In this recent post I discussed a paper on regional temperature divergence issues related to irrigation from Dr. John Christy saying:
New irrigation effects study counter to what Christy discovered
This press release below from Columbia University shown below suggests that irrigation cools the region undergoing irrigation. However, a study published three years ago of California’s central valley by Dr. John Christy suggests exactly the opposite. See this WUWT post from 2007, then read the Columbia story and decide for yourself.
From UAH: Irrigation most likely to blame for Central California warming
A two-year study of San Joaquin Valley nights found that summer nighttime low temperatures in six counties of California’s Central Valley climbed about 5.5 degrees Fahrenheit (approximately 3.0 C) between 1910 and 2003. The study’s results will be published in the “Journal of Climate.”
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Dr. Christy responds via email, and I’ve added graphs and links to enhance his presentation to us.
I would like to let the readers know (several of whom obviously did not read it) that the 2006 California paper (PDF here)was based on daily time series of 41 stations in the six south-central San Joaquin Valley and adjacent Sierra counties. 18 stations were in the valley, 23 in the Sierra (mainly the foothills).
The time series for each of these stations was divided into segments based on the examination of all NWS forms that NCDC was able to find – over 1500 pages. I examined each form and personally digitized its basic information (see attached.) In the example, you can see the results of reading 25 of these forms for Madera CA. I keyed in the
relevant information, then at the bottom of the spreadsheet summarized the results with a listing of the dates and reasons for establishing a segment breakpoint, in a sense treating each segment as a separate “station”.
See this PDF file showing metadata for Madera_045233
I sent the digitized metadata files for each station to the WRCC for safekeeping if for some reason I lose them.
I also hand-digitized several years of DAILY TMax, TMin too – for downtown Fresno, it was about 40 years worth … a very tedious project for a grandpa like me.
This method in essence provides a set of time series which can be debiased relative to each other through a method described in the paper that used mathematical game theory. By having this many stations (order 20 in Valley and Sierra separately) I have oversampled the region’s signal, thus allowing, as shown in the paper, several ways to test the resulting trends and issue statements of confidence.
We are very confident that TMin is warming rapidly in the Valley while the TMax trend is not significantly different from zero. The seasonal distribution of this result is consistent with irrigation. The Sierra time series show no such TMin trends – also consistent with
irrigation/development in the Valley but not Sierra. The fact trends in TMax and TMin in the Sierra are not rising is evidence against the notion that the lack of rise in TMax in the Valley is due to irrigation (though it could have some impact … but keep in mind that a number of these Valley stations have become urbanized in any case – perhaps a bigger daytime signal than irrigation.)
Since TMax is more highly coupled to the deep atmosphere (daytime mixing), TMax is therefore the better candidate to be used as a proxy for greenhouse warming since this type of warming is maximized in the troposphere according to model theory. The temperature results in this part of California (see also Christy and Hnilo 2010 on snowfall) do not provide evidence of greenhouse theory expectations.
Some have mentioned other factors that contribute to rising night temps, and these are discussed more fully in Christy et al. 2009 regarding East Africa temps (another tedious effort to digitize numerous stations here-to-fore never examined.) The key factor in all of these causes is the idea that the delicate, nocturnal boundary layer in which TMin is
measured can be easily disrupted by many factors – warmth from surface fluxes due to irrigation, IR forcing from aerosols, buildings which increase roughness (and thus mixing) etc. When the BL is disrupted, the warmer air above the inversion is mixed downward and is evidenced by a warmer TMin than would otherwise be the case.
I have not read the paper being discussed which suggests irrigation cools the temp stations. This would be a difficult thing to establish from typical datasets as these are “homogenized” in a way that smears the station trends from other stations of quite different micro-climate situations into each other. As noted above, I kept the Valley and
Sierra distinct and used many more stations (a station density of at least 10 times greater.)
John C.
—
John R. Christy
Professor, Atmospheric Science
Director, Earth System Science Center
Alabama State Climatologist
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Normally temperature stations log humidity as well as temperature.
The humidity values would seem to be very relevant to a theory that irrigation has a microclimate effect.
Are there any plans to revisit with an examinaton of humidity?
REPLY: Actually, only a small percentage of the nation’s COOP stations log humidity. Most are temperature and precip only – Anthony
John
As an amateur looking at the discussion you compiled the facts from the available data and noticed that warming of Tmin was an outcome of irrigation in the central valley as evidenced by the increase in Tmin. This new study looks at Tmax and asserts that the Tmax temperatures have been cooled by irrigation allowing them to appear to stay constant. With the water shortage (not mentioning the cause) could they not have compared irrigated land and non irrigated land in the same the same areas to establish the relationship. Further as less irrigation has been possible I might have expected a decline in Tmin although the relative change is probably hard to discover, while the crop decrease from cotton to cows is easier to discover.
the TMax trend is not significantly different from zero.
The temperature results in this part of California (see also Christy and Hnilo 2010 on snowfall) do not provide evidence of greenhouse theory expectations.
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Dr. Christy, thank you, now can we talk you into doing a hundred or so more of these?
Heavy irrigation raises the dew point. The dew point reduces falling night time temps.
There are always questions.
But in general:
Three cheers for the actual data.
Thank you Dr. Christy.
“The key factor in all of these causes is the idea that the delicate, nocturnal boundary layer in which TMin is measured can be easily disrupted by many factors – warmth from surface fluxes due to irrigation, IR forcing from aerosols, buildings which increase roughness (and thus mixing) etc.”
Have been waiting for some time for someone else with more understanding to verify that very thought. Seems that is also one of the keys aspects in UHI itself let alone irrigation. I would like to learn more of “inversions”. I know they are frequent at night, especially when still, but know little of their specific characteristics, average altitude, exactly what causes most to be nocturnal, is that partially why moist cloudy nights are generally warmer and not strictly ‘radiation’, etc.
Interesting Dr. Christy.
It seems reasonable to me that irrigation would raise nighttime temps. Water has a massive heat capacity relative to most other materials, so it would take some extra time to cool off land soaked in water.
Conversely, it would take longer to heat it up in the daytime for the same reason. That makes sense, right?
The humidity most likely increased due to irrigation. The increase in humidity increased the heat capacity of the atmosphere. This means more heat energy is required to raise the temperature of the atmosphere and greater heat energy loss is required to lower the temperature. This means you would expect lower maximum high temperatures and higher minimum temperatures.
The highest temperatures in the world are recorded where there are the least amount of green house gases (where the humidity is lowest).
Humidity by season can be inferred, to some extent as relatively wet/dry years, by subtracting TMin from TMax.
The higher the value, the drier the year/season.
A drought year has a high value, and an El Nino year has a low value.
I would expect irrigated areas to have a lower TMax-TMin.
wayne says: at 7:25 pm RE: inversion basics
a simple graphic summary of inversions:
http://irina.eas.gatech.edu/lectures/Lec18.html
and here is one place where orchardists find relief:
http://www.orchard-rite.com/wind.cfm?m=92
While a few folks once used a bale of old straw or hay and a guart of fuel oil to help stir the air the historical method involved an actual burner commonly called a smudge pot:
http://en.wikipedia.org/wiki/Smudge_pot
For the reasons why people grow apples and such in places where cold temperatures are common one needs to understand the development of shape and color, say, in red delicious apples. That’s a side issue as regards this post.
I am just an unconnected bystander observing the various discussions. I have become so skeptical of the recorded data I cannot trust any theory derived from it. The people involved almost always have an agenda and are therefor unreliable. Your loss of credibility has destroyed your ability to influence most people and the only ones jumping on your wagon seem to be politicians seeking riches or power.
johnmcguire says: at 8:46 pm “unconnected”
What? To whom do your refer? “Your loss of credibility . . .”
And where am I supposed to go if I click your screen name?
Kevin says:
September 12, 2010 at 7:28 pm
Almost – the key thing, especially when dew points are above 20°F or so (say, -10°C) is latent heat released by condensation. As the ground radiates heat to a clear sky and cools to the dew point, then water vapor begins to condense as dew or frost. The heat released by that visibly slows the rate of further temperature decrease. My home weather station shows the effect quite nicely, it you look at some private weather stations at http://wunderground.com that are near you, you may see the same thing.
My station is at http://home.comcast.net/~ewerme/wx/current.htm. The last couple of days don’t show the effect very well. I should write a web page with some good samples.
In really cold conditions, the air is so dry that frost development doesn’t involve enough freezing water to significantly slow down cooling.
In the morning, sunlight heats the ground. If there’s dew, it takes a little while to evaporate that, but eventually the cold air of the nighttime inversion warms up and convects upward. Frequently I’ll see the temperature rise to a plateau – that’s when convection begins, and the air is “well mixed” allowing air aloft to come down just as easily. This brings the daytime breezes that keeps the ground level air at a relatively steady temperature. Once the sun gets low enough, radiational cooling cools the ground, air on the hillside behind us flows downhill and the inversion returns.
On our property in the New Hampshire mountains, summer evenings near the road feature a cool draft flowing downhill through the valley. The draft is strong enough that we’ve built up the rock wall around a camp fire pit to catch some of the sparks the draft blows away.
Dr. John Christy, my hat is off to you. Finally, someone who cares about the data as much as I do. I came from the orbit determination/trajectory analysis side of applied mathematics and have been a data base analyst/ administrator and scientific programmer. Finally, some one who has looked at all the raw data and has not run it through the a data blender.
I had only scanned the original article so I kept my mouth shut. I grew up in Phoenix in a neighbourhood that was irrigated. I use to deliver papers ( back in the day when paper boys were actually boys). The areas that were being irrigated were often noticeably warmer then those that were not. While camping, I also noticed that arroyos with water, where we would camp, were usually quit a bit warmer then the adjacent dry areas that I visited in the very early morning. Of course this is only experiential information and not data, but it demonstrated to me micro-weather caused by humidity. (BTW, the desert can get really *cold* at night!) That humidity raises Tmin, does not surprise me at all. I can’t wait to get a chance to read the paper. It sound like an attempt at real science.
Old folks say there was regular snowfall here in Katoomba (Sydney Australia)-prior to the Warragamba Dam. Searching bom.gov.au isn’t a help on snowfall records.
When the crops are being watered, the water is cold. It heats up in the sun of the day and gives off that heat at night along with adding to the humidity. It all sounds like a good balance to me and we got some food out of the deal.
dave
I wonder how much that “homogenization” process is biasing the temperature record.
As an old desert farmer I can attest to the conclusions of Dr. Christy on irrigation effects in the inland valleys. T max is only generally effected during irrigation in the irrigated field. T min. is valley wide from humidity build up, mainly from increased transpiration of field plants day and night. Also plants will burn up carbohydrates at night to keep warm. Believe it or not. Night temperatures of 50F or less will cause burn of most or all of the carbohydrates made during the day. pg
Patagon says:
September 12, 2010 at 11:05 pm
I wonder how much that “homogenization” process is biasing the temperature record.
Yes, and while comparing it to Dr Christy’s detailed compilation, it would be nice to see it compared to the satelite record as well. Throwing in those few stations that do record humidity would also be of possible educational value.
trbixler says:
September 12, 2010 at 6:29 pm
This new study looks at Tmax and asserts that the Tmax temperatures have been cooled by irrigation allowing them to appear to stay constant.
Not sure when the study was conducted, but Tmax has been falling almost everywhere in California for the last several years. Even portions of the Mojave Desert have cooled.
A possible reason for the temperatures appearing to remain constant in the Central Valley may be a result of the warming caused by irrigation.
See the degree day maps at http://uspest.org.
But are we permitted to drink data that hasn’t been homogenised and pasteurised for our own good? It all sounds so terrifyingly natural and straightforward to me. What would the proper authorities think of this blatant transgression?
Christy says he hasn’t read the [Columbia] paper which is a pity. But since its claim is that Tmax is being depressed by irrigation, it would appear that Christy has already produced evidence countering that claim, insofar as his Sierra Tmax and valley Tmax march in sych whereas the valley Tmin trend rises and overtakes the Sierra Tmin trend.
However, the foothills Tmin trend shows a strange anomaly – falling in the 1980’s where both valley and mountains are rising.
Before the installation of large fans to prevent frosts, ie mixing and moving the air, some farmers used irrigation (overhead sprinklers). The water from the river or wells is obviously well above freezing.
Whether this has any bearing: We always irrigated at night to reduce evaporation. Daytime irrigation with sprinklers and in particular the high pressure single guns (Self propelled irrigators) could lose up to 30% to evaporation. That is some 12o gals per min per irrigator. A valley may contain hundreds of such irrigators. High electricity prices have caused most to go low pressure irrigation systems.
The key point is that you had oversampled data and therefore you can draw reliable conclusions from them. Most of the published records are severely undersampled, both in time and space, and from a signal processing perspective one cannot draw any reliable conclusions from them.
My congratulations on processing the original data by hand. It is the mark of a genuine scientist who does his own work rather than leaving it to his assistants.