tl;dr The Lower Colorado River Basin has gotten 10 million acre feet of “bonus water” since 2000, above and beyond its entitlement under the Colorado River Compact. But we’re about to have a formal shortage declaration because the Lower Basin keeps using more water than it perhaps ought to. (bad words in earlier draft deleted)

courtesy Brad Udall

Today’s release of the Bureau of Reclamation’s August 24-month study is what in my old newspaper days we would have called “a great news peg”. It’s been clear for a while that we’ll likely have a first-ever federal shortage declaration in the Lower Colorado River Basin in 2020, and that chance is growing. But in the interests of never letting a good Colorado River shortage news peg go unused….

A shortage on the Colorado River, which would force water supply cutbacks for users in Arizona and Nevada, is likely in January 2020, according to a new analysis from federal scientists released Thursday.

In the Bureau’s “most likely” scenario – essentially the median of a bunch of model runs reflecting various hydrologic scenarios under the current rules – Lake Mead would end 2019 at elevation 1,070.35. Anything below 1,075 and Arizona and Nevada have to reduce their use of Colorado River water.

This will happen even though Lake Mead is forecast to get more “bonus water” in 2019 – water released from Lake Powell above and beyond the Upper Basin’s legal compact delivery obligations* of 8.23 million acre feet. The current projected release is 9 million acre feet, but despite that bonus water, Lake Mead is projected to drop 9 feet next year.

I’m in the midst of a book chapter diving into this stuff, so let me obsessively share numbers because I spent all day staring at them, and they might shed some light on where the problem lies. That “bonus water” delivered by the Upper Basin is a big clue.

The Upper Basin has only been using ~4-4.5 million acre feet of water a year, well below its Colorado River Compact entitlement of 7.5maf.

Since 2000, the Upper Basin has delivered 9.7 million acre feet above the amount required under the current rules (8.23 million acre feet per year). So the Upper Basin is a) using less water, and b) delivering more to the Lower Basin. (Brad Udall, who’s been helping me think about all these numbers, sent me the graph above showing the accumulating surplus.)

By the time next year is over, the Lower Basin will have gotten 10 million acre feet of “bonus water” in the 21st century. 10 million acre feet more than the Colorado River Compact requires. Yet Lake Mead keeps dropping. It’s pretty clear where the “supply-demand imbalance” lies here. Looking at you, my Lower Basin friends.

Everyone can plausibly argue that they’re living within the rules here, but if we keep defending our actions with “But the rules say it’s OK!” the Colorado River system is going to crash.

* Upper Basin lawyers who wanna quibble take it up in the comments