A new study published in Science makes some progress untangling the roots of what’s known as the “irrigation paradox.”

Water is precious, and irrigating crops uses a whole lot of it – accounting for 70% of global fesh water extractions.  And, in many key agricultural regions, water availability is the key limiting factor to crop yields, and elsewhere, access to clean water is among the most pressing public health challenges.

As part of water conservation efforts, inspired in part by a changing climate, farmers and regulators have made strides in irrigation efficiency.  The mantra has been to maximize the “crop per drop,” and minimize evaporation, runoff, and other water losses.

However, the puzzling trend is that as infrastructure and behavior changes lead to improvements in irrigation efficiency, overall water use does not, in fact, go down.  A research team including scientists from around the globe, including Australia, China, Egypt, the US, and the UK took a closer look at the “Irrigation Paradox” — increases in water use efficiency “rarely delivers the presumed public-good benefits of increased water availability.”

What seems to happen instead is that water saved by efficiency improvements is used elsewhere on the farm or in farming regions. One reason is that farmers tend to shift towards more water-intensive, higher-value crops, or use the additional water to achieve higher yields or otherwise improve their harvest (e.g., more pounds of milk or meat per acre).

The authors articulate two key insights that contribute to this problem – the first being that irrigation systems are generally managed not for water availability, but to “maximize irrigated crop production.”

The second insight is related to how irrigators perceive the “lost” water that runs through irrigation pipes and systems, but is not consumed by crops.  Many farmers feel that this is a lost resource, but the authors point out that this water reenters the water supply via surface flows or groundwater recharge, and is typically recovered and used elsewhere at the watershed or basin level.

In other words, few drops of water are truly “lost,” they just move through the system and have value downstream somewhere to another farmer, a community, or perhaps fish or frogs.

Getting a better handle on water inflows/outflows is one of the steps the authors recommend for policy makers and resource managers.  Others include:

• Measuring water use based on net extractions, which include an estimate of return flows into the water supply,
• Developing comprehensive measurements of costs and benefits of different water uses, and
• Studying the behavior of irrigators to understand how increased efficiency impacts choices on the farm.

We can’t grow food without water, so untangling our complicated relationship with this essential resource is an important part of adapting to changing societal norms, not to mention the weather changes expected in the years to come.

Source:

R. Q. Grafton, J. Williams, C. J. Perry, F. Molle, C. Ringler, P. Steduto, B. Udall, S. A. Wheeler, Y. Wang, D. Garrick, R. G. Allen, “The paradox of irrigation efficiency,” Science, 24 Aug 2018, Vol. 361, Issue 6404, DOI: 10.1126/science.aat9314.