Study: irrigation causes 'significant cooling of global average surface temperatures over land'

Irrigation in a field in New Jersey

From the HockeySchtick: A paper published last week in Climate Dynamics finds man-made agricultural irrigation “causes significant cooling of global average surface air temperatures over land and dampens regional warming trends” by increasing cloud cover and precipitation.

According to the authors, “irrigation, however, is typically not included in standard” climate models, and thus, “irrigation should therefore be considered as another important anthropogenic climate forcing in the next generation of historical climate simulations and multi-model assessments.”

The negative feedbacks from evaporation & convection of water vapor, clouds, and precipitation illustrate how the climate is self-regulating, independent of CO2. 

The paper:

Irrigation as an historical climate forcingBenjamin I. Cook, Sonali P. Shukla, Michael J. Puma, Larissa S. NazarenkoAbstract:

Irrigation is the single largest anthropogenic water use, a modification of the land surface that significantly affects surface energy budgets, the water cycle, and climate. Irrigation, however, is typically not included in standard historical general circulation model (GCM) simulations along with other anthropogenic and natural forcings. To investigate the importance of irrigation as an anthropogenic climate forcing, we conduct two 5-member ensemble GCM experiments.

Both are setup identical to the historical forced (anthropogenic plus natural) scenario used in version 5 of the Coupled Model Intercomparison Project, but in one experiment we also add water to the land surface using a dataset of historically estimated irrigation rates. Irrigation has a negligible effect on the global average radiative balance at the top of the atmosphere, but causes significant cooling of global average surface air temperatures over land and dampens regional warming trends.

This cooling is regionally focused and is especially strong in Western North America, the Mediterranean, the Middle East, and Asia. Irrigation enhances cloud cover and precipitation in these same regions, except for summer in parts of Monsoon Asia, where irrigation causes a reduction in monsoon season precipitation. Irrigation cools the surface, reducing upward fluxes of longwave radiation (increasing net longwave), and increases cloud cover, enhancing shortwave reflection (reducing net shortwave).

The relative magnitude of these two processes causes regional increases (northern India) or decreases (Central Asia, China) in energy availability at the surface and top of the atmosphere. Despite these changes in net radiation, however, climate responses are due primarily to larger magnitude shifts in the Bowen ratio from sensible to latent heating. Irrigation impacts on temperature, precipitation, and other climate variables are regionally significant, even while other anthropogenic forcings (anthropogenic aerosols, greenhouse gases, etc.) dominate the long term climate evolution in the [climate model] simulations.

To better constrain the magnitude and uncertainties of irrigation-forced climate anomalies, irrigation should therefore be considered as another important anthropogenic climate forcing in the next generation of historical climate simulations and multi-model assessments.


49 thoughts on “Study: irrigation causes 'significant cooling of global average surface temperatures over land'

  1. Actually, I find that Class 1\2 stations (USHCN) in cropland had significantly higher trends, higher than urban station trends. So I find this report interesting, as it finds exactly the opposite. So are these guys measuring actual trends from actual stations?

  2. So how much cooling has irrigation caused and on the converse, how much warming has the draining of wetlands caused. Where does the loss of transpiration due to deforestation fit into this equation? How much is “significant cooling” in the scheme of things?

  3. The irrigated agriculture, I coined this as rural cool-island effect. Urban-heat-island is overemphasized with dense network of met stations around urban centres. At the same time rural-cold-island effect is under-emphasized with sparse met network. This is however is accounted in the satellite data. NASA in fact withdrew this from internet — which I included in my book published in 2008.
    Dr. S. Jeevananda Reddy

  4. There is the usual climate science “long-wave radiation” jargon in the abstract. Actually the reason irrigation causes cooling is that it enhances the much more effective (and usually larger) convective transport of (latent) heat upwards from the surface. The decrease in long-wave radiation is unimportant in comparison.

  5. ” dampens regional warming trends”
    Pet peeve — DAMPS not dampens. Dampen means to make wet. To damp means to reduce extremes. In a chimney, a damper is something that allows smooth airflow up the chimney in response to variable winds across the top of it.
    My other one is “preventative” it’s “preventive” but the former has become so widely used as to become accepted, much to my chagrin. I’m not often a grammar nazi, but damp/damping and dampen/dampening is one if my sore spots.

  6. I remember a study some years ago claiming the opposite. Irrigation leads to more water vapor in the air and more local warming.

  7. Further evidence that latent heat use cools. Been saying this for years.
    GHE is rubbish and impossible.

  8. Bullocks! Don’t you all know the “Science” is SETTLED!?
    C02: It warms. It cools. It wets, It dries. But wait, there’s more! It fertilizes, It slices. It dices and when properly applied can be a floor wax or food topping…

  9. Santa Baby says:
    June 25, 2014 at 1:18 am
    I remember a study some years ago claiming the opposite. Irrigation leads to more water vapor in the air and more local warming.

    Really? I thought the concept of enthalpy of vaporization was widely known among scientists.

    Heat of Vaporization
    The Heat (or Enthalpy) of Vaporization is the quantity of heat that must be absorbed if a certain quantity of liquid is vaporized at a constant temperature. In a solution with both a vaporized and liquidized states, the kinetic energy of the vapor is higher than the kinetic energy of the liquid. Temperature follows kinetic energy, showing a lower temperature in the remaining liquid.

    (from )
    That’s why I found the title of the article so obvious. I knew that since I was a child. My mom used to pour some water in the patio of her house to cool it, I thought everybody knew that.

  10. urederra says:
    June 25, 2014 at 1:58 am
    Indeed. water vapour blinds are sold in hot climates.
    One can install a system around say an enclosed terrace which sprays a a very fine atomised mist of water. This evaporates and cools. It is claimed in the adeverts for these systems that they can reduce temperature by 3 to 5 degC.

  11. There is presumably a difference between land that would be scorched earth without irrigation, and land that would have vegetation cover but be unsuitable for agriculture. As another thought, isn’t increased moisture content meant to warm night-time temps and cool daytime?

  12. Interesting but not likely to help explain the real climate change cycle commonly named the Quaternary glaciation. The Geo folks, maybe hoping the ice age cycles would end using the force of naming, stopped the Pleistocene epoc in favor of naming our epoch the Holocene. It’s comforting to know we humans get our own epoc.
    Regardless, other than local/micro weather forecasting, how pouring water on the ground impacts the coming climate change (glaciation) and building all those windmills should produce very good retirement funding for those receiving grants.

  13. Yeah, whatever. Some of what man does may cause some small amount of warming, and some of it may cause a small amount of warming. Basically, it all balances out, and man’s effect on temperature is still essentially zero.

  14. Irrigation, however, is typically not included in standard historical general circulation model (GCM) simulations along with other anthropogenic and natural forcings. To investigate the importance of irrigation as an anthropogenic climate forcing, we conduct two 5-member ensemble GCM experiments.
    Computer games. Since when were comparisons of modeling results considered “experiments”? How about some comparison of actual temperature readings between irrigated and non irrigated locations? You know, like Dr. John Christy did years ago?
    I’ll take observations over model runs any time.

  15. evanmjones wrote, “Actually, I find that Class 1\2 stations (USHCN) in cropland had significantly higher trends, higher than urban station trends…”
    Is that daytime or nighttime, and what seasons?
    Increased humidity and cloudiness from irrigation, and increased water-cycle cooling from increased evaporation, should moderate (cool) daytime highs in the summer. But increased cloudiness prevents some cooling at night. So to notice the effects of irrigation on temperature you might need to separate the trends for daytime highs from the trends from nighttime lows, and perhaps limit your examination to the seasons in which irrigation is employed.
    Also, note that lawn-watering in suburbia can significantly increase humidity.
    Also note that the effects of irrigation on temperature trends will only be apparent if the degree to which irrigation is employed changes. E.g., When “green” activists limit irrigation to protect the Delta Smelt / Minnow in California, it may increase the warming trend for daytime highs.

  16. The amount of water for evaporation is relatively constant (more here means less there). It plays a part in a locale’s temperature. But then is offset from where the water would be going.

  17. In continuation of my earlier post:
    Chinese Vaastu [science of Architecture, it is an important component in town planning] is known as Feng- Shue, which means wind and water (related to winter & summer) — during 6 months of around 24 hours of Sunshine in summer, to overcome the heat, they put water in front of the house on the Southern side in a canal that evaporates the water in the canal and keep the house cool.
    WMO 1996 publication presented few examples of constructing houses to keep cool inside and outside the house — The Palace of Justice in Klungkung, Chief City of Bali in Indonesia built in 1710 is a classical example in this regard. This in fact I quoted in my Vaastu: A Practical Guide book published in 1997.
    In 1980s I arrived at — cube root of precipitation a function of Global solar radiation and evaporation.
    Based on such factors, I introduced cold-island effect similar to heat island-effect, which is in use since more than 250 years.
    Dr. S. Jeevananda Reddy

  18. If irrigation causes significant cooling then it follows that man-made drainage causes significant heating. And drainage is everywhere. Around here many farm fields have drainage tile to prevent flooding. All cities, airports, roads, etc are designed to get rid of storm water. Parks, golf courses, ball fields, homeowners are constantly doing drainage improvement projects. How many tens of thousands of miles of corrugated plastic drainage pipe have been installed everywhere over the years? Drainage acts everywhere all year round while irrigation just goes on in some places just for a limited time.

  19. ‘typically not included in standard climate models’ – I’ve given up counting all the variables that I have found studies for (on this site often but elsewhere too) that were not included in the climate models. I have come to the conclusion that there are different classes or categories of problems that allow or don’t allow scientific modelling: for example, it is perfectly easy to predict Earth’s position on its way around the sun on any given date, any given fraction of a second even. However, if we wanted to “compute” this position by accounting for every single atom over time, the model would never work. In this case we can just take the earth “as a whole” and treat it as a “point in space and time” with all the mass collected in that one point. With But everyone knows that this point represents COMPLETELY the total mass and the vectors of Earth’s movement. In climate modeling however, they are trying to condense the future “temperature” into exactly such a “point” but they don’t have one underlying source of causation as, in the Earth’s movement, gravity, but an as yet uncounted (and I believe innumerable) amount of currents, cross-currents and counter-currents that each impinge on each other. This will never work but also it will never end until funding dries up. It is like a group of rogue mathematicians who set out to “remeasure” the sum of the angles in a triangle to see if they can come up 180 – and each time the result isn’t quite satisfactory, but we are getting closer, and closer … and closer.

  20. Irrigation […] causes significant cooling of global average surface air temperatures over land

    Who’d’ve thunk? Positive water vapor feedback, anyone?

  21. John Christy did a study on this YEARS ago, and the study was addressed on this blog.
    Thanks to transpiration, DAYTIME temperatures were lower than on non irrigated land, but
    NIGHTTIME temperatures were higher, with overall slight warming , and a moderation in temperature extremes.

  22. wow…they discovered that ground water is cooler than air temperature
    …next thing you know, they will discover that asphalt, air conditioners, and heaters make it warmer

  23. Now the climate nazis want to ban irrigation? Do they comprehend where their food comes from? What are they going to eat, each other?
    [your statement is both wrong and misguided – mod]

  24. My guess it that overall it causes warming, but cooling during the growing season. Albedo probably decreases during the off seasons (darker soil and darker/greener vegetation all around and downsteam from fertilization (probably in some in the ocean as well)).

  25. Lets see, cities don’t add heat to the environment and thus don’t raise recorded temperatures —
    but farmland irrigation cools the environment and lowers recorded temperature (And don’t forget suburbanites watering their lawns!).
    Now we see why rural station temperatures must be adjusted up to match the higher temperatures found in cites.
    Oh, God! It is too early in the morning for stuff like this!
    Eugene WR Gallun

  26. I should clarify some. Globally, I think it will cool/be neutral due to water cycle, transpiration, etc. At the surface level, I think it will warm spring and fall and cool in the summer. I think expanding farm land (increasing irrigation) will warm the upper troposphere because of high aerosol concentration mean more latent heat release. Transient warming, during expansion/growth and neutral/cooling long-term/steady state.

  27. Yes yes, water moderates temperature extremes, but in AGW theory water increases temperature. No doubt there is an elaborated theory to “prove” why this is so. This theory will be supported by more theory and the whole of the inverted pyramid of theory will rest on the absorbency spectrum of … yes, you guessed it: CO2.

  28. Yeah, all that evaporation not normally there.
    Will vary with efficiency of irrigation, though efficiency may expand areas irrigated thus evaporation roughly constant.
    What about less water elsewhere due diversion to irrigated areas?

  29. Local irrigation causes GLOBAL cooling, wow now that is what you call powerful stuff, we no longer need to control CO2 just put in a bit of irrigation.

  30. Well, things are not completely understood about irrigation and cooling, but here’s what we do know. . .
    1. Whatever it is that is going on, we are near a point of no-return.
    2. To get a better understanding of the situation, there is an urgent need for a massive increase in grants given to proper thinking academics. . . .
    3. To ensure that the future is kept safe for the children, the government in general and the EPA and the IRS in particular must be given massive powers to do whatever it is they would like to do. . . .its for the children, people!!!
    4. And oh yeah. . .the science is settled, and if you don’t agree with it, then you are a disreputable and despicable denialist. . . .
    5. The Koch brothers also have something to do with it, and they are on the wrong side of history. . .

  31. If visitors to Las Vegas, say in two weeks, walk around some of the newer outside shopping areas they can watch this miraculous new ‘research’ in action.
    Las Vegas outside venues have frequently installed misting systems to regularly ‘mist’ and cool the air. Shoppers can be surprised when they’re suddenly enveloped in mid-day spraying.
    A) Misting does lower the temperature of the immediate environs.
    B) Not all native Nevadan’s appreciate the frequent abuse of water as it drives up their home water costs and it raises the humidity levels around Las Vegas.
    Across the West, when one crosses a water course, if people got out of their cars and walked the area (without trespassing) they would notice that streams make the immediate area much cooler.
    Duh! One would wonder why these alarming folks don’t suddenly decide to add the irrigated area’s historical temperatures into the global average. That’ll take some forcing though, instead they’ll use fanciful model estimates plugged into their models to cool near term temperatures while preserving alarmist’s favorite predictions of gloom, doom and damnation.

  32. The latent heat required to evaporate a few millimeters of water at the surface is equal to that required to heat the entire column of atmosphere above it 1 degree C..

  33. Size of Kansas => 81,823 mi² = 52,366,720 ac
    Area under irrigation = Irrigated Area 3,123,271 acres
    Water Pumped 3,430,047 acre-feet
    1998 data
    So putting 12″ of water over 6 percent of the land causes ‘cat-astro’ effects on temperatures??

  34. DD More, A foot of water is the equivalent of cooling the entire atmospheric column 1 C over 6 % of Kansas about 75 times, but if only the bottom 1000 feet is cooled, then it is equivalent to cooling that 1000 feet about 2000 times, or cooling the bottom 1000 feet of the entire state about 120 times, so that surface thermometers would be skewed 1 C. cooler for 4 months of summer per year. I know that is making lots of assumptions, but gives you an idea of the cooling effect of water evaporation.

  35. Hmm and yet Phoenix is still hot. If anything the extra irrigation there made it hotter and more unpleasant.

  36. I don’t get it at all.
    The orders of magnitude are such that this is a meaningless discussion.
    Total Earth Area km2 510’072’000 (1km2 = 100 Ha = 247.1 acre)
    and according to FAO, in 2011:
    Land area 130’034’198 25.5%
    Agricultural area 49’116’227 9.6%
    Arable land and Permanent crops 15’529’766 3.0%
    Arable land 13’962’795 2.7%
    Total area equipped for irrigation 3’182’902 0.6%
    Anthropogenic cooling/warming with watering (or not) 0.6% the globe surface!
    Who is kidding?

  37. Irrigation has a minimal impact on the global surface temperature, however it can have a major impact locally. If you want to experience an example of Anthropogenic Local Warming (ALW) try visiting Palm Springs or Tucson. These desert communities, which used to enjoy cool evenings and mornings, are surrounded by a plethora of golf courses, which noticeably increases the humidity and reduces radiation cooling. I doubt the same could be said for increased levels of CO2 around urban areas.

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