Editor’s note: This is the first post by Eric Kuhn, former general manager of the Colorado River Water Conservation district and the co-author, with Inkstain’s John Fleck, of the forthcoming book Science Be Dammed: How Ignoring Inconvenient Science Drained the Colorado River, to be published this fall by the University of Arizona Press.

By Eric Kuhn

There has been considerable media attention to the travails within Arizona and California as water agencies work to complete the intra-state agreements so that along with Nevada, the three states of the Colorado River’s Lower Division can implement their drought contingency plan (DCP).  While there has been coverage of the juicy details of the day-to-day negotiations, less attention has been given to the more basic question: Why does the Lower Basin even need a DCP?

The most common answer to this question largely parrots the talking points of the basin water community – since 2000 the basin has experienced an unprecedented drought causing reservoir levels to plunge to unacceptably low levels, therefore we need to be prepared for deep cuts to our water use in the event the drought continues.  While this answer is partially true, it avoids important details that many basin water managers would rather be kept out of the public dialogue.

For nearly a hundred years experts have been warning the basin that ultimately water users in the Lower Basin would be facing a structural deficit of at least 1.2 million acre-feet per year. The math is quite simple:  When the Upper Basin is only making the releases required by the 1922 Compact, inflow to Lake Mead is about 9 million acre-feet per year; 7.5 million for the Lower Basin, a disputed 750,000 for Mexico, and about 750,000 of inflow between Lee Ferry and Lake Mead.  However, uses from Lake Mead, without additional conservation, average about 10.2 million acre-feet per year; 7.5 million for the three Lower Division states, 1.5 million for Mexico, and about 1.2 million acre-feet of reservoir evaporation and system losses. Thus, outflow exceeds inflow by about 1.2 million acre-feet per year, now commonly referred to as the “structural deficit.”

A structural deficit of more than a million acre-feet per year was first predicted by USGS hydrologist Eugene Clyde LaRue in the early 1920s.  In the 1960s Upper Basin water engineer Royce Tipton told Congress that once the Central Arizona Project was operational, the Lower Basin would have a deficit of 1.2 to 1.9 million acre-feet per year depending on the Upper Basin’s actual obligation to Mexico. So why has the basin waited until now to put in place a serious plan for living within its means?

The Colorado River system is primarily managed under what is referred to as the 2007 Interim Guidelines, a set of rules that defines annual releases from Glen Canyon Dam and the deliveries of water from Lake Mead to users in the Lower Basin, including the shortage criteria.  The Interim Guidelines were negotiated by representatives of the basin states and the Secretary of the Interior in the early 2000s.  At the time the negotiations commenced in 2005, the basin was dealing with the impacts of the exceptionally dry 2000-2004 period.  There was no doubt that the Lower Basin needed shortage criteria and there was little debate that the Secretary of the Interior had the authority to impose shortages pursuant to the 1964 decree in AZ v. CA.  The questions were when would shortages be triggered, how big would they be, and because of the Central Arizona Project’s junior status, what level of shortage would Arizona accept before it decided to plunge the basin into litigation rather accept consensus criteria?

The end-product that Secretary Kempthorne signed in early 2007 included many compromises. Even though it was well understood that at least 1.2 million acre-feet of cutbacks would be needed to stabilize Lake Mead during an extended drought (or under the reasonably foreseeable impacts of climate change which were well documented by 2007), the 2007 shortage criteria were limited to 600,000 acre-feet per year, which included participation by Mexico, only about half of what was needed.  Additionally, the 2007 guidelines have a provision that precludes agencies, such as MWD that fund conservation measures and bank the saved water in Lake Mead, from actually using the saved water during a declared shortage.  The provision is a little like suggesting families have emergency saving for an unexpected income loss, but not allowing them to use it when it happens. However, in hindsight, Arizona’s strategy worked. Under the proposed Lower basin DCP, California, even though not required to do so by the 2007 Guidelines, has offered to participate in additional shortages.

In short, the proposed Lower Basin DCP completes the job the 2007 Interim Guidelines process began, but due to politics, could not fully accomplish. Under the proposed Lower Basin DCP, when Lake Mead drops below critical storage levels, the total cutbacks exceed 1.2 million acre-feet, enough to stabilize storage, and entities like MWD that have banked water in Lake Mead, as a drought reserve, will have access to this water when it is truly needed.

What the Lower Basin DCP does not accomplish is to provide a framework to address a continuing decline in the long-term average flow of the river caused by climate change induced aridification. That will have to wait for the next round of negotiations, beginning soon, to replace the 2007 Interim Guidelines with rules that will manage the river after 2026.