Following a dip to historic lows in early 2023, Lake Powell, the second-largest reservoir in the United States, experienced a recovery during the summer of the same year. The surge in water levels, attributed to above-average snowmelt from the Rocky Mountains, provided temporary relief. However, the reservoir continues to grapple with a persistent long-term drought.
A visual representation of Lake Powell, situated on the Utah-Arizona border, is presented in the images captured on October 20, 2023 (right), compared to September 23, 2022 (left). As of November 12, 2023, the lake registered a height of 3,572 feet (37 percent full), slightly below the 1991–2020 average for that date. The images were obtained using the OLI (Operational Land Imager) on Landsat 8 for 2023 and the OLI-2 on Landsat 9 for 2022.
The Importance of the Colorado River
Lake Powell and its downstream counterpart, Lake Mead, are nourished by the Colorado River. Covering mainly arid or semi-arid regions with less than 10 inches (25 centimeters) of annual precipitation, the Colorado River Basin plays a crucial role. Managed by the U.S. Bureau of Reclamation (USBR) and other entities, the river serves water and electricity to approximately 40 million people, notably in cities such as Las Vegas, Phoenix, Los Angeles, and San Diego, and provides water to 4 to 5 million acres of farmland in the Southwest.
Weather Patterns and Reservoir Levels
A sequence of nine atmospheric rivers delivered substantial rain and snow to the western U.S. in December 2022 and January 2023. Nevertheless, a significant portion of the precipitation in the Colorado River Basin remained frozen at the elevated Rocky Mountain altitudes, hindering its contribution to Lake Powell. On April 13, the lake’s water level dropped below 3,520 feet, marking its lowest point since its inception in 1980.
With rising temperatures in spring and summer, above-average runoff from the Rockies offered a welcome respite. The reservoir’s water volume increased from 22 percent full in April to around 40 percent full in early July.
Persistent Drought Challenges
Despite the brief recovery, replenishing the reservoir to its “full pool” at an elevation of 3,700 feet will require more than just a single wet year. Two decades of drought in the American Southwest have significantly depleted the reservoir’s water levels, reaching a record low in 2022 and again in 2023.
In April 2023, the USBR released a draft Environmental Impact Statement for Colorado River Operations, evaluating the likelihood of the reservoir dropping below the critical elevation of 3,490 feet, known as the “minimum power pool.” This level is crucial for maintaining water flow through the dam’s intake valves to generate hydroelectric power. Initially, USBR cautioned a 57 percent chance of reaching this critical level before 2026. However, revised estimates in October 2023, prompted by above-average runoff, lowered this probability to 8 percent.
The impact statement emphasized the ongoing aridification of the Colorado River Basin due to climate change. Despite year-to-year variations in flow, the basin remains in an extended period of arid conditions, characterized by drought and low runoff from 2000 to 2022, constituting “the driest 23-year period in more than a century and one of the driest periods in the last 1,200 years.”