How the US-Mexico Colorado shortage/surplus sharing deal works

When the federal government and the seven US states that share the Colorado River signed their 2007 “Interim Guidelines for Lower Basin Shortages and the Coordinated Operations for Lake Powell and Lake Mead,” the final Record of Decision (pdf) included several chunks of legalese to the effect that the deal, while binding on the US side of the border, should not be interpreted as having any effect on sharing (or not sharing) of water across the US-Mexico border:

The United States will conduct all necessary and appropriate discussions regarding the proposed federal action and implementation of the 1944 Treaty with Mexico through the International Boundary and Water Commission (IBWC) in consultation with the Department of State.

That consultation’s been underway ever since, and we’re about to see the fruits of the discussion in the form of Minute 319, an addendum to the 1944 Treaty Between the United States of America and Mexico: Utilization of Waters of the Colorado and Tijuana Rivers and of the Rio Grande (pdf).

Under the current, pre-Minute 319 state of affairs, Mexico is entitled to 1.5 million acre feet of Colorado River water each year, along with some fuzzy treaty language that in “extraordinary drought” (whatever that means – it’s not defined), Mexico will have its water reduced the same as everybody else.

There’s a lot in Minute 319, much of it which I don’t yet understand (we haven’t seen the actual language, just incidental documentation). I’ll stick here to the details of the shortage and surplus sharing. Here’s how it works.

Under the 2007 Interim Guidelines, the level of Lake Mead is used as a trigger for reducing water allocations to the Lower Basin states. When Mead’s surface hits 1075 feet above sea level, the total Lower Basin allocation is cut from 7.5 million acre feet to 7.167 maf, with the shortage shared between Arizona and Nevada. When it drops below 1050, there’s a deeper cut, to 7.083 maf (also Arizona and Nevada take the hit – California’s senior rights on the river trump here).

Under Minute 319, Mexico now joins in the droughty fun, seeing its 1.5 maf cut by 50,000 acre feet when Mead’s below 1075. Below 1050, Mexico takes a 70,000 acre foot hit.

On the flip side, Mexico now also has the opportunity to share in surpluses. When Mead is above 1145 feet above sea level, Mexico gets an extra 40,000 acre feet of water. Above 1170, an extra 55,000 acre feet. Above 1200, an extra 80,000 acre feet.

There’s much more to the deal, including an expansion of Mexico’s ability to store water in US reservoirs, and environmental flows in the Colorado River Delta. I’ll try to avoid writing about that stuff until I actually understand it. In the meantime, here are some links to more information:



  1. John, this is a nice summary that gets to the heart of the new U.S.-Mexico agreement. I hope you will also write about its environmental restoration provisions, which are both hard-won and innovative. Water flowing again in the Colorado River Delta? Astonishing!

  2. Patrick – I plan to write about the environmental provisions too. Sadly, at this point the people who are closely involved and therefore are in a position to explain their importance have apparently been sworn to secrecy as part of Interior’s (in my view ill-advised) effort to control the message propagation until after next week’s signing.

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