2011-02-16 06:05:02The Dai After Tomorrow: Dai et al 2010
Daniel Bailey
Daniel Bailey
yooper49855@hotmail...
97.83.150.102

Let me first begin by saying that this was a more challenging paper review to take on than I had anticipated.  Given the scope of the paper, the challenge before me was to relate the substance of the paper while keeping it simple.  All without losing anything in translation.

If anyone knows Dai personally, I in no way mean anything disparaging with my headings; just trying to keep a serious topic light.

Any feedback, however brutal, is appreciated.  Well, except from Poptech.  ;)

Without further ado (http://www.skepticalscience.com/Dai_et_al_2010.html):


UPDATE:

Implemented suggested revisons per dana, Rob and Riccardo (thanks!).

Question for dana:  Is your rebuttal below published (I linked to it in the conclusion)?

http://www.skepticalscience.com/exponential-increase-CO2-warming.htm


The Dai After Tomorrow

Posted on ? February 2011 by Daniel Bailey

 

(or:  Water, Water Everywhere and Nary a Drop to Drink)

The goal of Skeptical Science is to explain what peer reviewed science has to say about global warming.  Our ability to put aside our preconceptions and beliefs and to evaluate things objectively - through the cold lens of rationality and reason - says a lot about ourselves. 

Much ado has been made recently in the media and the blogosphere of recent extreme weather events around the world: the flooding in Tennessee and Pakistan, the Moscow heat waves, record drought in the Amazon, and yet more flooding in Queensland and Brazil.

So let's leave the hype and agendas behind and focus instead on one of the basic juxtapositions of the warming world we live in: the co-existence of droughts and floods.

YesterDai Once More: the 2007 IPCC Fourth Assessment Report (AR4)

As of the time the IPCC came out with the AR4, predicted extremes in precipitation and droughts were being observed:

"In a warmer future climate, most Atmosphere-Ocean General Circulation Models project increased summer dryness and winter wetness in most parts of the northern middle and high latitudes. Summer dryness indicates a greater risk of drought. Along with the risk of drying, there is an increased chance of intense precipitation and flooding due to the greater water-holding capacity of a warmer atmosphere. This has already been observed and is projected to continue because in a warmer world, precipitation tends to be concentrated into more intense events, with longer periods of little precipitation in between. Therefore, intense and heavy downpours would be interspersed with longer relatively dry periods. Another aspect of these projected changes is that wet extremes are projected to become more severe in many areas where mean precipitation is expected to increase, and dry extremes are projected to become more severe in areas where mean precipitation is projected to decrease."

Other studies demonstrated that the percentage of Earth’s land area stricken by serious drought more than doubled from the 1970s to the early 2000s.

Today's Dai

This pattern continues today.  2010 witnessed flooding in Nashville, Pakistan, Queensland and Brazil.  The Amazon experienced its 2nd once-in-a-century drought, a bare 5 years after the previous once-in-a-century drought.

It has been more than 3 years since the last assessment (IPCC AR4) and the next (IPCC AR5) is still years away.  To help bridge this gap in our knowledge comes a new review study, Drought Under Global Warming, A Review, led by Aiguo Dai and his team.  Together they take on the formidable task of assessing the field to date.

A common measure called the Palmer Drought Severity Index (PDSI) classifies the strength of a drought by tracking precipitation and evaporation over time and comparing them to the usual variability one would expect at a given location in the low (equatorial) and middle latitudes. The more negative the number, the more drier the conditions.

Using an ensemble of 22 computer climate models and a comprehensive index of drought conditions, as well as analyses of previously published studies, the paper finds most of the Western Hemisphere (along with large parts of Eurasia, Africa, and Australia) may be at threat of extreme drought this century.  Note that in the paper they re-normalize the index to the local conditions; there would be no way to explain why the Sahara desert appears to be less arid than the USA. With the renormalization, the PDSI can thus be considered an anomaly.

Another finding of the paper is that precipitation was the dominant driver for changes in the terrestrial water budget before the early 1980's.  Changes since then are not only attributed to anthropogenic greenhouse gas induced (human-induced GHG) surface warming, but that those same human-induced GHG increases have contributed to the observed drying trend since the 1980's.

It was also found that despite increased precipitation, due to increased surface temperatures and increased surface runoff, higher atmospheric demand for moisture results in drier soils.

Figure 1:  Current Palmer Drought Severity Index [PDSI] 2000-2009.  A reading of -4 or below is considered extreme drought. Regions that are blue or green will likely be at lower risk of drought, while those in the red and purple spectrum could face more unusually extreme drought conditions. (Courtesy University Corporation for Atmospheric Research [UCAR])

 

The Dai After Tomorrow 

Tomorrow waits for no one.  What can we expect, based on this work?

By the 2030s, the results indicated that some regions in the United States and overseas could experience particularly severe conditions, with average decadal PDSI readings potentially dropping to -4 to -6 (extreme drought) in much of the central and western United States as well as several regions overseas, and -8 or lower in parts of the Mediterranean. By the end of the century, many populated areas, including parts of the United States, could face readings in the range of -8 to -10, and much of the Mediterranean could fall to -15 to -20. Such readings would be almost unprecedented.

 

Figure2:  PDSI 2030-2039(Courtesy UCAR)

 

Extreme conditions experienced earlier are expected to continue, and even worsen.  In fact, droughts may become so widespread and so severe that current drought indices may no longer be adequate to quantify them.

 

Figure 3:  PDSI 2060-2069(Courtesy UCAR)

 

If the drying is anything resembling that shown in these figures, a very large population will be severely affected in the coming decades over the whole United States, Southern Europe, Southeast Asia, Brazil, Chile, Australia and most of Africa.

 

Figure 4:  PDSI 2090-2099(Courtesy UCAR)

 

The End of Dai's 

The paper closes on a somber note:The above figures are themselves based on IPCC AR4 SRES A1B (medium GHG) emission scenarios.  Current Business-As-Usual (BAU) emissions are running higher than that (tracking the A1F1, or high emissions, scenario).  Thus, potential exists for conditions to be worse than depicted above.  And that is not a comforting thought.

 

Dai's  of Old

Aiguo Dai is a researcher with the National Center for Atmospheric Research (NCAR).  His past work includes (but is not limited to):

 

Further reading:

 

 

2011-02-16 11:54:33comments
dana1981
Dana Nuccitelli
dana1981@yahoo...
69.230.107.233

Nice post overall.  I thought the discussion in the intro about labels (warmist, skeptic, denier, etc.) seemed out of place.  I think you could do without it.

It's probably worthwhile to define AR4 before you use it.  For example, "the 2007 IPCC Fourth Assessment Report (AR4)".

In The Dai After Tomorrow section, you should be explicit that the numbers you list are PDSI values, and maybe put them into perspective (more negative means dryer).

I didn't get the Bueller reference, but maybe that's just me :-)

You should be explicit about what scenario the future PDSI projections are based on.  Is it one of the IPCC business-as-usual scenarios?  Which one?

Might be good to add some sort of take home conclusion message.

2011-02-16 19:07:35
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.247.191

Dana, Ferris Bueller's Dai off.

Yooper, yeah the intro doesn't fit. I like clever titles and humor, but perhaps you've "overcooked" things a bit?.  Like Dana, I think there needs to be a take-home message. Good post, although the projections are somewhat alarming.

2011-02-16 21:13:59
Riccardo

riccardoreitano@tiscali...
192.84.150.209
Nice narrative.
When you explain what the PSDI is, you should say that in the paper they renormalise the index to the local conditions; there would be no way to explain why the Sahara desert appers to be less arid than the USA. With the renormalization, the PSDI is similar to an anomaly.
In the "The Dai After Tomorrow" section you anticipate things relevant to the last section; i think you should move them there.
I agree that the intro doesn't fit.
2011-02-17 02:15:19Thanks!
Daniel Bailey
Daniel Bailey
yooper49855@hotmail...
97.83.150.102

Implemented your recommended changes (revised as shown above).

Anything else?

2011-02-17 04:22:39comment
dana1981
Dana Nuccitelli
dana1981@yahoo...
38.223.231.252

Suggsted edit for The Dai After Tomorrow section:

"By the 2030s, the results indicated that some regions in the United States and overseas could experience particularly severe conditions, with average decadal PDSI readings potentially dropping to -4 to -6 (extreme drought) in much of the central and western United States..."

2011-02-17 12:27:45Updated again
Daniel Bailey
Daniel Bailey
yooper49855@hotmail...
97.83.150.102
Thanks, dana!  That reads much better now.
2011-02-17 20:07:56
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.252.197
I suppose you'll be wanting one of these then?.
2011-02-17 21:23:06
Riccardo

riccardoreitano@tiscali...
192.84.150.209

Daniel

"If anyone knows Dai personally, I in no way mean anything disparaging with my headings; just trying to keep a serious topic light."

you may want to contact him yourself. I did when I wrote the post on Haig et al. paper asking if her thoughts were correctly reported.

2011-02-18 00:27:06
Daniel Bailey
Daniel Bailey
yooper49855@hotmail...
97.83.150.102
Thanks, Riccardo.  I'll send an email out to him ASAP.
2011-02-18 04:26:22Self-thumb
Daniel Bailey
Daniel Bailey
yooper49855@hotmail...
97.83.150.102

 

Thumbs up from Dr. Dai (below), so we're good to go.

 


Dear Mr. Bailey,


Thanks for interest in our drought paper. Your write-up is very interesting and broadly conveys the original message.

Best regards,
Aiguo 

2011-02-18 05:26:02published
dana1981
Dana Nuccitelli
dana1981@yahoo...
38.223.231.252
Cool Daniel. I published this morning, but there was some weird glitch (my browser crashed in the process) so there's no comment box at the bottom and I can't edit it anymore.  Hopefully John can sort it out.
2011-02-18 06:20:22re-published
Daniel Bailey
Daniel Bailey
yooper49855@hotmail...
97.83.150.102

Weird.  Went into my author admin; it said published.  I re-checked it as published & saved it.  That brought up the screen to email it out, which I did.

 

I don't twitter or FB, so I didn't do that portion.

2011-02-18 08:16:07YouTube glitch
John Cook

john@skepticalscience...
144.131.205.143
The glitch was because of how our wysiwyg tends to mangle YouTube code. I'll try to tweak the wysiwyg so it stops doing this.