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:
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.
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” :
@borenbears one my toughest challenges. Explaining to linear thinkers that dry/drier, wet/wetter is expected. They want either or.
— Marshall Shepherd (@DrShepherd2013) April 30, 2014
So much for certainty.
(h/t to The Hockey Schtick)
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.
“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.
“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. 😉
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.
In Western Washington, if you can’t see the mountain (Rainier), it’s raining.
If you can see the mountain, it’s going to rain.
Works every time.
I can’t see it from my house most of the time. Has to be a really clear day. But I’m pretty far north.
Jeff,
Baker will do
“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.
dry/drier, wet/wetter is expected….
They don’t realize how stupid they sound.
They truly believe they’re the smart ones.
Now that’s scary.
Following their model, we could say “the dumb get dumber”.
Stupid is as stupid does.
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.
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.
“..Dry gets drier’ also corresponds to indications in the Sahel region,…”
Hmm, the Sahel (strip south of the Sahara) is actually greening and getting wetter.
http://www.thegwpf.org/images/stories/gwpf-reports/mueller-sahel.pdf
In case the Kool Aid set is lurking, here is one from your beloved National Geographic:
http://news.nationalgeographic.com/news/2009/07/090731-green-sahara.html
For direct information on part of the Sahel, you might want to look up “Friends of Burkina Faso.”
…and bulls**t gets bulls**tier.
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:
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.
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.
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…….
https://www.flickr.com/photos/127763581@N04/15251204682/
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