To be clear: I think the Bureau of Reclamation’s announcement today that it is curtailing releases from Lake Powell in 2014 is a big deal. But one of the members of my brain trust (journalism is a mashup – I just repackage the ideas of people much smarter than myself) points out that there’s an interesting argument to be made that the shortfall that has us all doing the hair-on-fire thing is not really all that large.

Under the Law of the River (the hairball of rules governing Colorado River operations), the states of the Upper Basin are required to release 8.23 million acre feet per year* from Lake Powell. But because of year-to-year variability, it’s calculated as a ten year rolling average. That allows for excess water during wet times and reduced deliveries during dry times.

Here’s the actual deliveries over the last decade, including the estimated 2014 curtailment to 7.48 maf:

Powell releases

You can see that for nine of the ten years, deliveries have been at or above 8.23 maf. In 2011 and 2012, they were over by quite a bit. I like to call it “bonus water“. Here’s another way of looking at the numbers, a bar chart showing simply the over- or under-delivery relative to the 8.23 maf standard:

Powell over/under-delivery

You can see that the sticky-up bits in 2011 and 2012 are a lot bigger than the sticky-down bit in 2014. So really, my brain truster has a point. The shortfall out of Lake Powell in 2014 is not all that large compared to the recent over-deliveries. Or maybe this really makes the case that the Lower Basin is not living within its means, where “its means” are defined as 8.23 maf per year. (Related snark here.)

* Stipulated that not everyone agrees the Upper Basin is required to deliver 8.23 maf. It might really only be 7.5 maf. Who knows? (pdf)