Guest Post by Willis Eschenbach [Updated, see end of article]
One of the claimed dangers of a few degrees warming of the Earth is increasing drought. Drought is a very difficult thing to fight, because it is hard to manufacture water. So this is a frightening possibility.
I have long claimed that “a warmer world is a wetter world”. I have said this without any actual data, based solely on the following logic.:
Increased temperature —> increased evaporation —> increased precipitation.
Today I graphed the numbers for the US precipitation. I used the USHCN state-by-state precipitation database, which also includes area-averaged values for regions of the US, and for the US itself.
First, here is the change in precipitation in the US since 1895:
Figure 1. Annual precipitation in the US. PHOTO SOURCE
Since the both the US and the globe have warmed since 1895 it seems that a warmer US is a wetter US. However, precipitation is spotty and unevenly distributed. One area can be very wet while a nearby area is dry, so what about the precipitation in each of the states?
The USHCN database contains state data. Since there are drier states and wetter states, I looked at the percentage increase in precipitation rather than the absolute change in precipitation. Here are the state-by-state results:
Figure 2. State by state changes in precipitation, 1895-2009. Values are change per century divided by average annual rainfall.
One of the things that AGW supporters have been saying would result from warming is that the desert belts would move poleward. These are the great belts that circle the earth at about 30° North and 30° South latitude. The North American belt encompasses the Southwestern US (Southern California, Arizona, New Mexico, and Texas) and Northern Mexico. If these belts were actually moving poleward as the globe warmed over the last century, we should see decreased precipitation in the Southwestern US.
Instead, all of the southwestern states have increased rainfall. The main area with decreased rainfall encompasses the Rocky Mountain states in the central Northwestern US.
My conclusions? Precipitation is indeed spotty. A warmer US is indeed a wetter US. And there is no decrease in the Southwestern US data which would show that the great northern desert belt is moving polewards. So either the desert belt is not moving poleward, or the movement is offset by the overall increase in precipitation.
[UPDATE] Some commenters have correctly pointed out that I have only shown the precipitation, which doesn’t show the change in droughts. This is because droughts are a combination of soil moisture, temperature, rain, and other factors. This is measured by the Palmer Drought Severity Index (PDSI). The PDSI index values have the following meaning:
-4.0 to less (Extreme Drought)
-3.0 to -3.9 (Severe Drought)
-2.0 to -2.9 (Moderate Drought)
-1.9 to +1.9 (Near Normal)
+2.0 to +2.9 (Unusual Moist Spell)
+3.0 to +3.9 (Very Moist Spell)
+4.0 to above (Extremely Moist)
I used the USHCN database cited above to look at the state-by-state trends per century in the PDSI. Note that these are not the average PDSI values by state, which are without exception in the range -1.9 to +1.9 (near normal). Figure 3 is a histogram of the trends per century. A “histogram” shows the number of states (left scale) that have a certain trend range (bottom scale).
Figure 3. Histogram of state trends per century of the PDSI
The trend in most of the states (39 out of 48) is toward less drought (increasing PDSI). However, most of the trends (32 of 48) are between 0 and +2.0, which is not a large change. As a result, most of the trends are not statistically significant. Figure 4 shows the significant state trends:
Figure 4. Significant trends in the PDSI in the US states.
As you can see, despite the warming of the last 115 years shown in the USHCN dataset, while some of the PDSI trends have decreased, almost all of the statistically significant changes in the PDSI are positive (less drought). And few of the changes are statistically significant.
The IPCC models say that increasing warmth will lead to increasing drought, particularly in the mid-latitudes:
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.
Despite these model prediction, we have seen no such increase in drought in the US. For most of the US, there has been so statistically significant change in the PDSI index showing the number and strength of droughts in most US states. And where there has been a statistically significant change, it is in the direction of reduced drought.
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“”” Willis Eschenbach (11:01:39) :
mikael pihlström (06:21:15)
… Poleward movements of species: it is not a closed case yet, but yes there is movement. I remind you that a catastrophic escalation in the worst IPCC scenarios could trigger mass extinction. “””
Well have you ever heard of the Ballroom floor phenomenon ?
In ballroom dancing; in contrast with what the Teener set thinks of as dancing these days; it is actually traditional to hang on to your partner; so that everybody on the floor, knows that is who you are dancing with; and not that gal/guy over there in that distant corner.
And you always dance with your hands held high and your elbows sticking out prominently to erect a barrier of encroachment. If some other churl comes waltzing into your spot; well you just nudge hom out of the way, with a well planted elbow right in the middle of hs back or ribs. It is not gentlemanly to nudge the invading lady out of the way; your partner however is free to do that (or step on her ankle).
From time to time, open spaces appear on the ballroom floor, where nobody is dancing; and every leading man in the vicinity, steers his partner over to that vacant space to shwo their prowess to the rest of the dancers.
Well in the process of course the hole in the ballroom floor, moves off to some other place; to be chased again by the dancers.
The people move inot what seems to be underutilized quarters.
Who wants to bet, that flora and fauna species don’t do exactly the same thing as the ballroom hole migration.
To argue that because the mocking birds woke you up five minutes earlier this morning, means that something catastrophic is happening, just isn’t realistic. Animal populations do move around in response to periodic changes in the competition for resources; the trees get up and move to where there is more sunlight in the forest; well an individual tree might not; but it will certainly try to spread its progeny into a nice sunny clearing nearby; and those offspring will try to outgrow the competitors to reach the canopy and bask in their new found glorious sunshine.
Too much is read into these random walk processes, that are just Gaia redistributing her resources to use the available space efficiently.
The Boston area had a 100 year event or more last march. 18 inches of rain from 2 storms was the most in a month since records were kept going back to the 1870’s.
Doesn’t mean anything of course, but it seems every year I go back to visit it is wetter and wetter there.
As for the Southwest, that has historically been a dust bowl. The 20th century was actually unusually wet for the area. If average climate over the last 1000 years returns, they will be looking at drought conditions. Nothing to do with AGW though.
A clear signal for the poleward movement of the North American desert belt must surely be there as the models say. It is hard to detect because It is currently being obscured by an obviously temporary 114 year weather phenomenon.
Willis, you must be careful not to let these transient weather phenomena obscure the century-scale wisdom of the models. It just confuses folks.
Chris Edwards (16:53:46) :
“….. no research behind this travesty just thought it was good for us, the cat converter in our cars and the paint thinner and alcahol masquerading as real gas???? the technology changes but the solution stays the same, biofuel, another really daft idea, did no one think it through,…”
Of course “they” thought it through Cargill and Monsanto posted record earning in 2008.
It is no coincidence that Robert Shapiro CEO of Monsanto was chief foreign trade adviser to Bill Clinton when VP of Cargill Dan Amstutz wrote the World Trade Organization’s Agereement on Ag and the 1996 “freedom to farm bill”
Nicole Johnson does a much better job of going into the history (with 5 pages of references) at History HACCP and the Food Safety Con Job
Food is a target for control as well as the control of energy through “green” taxes and regulations. They already succeeded in getting control of the money supply at the G20 summit last year in April. Obama agreed to sign off on International control over our US financial institutions by the Financial Stability Board. “They want control over every detail, not surprisingly right down to setting pay and compensation levels….” See Investors Insight: The End of America’s Financial Independence
Also see my comment at Gail Combs (20:33:26)
http://wattsupwiththat.com/2010/04/16/reply-to-ice-cap-thaw-may-awaken-icelandic-volcanoes/
Willis-Have you considered looking at the “climatological division” network for more high spatial resolution PDSI results? Could be interesting-droughts can often be very localized.
The divisional data is available here:
http://www.esrl.noaa.gov/psd/data/timeseries/
Pick US Climate Division.
George E. Smith (15:13:56) :
“”” Willis Eschenbach (11:01:39) :
mikael pihlström (06:21:15)
… Poleward movements of species: it is not a closed case yet, but yes there is movement. I remind you that a catastrophic escalation in the worst IPCC scenarios could trigger mass extinction. “””
The only poleward migration I have personally observed in Kansas is the northward movement of the Texas lapdog (armadillo). My fervent desire is that some action by me would trigger a catastrophic mass extinction.
” Geoff Sherrington (01:34:13) :
A couple of clarifications, if I may.
The sand deserts of Australia are extensive. Goat herders are, for all reasonable study, negligible, and always have been. The carrying capacity of much land is about one wombat a square mile.”
You will find that the great Australian deserts are a product of the Australian Aboriginals behavior; they burnt down the rain forests that were there. It is not PC to point the finger of blame at the aboriginals, but they ancestors did make the great Australian deserts. The carcoal is a bit of a give away.
They also, accidentally, made Eucalyptus a fire resistant tree and wiped out huge numbers of large animals and birds.
Willis—
Nice plug tonight on the John Batchelor show (WABC radio, 9 PM-1AM, syndicated nationwide, and streaming from WABCradio.com) from Bob Zimmerman, specificially mentioning this post about precipitation.
John and Bob are clearly avid readers of WUWT, and fans of your technique of showing how much the warmists make of so little.
I just wish the useful idiots of the MSM were listening to them.
/Mr Lynn
******
19 04 2010
RayB (00:03:16) :
It seems that every time a storm threatens to get north of Green Bay, high pressure comes from the north and blocks it. It is uncanny the excuses and strange patterns that keep it from raining here. It has been going on long enough that it is heading from weather to trend status. We are seeing a lot of stress on the plant kingdom, and are seeing record low levels in lakes and rivers. We are not at desertification yet, but there are changes like trees sprouting in dry lake beds.
*******
Local and/or regional drought tends to perpetuate itself. Rainfall is a result of imbalance — rising air vs sinking air. A drought area will be less moist than surrounding areas, so high-pressure tends to form/reform above because dry air is heavier than moist air. A drought gradient (dry area right up against a wet area) reinforces itself because it’s a perfect place for a relatively local imbalance to develop when cloud moisture comes over. Moist air will rise & then rain over the moist area at the expense of the dry area (which provides the sinking air to support it).
Such a north/south drought gradient was present just a few yrs ago here in the northern mid-Atlantic states. The “line” was just a few miles south of and parallel to the MD/PA border. Rainfall would continuely pass over the wet areas to the north but dissipate just south of the gradient border.
Mr Lynn says:
April 20, 2010 at 8:37 pm (Edit)
Thanks for the info, Mr. Lynn. I’ll look it up and have a listen.