Lower Basin water use since 1964. 2025 data provisional, based on USBR projections Oct. 29, 2015.

California’s projected use of Colorado River water this year, 3.76 million acre feet as of Reclamation’s Oct. 29 modeling runs, would be, as near as I can tell, the state’s lowest use since 1949.

Also notable:

• Nevada’s 197,280 acre feet would be the lowest since 1992.
• The two lowest years in Imperial Irrigation District’s history (my dataset goes back to 1941) were last year and this year.
• This will be the third year in a row that Arizona’s main stem use has been below 2 million acre feet. The last time that happened (three consecutive years below 2maf) was in the 1980s.

Total take by the US Lower Basin states is projected to be 5.917 million acre feet, the lowest total US main stem use since 1983.

A few things to note.

First, the tenuous fabric of the Basin States negotiations is predicated right now, in part, on the Lower Basin cutting 1.5 million acre feet of annual use. They’ve already done that.

Second, the current cuts are enabled by significant federal payments to compensate the water agencies for their cuts. As my colleagues and I wrote back in September, counting on that money in the future would be unwise.

Third, the economies of Arizona, southern Nevada, and southern California are chugging along just fine right now. As I have written in the past, having less water does not mean scary doom. We can do this.

A note on the data:

The projection of total 2025 use by Lower Basin water users is based on model runs done by the Bureau of Reclamation every few days. It’s a rich source of data, with detailed accounting of the various conservation programs being run by the Lower Basin agencies. PDF here.

The comparison with prior years is based in part on the Lower Basin accounting reports, prepared each year since 1964. For prior years, I have a dataset I got years ago from the technical staff at the Metropolitan Water District of California, who had pieced together California numbers back to 1941. (Thanks, Met!)

We have no comparable data for the Upper Basin that might allow us to track water use at this level of detail, and with this kind of immediacy. This is a problem.