The Colorado River is regulated under a series of laws, court decisions, compacts, and a Treaty with Mexico. Collectively, these are known as The Law of the River. The Law of the River dates back to 1922, fourteen years before Hoover Dam was completed. As modified over the years, The Law of the River allocates water to the states of Wyoming, Colorado, Utah, and New Mexico, which are known as the Upper Basin States, and to Nevada, Arizona, and California, which are the Lower Basin States as well as to the Country of Mexico. The Law of the River and several dams, hydroelectric power plants, and associated facilities are overseen by the United States Bureau of Reclamation or USBR.
California, Nevada, and Arizona hold the oldest rights to water from the Colorado River, and it is only recently that Arizona and Nevada have begun to withdraw their full allocations. The Upper Basin States still do not use their full allocations, but they are growing and plan to use them soon. For decades, California could use water allocated to other states they did not need. That is no longer an option for California.
Demand is Increasing while Supply is Decreasing
Approximately 15 million acre-feet (MAF) of water per year have been allocated under the Law of the River based on a 100-year average flow of 16.4 MAF. Still, since 2000, the average flow has only been about 12.3 MAF. Clearly, this is not sustainable. Collectively, the users of Colorado River water have gotten by drawing down water stored behind a series of dams on the Colorado River and its tributaries. These reservoirs can store almost four years' worth of allocated water.
Just before last winter's record rain and snowfall, both Lakes Mead and Powell, the two largest reservoirs in the country, were at less than 30% of their storage capacity. Even after the record winter precipitation, as of this past weekend, Lake Mead was at less than half its normal level for this time of year and at only about 27% of its capacity. Lake Powell was at 63% of average for the date, but that is only 36% of capacity. Lake Mead and Lake Powell are anticipated to finish the water year well below 50% of capacity. It will take several consecutive winters like this last one to return these key reservoirs to 100% capacity.
Impact on Hydroelectric Generation
Every reservoir that powers a hydroelectric generation station must have sufficient water in it to be able to divert water into the generating plant. This is some distance above the bottom of the reservoir. When water falls below this level, it is known as a "Dead Pool," and the generating facility cannot operate. Hydroelectric generation is inexpensive, clean, and renewable. Loss of the electricity generated at the dams along the Colorado River would significantly affect the cost and availability of electricity in the southwest, including California.
Colorado River Water Must be Reallocated at a Sustainable Level
The USBR has called for the seven states that take Colorado River Water to voluntarily agree on reducing two to four MAF in use of Colorado River water. The Lower Basin States have met several times to discuss what they can do. California, Nevada, and Arizona have offered a plan to reduce about three MAF a year by 2026, when a new agreement will be adopted. California's share of the three MAF is 400,000 acre feet per year. Unless we have very little precipitation in the Colorado River Basin in the next few years, it appears the short-term problem has been addressed. If we have very dry years, additional steps may have to be taken.
The 2026 redrafting of allocations may be contentious. The Lower Basin States have the most senior water rights and feel they have the right to keep them. The upper Basin States argue that they use the least Colorado River water, and the Lower Basin States should give up more. California has done far more than any of the other six states to conserve water in both the agricultural and urban sectors and in wastewater reuse. There is an argument that the other six states could save the entire two to four MAF with California-like water conservation and reuse programs and that California should not give up much additional Colorado River water until the other states complete those efforts.
There are also arguments that certain uses of Colorado River Water should be disallowed. A major example is agriculture for export. There are thousands of acres in Arizona where alfalfa irrigated by Colorado River Water is grown and shipped to Saudi Arabia to feed racehorses. Several California crops, like almonds, are water-intensive and sold internationally. Arguments for banning certain uses conflict with landowner and business rights and could impact the worldwide food supply and balance of trade.
The short-term agreement is encouraging and shows that the states can work together. With a changing climate resulting in longer periods of drought and more intense periods of precipitation, it is clear that we must implement a long-term change in how the Colorado River Basin is managed. Under USBR's leadership, we can establish a sustainable water supply and avoid unexpected curtailment and impact on the Colorado River ecosystem. This will likely have a greater impact on the other six states than on California. Still, we in California will have to make changes as well.