Yeah. They missed the ball on this one. I mean, they talk about field and basin efficiency on pages 14-16, but didn’t follow through. If water is used several times in a basin, then the amounts you could save by practices that make each field more efficient aren’t additive. If you improve the top field from 70% efficient to 85% efficient, all the downstream users have also had a chunk taken out of their supply. If they applied management and money to adjust for that missing chunk, their efficiencies would all move upward some small percent. If they don’t adjust their field efficiencies up, they’ll go get more real water from somewhere. Either way, you can’t add up all the yields from improving field efficiencies as if they were separate. Shit. This is hard to explain. Ummm…
The potential for wringing water out of California agriculture is NOT:
(new improved field efficiency – old sloppy field efficiency)(annual applied water) = bonus water for fish AND cities AND still plenty for ag!
It would be like that if all of the farmwater were completely independent. Then you could add each efficiency improvement up separately the way the Pacific Institute report does.
The potential for wringing water out of California agriculture IS:
(new improved basin efficiency – old sloppy basin efficiency)(annual applied water) = not a whole hell of a lot.
Keeping in mind that I don’t like the concept of basin efficiency any more than you do (because people with an agenda use it for evil), when I hear estimates for basin efficiencies in CA, they’re on the order of 95%. Considering that groundwater levels are dropping drastically, I do not believe that there is a free 10% of inefficient water use sloshing around aggregate Great Valley agriculture. It is also worth remembering that is gets pretty expensive to go after the last few percents of efficiency. Your early gains are all big and cheap, but your last gains start to cost real money.