Understanding the historical probability of drought

While there is wailing and gnashing of teeth over the current midwest drought,

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We have this interesting piece from the American Society of Agronomy :

Droughts can severely limit crop growth, causing yearly losses of around $8 billion in the United States. But it may be possible to minimize those losses if farmers can synchronize the growth of crops with periods of time when drought is less likely to occur. Researchers from Oklahoma State University are working to create a reliable “calendar” of seasonal drought patterns that could help farmers optimize crop production by avoiding days prone to drought.

Historical probabilities of drought, which can point to days on which crop water stress is likely, are often calculated using atmospheric data such as rainfall and temperatures. However, those measurements do not consider the soil properties of individual fields or sites. 

“Atmospheric variables do not take into account soil moisture,” explains Tyson Ochsner, lead author of the study. “And soil moisture can provide an important buffer against short-term precipitation deficits.”

In an attempt to more accurately assess drought probabilities, Ochsner and co-authors, Guilherme Torres and Romulo Lollato, used 15 years of soil moisture measurements from eight locations across Oklahoma to calculate soil water deficits and determine the days on which dry conditions would be likely. Results of the study, which began as a student-led class research project, were published online Jan. 29 in Agronomy Journal. The researchers found that soil water deficits more successfully identified periods during which plants were likely to be water stressed than did traditional atmospheric measurements when used as proposed by previous research.

Soil water deficit is defined in the study as the difference between the capacity of the soil to hold water and the actual water content calculated from long-term soil moisture measurements. Researchers then compared that soil water deficit to a threshold at which plants would experience water stress and, therefore, drought conditions. The threshold was determined for each study site since available water, a factor used to calculate threshold, is affected by specific soil characteristics.

“The soil water contents differ across sites and depths depending on the sand, silt, and clay contents,” says Ochsner. “Readily available water is a site- and depth-specific parameter.”

Upon calculating soil water deficits and stress thresholds for the study sites, the research team compared their assessment of drought probability to assessments made using atmospheric data. They found that a previously developed method using atmospheric data often underestimated drought conditions, while soil water deficits measurements more accurately and consistently assessed drought probabilities. Therefore, the researchers suggest that soil water data be used whenever it is available to create a picture of the days on which drought conditions are likely.

If soil measurements are not available, however, the researchers recommend that the calculations used for atmospheric assessments be reconfigured to be more accurate. The authors made two such changes in their study. First, they decreased the threshold at which plants were deemed stressed, thus allowing a smaller deficit to be considered a drought condition. They also increased the number of days over which atmospheric deficits were summed. Those two changes provided estimates that better agreed with soil water deficit probabilities.

Further research is needed, says Ochsner, to optimize atmospheric calculations and provide accurate estimations for those without soil water data. “We are in a time of rapid increase in the availability of soil moisture data, but many users will still have to rely on the atmospheric water deficit method for locations where soil moisture data are insufficient.”

Regardless of the method used, Ochsner and his team hope that their research will help farmers better plan the cultivation of their crops and avoid costly losses to drought conditions.

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The full article is available for no charge for 30 days following the date of this summary. View the abstract at https://dl.sciencesocieties.org/publications/aj/abstracts/0/0/agronj2012.0295.

A peer-reviewed international journal of agriculture and natural resource sciences, Agronomy Journal is published six times a year by the American Society of Agronomy, with articles relating to original research in soil science, crop science, agroclimatology and agronomic modeling, production agriculture, and software. For more information visit: www.agronomy.org/publications/aj

The American Society of Agronomy (ASA) www.agronomy.org, is a scientific society helping its 8,000+ members advance the disciplines and practices of agronomy by supporting professional growth and science policy initiatives, and by providing quality, research-based publications and a variety of member services.

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39 thoughts on “Understanding the historical probability of drought

  1. Searching for solutions to problems arising from fickled Mother Nature seems like a much better place to invest research dollars than in the nonsensical doom-and-gloom model-generated studies we see all of the time from the climate science community. Throw money at Ochsner et al and other research groups like them–and pull it from the others.

  2. Bob Tisdale says:
    January 30, 2013 at 4:40 pm
    ==========
    I don’t know Bob, looks like more of the same to me….

    “Those two changes provided estimates that better agreed with soil water deficit probabilities.”

    Those two guesses provided guesses that better agreed with soil water deficit maybes.

  3. As the emphasis in education shifts away from knowledge to emotion and the visual, you will see more of these attempts to manipulate CAGW using every weather event with graphic visuals. A compelling narrative is easy to manufacture. It’s not like these guys don’t know any screen writers.

    But as I reminded today, the position of UNESCO for every school in the world, including privates. is that “Responding to climate change also starts in the classroom. Education is the way to shape new ways of thinking and forge new sustainable behaviour.

    Fundamentally, education is about values.”

    I have seen the software models for the classroom and the videos based on Jay Foresters systems theories and the Meadows work for the Club of Rome. Our K-12 students are about to spend years visualizing and being told that weather is climate and each of their behaviors has an effect overall.

    And everything that occurs will be spun based on how it can make people FEEL insecure unless the government takes action now. On their behalf of course.

  4. Latitude,

    At least these guys seem to have gotten their hands dirty and measured something in the real world. That does make it different than the climate catastrophists.

  5. My wife and I grew corn for our dairy herd in Rhodesia (now Zimbabwe) in the 70’s. The soil was granite sand and with summer rains. Whether we planted in dry lands or wetland margins was dependent on el nino and the winter rainfall in the South African Cape. Ken Alexander has written extensively on Southern African droughts. I would rather rely on some knowledge of my local climate than rely on soil moisture statistics.

  6. Owen in Ga says:
    January 30, 2013 at 5:03 pm
    =====
    I don’t give them that much credit…..people measure temps and ice thickness too

    This says computer models…
    “Those two changes provided estimates that better agreed with soil water deficit probabilities.”

  7. This research looks promising as they’re trying to identify what is important; not trying to make their measurement of something else (usually “noise”) important.

  8. Alarmists who have been pushing CAGW drought but have not published the science found in this article should attach a sign to the seat of the pants that reads “Kick Me.”

  9. I call Bullshit! I simply do not believe the U.S. Drought Monitor shown above.

    I live in an area shown to be in a moderate drought (D1 on the map), yet I can look out my window and see two ponds where the water table is at its normal winter high level. I work in an adjacent county (also shown to be in a moderate drought) where ponds and rivers show the water table is equally high. And nowhere in the area where I live and work is there any evidence of stressed vegetation or drought conditions of any sort. Just two days after the date shown on the U.S. Drought Monitor map I called the Forestry Service to request permission to burn outdoors. Permission was granted based on a ‘low’ risk of fire danger. To top it off, the forecast for tonight calls for thunderstorms and heavy rain.

    NOAA and the USDA obviously don’t think normal citizens know what a drought is.

  10. I once knew a Kansas farmer whose family survived the Dust Bowl and the drought of the 1950’s. Judging from the tales he told, last summer was child’s play, compared to the Dust Bowl. The 1950’s weren’t so bad, and were more like last summer.

    If you try to squeeze everything into a sixty year cycle, we are actually overdue for a drought.

    There were droughts before that land was settled that were worse than the Dust Bowl. If you can find a map from around the time of the Civil War, you’ll see some of our best wheat fields are called, “The Great American Desert.”

  11. Latitude says:
    January 30, 2013 at 4:57 pm
    Bob Tisdale says:
    January 30, 2013 at 4:40 pm
    ==========
    I don’t know Bob, looks like more of the same to me….

    “Those two changes provided estimates that better agreed with soil water deficit probabilities.”

    Those two guesses provided guesses that better agreed with soil water deficit maybes.

    Not at all the same. The actual soil moisture seems to be an obviously superior measure of the potential stress on food crops, since none, that I’m aware of, are aerophytes. So they get real, hard data and compare it to another set of real, hard data. No “guesses”. Though well correlated, they find a deficiency in the current method and attempt develop an “offset” (or model) that brings the current method in line with the better method so that the current method becomes a better reflection of true plant stress. No models, no handwaving, just good science. Maybe 5 or 10 years from now, when soil moisture data is more prevalent and there’s more of a track record, someone will revisit this work and refine it. People on this site need to stop this knee-jerk condemnation of every study that even hints of a model and LOOK AT THE WORK.

  12. Louis Hooffstetter says:
    January 30, 2013 at 6:12 pm
    ______________________
    We are in drought, here, for about 3 yrs. It is nothing like the dust bowl.
    It is not as bad as my childhood memories of the 50’s drought, either.

  13. D.J. Hawkins says…

    D.J. You seem to have more knowledge of this science than most posters (myself included). Please give us the benefit of your knowledge. Try as I may, I’m having a real hard time seeing this ‘drought’ in the area where I live. To me, high water tables and a complete lack of stressed vegetation is the opposite of a drought. What am I missing? Straighten me out. What is the current definition of drought, and how has it changed since the dust bowl of the the 1930s?

  14. As these things were well known 60 years ago, I am not sure what is “new” about this scientific work. Must be based on a new grant! Any good farmer on the “Great Plains” is well aware of the need to have enough soil moisture available for the crop to be planted or if a crop should be planted at all. This is old science dressed up in a new suit. pg

  15. I think that part of the problem is the ‘drought’ definition. As I understand it, an area doesn’t get out of a drought just by enjoying normal rainfall; an area isn’t out of drought conditions until they have made up ALL of the deficiencies from the previous reduced rainfall years.

  16. Indeed all drought models need to incorporate land use induced moisture changes with circulation variables. Climate models that are forced with known ocean surface temperatures are able to simulate reasonably well most past droughts such as the droughts of the 1950’s. Thus the PDO plus La Nina and the Atlantic Multidecadal Oscillation are important variable in drought prediction. However when they apply those same models to the Dust Bowl the models fail. As the wheat farmers ripped up a region of Buffalo Grass equal to the size of the State of Ohio, the natural ability of the land to hold moisture was lost. The surface feedbacks from drier surfaces altered the regional climate. While El Nino years brought heavy flooding to the Ohio RIver, the Dust Bowl drought was raging. Analysis of the Russian drought/heat wave also reported surface feedbacks that intensified the event. The models the Hansen uses to predict droughts are driven by the simplistic models that more CO2 makes more heat that evaporates the soil and thus Co2 causes more droughts. (See Dai, A., (2012) Increasing drought under global in observations and models. Nature Climate Change, DOI: 10.1038/NCLIMATE1633.) However those models failed miserably when predicting the last 50 years. The western USA was wetter from 1950 to 2000 but their models predicted drought while the same models predicted a wetter Sahel but Africa suffered drought.

  17. The abstract is not well written, the pfd seems much better and most of the immediate questions, why 15yrs, define drought, soil types and crop type are dealt with there, I have only skimmed it, but found my initial cynicism misplaced. This does not seem to be team science, rather an attempt to better define drought conditions and compare soil water content deficit to the average weather standard of drought.Looks as if drought claims would be reduced using their suggested standard.

  18. D.J. Hawkins says:
    January 30, 2013 at 6:20 pm

    Latitude says:
    January 30, 2013 at 4:57 pm
    Bob Tisdale says:
    January 30, 2013 at 4:40 pm
    ==========
    I don’t know Bob, looks like more of the same to me….

    “Those two changes provided estimates that better agreed with soil water deficit probabilities.”

    Those two guesses provided guesses that better agreed with soil water deficit maybes.

    Not at all the same. The actual soil moisture seems to be an obviously superior measure of the potential stress on food crops, since none, that I’m aware of, are aerophytes. So they get real, hard data and compare it to another set of real, hard data. No “guesses”. Though well correlated, they find a deficiency in the current method and attempt develop an “offset” (or model) that brings the current method in line with the better method so that the current method becomes a better reflection of true plant stress. No models, no handwaving, just good science. Maybe 5 or 10 years from now, when soil moisture data is more prevalent and there’s more of a track record, someone will revisit this work and refine it. People on this site need to stop this knee-jerk condemnation of every study that even hints of a model and LOOK AT THE WORK.

    Agreed. Models in themselves aren’t a problem. Only when assumptions that don’t match observation are built into the algorithms or the code is tinkered with unjustifiably do problems arise. Basically, the biases of the person developing the model or inputting data. I’m sure there are a few other instances where modeling could be a problem.

  19. Louis Hooffstetter says:
    January 30, 2013 at 6:12 pm
    I call Bullshit! I simply do not believe the U.S. Drought Monitor shown above.

    Does your D1 area have an “L” by it? The addition of the “S” & “L”, Short-term & Long-term, on the drought maps would allow the drought level to show on the map sooner & stay on the graph longer, even after moisture levels have returned to normal levels. This causes the maps to look worse than they did in the past for similar moisture conditions.

  20. I have been following the DM for quite a while. It has bothered me that the model does not have a centerline where you may have more moisture than normal or less. It is all skewed to either “normal” or drought. Odd.

  21. To Louis re not trusting US Drought Monitor, Palmer index was used in the recent 2012 “hottest” report by NOAA. May or may not be connected but here’s an article about Palmer Index saying it’s only valid for short term term purposes. This was also reported in a Nature Letters submission (relevant part is halfway into the paragraph). I don’t know the exact time frame Palmer is supposed to be useful in measuring, but it’s being used in error by the US government to predict long term drought. 11/19/12, “Study: Drought Trends, Estimates Possibly Overstated Due To Inaccurate Science,” washington.cbslocal.com

    “An index frequently used by scientists to predict drought trends – trends whose increased frequency and intensity were blamed on global warming – may have been misused, resulting in possibly inaccurate findings.

    The Palmer Drought Severity Index is primarily used by scientists to keep track of short-term drought trends. Researchers at Princeton University have now found that the index may not properly reflect what’s to come.

    The findings were published Thursday in the journal Nature, whose offices are located in Washington, D.C.” 11/15/12, “Little change in global drought over the past 60 years,” Nature, Justin Sheffield, Eric F. Wood & Michael L. Roderick

  22. My Dad lived through the Dust Bowl, though in north Iowa. And it was as dry this summer as he has ever seen. This summer was one of the hottest in this part of Minnesota yet recorded. So while it is hopefully a cycle, it is very severe, and I watch for ENSO to switch over, anxiously.

  23. Anthony – not a correct headline or label. According tot the map, the drought is in the Great Plains, not the Midwest.

    And Caleb is correct – it WAS called the Great American Desert. Gee, d’ya think that it might be dry sometimes in The Great American Desert?

    Steve Garcia

  24. It’s well known that you can mitigate the effects of drought through application of biological compost where crops grow. Well known.

    Perhaps if a new billion ton industry mixing cow shit, horse shit and organic waste emerged, the US farmers could mitigate potential drought through environmentally friendly means??

  25. Didn’t Theodor L predict a major drought in the US in 2018 and again for 2025? If we are repeating a 60 year cycle then it should be about like the ’50s again, not so? Let’s keep an eye on this as we explore other issues.

  26. Might be a good study IF they can keep away from climate alarmism and stick to the facts. I am sure that the US rainfall patterns are cyclic and follow the ENSO/PDO

  27. D.J. Hawkins says:
    January 30, 2013 at 6:20 pm
    People on this site need to stop this knee-jerk condemnation of every study that even hints of a model and LOOK AT THE WORK.
    ==================
    I did……….and it’s a bunch of hooey

  28. John Marshall @ January 31, 2013 at 2:51am:

    If they leave out the alarmism, they don’t get the money!
    So we’ll call it “gratuitous alarmism”.

  29. “Researchers from Oklahoma State University are working to create a reliable ‘calendar’ of seasonal drought patterns that could help farmers optimize crop production by avoiding days prone to drought.”

    I hope the research is better (and more important) than the press release makes it sound. “Avoiding days prone to drought”? Drought is not a daily or weekly phenomenon. How does a farmer avoid drought “days”? He needs to know if it’s going to be a monthly (irrigation) to seasonal (crop selection) event, and he needs it as a forecast if he’s going to make decisions.

    For example, in the Midwest and Plains crop selection will have to be made very soon. Knowing there is a soil moisture deficit now may make a farmer assume he should plant drought-tolerant crops. However, if he does so, and he has near to above-normal rainfall this year, he has lost an opportunity to plant regular hybrids that have a higher yield potential if there is no water stress.

    I agree that more detailed measurements of soil moisture, combined with soil characterization, should yield better estimates of the water deficit and resulting crop stress. The trouble is planning on a monthly or seasonal basis how to react to water deficits. This also requires good monthly to seasonal forecasts of precipitation amounts in addition to a fuller assessment of current conditions. I don’t think CPC offers actionable forecast capability here.

  30. Looks like reasonable work, to me. They look at rain-fall, relative humidity of the air, soil cubic cm of water per cubic cm of soil.

    In the 1930s, it was drought when the farmers noticed it hadn’t rained for over a week, saw low levels in the cricks and ponds, saw the leaves turning brown, then felt how the soil crumbled in their hands. It boils down to much the same, except now we’ve got numbers we can run statistics on.

  31. I do like the fact that they are exploring the soil moisture content in this study, and do think they should also take into consideration what farmers do to help the soil retain moisture for future crops. Many farmers here in the prairies do things like grow certain crops to help soil retain moisture.

    Like in Southern Saskatchewan, many grow flax now to increase that water retention of the soil itself. I did find this, but only an abstract, sounds like it is interesting in way of using crop rotations to help soil retain moisture.

    http://www.tandfonline.com/doi/abs/10.1080/03650340109366165

    I found this of interest too, as it gives a person a greater understanding of soi content.

    http://www.prairiesoilsandcrops.ca/articles/Issue-3_Article_8_scrn.pdf

    This paper mentions the Drought Palmer Severity Index, and how it should not be used for Western Canada, as it is based from classifications of conditions in central Iowa, and western Kansas, mentioned on page 11 of this paper itself. Still great reading material even though it mentions the dreaded words “climate change”.

    http://www.parc.ca/mcri/pdfs/papers/iacc040.pdf

    There is tons of great reading material. I found this of interest also as it talks about the equations used to map the soil water curve, in this paper here. The data they used was experimental data and not models.

    http://www.soilvision.com/downloads/docs/pdf/research/cangeoequa.pdf

  32. There is nothing wrong with using a model as long as the science behind it is sound. In engineering we use models to predict stresses on structures without having to build a prototype. Often the model may be created using data from testing a scale model of the structure, but behind it all are sound, proven engineering laws. Nobody has created a working atmospheric model as nobody fully understands have everything interacts. Sadly, billions of many currencies are being wasted trying to prove CO2 AGW link that looks less and less likely with every cooling year.

    At least this is trying to produce useful data that will be important now that we have entered a new little ice age. Food production is going to be under pressure as growing ranges shrink and weather gets more variable.

  33. Perhaps the greatest question to be addressed is the ability of the soil to absorb and retain water in the root growing zone under various conditions and scenarios, since the manifestations of drought are greatest when the soil’s ability to retain moisture is impaired.

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