July 2012, Issue 62: Editors’ Notes

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Although often misunderstood or ignored in favor of “gloom and doom” scenarios, the allocation system for Colorado River water is robust and underpins the water security of our state.

Embodied in the complex body of legal and policy documents known as the “Law of the River,” shortages on the Colorado River have been anticipated since flows were originally allocated 90 years ago. As a result of this evolving body of governance, the impact to Arizona during a shortage is not only well defined but also limited — a reality that contradicts the notion that our water-dependent communities are on the verge of collapse.

At the risk of oversimplifying a complex, integrated body of law, court decisions, treaties, and regulations, the Law of the River basically gives the Lower Basin priority over the Upper Basin states for the first 75 MAF over a 10-year period; this operationally translates to 7.5 MAF/yr. Additionally, Mexico is entitled to 1.5 MAF/yr (half from the Upper Basin, half from the Lower Basin). Thus, the Lower Basin plus Mexico have priority over the Upper Basin for 8.25 MAF/yr, while the Lower Basin has obligations to its states and Mexico of 9 MAF/yr.

Consequently, during a shortage year, the Lower Basin states must absorb the difference between what the Upper Basin is required to deliver and the total obligations to Lower Basin states and Mexico — a maximum of up to 0.75 MAF/yr. Beyond that, the burden to make up shortages shifts to the Upper Basin states. Arizona’s share of this shortage, still unquantified, will likely top out at around 0.65 MAF/yr, with the remaining going to Nevada and Mexico. To put this amount in perspective, Arizona’s shortage cut of 0.65 MAF is…

  • About 40 percent of CAP’s allocation (plus on-river Arizona Priority 4 allocations)
  • Less than 25 percent of Arizona’s total 2.8 MAF allocation
  • Twice as much as the 0.32 MAF reduction in deliveries to Arizona (primarily CAP) that are triggered at the first shortage level, when Lake Mead falls to 1,075 feet msl
  • About 75 percent of the 0.48 MAF reduction in deliveries to Arizona (primarily CAP) when the third shortage level (1,025 feet msl) is reached in Lake Mead

As we discussed in last month’s editorial, CAP will be cut first; however, the priority system for CAP water is a farsighted program that protects certain categories of users for the foreseeable future. Thanks to the groundwork laid by the Law of the River, there is indeed a limit on how deep those cuts will be, giving Arizona the certainty it needs to plan its water future.

Next month, we will continue this thread and discuss how the basin states are preparing for shortage.

An overview: Evolution of shortage-management on the Colorado River

  • 1922: The Colorado River Compact gives the Lower Basin states (Nevada, California, and Arizona) priority over the Upper Basin states for the first 75 MAF over a 10-year period. It also specifies the Upper Basin’s obligation to deliver up to half of any future Mexican treaty obligation every year in normal (nonsurplus) years.
  • 1944: The Mexican Water Treaty quantifies the U.S. obligation as 1.5 MAF/yr in a normal flow year.
  • 1968: The Colorado Basin Project Act stipulates that during a shortage, California’s entire 4.4 MAF annual allocation takes priority over all of Arizona’s remaining river water supply not yet under federal contract (about 1.6 MAF/yr of Priority 4 water contracted to CAP and on-river users).
  • 2007: The Interim Shortage Sharing Guidelines define the levels in Lake Mead that trigger shortage and the amount deliveries will be reduced to each state.

Juliet M. McKenna, MS, PGMichele Robertson, PG