Kudos to Chris Austin, who was out ahead of everyone else earlier this week in laying out the details of the pending US-Mexico Colorado River water deal. I encourage you to head over to Chris’s blog for more on the deal, which was first presented last Monday to the board of the Metropolitan Water District of Southern California, the first step in a rollout that’s now happening all across the seven US states that share the Colorado. Since Chris’s piece, some of the news types have jumped in, though Chris’s piece is the best explanation of what’s going on.

I’ll know a lot more next week, when New Mexico gets its briefing at a meeting of the state’s Interstate Stream Commission. But in brief, this has the potential to be an extremely important deal because of the way it extends the Colorado River’s complex accounting system across the US-Mexico border, in the process addressing one of the major unsettled package of questions regarding Colorado River management.

The underlying problem the negotiators have been trying to address is how to equitably share shortages between the United States and Mexico. The US-Mexico treaty of 1944 (pdf) calls for reduction of Mexico’s share of the river in the case of “extraordinary drought”:

In the event of extraordinary drought or serious accident to the irrigation system in the United States, thereby making it difficult for the United States to deliver the guaranteed quantity of 1,5000,000 acre-feet (1,850,234,000 cubic meters) a year, the water allotted to Mexico under subparagraph (a) of this Article will be reduced in the same proportion as consumptive uses in the United States are reduced.

But how “extraordinary drought” might be defined, and the details of how the shortage sharing contemplated in the treaty might be implemented, was left as an exercise for future generations. It’s taken a bit longer than I imagine anyone expected to get back to to it. Beyond the shortage/surplus management issue, the deal also appears to address a couple of major steps forward in trans-boundary river management, including the creation of a framework for Mexico’s storage of water in US reservoirs, and some management tweaks that seem aimed at providing environmental flows in the de-watered Colorado River delta.

For background on the outstanding issues, I recommend Jason Robinson’s “Respective Obligations of the Upper and Lower Basins Regarding the Delivery of Water to Mexico: A Review of Key Legal Issues” (pdf), a white paper produced with the University of Colorado School of Law Colorado River group.