3 Mar 2011

Never say never irrigation

Anonymouse sent this email to me, John Bredehoeft and Peter Gleick:
The article by John Bredehoeft was recommended to me, and I then read the comments. Otherwise, I have not read other postings between Mr. Zetland and Mr. Gleick, so don't know the history of the back-and-forth. Not being of the same caliber as the other commenters, I thought I'd send my comments to you.

I was impressed by the depth of knowledge expressed by all. However, the comment that "[t]he whole system needs to be evaluated," resonated with me. Water savings have to be calculated in a holistic manner as opposed to simply from one set of actions, such as installing a drip system. As mentioned, conserving and reallocating the saved water will not result in a reduction of demand.

And water is place-based. Some folks seemed to be familiar with groundwater irrigation while others referred to surface water diversions. While benefiting from lessons learned elsewhere, it's not helpful to try a cut-and-paste approach. "Inefficient water" depends on where one is. In some places, for instance, excess water may percolate and recharge an aquifer as opposed to simply not being recoverable. An irrigation system may replicate services once provided by a pre-development river.

These decisions involve policy questions as to how we should manage our resources. Should groundwater be considered a commodity to deplete, even if not recharged, and if so, over what time frame? Should current activities be modified when considering the looming climate change impacts to surface water supplies? How might we incentivize behavior which best accomplishes our decisions? And shouldn't such discussions be held in a public forum?
I replied to Anonymouse:
I agree with everything you say, with particular emphasis on public discussions of place-specific solutions...
Peter replied to Anonymouse:
It is certainly true that "water savings have to be calculated in a holistic manner..."

But my complaint about John's essay (and the repeated arguments from some ag irrigation experts) was his generic, but false, conclusion that conserving water (or improving water use efficiency, as I prefer) never results in a reduction in water demand. I'm sure that if he and I were to talk face to face, he would say that he wouldn't say "never" -- but that was the implication of his essay.

His example is fine, except that it is a cartoon of reality. Under his assumptions, yes, there is no "saved" water. But his assumptions are wrong. There is always unproductive evapotranspiration; there is often loss of excess applied surface water to sinks that could be recovered productively, and there is very often improvements in productivity and crop quality that accompany irrigation efficiency improvements.

When ANY of these three things occur, than improving irrigation efficiency results in a water benefit.
Anonymouse replied to Peter:
"When ANY of these three things occur, than improving irrigation efficiency results in a water benefit."

Perhaps, but not necessarily. For instance, if one uses a drip system on one's crops, it will bring that water directly to the crop. A savings. But, no recharge occurs. More water might be left in the river and evaporated. If the holistic system is depending upon the recharge, such as in a riverine system, then perhaps more water will be leaked from the stream to satisfy past depletions. And so on. Again, it depends on the place and circumstances.
I replied to everyone:
I, for one, have never said never in these discussions (and I didn't read John's piece as if he was saying never). Sometimes water efficiency gear "saves" water (less evaporation, e.g.) and sometimes not (water is re-used on a crop or goes into the g/w). Those are just the facts of irrigation. My point has always been that farmers will do what's best ("wasting" or "saving" water) for their bottom line. If they are ignorant of water flows (a rare, but possible thing), than information may push them to change behavior but only towards their bottom line. That's why I've always recommended efficiency improvements be combined with incentives to use less water, allowing the farmers to pay for efficiency and sell the extra water.

It's all about helping people understand the nuances.
And I'll leave the last word to John, who was kind enough to reply while he was on the road, working:
In my earlier post I presented a simple, back of the envelop model of an irrigation system in which I explored the implications of increasing farm efficiency on the overall performance of the system. Peter Gleick criticized my model as being overly simplistic. I accept that criticism; even so, I have been in a number of meetings where water allocation was discussed, and these principles needed explanation even to a sophisticated group.

Peter made several other criticisms:
  1. He suggested that improving on farm water efficiency resulted in eliminating evaporation from free water surfaces, and transpiration by undesirable riparian vegetation which in turn saves water. I agree with Peter. However, my agronomist friends suggest that this savings is on the order of 10%, at best—significant, but no panacea.

  2. Peter also correctly suggested that where the return flow (or drainage) from irrigation is seriously degraded by dissolved salts, one wants to minimize the irrigation application, if indeed one irrigates at all. Selenium in drainage water from irrigation on the Westside of the San Joaquin valley is a prime example of what can happen.

  3. Peter suggested that improving water efficiency results in improved crops. This is more problematic. If, as is often the case, plants are provided sufficient water in either a less efficient or more efficient irrigation method, energy from the sun becomes the limiting input in plant growth. Improving efficiency, where water in not limiting, does not yield better crops. On the other hand, where the water application is less than optimum, water becomes the limiting factor in plant growth. In this case higher efficiency irrigation can deliver water to the best site for plant use and can improve the crop.
Finally, there are a number of economic and policy issues. Improving on-farm irrigation efficiency involves the issue of who is entitled to the water saved; various states have differing answers to this question. Increasing efficiency generally means an added investment in irrigation facilities. Currently, the cost of increased on-farm efficiency is paid by individual farmers—farmers see a net benefit from improving efficiency. Often the farmer expects to use the saved water. This raises the issue of water for other farmers who count on return flow from a less efficient on-farm system.

Anonymouse suggested that water resource problems are local and regional.

Peter’s and Anonymouse's point is well taken--it is dangerous to over generalize.