Previous rules of thumb for climate change worsened wet/dry turned upside down

You might remember this claim from Australia’s CSIRO back in 2012 published in the Sydney Morning Herald. It’s been busted by a new paper:

wet-dry-climate-change

The wet gets wetter, the dry dryer, thanks to climate change

WET areas have become wetter and dry areas drier over the past 50 years due to global warming, a study of the saltiness of the world’s oceans by a team including CSIRO researchers has shown. The intensification of rainfall and evaporation patterns, which is occurring at twice the rate predicted by climate change models, could increase the incidence and severity of extreme weather events.

From ETH Zurich on Sept 14th:

Based on models and observations, climate scientists have devised a simplified formula to describe one of the consequences of climate change: regions already marked by droughts will continue to dry out in the future climate. Regions that already have a moist climate will experience additional rainfall. In short: dry gets drier; wet gets wetter (DDWW).

However, this formula is less universally valid than previously assumed. This was demonstrated by a team of ETH climate researchers led by Peter Greve, lead author of a study recently published in Nature Geoscience. Traditional analyses use metrics that can comprehensively describe climate characteristics above the ocean, but is problematic over land. While this fact was mentioned in said studies, scientific and public discourse has overlooked this aspect so far. In their new study, the ETH researchers in the group headed by Sonia Seneviratne’s, professor for land-climate dynamics, take into account the specific climatic properties of land surfaces, where the amount of available water is limited when compared with the ocean.

In their analysis, the climate scientists made use of measured data compiled solely on land, such as rainfall, actual evaporation and potential evaporation. The data derived from various sources was combined by Greve and his co-authors – this allowed them to extract trends in terms of a region’s humidity and dryness. Furthermore, the researchers compared data from between 1948 and 1968 and 1984 to 2004.

Half of the surface areas show divergence

The evaluation shows no obvious trend towards a drier or wetter climate across three-quarters of the land are. There are solid trends for the remaining quarter. However, only half of this surface area follows the DDWW principle, i.e. one-eighth of the total landmass, while the trends seem to contradict this rule over the other half.

Some regions which should have become wetter according to the simple DDWW formula have actually become drier in the past – this includes parts of the Amazon, Central America, tropical Africa and Asia. On the other hand, there are dry areas that have become wetter: parts of Patagonia, central Australia and the Midwestern United States.

Nevertheless, the ‘wet gets wetter’ rule is largely confirmed for the Eastern United States, Northern Australia and northern Eurasia. ‘Dry gets drier’ also corresponds to indications in the Sahel region, the Arabian Peninsula and parts of Central Asia and Australia.

However, the DDWW principle does still applies to the oceans. “Our results emphasise how we should not overly rely on simplifying principles to asses past developments in dryness and humidity,” Greve explains. This can be misleading, as it cannot do justice to the complexity of the underlying systems.

###

The paper:

Greve P, Orlowsky B, Müller B, Sheffield J, Reichstein M, Seneviratne SI. Global assessment of trends in wetting and drying over land. Nature Geoscience, Advanced Online Publication 14th September 2014. DOI: 10.1038/ngeo2247 http://dx.doi.org/10.1038/ngeo2247

Changes in the hydrological conditions of the land surface have substantial impacts on society1, 2. Yet assessments of observed continental dryness trends yield contradicting results3, 4, 5, 6, 7. The concept that dry regions dry out further, whereas wet regions become wetter as the climate warms has been proposed as a simplified summary of expected8, 9, 10 as well as observed10, 11, 12, 13, 14 changes over land, although this concept is mostly based on oceanic data8, 10. Here we present an analysis of more than 300 combinations of various hydrological data sets of historical land dryness changes covering the period from 1948 to 2005. Each combination of data sets is benchmarked against an empirical relationship between evaporation, precipitation and aridity. Those combinations that perform well are used for trend analysis. We find that over about three-quarters of the global land area, robust dryness changes cannot be detected. Only 10.8% of the global land area shows a robust ‘dry gets drier, wet gets wetter pattern, compared to 9.5% of global land area with the opposite pattern, that is, dry gets wetter, and wet gets drier. We conclude that aridity changes over land, where the potential for direct socio-economic consequences is highest, have not followed a simple intensification of existing patterns.

The paper points out that only about 10% of land area follow the old rule:

“assessments of observed continental dryness trends yield contradicting results. The concept that dry regions dry out further, whereas wet regions become wetter as the climate warms has been proposed as a simplified summary of expected as well as observed changes over land, although this concept is mostly based on oceanic data.

We find that over about three-quarters of the global land area, robust dryness changes cannot be detected. Only 10.8% of the global land area shows a robust ‘dry gets drier, wet gets wetter’ pattern, compared to 9.5% of global land area with the opposite pattern, that is, dry gets wetter, and wet gets drier. We conclude that aridity changes over land, where the potential for direct socio-economic consequences is highest, have not followed a simple intensification of existing patterns.”

The paper joins at least one other finding the “wet gets wetter and dry gets drier” meme is false on local scales, although this belief is still commonly held in the climate science community. American Meteorological Society President Dr. Marshall Shepherd tweeted a few months ago that one of his “toughest challenges” is “explaining to linear thinkers that dry/drier, wet/wetter is expected. They want either or” :

So much for certainty.

(h/t to The Hockey Schtick)

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81 thoughts on “Previous rules of thumb for climate change worsened wet/dry turned upside down

  1. They call the Climate a “Chaotic System” for a reason, trying to apply simple “Rules” to it is sheer stupidity.
    As your last line says “So much for Certaintity”.
    Settled Science, they must be joking.

    • Couldn’t agree more. I am constantly dumbfounded that so called scientists just can’t seem to understand the word chaos.It would be much easier to forecast next Saturday night’s Lotto draw than some of the stuff they spend their time (and our money) doing.

  2. However, the DDWW principle does still applies to the oceans.

    Interesting! Oceans are getting both wetter and drier!
    Funny, I’ve never seen a dry ocean, have you?

  3. So what is the role of CO2 in all this? it obviously is nothing to do with warming for another simple reason.

  4. Actually its very simple, try to keep up.
    Wet areas that get wetter are more wet
    Dry areas that get dryer are more dry
    Wet areas that get dryer are less wet
    Dry areas that get wetter are less dry
    As you can see, climate change causes a variety of changes to the climate – the clue is in the name.
    THE PLANET HAS A FEVER – AND A RUNNY NOSE. iT IS AN EMERGENCY AND WE MUST ACT NOW OR MORE PLACES WILL GET WETTER OR DRYER OR STAY THE SAME.

  5. Well, lets hope Australia, a land of both droughts AND floods, will be in the 10% where the wet gets drier and the dry gets wetter.
    Still, 10% follow the rule, 80percent show no correlation, and 10 percent opposite correlation- isn’t that just the statistics of random chance?

  6. It always was utter drivel anyway. The SW of Western Australia and Tasmania are both wteer areas but have got drier and that has been a trend for a century or so. The rest of the continent has got wetter, especially the north but also generally. More cherry picking by our idiot climate ‘science’ perpetual undergraduates.

    • I think you’re being fooled by unadjusted ‘raw’ data. Once the data is properly calibrated it’ll show that any increase in droughts (or floods) before about 1960 was slow and gradual (virtually flat) then shooting up at the end of the last century as the CO2 increases kick in.
      This is the case with all negative climate effects, but often the raw data is corrupted by errors that mask the real trends.

    • In 2007, ex Climate Commissioner, Prof. Tim Flannery (recently fired by the current federal government) predicted cities such as Brisbane,Melbourne, Adelaide and Sydney would never again have dam-filling rains, as global warming made the soil too hot, “so even the rain that falls isn’t actually going to fill our dams and river systems ..”.
      At the moment those dams are over 85% full with a number of expensive desalination (built partly based on Prof. Tim’s Global Warming mantra) in mothballs and costing the tax payers billions of dollars.

  7. Well 25 k years ago most of Australia was a giant sand dune field else covered in gibber plains where the sand wasn’t, with stuff all vegetation anywhere away from the coast, and the continental high was constantly blowing huge dust storms into the Tasman sea and South Pacific basin and deflating and destroying whatever soil was considering forming.
    So in those terms it seems pretty clear that very dry gets much wetter when very cold gets much warmer.
    The result of the warming was soil re-development and vegetation colonization and stabilization of the prior continental scale sand dune fields and an explosion of wildlife colonization which followed.
    In other words Australia loves warmth because the permanent high pressure drops south of the continent, lows form over land again which brings back the humidity, soil reforms as plants re-colonize where it had been impossible to survive and the animals come surging back across the continent again. It is indisputable that a warmer Australia is on average a wetter Australia, with more lows and less highs for more of the year. The dry season is made shorter and the wet season is made longer.

  8. We could probably fix the dryness in Australia by leveling the Himalayas to a flat plain. Take a bit of excavation, that, but it would change the flow pattern of the monsoons enough to bring persistent rainfall back to Australia. Plate tectonics and the resultant mountains have really played havoc with the climate patterns. Pity.

    • Nah to knocking them down, two can play their game and I’m still a bit partial to an inland sea and wouldn’t mind an Australian version of the Rockies from the Georgina province to the canning basin and sink the Nullarbor a few thousand meters for a few nice harbors and fishing spots. [and no more GAFA 😀 ]

    • No thanks- I love my subtrend country, a land of sleeping brains, of mounting shagged rangas, of rorts and flooding drains.

  9. No, no no, it is not DDWW, it is DDWWDWWD
    dry gets drier;
    wet gets wetter
    dry get wetter
    wetter get dryer
    Anyways, luckily Marshall Shepherd is not a linear thinker, but apparently more of a circular thinker. After all climate change is caused by climate change.

    • You are mistaken.
      dry gets drier and wetter,
      wet gets wetter and drier,
      dry get wetter and drier,
      wetter get dryer and wetter or maybe dry,
      normal gets drier and wetter in a wetdry kind of way.
      Now falsify that! This is climate science in a nutshell.

  10. Climate models predict that a warmer world means more variability in precipitation: dry areas get drier and wet areas get wetter. An Australian research group let by Sun looked at precipitation over the last 70 years (1940–2009) and were surprised by the results. Not only did they found no increase in precipitation variability, they report that “on average, the dry became wetter while wet became drier.”
    Changes in the variability of global land precipitation
    http://www.agu.org/pubs/crossref/2012/2012GL053369.shtml

  11. Annual rainfall in the relatively weak rain-shadow of the mid-Appalachian ridge & valley region has increased over 10% (30 yr averages) since the 50s to 80s. So, is that wet-getting-wetter or dry-getting-wetter?

  12. The paper was published this September. Does anyone know why they stopped at 2005? Is there no data they could have used up to 2012?

    Here we present an analysis of more than 300 combinations of various hydrological data sets of historical land dryness changes covering the period from 1948 to 2005.

    It may be nothing but I always get suspicious of cut-off dates.

    • Sometimes the data goes the wrong way and can’t be used as it is clearly erroneous, sometimes the gap can be filled with different data that comes from somewhere else but goes the right way. It’s all very complicated and sciency and only real climate scientists understand the process.

  13. These guys stopped at 2009. See what they found.

    Abstract – 16 October 2012
    Changes in the variability of global land precipitation
    Fubao Sun et al
    [1] In our warming climate there is a general expectation that the variability of precipitation (P) will increase at daily, monthly and inter-annual timescales. Here we analyse observations of monthlyP (1940–2009) over the global land surface using a new theoretical framework that can distinguish changes in global Pvariance between space and time. We report a near-zero temporal trend in global meanP. Unexpectedly we found a reduction in global land P variance over space and time that was due to a redistribution, where, on average, the dry became wetter while wet became drier. Changes in the P variance were not related to variations in temperature. Instead, the largest changes in P variance were generally found in regions having the largest aerosol emissions. Our results combined with recent modelling studies lead us to speculate that aerosol loading has played a key role in changing the variability of P.
    Geophysical Research Letters – Volume 39, Issue 19
    DOI: 10.1029/2012GL053369
    http://onlinelibrary.wiley.com/doi/10.1029/2012GL053369/abstract
    =====================================
    Letter To Nature – 11 September 2012
    Justin Sheffield et al
    Little change in global drought over the past 60 years
    …….Previous assessments of historic changes in drought over the late twentieth and early twenty-first centuries indicate that this may already be happening globally. In particular, calculations of the Palmer Drought Severity Index (PDSI) show a decrease in moisture globally since the 1970s with a commensurate increase in the area in drought that is attributed, in part, to global warming4, 5……..Here we show that the previously reported increase in global drought is overestimated because the PDSI uses a simplified model of potential evaporation7 that responds only to changes in temperature and thus responds incorrectly to global warming in recent decades. More realistic calculations, based on the underlying physical principles8 that take into account changes in available energy, humidity and wind speed, suggest that there has been little change in drought over the past 60 years. The results have implications for how we interpret the impact of global warming on the hydrological cycle and its extremes, and may help to explain why palaeoclimate drought reconstructions based on tree-ring data diverge from the PDSI-based drought record in recent years9, 10.
    http://www.nature.com/nature/journal/v491/n7424/full/nature11575.html

    • Oh Dear, do we have to have Mr Palmer and his Palmer United Party giving us a Drought Severity Index. We already have enough trouble with them in the Senate!

  14. This is not a problem for post-modern climate theory. Change gets changier and changiness gets changified, unless things stay the same. In which case it is the change that has changed, so it still fits the theory.

  15. The wet gets wetter, the dry dryer appears to be just one more claim by the Warmist/Alarmist crowd that is incorrect, although since it is being blamed on “climate change” and not specifically CAGW, there will be some places, as the OP notes, where the wet does get wetter and the dry does get dryer.
    Except, when the wet gets wetter and the dry gets dryer, can that really be classified as “change”?

    • Didn’t I see this script in a 007 movie?
      Bad guys take control of the weather machine. (etc etc)
      Or was that Matt Helm?
      Sokay, I didn’t believe it then, either.

  16. “Only 10.8% of the global land area shows a robust ‘dry gets drier, wet gets wetter’ pattern,,,,”
    IMHO we need to be careful about what tense we use. That is, are we describing a general principle for which causation has been proved, or merely describing actual data?
    As I understand it, the paper addresses only data. It says that10.8% of the global land area consists of wet area that got wetter or dry areas that got drier within the time period reviewed. However, the fact that these changes are “robust” does not prove that they were caused by global warming or that these changes will continue in the same direction going forward.

  17. “American Meteorological Society President Dr. Marshall Shepherd tweeted a few months ago that one of his “toughest challenges” is “explaining to linear thinkers that dry/drier, wet/wetter is expected. They want either or””
    I’m a nonlinear chaotic laterally lucid thinker, and I don’t buy the “expected” at all; as no climate model has ever demonstrated predictive skill beyond time scales of days.

    • Thanks, DirkH. You forced me to read that quote twice, and confirmed my earlier impression that it makes no sense at all.

  18. So yet another climate obsessed prediction bites the dust. And skeptics are proven correct, yet again: There are no significant, dangerous or dramatic trends in the climate.

  19. Using the last 12 months, the USA is slightly above normal in precipitation.
    0.57″ above the long term 29.94″ average.
    http://www.ncdc.noaa.gov/cag/time-series/us/110/00/pcp/12/08/1895-2014?base_prd=true&firstbaseyear=1901&lastbaseyear=2000
    However, if you set the base period to 1945-2014 it is 0.18″ above normal.
    So … it is normal. Especially considering there is a 10″ swing from lowest to highest since 1895.
    Does CO2 affect precipitation? No.

  20. “We find that over about three-quarters of the global land area, robust dryness changes cannot be detected. Only 10.8% of the global land area shows a robust ‘dry gets drier, wet gets wetter’ pattern, compared to 9.5% of global land area with the opposite pattern…”
    I wonder what the error bars looked like?
    You’ve got a 10% chance the area will get more of what ever it’s got and a 90% chance It will change.
    Not sure what happens if you neighborhood is normal/average.
    btw
    What happened to global warming making things hot?
    You know, CO2 goes up evenly all over the globe.
    Then the sun warms the CO2 and makes “global warming”.
    Or does it make hot hotter and cold colder?
    I’m sure Marvel Comics could have come up with a better storyline.

  21. “The intensification of rainfall and evaporation patterns, which is occurring at twice the rate predicted by climate change models, could increase the incidence and severity of extreme weather events.”
    So, is this yet another failure of GCMs?
    People say these models are useless, and they are.
    Never mind the DDWW, it is just a scary tale. And they forgot MM; mild weather regions get milder. 😉

  22. All these studies do is amplify what I like to call the “Rainy Day Fallacy” (Maybe it’s already got a name, dunno). The very short time we’ve been studying this stuff with any accuracy is tantamount to sticking your hand out the window to discover it’s raining. Then 10 minutes later you discover it’s raining harder. Extrapolating that trend will get you a global flood in no time flat.

  23. “Half of the surface areas show divergence” – so half of the land area shows ‘climate change’ and the other half doesn’t.
    In half that does show climate change, part shows the ‘dry gets drier, wet gets wetter’ the pattern.
    The other part shows the opposite pattern: dry gets wetter, and wet gets drier.
    This is all over about 1 cycle of the PDO.
    The climate is changing, except where it isn’t, and the climate is getting worse, except where it is getting better – for now.
    Net change: NULL.

  24. If somebody could please explain what a “normal” climate looks like,then I could see when its abnormal

    • Shawn: If you look out of the window, that’s a normal cliamte, whenever you look, no matter how often you look.

  25. The evaluation shows no obvious trend towards a drier or wetter climate across three-quarters of the land are. There are solid trends for the remaining quarter. However, only half of this surface area follows the DDWW principle, i.e. one-eighth of the total landmass, while the trends seem to contradict this rule over the other half.

    In other words: precipitation over land varies in an utterly unpredictable fashion.
    With lots of random time series most of them shows no trend, but the rest either goes up or down. This is what Greve et al. have found. Clever.

  26. The new paper claims that the “dry gets drier” rule is upheld “in the Sahel region.”
    This is in contradiction with the well established “greening of the Sahel” during the last two decades of the 20th century. Here, for instance, is a National Geographic report on a 2009 study:

    Images taken between 1982 and 2002 revealed extensive regreening throughout the Sahel, according to a new study in the journal Biogeosciences.
    The study suggests huge increases in vegetation in areas including central Chad and western Sudan.
    The transition may be occurring because hotter air has more capacity to hold moisture, which in turn creates more rain, said Martin Claussen of the Max Planck Institute for Meteorology in Hamburg, Germany, who was not involved in the new study.

    Looks like the “dry gets drier” walk-back might still need some more walk-back. That is bad news now that we seem to be in for a substantial turn of global cooling, which will probably undo that greening of the Sahel.
    In typical eco-“reporting” fashion the National Geographic piece above does not name the paper, just giving the journal and the 1982-2002 dates. That is enough to find the paper via Google. It is titled “Disentangling the effects of climate and people on Sahel vegetation dynamics” and the abstract is hilarious, in a weeping-world kind of way.
    They studied whether this unambiguous greening could be due to human land use changes, and as the title makes clear, the competing hypothesis is that this benign change would have been due to “climate,” which warmed a little bit over the period, but the abstract never mentions the competing hypothesis. They just say that the change seems not to have been caused by human land-use changes (greening happened everywhere, regardless of human uses or changes in human uses). Despite the paper’s title, the abstract studiously ignores how the “disentangling” they have successfully conducted implies that the greening was likely caused by global warming.
    The implications seems to be that they were afraid of losing funding if they actually stated the implications of what they found, but they must have wanted to say what they found because they state in their title what a negative human-use finding would imply. They just never connect up that implication when they report their findings, even though it is in their title. Amazing.
    So this is what 100% politically funded science looks like. Scientists whose findings point in the politically-disfavored direction still report their findings but just omit to mention in which direction they point. It’s like reading Pravda during the cold war. People in the know see to read between the lines while the “useful idiots” fool themselves that their presumptions remain unchallenged.

  27. Please can someone explain what they meant by “Each combination of data sets is benchmarked against an empirical relationship between evaporation, precipitation and aridity. Those combinations that perform well are used for trend analysis.“. That looks like confirmation bias to me.

  28. Why is it so hard for them to say that they don’t really know how these major climate systems work? wouldn’t that be the scientific position? Would something bad happen? Earthquake, giant Williwaw, a cut in grant allocation?
    When’s the next big assembly of climatologists because we still have a “research aircraft” available to help them…….

  29. Precipitation presents a natural rhythmic variation. The temperature follow this in opposite way. If we select a truncated data within a cycle, based on the period of the cycle, we get different conclusions. This is generally happening. Two years back, a minister informed to Indian parliament that monsoon rainfall is decreasing. This year researchers from Stanford University published a paper contrary to this. Here the fact is monsoon rainfall presents 60-year cycle — already completed two cycles and third cycle started in 1987 with the above the average part and is going to complete by 2016. Former used data part of last but one sine curve [0 to +1 to 0 to -1 to 0] and the later used data part of last sine curve [0 to -1 to 0 to 1 to 0]. It has become common.
    In Mumbai, Santacruz Airport for building international airport terminal they cut the hillock in the runway over a period of time. This reduced the precipitation. With passing of time all around high raise buildings have come up. The scene come back to original.This can be seen by comparing rainfall of Alibag and Santacruz in Mumbai.
    Dr. S. Jeevananda Reddy

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