Megadrought to Spur Discussion on Hydropower’s Role

A look into hydropower’s future as a reliable source of clean energy in the American West

The likelihood that future aridification in the American West will far exceed the magnitude of change seen in the last millennium is challenging hydropower’s role as a reliable source of clean energy generation. 

Last summer hydroelectricity generation in the Pacific Northwest was at substantial risk due to drought, and this summer the 23-year long drought and low runoff conditions in the Colorado River Basin are threatening hydroelectricity generation at Glen Canyon Dam, located at Lake Powell, and Boulder Canyon Dam (aka Hoover Dam) on Lake Mead, according to Gro’s Hydropower Drought Index

Both Lake Powell and Lake Mead, the US’ two largest reservoirs, are at historically low levels, with Lake Powell at 26% capacity and Lake Mead at 27%. At this level of storage capacity, minimum power pool elevation - the point at which a dam no longer has enough water to generate hydroelectricity - emerges as a genuine risk

Hoover Dam and Glen Canyon Dam are the largest and second largest hydropower plants in Arizona, respectively, and the 4th and 7th largest in the US in terms of power generation capacity

In addition to providing 40 million Americans with drinking water, the Colorado River system supplies irrigation to about 5.5 million acres of land, and hydropower facilities along the river generate between 3000-4000 megawatts of electrical capacity, helping states with ambitious carbon-free electricity commitments - like California, Colorado, and Nevada - reduce their use of fossil fuel power generation.

Rapidly Dropping 

In July, Gro’s Hydropower Drought Index level for Arizona, where the Hoover Dam and Glen Canyon Dam are located, was at 3.2, indicating “severe” drought and its second highest reading since 2003 (only lower than 2021). By comparison, between 2017-2021, Gro’s Hydropower Drought Index for Arizona for July has averaged 2.1, indicating a “moderate” drought. 

Gro’s Hydropower Drought Index, which is based on the Gro Drought Index, measures drought severity on a scale from “0” (no drought) to “5” (exceptional), and is weighted by each county’s hydropower capacity to show the risk to hydroelectric power generation.

Along the Colorado River, Lake Powell is currently 42 feet above its minimum power level and 162 feet above dead pool elevation, the point when water in a reservoir drops so low that it can’t flow downstream from the dam. Lake Mead is 44 feet above its minimum power level and 149 feet above dead pool elevation. 

Reservoir levels have been declining for years. Since August 2017, Lake Powell levels dropped 99 feet, where Lake Mead dropped 37 feet. Also, during the last year, water levels in both lakes have dropped faster than expected; Lake Powell fell 17 feet compared to August 2021, and Lake Mead dropped 24 feet. Also, the “martini glass” shape of both reservoirs means that as levels in the lakes decline each foot of water holds less water. 

Beyond the current drought, under the Intergovernmental Panel on Climate Change’s middle of the road scenario, SSP2-4.5, Gro Hydropower Climate Index Projections predicts that, on average by 2050, the Western US’ annual average temperature will increase to 17.9 ± 0.6°C compared to the current average of 16.7°C (an increase of 1.2°C or 7% from current) while the annual average precipitation will see only minimal change, suggesting an even more difficult future for hydropower generation in the area.

The chart above shows the Western US’ annual average temperature by 2050. The IPCC's trajectory estimate for global warming falls between SSP 2-4.5 and SSP 3-70. The blue line, SSP 5-8.5, is the IPCC's highest emissions scenario.
In Western US states, average precipitation looks set to stay near current levels through 2050. 

Currently, much of the Western US is experiencing drought conditions, according to the Gro US Drought Index. Customers can use Gro's Hydropower Drought Index to study strains on the US hydropower system by geography, comparing, for example, the Pacific Northwest to the Colorado river basin currently and historically.    

Forcing A Wider Discussion  

Unlike Washington state, which has largely recovered from drought in 2021 that in some areas was the worst on record, there is no end in sight for the upper Colorado River Basin’s region’s epic drought. La Niña conditions, which contributed to drier than normal conditions for the region in 2020 and 2021, are lingering for a rare third year. And while the current summer monsoon season may provide some relief, it is unlikely that these rains will eradicate the region’s megadrought. 

In mid-June, the US Bureau of Reclamation (USBR) announced plans to retain more water at Lake Powell and Lake Mead, and it said that it would release an additional 500,000 acre-feet from Flaming Gorge Dam, which flows into Lake Powell via the Green River. One acre-foot is about 325,000 gallons of water. 

During a Senate hearing on June 14, the USBR also gave the seven states in the Colorado River watershed an ultimatum and a 60-day deadline: come up with a plan to conserve an additional 2-4 million acre-feet of water to stabilize Lake Powell and Lake Mead and protect hydropower generation at their dams or the federal government will impose a water conservation plan. On August 16, the federal government announced more water cuts for Arizona, Nevada and Mexico, but these cuts combined are less than 2 million acre-feet.

The USBR is seeking ideas and operational strategies to consider when updating key reservoir and water management decisions and agreements along the Colorado River.