14 February 2011

The Irrigation Efficiency Conundrum

A guest post by John Bredehoeft (Hydrodynamics Group, Sausalito, CA)*

There is a well-known misconception that improving farm irrigation efficiency can save water in an entire water system. Often the argument associated with irrigation efficiency is analyzed with a large and complex model of a real system—I have done some of these models. With these large models it becomes difficult to see the clearly the relevant hydrologic principles—one gets lost in the trees and loses sight of the forest. Often it is useful in both science and engineering to use a zero-order analysis, a back of the envelop calculation, to illustrate a basic principle. A simple explanation will illustrate the problem associated with improving farm irrigation efficiency:

Nevada has several rivers that flow east out of the Sierra Mountains into the western part of the state where irrigation uses all of the water in the river, except in the wettest years. The Walker River is one of these; Walker Lake is drying up because of irrigation upstream along the Walker River. The irrigators are very efficient in capturing the streamflow.

Let’s use the Walker River as a rough prototype for a very simple irrigation system. Let’s assume that the River flows during the average irrigation season at 100cfs, and that there are 10 farmers along the river, with more or less equal water rights of 20cfs each. Typically the irrigation system including, the canals and laterals and the farms, are 50% efficient; we need not complicate our analysis with where the inefficiencies occur. So we have:
  • 100cfs of streamflow
  • 10 farms
  • 20cfs water rights/each
  • 50% efficiency
Each farmer diverts 20cfs, uses 10cfs for ET for his crops, and 10cfs returns to the stream, available to the next farmer downstream. Everything is fine until we get to farmer number 10; he finds that there is only 10cfs left in the stream. This is not sufficient for his needs, and he does not farm—so 10cfs remains in the stream, is used by riparian vegetation or the aquatic ecosystem.

If we now examine the entire system, 90% of the water is used productively, even though the farm efficiency is only 50%. We need to distinguish a system efficiency, as well as a farm efficiency.  

IMPROVED EFFICIENCY

Now let’s improve the farmer’s efficiency. For the sake of argument, to make our point, let’s assume the efficiency is improved to 100%: meaning we line canal and laterals, and go to drip irrigation on the farms: Now we have a decision -- What is meant by a water right?
  1. Is the farmer entitled to use all the water his right allows him to divert, or
  2. does the water right apply to water that he previously consumed?
In the United States various state courts have decided this issue both ways.

Let’s first look at the situation where the farmer is entitled to use his entire 20cfe right. With 100% efficiency, the first 5 farmers use their 20cfs, drying up the stream, and the other 5 farmers get no water. The system is 100% efficient, all the water goes to crops. Of course, only five of our ten farmers get water.

In the second scenario each farmers gets 10cfs—his previous consumptive use. Now all the farmers get water. Again, the stream is dried up, and all the water goes to crops—the system is 100% efficient.

COMPARISON OF THE TWO SYSTEMS—50% versus 100%

When we compare our two systems; the 50% farm efficient valley uses at least 90% of all the water available. Of course, the 100% efficient system uses all the water. In terms of the entire valley, we gained, at best, 10% by going to 100% farm efficiency. This is hardly a policy one wants to subsidize. There is the issue of how to pay for the increase in farm efficiency. An individual farmer may increase his output by using his water more efficiently, but usually his increased water use comes at the expense of less water in the system for his neighbors—he beggars his neighbors.

Bottom Line: In focusing on increasing farm efficiency, one often loses sight of looking at the efficiency of the entire system. From a policy perspective, it is usually the performance of the system that is of ultimate concern. Increasing farm efficiency usually does not save water in the system.

* In response to my posts (here and here) criticizing the Pacific Institute's claims about "saving" water from efficient irrigation.

For academic studies on this issue, see:
  • Ward, F. A. & Pulido-Velazquez, M. "Water conservation in irrigation can increase water use" in Proceedings of the National Academy Of Sciences, 2008, 105, 18215-18220.
  • Pfiffer, L. & Lin, C.-Y. C. "Incentive-Based Groundwater Conservation Programs: Perverse Consequences?" in ARE Update [PDF], 2009, 12, 1-4.

20 comments:

  1. "Carriage water" (the water that is necessary to provide adequate flow in a larger channel) is another factor the priests at the Temple of Conservation tend to ignore.
    People conserve a resource when there is a value associated with doing so, not because some nag pesterd them. In the case of water, when it is priced correctly, and when a water right owner can sell some portion of the water they have conserved without threat to his property, he will maximize returns by improving his irrigation systems.
    We have seen a similar situation in wildlife management in Africa. Countries that banned hunting saw their game wiped out. Botswana, on the other hand, carefully managed their game populations, and paid farmers for the crop and livestock damage consequent on large beasts wandering the neighborhood. (After all, that elephant is not so magnificent when it has eaten your family's next six months' food, and trampled your son.) With losses mitigated, and a positive benefit from tourism and hunting fee revenues, the rural inhabitants saw value in conserving game. They drove away the poachers that were welcomed in other countries.

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  2. John,

    Thanks for a really clear description of a problem that still seems to challenge a lot of policy makers.
    In standard economic theory, farmers have already optimized their crop portfolio based on their allowed consumptive use of water so given their water rights, the low value high water use crops they grow must be efficient. In theory then, the change to more efficient water delivery systems wouldn’t change the cropping portfolio, because a farmers cost of water wouldn’t be any different, he would just cut down on the waster. Robert Young has a paper somewhere that talks about that effect. If the irrigation improvements are subsidized, cost of water to the farmer wouldn’t change. If irrigation improvements _aren’t_ subsidized, farmers average cost of water increases, and so he might be more inclined to consume less water, or change his crop portfolio. This might change the economic value of the irrigation system I think that when looking at the efficiency of the entire system, it could be important to look at both water use and the economic benefits generated from its use.

    David,

    Given that we know the challenges associated with consumed vs diverted water, how would auctions in an irrigation district work? Urban water districts like MET don’t have challenges with return flow in an auction system, as their waste water is easily quantified. However, the additional cost to plumb and quantify return flows in an irrigation district seem prohibitively high. As far as I can tell, there aren’t even effective diversion measurements for most IID farmers. The political challenges associated with redefining farmer rights in terms of consumption also seem a bit hairy. Have you written about that somewhere? Your All-in Auction post doesn’t discuss return flows.

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  3. This point about basin efficiency being more important than farm efficiency is fair but should not be taken so far as to mean that there are no improvements to be had in how agriculture is managed from a regional or individual perspective. Let's move the discussion beyond this simplistic point into areas where we can help maximimize agricultural productivity under whatever amount of water is available.

    A couple of points: Some contend that the evaporation from a field with flooded furrows is negligible since the moisture is retained under cover of the crop. Others disagree. Has anyone done a definitive study that employs a useful example?

    And efficiency in terms of acre-feet per acre (leaving crop choice aside for now) is often not the right measuring stick in a place with more land than water - probably better to measure "crop per drop".

    There are other issues as well, such as the timing and quality of return flows and what it means in terms of groundwater recharge, not ot mention that drip allows lesser use of nutrients and other chemical inputs.

    The physical and political parameters are vary different even in adjacent areas so it is hard to find a one size fits all solution.

    We at the Environmental Defense Fund have long encourgaed the appropriate use of water markets as a tool to maximize agricultural productivity.

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  4. Nobody is saying that conservation automatically equals more water in the system if the system is not managed in a way to allow it to happen.

    For example, urban water conservation has achieved stunning savings by switches to low flush toilets and outdoor landscaping changes. They have not resulted in more water in the overall system because the proceeds were in part lost to growth.

    You don't need a hydrologist to model that for you, and in the case of John Bedehoeft, you don't need to put foreign signature phrases such as "bottom line" in his perfectly capable mouth to drive it home.

    It flies in the face of common sense to suggest that if you lose less, there won't be more. You have a good point that more won't make a difference if it isn't managed properly. But this taking of endless shots at Peter Gleick, this time using a distinguished hydrologist as sock puppet, brings to mind a movie line "You can rock on a rocking horse all day but it doesn't get you anywhere."

    This isn't getting us anywhere.

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  5. @Christa -- AiA are meant to be run for consumptive water, not diversions. I agree that diversions are what farmers take, but consumptive use can be measured fairly accurately if there's a need to divert x to get consumption of y. (As mentioned by others, AiA are easier for urban water allocations).

    @Spreck -- evaporation in places like IID is huge. There are probably hundreds of studies (by agronomists) on ET vs. diversions. I'd also add that farmers have lots of incentive (but maybe not the information) to reduce application of chemicals and fertilizers.

    @Emily -- not sure why your comment is so hostile. John is a real person, not a sockpuppet, and he volunteered to write this post. His point is useful, especially when discussing ag water, which is exactly what Gleick (and many many others) focus on as a source of "excess" wasted water that can be conserved and sent to cities. Quite frankly, I could give a shit about Peter Gleick. He's a guy who works hard on water issues. I care more about the ideas that he's spreading, that have no usefulness in terms of fixing water problems (e.g., farmers can just get more crop per drop and there will be lots of water left for urban users). We need to consider the incentive to use less (none, if there's a property right but no profit), what's available (the addition and subtraction), and the politics of moving water from ag to urban (or ag, or enviro). It's a three-dimensional problem that can't get fixed from only one side.

    Thanks for reading, but your comment is not getting us anywhere.

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  6. It seems to assume that 100% irrigation efficiency means that the farmer uses up his whole allotment of water and doesn't return any of it to the stream.

    It would seem to me that a more efficient irrigation system would mean the farmer would use less water than he is allocated, leaving more in the stream.

    Is the authors base assumption wrong? He seems to think that being more efficient means using more water on his land, not less.

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  7. Ironically, some on farm conservation measures may well increase annual farm water consumption, if the improvements allow a grower to double-or even triple-crop a field (jargon for being able to grow several succeeding short lived crops in one season). Many valuable "specialty" crops require extremely precise delivery of water and nutrients. They are risky and expensive to grow, and use as much water as anything else. In fact, the added income from double cropping, made possible by the better control of water, may be the economic driver for the investment in the new irrigation system.
    I don't think anyone is saying that conservation is a bad thing, just that it is not the panacea some think it is. It is also important to point out that sprinklers, drip, greenhouses, all require substantial energy costs. Gravity comes free.

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  8. Holy crap. I have to respond AGAIN to these misrepresentations, mischaracterizations, and gross simplifications?

    First of all, Zetland is wrong when he simplistically claims that we (the Pacific Institute) look for ag efficiency improvements to satisfy growing urban demand. Once again READ our reports. We don't. That's certainly a possible policy option (one which Zetland himself has long endorsed through the use of markets and prices). But efficiency improvements can be used for ecosystem restoration, increase ag production somewhere else, or many other things.

    But more importantly, John repeats the same gross misconceptions about ag efficiency that characterize much work in this area. Explicitly: just in the example he gives, in the very first case the last farmer in the line (who only has 10 units left in the river) can still satisfy his needs, just leaving nothing in the river. This is a minor point, but relevant for what follows

    More importantly, this argument about basin efficiency (which everyone understands, yes, even me) once AGAIN ignores FOUR key things that WE address in our work on efficiency: (1) the energy cost of taking unneeded water out of the river; (2) the water quality problems associated with using too much water on a field resulting in contaminated return flow; (3) the potential (quite real in practice) that improved irrigation efficiency doesn't just reduce water use but increases crop yield and quality; and (4) the false assumption that the 50% excess applied to the fields in John's example ALL returns as return flows. This last point is repeated over and over and over in the simplistic assumptions used to discredit efficiency potential. In fact, some inefficient water (the amount varies from place to place and case to case) does NOT return as return flow: it goes to unproductive evaporation, or some may go to groundwater that cannot be recovered. In John's example, the downstream farmers would run into trouble faster, and efficiency would serious improve their water availability... Thus, the incredibly narrow focus of the traditional ag efficiency academics on "quantity" grossly misrepresents the benefits of efficiency, and even the discussion of quantity is wrong.

    I'm sorry that John does not address these, that Zetland continues to post misrepresentations and misunderstandings of the Institute's work, and that neither seem to be willing to discuss these.

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  9. I regret the appearance of hostility. It is exasperation. I am a big fan of yours and your site, but this endless taking of pot shots at Peter Gleick/the Pacific Institute is getting old. I am familiar with John Bredehoeft's work and have never seen him end an article "bottom line." As such, it looks like he's being spun and this doesn't strike me as an honest post.

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  10. I'm still scratching my head on this one.

    But, what is bad about increasing farmer efficiency ? They should use "their" water as efficiently as possible.

    Even if it doesn't result in "extra water" at the end of the user group, the farmer has responsibly used the water appropriated to him. Yes?



    But it is certainly counter intuitive. If the farmer uses less water, what is left should run down stream or in my opinion go back to the appropriator. In Alaska we have a very strong use it or lose it law, but you also have to be responsible in your use. If you don't use it over a 5 year period it automatically reverts to the state. Your water appropriate is ONLY what you actually "beneficially use" not what it says on the appropriation.

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  11. @DW and RD -- The question really boils down to "beneficial flood irrigation" vs "beneficial drip irrigation" -- both grow the same amount of crop; the former "uses" more water while the latter "uses" less water but more equipment.

    Either are allowed under beneficial use, which does not define the cost/benefit of beneficial.

    @Kurtz -- yes, there are costs and benefits, in terms of water, equipment, labor, price, management time that all drive water use decisions.

    @Peter (we can use first names, yes?) -- thanks for your thoughts. (1) drip irrigation often uses energy, right? (2) water quality in return flows may be balanced by gains from flooding -- to the farmer (e.g., WWD). (3) If efficiency improves yield, then farmers would already do that (that's what I said 2 yrs ago), (4) I agree that evap can matter, as I mentioned in the comment to Spreck (and in emails to John, who wanted to make a simple point).

    Sorry that I don't seem to get PI's work; I pay a lot of attention to the headlines and how others (mis)read it.

    @Emily -- I added BL to the post, as I do to many guest posts. All the words AFTER "Line:" are John's. As for potshots? I am tired of reading this crap as well, but someone's gotta present the missing links (Bob Park has been rebutting "cancer from cell phones" for 15 years. He's more patient than me.)

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  12. Our biggest problem is in mining. they apply and get a water right, and then only use a fraction of it, but claim that "may" need it later.

    I cut back on a number of these "permits" and told them that when they were ready to use the water to apply for that increase. They claimed they needed this amount of water in their "plan". I said that was fine, but ask for the water when you need it, not "some time when you think you might need it".

    It was in part these experiences that caused me to put up the legislation on bulk exports that authorized "up to X per season". If it wasn't used in 5 years, the "right" was lost.

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  13. DZ -- "If efficiency improves yield, then farmers would already do that..."

    I think you're ignoring (or discounting out of existence) the human factor that may be involved on this issue: inertia. "But we've always done things this way and things have worked out fine" might be a real practical impediment to both increasing the efficiency of water usage and, ironically, increasing yeild through use of water efficiency improvements.

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  14. @Anon -- then are you implying that they should be forced to end the inertia? bribed? Neither is sound fiscal or political policy :)

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  15. I have to ask what farmer/business person is going to invest $1000/ac in a new, highly efficient irrigation system and then decide to grow the same production as before - thus conserving real water?

    Our irrigation system upgrades invariably found the producers: 1) irrigating additional acres with the "extra water"; 2) planting a higher water use crop (milo to corn; corn to alfalfa, etc.); 3) fully irrigating the same acres they had been deficit irrigating before (stretching the water); 4) doing pre and post irrigations because the new subsurface drip system (SDI) can now irrigate 3 weeks earlier and later in the season than the old system; and/or 5) they decided to continue irrigating rather than converting the irrigated acres to dry land because of decreasing well yield. Every one of these choices increases the consumptive water use of irrigation in the West - even though in some cases less water is actually pumped. My bottom line is that the producers' choices will always be about their bottom lines. These choices will almost always maximize production and CU.

    This issue is complex and not simple to understand. While the above outcomes were always the rule in our water situation (a closed groundwater system where irrigation inefficiencies were diverted to crop production with the new, high efficiency system) there are a few situations were improved irrigation efficiency can save water to the system. Perhaps Mr. Gleick is referring to these cases, whereas others are not.

    Just an inkling, but out of 100 irrigation system conversions and all the decisions the operators subsequently make, my guess is that 10 will save water, 30 will use the same water as before, and the rest will increase production and CU - one way or another - and for a much longer time into the future. The net change I believe will always be an increase in consumptive water use to the system - except in those few (rare) cases I mentioned above. There will always be examples to point to that look undeniable good, and examples that don't look good. The whole system needs to be evaluated - before and after - interms of CU - before you'll ever really know. I believe if these full evaluations are done, the change in CU will always be an increase, not only because more are increasing than saving, but the increases are usually larger than the decreases. At least that's what we've been finding in our system conversion evaluations. Because of all this, I'm guessing we'll be arguing over this issue for many years, but that's my 2 cents worth.

    I am enjoying the discussion regardless, but agree with Emily - I'd much prefer a toned down, less confrontational discussion in the future.

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  16. You Berkeley guys need to start getting along better...maybe strum a guitar and sing kumbayah.

    Go Bruins!

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  17. @Wayne -- excellent comment and context. Good to hear from someone with decades of irrigation experience.

    @Buffalo -- I'm in Amsterdam, of course, but I'll note that my side of this debate has always focused on a correct statement of the problem and facts. I've offered to have lunch and sing kumbaya with Peter, but he's not accepted that invitation :)

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  18. that is a vigorous discussion!

    three points that I should make are:

    1) return flows from irrigation areas in the MDB are already quite low.

    2) the absence of the hierarchical allocation regime changes the debate in Australia somewhat. All allocations are regulated from storage. There are not a bunch of farmers downstream waiting in the wings for more water derived from upstream returns.

    3) a broader point - if you want to turn an efficiency saving into an environmental good, you must create an environmental entitlement (with the same reliability as the ag entitlement) from the saved water, rather than just leave it in the system and hope for a benefit.

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  19. Not sure if you have read Herfindahl's 1961 article http://e-teacher.clanteam.com/conservation.pdf [pdf], but reading the blog made me think about the article. It starts off with the following:

    A discussion between two conservationists who are interested in conserving different things often degenerates into polite name calling or worse1. Smith will tell Jones that he doesn't know what true conservation is. And Jones will reply acidly that what Smith proposes -- far from being conservation -- is profligate waste. Finally the discussion ends from boredom or exhaustion, with each conservationist walking away shaking his head and saying to himself that he doesn't see how anyone could hold such inane views.

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