About the river

Overview

The Colorado River is a vital source of water, hydropower, recreation, ecosystem services, and other amenities for people in the seven basin states (Colorado, Wyoming, Utah, New Mexico, Arizona, Nevada, and California), over two dozen federally recognized tribes, and the Republic of Mexico. Over 40 million people rely on the Colorado River and its tributaries in part or in full for their municipal water supply, while 5.5 million acres of irrigated crops and pasture depend on this water too.

The enormous storage capacity of the system’s reservoirs (about 60 million acre-feet), mostly held in Lake Powell and Lake Mead, buffered most of these uses from the large variability in the river's flow even as overall basin water use increased by over 50% between 1960 and 2000. But starting in 2000, an extended dry period along with warming temperatures led to average annual streamflows about 20% lower than the long-term average. During this period of low inflows, consistent water deliveries to the Lower Basin states (California, Arizona, Nevada) and Mexico continued under the Law of the River, while Upper Basin water use stayed relatively constant as well.

As a result of this chronic imbalance between supply and demand, system storage has declined to levels that had only been seen in model scenarios. Lake Powell, as of October 2022, is at 25% of capacity and is uncomfortably close to the minimum level for producing hydropower--and possibly for reliably delivering any water downstream. Lake Mead is at 28% of capacity, also close to its minimum power pool, and closer to dead pool (i.e., unable to deliver any water downstream) than to half-full.

Under agreements made in 2007 and 2019 to avoid more severe system impacts, mandatory ("Tier 1") curtailments of Lower Basin water use were first triggered in August 2021, with larger "Tier 2" curtailments triggered in August 2022. Despite these measures, the vulnerable state of the system led the Commissioner of Reclamation to demand, in June 2022, that the seven basin states collectively reduce their annual water uses by 2 to 4 million acre-feet by 2023 to ensure no near-term (1-4 years) loss of hydropower or worse, water releases, from Powell or Mead. As of October 2022, there has been limited progress by the states in committing to specific reductions, or to measures that would plausibly lead to reductions.

This recent drought, along with the increasing recognition that rising temperatures impact the hydrology of the basin, has led to further concerns about the long-term reliability of basin water supplies. Warming temperatures observed across the basin in the last few decades have discernibly impacted snowpacks, melt and runoff timing, runoff efficiency, and total basin runoff. It is unclear whether the period of below-normal precipitation since 2000 is indicative of future precipitation, but unless average basin precipitation increases substantially, system runoff and water supply are expected to decline over the next several decades due to warming alone.