I asked Lloyd Carter, whose post I had cut and pasted, if he had sources for the consumption figures. He said that the figures originated in Reisner's Cadillac Desert and sent me two stories published in the last year (LA Times and Christian Science Monitor) that said that "cotton, rice, alfalfa and irrigated pasture" were responsible for 30-50% of irrigated water.
Well, I'm an academic (right?), so I went to primary sources to see what kind of data I could get. Here's what I got from the 2003 USDA Census of Agriculture [PDF].*
These crops -- the top ten -- use 95% of the irrigation water in California:
These numbers are applied water per acre -- not consumptive water/acre.
So -- the four "low value crops" are responsible for 39% of water used in irrigation in California, so that statistic is holding up -- as least as far as the most-recent data are concerned.
- According to this table [PDF], California has 47,000 farms using a total of 25 million AF of water.**
- California has over 60 percent of national acreage for orchards and 40 percent for vegetables.
* The 2008 Census will probably come out next year.
** These statistics do NOT match information provided by the California's Departments of Food and Agriculture (88,000 farms) or Water Resources (34 MAF of water) unless you think there are 40,000 non-irrigated farms. Given the CDFA's interest in inflating the number of farms, I am willing to trust USDA figures on farms, but the 9 MAF difference may be due to different supplies in different years.