The Irrigation Efficiency Paradox
Center pivot sprinkler irrigation, Bozeman, Montana (USA). Photo by Brian Richter
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In an excellent New York Times article published on July 23rd about the effects of drought on Montana’s famous trout streams, author Jim Robbins makes a statement that I’m sure many readers found very confusing:
“Other factors threatening Montana’s trout include agricultural changes. Ranchers used to primarily flood irrigate their fields, which returned about half the water to the river system. Now many use pivot irrigation systems, which are far more efficient and use nearly all of the water.”
Many readers of that article must have thought: “Why are farmers using more water if they are becoming more efficient in their irrigation?”
This paradox has been labeled by agricultural water scientists as the “irrigation efficiency paradox.” In the midst of horrific droughts in many regions around the globe, and with growing pressure to use less water in irrigated agriculture (which accounts for 86% of all water consumed in the Western US and 84% globally), it’s very important that we understand WHY this paradoxical outcome emerges in farming regions striving for greater efficiency in water use.
To understand the paradox, let’s first take a look at what “irrigation efficiency” means. It is typically expressed as a ratio or percentage, and it refers to the volume of water actually used by crops as compared to the total volume of water applied to the field. Most of the water applied to a field is taken up by the crops, but some is lost to evaporation or deep percolation into the soil, or simply runs off the field as excess water.
Now let’s make up a realistic scenario of a farm irrigated with river water. Let’s say that you originally applied 200 units of river water to your farm field using “flood” or “furrow” irrigation, as pictured below. 100 units are consumed by the crops, 50 units evaporate, and 50 units drain off the field and return to the river. Your irrigation efficiency is 50% because only 100 units of the 200 units applied are going to support crop growth.
Now let’s say that you invest in a sprinkler system such as the one pictured above. Your crops still require 100 units of water, but with your sprinkler system you need to apply only 130 units, because you are evaporating only 30 units (23%) and no water drains back into the river. Your irrigation efficiency is 100/130 or 77%.
The net loss to the river under the former scenario is 200 units extracted minus 50 units returned, resulting in loss of 150 units.
The net loss to the river using more efficient irrigation is 130 units extracted with nothing returned, resulting in loss of 130 units.
This means that the river retains15% more water!
A flood irrigated field in the Imperial Irrigation District of California. Photo by Brian Richter
Reducing the amount of water lost from rivers for agricultural irrigation could really help to reduce water scarcity and improve the ecological health of our rivers.
But it almost never happens that way!
Instead — in the vast majority of cases around the world — farmers continue to apply the same original volume of water (i.e., 200 units) to enable them to grow more crops, either on the same farm area by expanding their farm area (important note: under the prevailing water laws of the Western US, farmers can lose their entitlement to a portion of their original water rights if they begin extracting less water, so they are perversely incentivized to use their full allotment).
With their improved irrigation efficiency of 77%, they continue to apply 200 units but crops are now consuming 166 units instead of 100, and the remainder is lost to evaporation, resulting in a net loss to the river of the full 200 units!
Herein lies the paradox! Governments around the world have financially incentivized farmers to improve their irrigation efficiency in an effort to reduce water scarcity, but in the process they end up enabling farmers to use more water and worsen the scarcity problems.
However, IT IS POSSIBLE to reduce water consumption in irrigated agriculture with efficiency improvements — and thereby allow more water to remain in our rivers and aquifers — but it must be implemented very carefully, as my research group has explained in this paper. For example, if a government or private/conservation entity wants to pay a farmer to use less water — such as by implementing efficiency measures designed to reduce water consumption by 20% — then the volume of water DELIVERED to the farmer should be reduced by 20%. In that way, the farmers cannot increase their crop production and the paradox is averted. Our paper highlighted a couple of real-world examples in which this has been achieved, such as in the collaboration between the Imperial Irrigation District and the San Diego County Water Authority in California.
In truth, very few successful examples of irrigation efficiency projects exist anywhere in the world — if “success” is measured as water allowed to remain in a river or aquifer, or to flow downstream to a reservoir, or to be made available for an urban water user. The ubiquitous failures of irrigation efficiency projects can be attributed to a lack of adequate measurement and monitoring of water use and savings; lack of regulatory control over how much water is diverted or extracted and applied to farm fields; and the understandable motivation of farmers to use as much water as they can to produce food and generate as much revenue as possible.
The Way Forward
Due to these implementation challenges, a far more promising approach is to incentivize farmers — where feasible — to shift into growing different crops that use far less water, or to simply retire some portion of their farmland. Ideally, the crop shifts will not only reduce water consumption but may also improve long-term farm revenues (see table below for examples), thereby enhancing farm viability while conserving water. Similarly, retired farmland may be suitable for renewable energy production or other purposes that can compensate the farmer.
As always, I’m trying to make our options as clear as possible. If you think I’ve got it wrong, please comment in the box below.
Table from: Richter, B.D., J.D. Brown, R. DiBenedetto, A. Gorsky, E. Keenan, C. Madray, M. Morris, D. Rowell, and S. Ryu. 2017. Opportunities for saving and reallocating agricultural water to alleviate scarcity. Water Policy, Available Online 5 April 2017, wp2017143; DOI: 10.2166/wp.2017.143
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Thanks for this Brian, and the important work you’re doing. This is an increasingly timely topic, not just in water, but in carbon, biodiversity, and other dimensions of the environmental problems many of us are working to solve.
Efficiency is a means to some end, and not a terribly useful end in itself. We have about a hundred and fifty years of facing, and sometimes solving, this paradox. As you likely know, it was first described when (of all things) coal consumption began to rapidly increase as industry got better at using it efficiently. Coal essentially became more valuable (more economic output per unit of input) and, no surprise, demand went up. Willian Jevons pointed this out and his name has stuck to this “paradox.” Your readers can go deeper here:
https://www.sciencedirect.com/science/article/abs/pii/S0921800905001084
and here:
https://en.wikipedia.org/wiki/Jevons_paradox
But there are great examples of where efficiency has made a great contribution. The SOx markets created by the US Clean Air Act drove a new, efficiency approach to hitting emission targets: fuel switching. Lower sulfur coal replaced high sulfur coal (more heat per unit of sulfur) and the laws targets were hit at vastly lower costs than even the laws strongest advocated imagined.
The good news in your story is that water is being valued more. The bad news is that our institutions seems a bit under-prepared to manage this increase in value.
Great to hear from you, David, and thanks for these relevant examples from coal and sulfur. I think that many of our colleagues have been too quick to dismiss the value of efficiency — and even water or energy conservation in general — simply because of these unintended paradoxes. It is very important that we’re all aware of the pitfalls, but when carefully managed, saving water or energy is a good thing and we need to deploy all valid strategies!
Thank you Brian. It’s nice to see the issue succinctly and clearly explained. A couple thoughts, speaking here from Colorado, how about the clear illegality of expansion of historical water use by an irrigator? You do not mention that which is of interest. I would love to see a discussion on that topic. How can that part of Colorado/Western water law be better applied in these irrigation efficiency conundrums? It also appears the state of CO may be complicit in allowing many irrigators who change to sprinkler irrigation and expand their consumptive use to do just that. Why is the state looking the other way? Simply because these landowners have pre-compact water rights, correct? That’s a tough topic. The irrigation efficiency issue is tough, but so necessary to address in the new aridity if we are ever going to get to any help for rivers. I am very appreciative of the post!
Thank you for this feedback, Lisa. I’m going to check with some of my water attorney friends to get their take on this issue. I’ll encourage them to post a reply so that we can share their insights with others!
If the producer uses the additional water to expand acreage, that in theory should fall afoul of the prior appropriation doctrine (or, at least, require a new and junior water right for the new acres coming under production). But the US Supreme Court has construed the prior appropriation doctrine (specifically in Montana and Wyoming, but the principle is likely broadly applicable across the west) to generally protect a producer’s ability to increase consumption under their original right so long as they stay within the footprint of their original place of use. See Montana v. Wyoming, 563 U.S. 368 (2011).
Thanks very much for these insights, Jay.
What you didn’t recognize is that many farms are water short to begin with. Increasing efficiency simply gives the crops a better water supply which they take advantage of.
That’s true, Mike, but the same basic concepts hold. Improving irrigation efficiency can create the opportunity for farmers to grow more, but it doesn’t benefit the river. It’s great when farmers improve their yields with improved water efficiency but it should not be viewed as beneficial to the overall hydrologic system.
Thanks for the article.
Investing in improved irrigation efficiency is a good thing, however you can get bad river outcomes if there are underlying flaws in water governance, which is often the case. For me the key message is, ensure you have good water governance before governments spend money on any water investments.
If you cap water resources, have accurate measurement and an active compliance program to prevent over-use you can ensure irrigation efficiency benefits both the irrigator and the river.
If you have these fundamentals in place, you can avoid the efficiency paradox.
I agree 100% Paul! In my Chasing Water book I emphasized the benefits – in fact, the necessity – of a cap or limit on consumptive use as a cornerstone of good water governance. Thanks for emphasizing this!
One concept , the Green Revolution, from development theory ( US AID , 1970s) is that with a rising population every year farmers are expected to deliver larger harvests, which can be achieved partly with efficiently. I think Water is part of our food supply system and to only look at the water “consumption “ of agriculture in isolation misses the connection to the necessity of feeding ourselves.
Of course we all need water but I think we should be. Prioritizing. Farm water supply for food supply security.
The. Fresh water fisheries also. Qualify as an important. Food supply. The focus on what crops are essential or not is an important discussion.
I think the other point that could be discussed is “dry farming” vs. The irrigated farming. The crops used in the dry farming developed deeper roots whereas the drip irrigation (most efficient water use) plants have a shallow root system.
However, the real emphasis on crop yield makes dry farming closer to subsistence production and unable to produce modern food demands.
Jed, I agree that we should be having a discussion about the foods that we must grow to feed ourselves, and how they should be grown. Given shrinking water supplies under climate change, we should be actively engaging in this conversation!
Hi Brian,
Thanks for the post. Indeed, the “Jevon’s Paradox” shows that there are often “rebound effects” by which improvements in technological efficiency often bring about an increase in consumption rather than a decrease.
In Israel, widely regarded as a world leader in irrigation efficiency, much of the irrigation is done by ultra-efficient drip irrigation systems. For this reason, it was designated a “success” in this sense in the FAO report you link to in this post. But the move to drip irrigation there, undertaken decades ago due to the high price of water, did not lead to a reduction in water consumption, but rather to an increase in yields, as farmers got “more crop per drop”, but continued to use all of their allocations. Agricultural water consumption decreased only when the government cut allocations in the late ’90s after years of drought.
The move to more efficient irrigation also has another component – that of consumptive vs. total use. More efficient irrigation generally means less recharge of groundwater as well. For both of these reasons, increases in irrigation efficiency, while welcome, are unlikely to be the answer to water scarcity unless part of a more holistic and integrated water policy.