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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The real savings of water however is in the growth rate of crops. Currently it would take from ten to twenty percent more water to grow the amount of food we currently grow if C02 was still at 280 PPM!
Does morning dew count? Part of it gets absorbed by plants and soil, part evaporates. What proportions of each? I usually water my garden in the early morning to take advantage of the dew. How about sublimation, in addition to evaporation? Or lag times of water movement thru the ground ( varying porosity ) to replenish aquifers, etc. etc.
My point is that there are so many unknowns, and chaotic behavior, in the hydrologic cycle that trying to model the granularity of it is impossible. You can drive yourself nuts trying to figure it out.
OT Warning:
If Piltdown Man was the scientific frauf of the 20th century, then Meltdown Mann must be the scientific fraud of all time.
Patrick Davis (04:50:18) :
http://www.whoi.edu/page.do?pid=12455&tid=282&cid=897
I do not know about the hundred year cycle but this is the website for the info on salinity changes done in 2003.
Do you results change in any way if your start date is 1855?
Just interested….
30% of the suns rays are reflected by clouds.
70% of the Earths surface is water, the rest mostly land.
On a day without clouds, the ‘average’ temperature of land increases proportionately more than the ‘average’ temperature of the air above the seas; compared with cloudy days.
So, the global ‘average’ temperature will be hotter if 29% of the clouds are over land and much colder if 31% of the clouds are over land.
Small changes in where clouds actually are will have a huge effect on the reported average global temperature, even though the same amount of energy is entering the system.
The rainfall pattern, linked to some clouds, is indicative that the ratio of clouds over land:sea’s changes in time, and does so quite quite dynamically +/- 25% per years.
Why don’t people talk about wind, wind patterns and changes and location of high and low pressure? I have done yacht racing for 4 decades and track the same and know how this effects rainfall and weather. If you have some humidity, some low pressure you get lift. I have seen clear skies turn into a thunderhead and deluge in a single hour. Add heat and the lift takes it up to cold air. This surface temp stuff it not complete. Air temps at 50,000 feet have never become hot.
Much of the folklore about drought in the southwest is due to fact that water usage has increased dramatically in the last 50 years.
When lake levels drop, people assume that it is due to decreased inflows rather than increased outflows. A lot of water in the west is being used to raise biofuels crops, particularly corn. When I see people out here driving cars advertising “green” biodiesel, I immediately question their IQ.
You must remember about these eco-idiots that, in their myopic minds, global warming only produces negative benefits. Positive benefits of global warming cannot be used to control and tax people. That is why such people say global warming means more droughts.
Where is the arbitrary 21 year base line and the corresponding anomaly graph?
Also, your y-axis scale needs to be much smaller to make the changes look much bigger. 🙂
“sphaerica (04:44:07) :
[…]
The fact is, at the moment the amount of warming that has been seen is minimal, because the planet doesn’t warm instantly, but the CO2 in the atmosphere now has already committed us to at least 1.5C warming, where we’ve only seen 0.5C to date.”
The fact is that you confuse assumptions with facts.
There has been a large increase in snowfall in central Colorado over the last century.
http://wattsupwiththat.files.wordpress.com/2010/01/crested_butte_annual_snowfall.png
http://wattsupwiththat.com/2010/01/30/debunking-nwf-claims-part-2/
Do any climatologists read geology? It is pretty well established that in geological time warm eras are wet and cool eras are dry.
Willis,
One thing I have been studying is density changes in the atmosphere as rotation pulls along the atmosphere which is very elastic. With this volcano blocking sunlight, it is also putting more dust and debris into the atmosphere in the northern hemispherical cycle. Gravity(joke name) as mass has no power of it’s own. The magnetic field will pull on the debris field.
Expect colder temperatures to come from this in the northern hemisphere.
Here in New Hampshire we have seen an annual increase of about 12% (5.5 inches) over the 114 year period. With the majority of the increase occurring in the months of June, July and October.
Also interesting is that the months of January, February and September have shown a decrease during this period.
There is a case to be made that we need to be able to move water more efficiently over long distances. But then even looking at California, we’ve really done near to nothing about desalinating sea water for drinking/irrigation use.
I’m reminded of a great old quote from just after the American civil war. President Grant sent his secretary of the interior out to look at the far west so far as population expansion into that area. That worthy reported “All this land lacks is water and good people.” Grant fired back, “That’s all Hell lacks.”
I grew up on a sand farm in SE Missouri. About 15 miles from the Southernmost part of the hilly, forested area called Crowley Ridge. We had a sand hill that was rich in Bison Skulls, arrow heads, etc.
It was the driest couple of square miles, probably, in all Missouri, and Arkansas. No joke. My father got ulcers watching the storm clouds come down from the North, and Split, going right around us.
There was a U.S. Army Air Corps flight school a few miles away. The instructors told (I’m sure of this because our local crop-duster trained there) the trainees that in case of Bad weather to fly over to the area of our farm. They told the recruits that if there was going to be clear skies anywhere in the area it would be there.
Weather is really complicated. “There is much more, Horatio, than is dreamed of in your philosophee.”
@David A (04:00:00) :
Yes. I learned this several years ago. It’s not commonly known. Plants use less water per unit of biomass as CO2 concentration rises. If I recall correctly the mechanism whereby this occurs is due to the way stomata regulate gas exchange. Stomata are microscopic pores in leaf surfaces that iris open and closed to regulate gas (CO2 and O2) exchange. Water vapor escapes from the plant (transpiration) during the exchange. When the CO2 concentration is higher in the air less total air volume is required for the gas exchange. The stomata don’t open as much and less water vapor escapes in the process. Pretty cool.
Willis – your post reminded me of an interesting video I saw on YouTube a couple of years ago. It looks at water vapour trends in the US. I don’t know much about the author, and the presentation is a little basic. But the points are well made – I’d encourage you and others here to watch the vids and consider the points raised. The presentation is in two parts:
http://www.youtube.com/watch?v=ePLw6DyTYmI&feature=related
On a loosely related matter, disappearing Lake Chad was the poster child of the AGW movement a few years ago. I have looked for more recent trends, but nothing much to find. I recall there were serious floods across North Africa a year or two ago and I wondered how much would have drained into Lake Chad. Is it a case of “no news is good news”? Does anybody have anything on the latest postion of Lake Chad?
One of the Google ads running on this page was this:
http://www.stoptheenergywaste.blogspot.com/
I suspect the money to fund this kind of indoctrination is coming from our own treasury as “stimulus”
Thanks Willis, good post.
Nothing new . Read
The Past and Future of Climate
David Archibald
May, 2007
Figure 7: The Last Four Ice Ages
Also interesting is the amount of dust. Colder is drier and warmer is wetter, generally.
Large areas of Australia are covered by sand dunes that formed in these ice ages and are now stabilised by vegetation.
http://www.climatepolice.com/Past_Future_climate.pdf
sphaerica (04:44:07) :
“Increased temperature —> increased evaporation —> increased precipitation
But the water doesn’t evaporate and then precipitate in the same place, or in a dramatically changed climate in the same places as it used to. In addition, more of that added precipitation will quickly be lost again by evaporation.”
Global precipitation trends can (are) be folllowed, but it is easy to agree
that it is more fruitful to look at regional to local climates, because of the
reasons given by spaherica. Also locally, if you want to say anything
meaningful about drought, which was Willis opening phrase, you would
have to plot temperature, precipitation, transpiration over the seasonal
cycle and identify periods of concern; your local farmer will help you.
fredb (04:51:05) :
says the essential about drought in his post, but for some it seems to
be to analytical a text.
Should there be concern about rain records with respect to how/where they are measured, much like the concerns about the sitings of temperature gauges? Will Anthony begin a ‘rain stations’ project when the surface stations is complete?
Dear Willis
Thank you very much for your very good posts.
A way to look at rain fall might be the variation in the amount of dam water reservoir of the region under analysis. In Spain that amount right now is more than 20% of the mean of the last ten years and at 82% of its capacity. See http://www.embalses.net/
Footnote to good observation by David Middleton (04:55:14) :
I believe only reason Lake Mead is minus 21% is that dam operators are filling Lake Powell first; and for the most part (except for relatively minor ”flushing” operations) are not letting anything in excess of that which is run thru the turbines go thru Glen Canyon Dam; i.e.:
All spring runoff in excess of power generation needs is being held behind that dam.
Lake Powell has been WAY down from full capacity. Several of us drove by Glen Canyon Dam on the way to row the Colorado River thru Grand Canyon last year, and the ”bathtub ring” on Lake Powell was striking. And note the Park Service just opened a long road extension to the Pierce Ferry river-runner takeout at the end of the Grand Canyon river run; after that takeout was closed for a number of years due to extreme low water in Lake Powell.