The 1922 compact, which divided the flow of the Colorado River among seven western states, allocated 7.5 million acre-feet to the Upper Basin states of Colorado, Utah, Wyoming and New Mexico.
Colorado’s share amounts to 51.75 percent of 7.5 million acre-feet, or slightly more than 3.88 million acre-feet annually. Colorado diverts less than the state’s allotment, so, it would seem that we could tap the river for more.
This view was endorsed by the authors of the Statewide Water Supply Initiative, commissioned by the Colorado Water Conservation Board in 2003. The report still guides statewide water planning, although its premises might be wildly inaccurate.
According to the SWSI, “… gross water use is expected to increase statewide by about 53 percent or 630,000 acre-feet per year between 2000 and 2030. Presently, all but approximately 100,000 AFY of the new demand are projected to be met by proposed projects …. (We) estimate that the amount of water available for development in Colorado under the 1922 and 1948 compacts to be around 700,000 AFY.”
The SWSI’s conclusion: we have plenty of water. But it might be phantom water.
The authors of the SWSI failed to consider the “inconvenient hydrology” of the Colorado River Basin.
Eighty-five years ago, the architects of the 1922 Colorado River Compact assumed that the river’s annual flow was in excess of 15 million acre feet — more than enough for every state to develop its full allotment. This estimate was based on less than 20 years of metered flow records — years that were among the wettest in the history of the Colorado River Basin.
In reality, the average flow for any given year between 1922 and 2000 has often been less than 15 million acre feet.
Even as demand has increased during recent decades, this has been adequate to support the river’s users. The vast storage capacity available in Lake Mead and Lake Powell has allowed river managers to capture excess water during wet years to be released in times of drought.
But during an era of rising temperatures, declining precipitation and drought, which, far from ending, shows every sign of becoming “the new normal,” such strategies might no longer work.
Lake Mead and Lake Powell are at historic lows.
As Brad Udall, the director of the NOAA/Colorado University Western Water Assessment said during testimony before Congress: “The recent drought, which has featured extended low flows not seen in the 100-year gauged record, has resulted in the loss of 30 million acre-feet of water, the equivalent of two years of annual flow and half of the maximum total storage. The two largest reservoirs, Lakes Mead and Powell, are now approximately half full.”
SWSI is correct in stating that the 1922 Compact allocates 7.5 million acre feet to the Upper Basin states, but the compact also obliges the Upper Basin states to deliver 8.25 million acre feet annually to Mexico and the Lower Basin states of Arizona, California and Nevada — and someday soon, that might not be possible.