global in scope, with a positively correlated co-oscillation in parts of the North Pacific, but it is most intense in the North Atlantic and covers the entire basin there. During AMO warmings most of the United States sees less than normal rainfall, including Midwest droughts in the 1930s and 1950s. Between AMO warm and cool phases, Mississippi River outflow varies by 10% while the inflow to Lake Okeechobee, Florida varies by 40%. The geographical pattern of variability is influenced mainly by changes in summer rainfall. The winter patterns of interannual rainfall variability associated with El Niño- Southern Oscillation are also significantly changed between AMO phases.

Enfield et al (2001) has been cited more than 700 times.


The draft of the upcoming NCADAC Climate Assessment Report was released for comment earlier this year. The NCADAC stands for “National Climate Assessment and Development Advisory Committee”. From that NCADAC webpage (my boldface):

The NCADAC, whose members are available here (and in the report), was established under the Department of Commerce in December 2010 and is supported through the National Oceanic and Atmospheric Administration (NOAA). It is a federal advisory committee established as per the Federal Advisory Committee Act of 1972. The Committee serves to oversee the activities of the National Climate Assessment. Its members are diverse in background, expertise, geography and sector of employment. A formal record of the committee can be found at the NOAA NCADAC website.

The National Climate Assessment is discussed here (my boldface):

The National Climate Assessment (NCA) is being conducted under the authority of the Global Change Research Act (GCRA) of 1990. The GCRA requires a report to the President and the Congress every four years that integrates, evaluates, and interprets the findings of the U.S. Global Change Research Program (USGCRP). The Act requires assessment of the effects of global change (both human-induced and natural) on the natural environment, agriculture, energy production and use, land and water resources, transportation, human health and welfare, human social systems, and biological diversity. The time periods for analysis include current conditions as well as projections of major trends for the subsequent 25 to 100 years.

The full draft of the NCADAC report is a large file (147MB) and it’s available here.

Drought is logically one of the topics of the NCADAC draft report. The word drought appears more than 400 times in it. References to drought begin with the alarmist speculations in the opening paragraph of the Executive Summary:

Climate change is already affecting the American people. Certain types of weather events have become more frequent and/or intense, including heat waves, heavy downpours, and, in some regions, floods and droughts. Sea level is rising, oceans are becoming more acidic, and glaciers and arctic sea ice are melting. These changes are part of the pattern of global climate change, which is primarily driven by human activity.

The references to drought end with the last two sentences of the final page of text:

Extreme summer ice retreat also appears to be increasing the persistence of associated mid-latitude weather patterns, which may lead to an increased probability of extreme weather events that result from prolonged conditions, such as drought, flooding, cold spells, and heat waves (Francis and Vavrus 2012). However, the combination of interannual variability and the small sample of years with extreme ice retreat make it difficult to identify a geographically consistent atmospheric response pattern in the middle latitudes.

The NCADAC’s politically motivated attribution of extreme weather events to human activity, of course, contradicts the findings of the IPCC’s Special Report. As Roger Pielke, Jr., reported in his blog post A Few Comments on the IPCC SREX Report:

Most importantly, the IPCC should be congratulated for delivering a message that cannot have been comfortable to deliver. The IPCC has accurately reflected the scientific literature on the state of attribution with respect to extreme events — it is not there yet, not even close, for events such as floods, hurricanes, tornadoes, bushfires and on other topics there remain enormous uncertainties. That is just the way that it is, so that is indeed what the IPCC should have reported.

Droughts are one of those other topics.


The data-based analyses like Enfield et al (2001) and McCabe et al (2004) found the Atlantic Multidecadal Oscillation to be a major contributor to drought conditions in the United States, so one would think the Atlantic Multidecadal Oscillation would be a frequent topic of discussion in the NCADAC report. It was mentioned once, and that reference had nothing to do with drought.


Under the heading of “29. Research Agenda for Climate Change Science” and subheading of “Research Goal 1 – Deepen understanding of the climate system, feedbacks, and impacts” the NCADAC draft report states:

High priority research needs include…

…Improved understanding of the interactions of climate change and natural variability at multiple time scales, including seasonal to decadal changes (and consideration of the El Niño Southern Oscillation, Pacific Decadal Oscillation, North Atlantic Oscillation, etc.), extreme events (hurricanes, droughts, and floods), potential changes in ocean circulation related to climate change, and the global transfer of heat laterally and toward the poles;

That of course raises a couple of fundamental questions: If research is needed to improve the “understanding of the interactions of climate change and natural variability at multiple time scales”, how then is the NCADAC so certain that weather, which we’ve experienced before and will continue to experience in the future, is now being forced by manmade greenhouse gases to the point where carbon dioxide has become the primary cause of extreme weather, including drought, in the United States? Shouldn’t natural variability have been studied already so that researchers were confident about its influences? Better yet, shouldn’t existing data-based studies of the influences of natural variability on U.S. climate be at least acknowledged in the NCADAC report?

Not too surprisingly, the draft of the NCADAC report does not mention McCabe et al (2004) or Enfield et al (2001).


The recent drought conditions in the United States may persist for another few decades based on the mode of the Atlantic Multidecadal Oscillation. If the drought does last for another couple of decades, it would impose a significant load on water resources in the United States, which are already being strained in some parts of the country. The scientists behind the NCADAC apparently have no interest in existing research into the impacts on drought of known modes of natural variability. Instead they elect to promote a political agenda. No surprise there.

At the minimum, shouldn’t the NCADAC report include a warning to the country about the possibility of a naturally caused persistent drought over the next few decades? A warning that would allow state and federal agencies to attempt to adapt and take measures to help the people of this country live with the upcoming water deficits?

Climate science since the 1980s has been dominated by government-funded, computer-generated speculation about the assumed hypothetical impacts of manmade greenhouse gases, not about the factors that actually drive climate.

If the vast majority of the funding is going to the agenda-driven, carbon dioxide-centered research, is it any wonder the majority of the papers and their authors support the hypothesis of human-induced global warming and climate change? If my income and well-being depended on that government funding, I too would be peddling the evils of carbon dioxide just like all the other snake-oil salesmen.

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June 16, 2013 8:24 pm

How Long Will the Naturally Caused Drought Persist in the U.S.?
Only between the naturally caused flash floods.

Richard M
June 16, 2013 8:29 pm

The most likely situation is the AMO will remain positive for at least 5 years. We should see similar conditions to the 1950s. After that the big question is will we see a solar minimum that extends for years and years. That could have a major impact on all the cyclic patterns.

John F. Hultquist
June 16, 2013 9:42 pm

Thanks Bob.
The U. S. political types and their creations (NCADAC, and many others) seem interested in an agenda that is non-science in its origin. Follow the money. Folks that actually have to make a profit to sustain their families operate on a different level. The WSJ recently noted a shift of corn planting to the north.
This was in the print edition but is available on line:
June 13, 2013, 9:30 p.m. ET by Owen Fletcher
U.S. Corn Belt Expands to North
Warmer Climate, Hardier Seeds Help Crop Gain on Wheat, North Dakota’s Staple
The shift, which is occurring in northern Minnesota and Canada’s Manitoba province as well, shows how warming temperatures and hardier seeds are enabling farmers to grow corn in areas once deemed inhospitable to the crop.
And . . .
In Kansas, farmers are expected to plant 2% fewer acres with corn and instead grow more sorghum, a less water-intensive grain.
The hardier plants and the farming techniques are on target but major investments based on the assumption that warmer temperatures will continue might end badly.

June 16, 2013 10:00 pm

What is “conterminous” supposed to mean? It does not make any sense here, applying the definitions from or other dictionaries…

June 16, 2013 10:11 pm

Sharing a common boundary.
Having the same area, context, or meaning.
contiguous – conterminal – neighbouring – neighboring

Ian Cooper
June 16, 2013 10:36 pm

Regarding Figure 2, are you able to tell me the number for the PDO for the first quarter of 2013? I have just plotted the dates of the four previous El Nino neutral/La Nada droughts in my part of New Zealand onto the blue line of the PDO as shown. FYI those dtaes are (austral summer) 1947-48, 1969-70, 1977-78. and 2002-03. Have a look for yourself. In reality the four droughts listed and the one that occurred here last southern summer were amazingly similar, but not identical, and I believe for similar reasons.

June 16, 2013 11:28 pm

AMO might be driving arctic sea ice. At least the more recent AMO increase seems to correlate with the decrease shown on the Sea Ice Page and clearly the impact is mainly in the North Atlantic around Svalbard and Novaya Zemlya. See figure “Arctic Sea Ice Extent With Anomaly”.
OT: What’s with the creepy lady on the swing?

Bloke down the pub
June 17, 2013 2:26 am

They will create a state of mind in the Administration similar to that created in Australia, where everyone knew they were in a permanent drought, up to and past the time that large chunks of the place were under water.

June 17, 2013 2:27 am

Why is it that so many genuine Warmists think that droughts are something new in N. America and caused by the trace gas carbon dioxide? If the following were to occur today they would NO DOUBT be blamed on man’s eeeeevil co2.

Abstract – Steven L. Forman et. al. – May 2001
Temporal and spatial patterns of Holocene dune activity on the Great Plains of North America: megadroughts and climate links
Periods of persistent drought are associated with a La Niña-dominated climate state, with cooling of sea surface temperatures in the tropical Pacific Ocean and later of the tropical Atlantic Ocean and the Gulf of Mexico that significantly weakens cyclogenesis over central North America.
Abstract – Scott Stine – 16 June 1994
Extreme and persistent drought in California and Patagonia during mediaeval time
California’s Sierra Nevada experienced extremely severe drought conditions for more than two centuries before ad ~ 1112 and for more than 140 years before ad ~ 1350…I also present similar evidence from Patagonia of drought conditions coinciding with at least the first of these dry periods in California….
Abstract – Connie A. Woodhouse et. al. – December 1998
2000 Years of Drought Variability in the Central United States
…..Historical documents, tree rings, archaeological remains, lake sediment, and geomorphic data make it clear that the droughts of the twentieth century, including those of the 1930s and 1950s, were eclipsed several times by droughts earlier in the last 2000 years, and as recently as the late sixteenth century. In general, some droughts prior to 1600 appear to be characterized by longer duration (i.e., multidecadal) and greater spatial extent than those of the twentieth century……;2
Abstract – Brian F. Cumming et. al. – 2 December 2002,
Persistent millennial-scale shifts in moisture regimes in western Canada during the past six millennia
…After periods of relative stability, abrupt shifts in diatom assemblages and inferred climatic conditions occur approximately every 1,220 years….

June 17, 2013 2:39 am

have a go at what the Australian climate commission has to say about Australias wheatbelt

Paul Vaughan
June 17, 2013 3:44 am

“What is possible to do at present is to calculate the probability that a change in the AMO will occur within a given future time frame.”
Caution: That’s a conditional probability. It’s based on untenable assumptions. As such, it’s just a gamble — a potentially costly one. There will be no magical statistical substitute for deeper multivariate awareness — the only sensible path forward. We need to buckle down and do the careful exploratory work, roundly ignoring all criticism.
One thing I can add: We are flatly NOT currently in the same area of multivariable space that we were in during the 1930s. Several key variables are in completely different territory — and there’s no use pretending as many do that climate change is monotonically uniform throughout the year. I can give one key example of a time when climate change went in starkly contrasting opposite directions at different times of the year: the 1930s. Perhaps the time has become ripe to share some new illustrations of seasonally contrasting early-to-mid 20th century SOI & CET patterns …that later systematically vanished…

June 17, 2013 5:08 am

As I said before; it will be only six or seven years before the droughts on the great plains begin in full. This is what my records also show. Unfortunately there is too much money in agw to make them see what Joseph saw 5000 years ago simply by observing wind direction and the retreat of the Nile rIver.

Frank K.
June 17, 2013 6:00 am

My only question is this. What is NCADAC’s budget? What a colossal waste of our tax money!

June 17, 2013 6:14 am

I don’t know if anyone else has noticed that PDO has gone positive [o.08] again . AMO is still positive [0.134] . IF both stay positive in a sustained way , we are setting up the conditions similar to the 1930’s drought as per the McCabe et al [2004]paper. There could be drought in the northern 2/3 of US this summer but not in the southwest. Interestingly AMO has been declining since Nov/2012 and PDO has been going less positive since September 2012, so things are shifting again.

June 17, 2013 6:31 am

My previous post should read .PDO has been going less negative[ not less positive] since September 2012 from -2.21 to +0.08. Sorry for the wrong statement..

June 17, 2013 8:55 am

Could this be what led to the dust bowl? Except this time, with modern agriculture methods and irrigation, the conditions leading to vast dust storms won’t happen.

June 17, 2013 10:50 am
Don’t remember the Atlantic looking like that this time last year

June 17, 2013 10:51 am
Ian Cooper
June 17, 2013 2:45 pm

Paul Vaughn, June 17, 3.44a.m.
Your comments about climate variability throughout any given year especially in the 1930’s are very interesting. Before the locally infamous wet year of 2004 took out the record for the wettest year since records began in Palmerston North, New Zealand, 1935 held that record. What had always puzzled me though was the fact that 1935 was also the sunniest year in the 85 year record!
The months of Feb,May,June,Aug,and Oct were very wet while the late autumn-early winter months May-July were 13% above the long term mean in sunshine hours, while August & September were 44% above the same mean. The year finished with a december that was 16% above the long term average in sunshine.
The (austral) summers of 1934-35 & 1937-38 are still the hottest using T-Max in the recorded period. The summer of 1935-36 also produced what is reputed by some to be the most devastating ex-tropical storm to make landfall in New Zealand during the 20th century, and my home town copped the brunt of that. The coldest T-Max winters occurred during this period as well, 1930,1931 & 1941.
When people talk about climate extremes nowadays I like to point out just how extreme it was when my father was born, not that he still remembers the details of how hot the summers were when he was a kid, compared to the variations we have today.

James at 48
June 17, 2013 4:49 pm

Based on paleo data, we who currently reside in NoAm have no idea (other than old Native American legends) just how bad it can be.

Janice Moore
June 17, 2013 6:38 pm

[v. a v. Henry P. at 5:08AM]
Re: Joseph’s Prediction of 7 Years of Plenty Followed by 7 Years of Famine
The only record we have of Joseph’s thinking process on this event is the Jewish history book called in English, “Genesis.” In chapters 41 – 47 the famine is mentioned many times. There is no mention of Joseph basing his prediction on anything but what God told him about Pharaoh’s dreams. That is, the meaning of the 7 skinny cows eating up the 7 fat cows and the 7 thin heads of grain swallowing up the 7 fat heads of grain.
God, according to the only historical record we have, and not Joseph’s observations, told Joseph the famine was coming.
[Yes, yes, O Wonderful WUWT scholars, I realize that many of you think Genesis is fiction — I’m simply correcting the mistake about what Genesis actually says.]
I certainly don’t think God is telling the Humans-Control-Earth’s-Climate people anything. At least, not anything they are willing to listen to.
THEIR “predictions” are: 1) intentional lies; OR 2) pitifully inept attempts at “science.”

June 17, 2013 8:17 pm

How about we disband the NCADAC and use the money to educate people in droughty areas on ways to do things that are more conservative of water? You can have quite beautiful gardens that you never have to water – the plants get by on little (like sages). Astroturf can make a great lawn (and fire ants have a hard time with it). 😉 I am sick to death of these drum beaters being paid by my taxes.

Janice Moore
June 17, 2013 10:18 pm

Uh, Hoser? Sorry old boy, but, …. well, no one can see her except you.
No more blogging-while-under-the-influence for awhile, okay, buddy?
LOL. I’m guessing you got a weird ad none of the rest of us (well, I at least haven’t seen that one) got. I think the ads in the box just above the Comments section are based on your own internet search history. Mine don’t always seem to be on target, though. Lady on a swing, eh? [:)] Who knows.

Janice Moore
June 17, 2013 10:29 pm

HOSER!! I just saw the lady on the swing! She was over on the ERL rejects Richard Tol’s paper thread!
Looks like she’s in a creepy circus act or something. Part of the Ringling Bros. and Barnum and Bailey’s Envirocircus where “a sucker is [fleeced] every minute.”

Mario Lento
June 18, 2013 12:13 am

Janice and Hoser: It’s the Nokia smart phone with “better” pictures in low light….

Brian H
June 18, 2013 12:33 am

Would you indeed be shilling for the consensus if your income mostly depended on it? Are we then totally reliant on those of independent means and retirees to report sceptically?

Janice Moore
June 18, 2013 12:27 pm

Thanks, Mario. [:)]
I guess that creepy looking woman doesn’t look so creepy to whomever Nokia is targeting with that ad.

June 18, 2013 12:52 pm

perhaps you should read the story again
especially Genesis 41:23 and vs 27
the Egyptians were famous for keeping records of the flooding of the Nile
and a variation within the solar cycle can be picked up
My own story is here
I am sure my story is as important as was Joseph’s then and Bob’s now
Unfortunately, no one is listening (yet…)
It seems the pressure is important (that Bob ignored here in this post)
You can see this in Willis post on the PDO.
If there is no pressure difference, there is no “weather” (read: rain)

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