I will never explain the unit “acre-foot” on this blog.

I’ve been slow to finish up my review of the Pacific Institute report, because that will mean that I have to get into the concepts of field and basin efficiency and I dread that.    I don’t mean to be a tease; I know how badly you’ve been craving more of this series.  I’ll put some peripheral thoughts here,  so we can have a clean discussion of field and basin efficiency and the core conclusion of the Pacific Institute report without them buzzing around and plaguing us.

A thought:

I agreed with the technical critiques in the irrigation professors’ report, which isn’t too surprising, since one of them trained me.  If you have any technical questions about anything in those reports, I’d be happy to take my best shot at answering it.  As much as those critiques cast doubt on whether the Pacific Institute report is identifying real potential for water savings, I’m also a doubter.

Another thought:

I said that I’d critique the Ag Water Management Council’s report.  Here goes.  This is self-reporting by a self-selected group of the most progressive ag water districts.  I don’t think the claims are very impressive; there’s a lot of hedging about how far along the districts are in adopting Efficient Water Management Practices.  That said, these leading districts are alert to the practices and implementing them at some rate unspecified by the report.  I don’t take this report as proof that ag is doing everything it can.  It is more like the best likely spin you could put on ag’s water use practices.  Also, man.  Love the pictures. 

Yet more thought:

For your sense of scale, here are some recent rough numbers.

3.5 million acre-feet/year – the Pacific Institute report thinks this is the amount ag could yield without hurting, or maybe even while doing better.

31.5 million acre-feet/year – this is roughly how much ag applies overall.  Am I really doubtful that irrigated ag could give up 10% of its applied water without hurting?  Are they really so tight that there isn’t 10% slack in the system?  Yeah, I really am doubtful, and I’ll tell you why when I tackle the field and basin efficiency talk.  But OH LOOK!

6 million acre-feet/year – this is how much warmer winters will cost CA in snow storage of water by mid-century.  That’s twice the amount we’re wrangling about in the Pacific Institute report, so as much as the Pacific Institute report seemed to be making bold claims, this should be twice as dramatic.

I’ll give you three more numbers that I find really handy.

10 million acres – the rounded-up area of irrigated ag in California.  It is closer to 9 million acres these days, but 10 million acres is easier to use.

California is about 100 million acres. 

As a very, very rough estimate, one irrigated acre uses about three acre-feet of irrigation water a year.  (This goes neatly with the 10 million acres and 31.5 million acre-feet/year.)

These are the numbers I use to get a gut sense of things*, decide whether a claim is big or little or ridiculous.  You may use them too.





*You know what I have no good sense of?  Flow.  I haven’t worked out any gut feel for cfs.  Is 20 cfs a kitchen faucet flow?  The Amazon River?  Fuck if I know.


Filed under Basic stuff, Irrigation!

4 responses to “I will never explain the unit “acre-foot” on this blog.

  1. TJ

    20cfs will fill a 2m deep Olympic pool in about a day… It is like two fire hoses.

  2. Margie

    Nah…20 cfs will fill the pool in about 1 hr 15 minutes. 1 cfs will fill the pool in about a day.

  3. TJ

    That is so totally what I meant

  4. aquafornia

    Oooohh… field and basin efficiency!

    I’m drooling…