I’ve seen this more than once:
Fifteen percent of all U.S. crops are grown with irrigation water that originates in the Colorado River Basin.
I am skeptical. I’ve been unable to find anyone who cites an original source, but the data I’ve been able to find suggests it’s off. By a factor of a lot.
The best attempt I’m aware of to quantify total agricultural production in the Colorado River Basin was done as part of the Bureau of Reclamation’s Moving Forward report (pdf). They went through Census of Agriculture data county by county and concluded that total agricultural production attributable to Colorado River water, both crops and livestock, was on the order of $5 billion.
Total ag production for the United States as a whole for the same year they used for the calculations was $297 billion. That’s around 1.7 percent by this measure.
The salient feature of the basin here is that it is largely an arid and/or mountainous region, and the river’s water only allows for the irrigation of a small portion of the land. Exports from the basin (which are considered in the Bureau of Reclamation analysis) expand the arable land to which Colorado River water is applied, but don’t change the numbers all that much.
Here’s a way to get a sense of the scale. According to the Moving Forward report, Colorado River water irrigates 4.7 million acres of cropland both in the basin and as a result of out-of-basin diversions. Consider that Iowa alone has 24.5 million acres of harvested cropland. For the U.S. as a whole, the number is 310 million acres. Colorado River Basin agriculture makes up about 1.5 percent of U.S. harvested cropland, which matches up pretty nicely with the 1.7 percent share of ag revenue.
This is not to say that agriculture in the Colorado River Basin is not important. A lot of my book is devoted to a defense of the importance of Colorado River Basin ag.
As I said, I’ve been unable to find an original source, just an echoed stat. I’d love to hear from anyone, especially folks who have been using this number, who has some idea of where it came from. Maybe I’m missing something?