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​Editor’s note: The following report summarizes data from WAPA’s Hydropower Conditions webpage for straight power purchase costs, which are based solely upon hydrology, actual hydropower generation and related generation shortages. Readers may review all data by visiting, Power Marketing, Hydropower Conditions.

​By Philip Reed

One of the biggest challenges for hydropower is water variability due to intermittent drought and flooding. By definition, hydropower needs water to generate electricity. Without it, WAPA must buy power on the open market from other sources to meet contractual obligations to its customers. This is referred to as purchased power.

In an ideal year, snowpack around the West is average or above average, yielding snowmelt runoff to recharge reservoirs behind the dams and powerplants that provide the power WAPA markets. Federal dam owners such as the Bureau of Reclamation, the Army Corps of Engineers and the International Boundary and Water Commission move water to federal hydroelectric powerplants.

WAPA markets the subsequent power generated to more than 700 preference customers. Its customers, in turn, sell that power to more than 40 million Americans.

Water around WAPA in 2019

WAPA’s actual generation was 108.9% of average in water year 2019, for a total generation of 28,524 gigawatt-hours. For the same period, total purchased power was 2,488 GWh with actual purchase power expenses of $75,169,620 equating to $30.21 per megawatt-hour.

The Colorado River Storage Project Management Center projected most probable purchase power expenses for water year 2019 to be $19,291,789. Actual purchase power expenses were $24,660,358. The cost per MWh was $34.05.

Lake Powell ended the water year with an elevation of 3,615 feet, which is about 85 feet below the maximum reservoir level and 125 feet above the minimum generation level. At the end of water year 2019, inflows into Lake Powell were 35% percent of average. Water year 2020 forecasts are for an inflow of 88% of average—9,500,000 acre-feet—and an annual release of 8,230,000 acre-feet.

Desert Southwest’s hydrology is mostly dependent on the Colorado River Basin snowpack and precipitation above Lake Powell. Precipitation was 26% of average at the end of September. The region’s most probable projected purchase power expenses were $11,221,729. Actual purchase power expenses were higher at $12,932,391, with a cost per MWh of $49.07. Lake Mead ended the water year with an elevation of 1,083 feet, about 137 feet below the full storage level and 133 feet above the minimum generation level. During water year 2019, Lake Mead’s elevation dropped to a low point of 1,078 feet in November and rose to a peak of 1,090 feet in March.

In Rocky Mountain, reservoir inflows ranged from 90% to 169% of average, with the low point coming in September and the peak in July. Only December and September were below average. The projected purchase power expenses were $8,167,404, but actual purchase power expenses were $9,912,420. The cost per MWh was $28.27.

Sierra Nevada ended the water year with 143% of the 15-year average reservoir storage for Trinity, 138% for Shasta, 150% for Folsom and 147% percent for New Melones. Accumulated inflow for the same date was 133% of the 15-year average for Trinity, 135% for Shasta, 144% for Folsom and 153% for New Melones. The region began water year 2019 with a most probable projection of purchase power of $6,114,200 but ended with an actual expense of $9,063,870. The cost per MWh was $18.19.

In Upper Great Plains, the active conservation pools ended the water year 85.8% full at Canyon Ferry Dam and 99.4% full at Yellowtail Dam. The yearly runoff was 241% of average. Abnormally dry and moderate drought conditions were reported for seven months this water year. The region’s most probable projection for purchase power was $11,432,556. Actual purchase power expenses were significantly higher at $21,350,484. The cost per MWh was $28.12.

Anticipating water year 2020

The Seasonal Drought Outlook provided by the National Weather Service’s Climate Prediction Center in November 2019 predicted drought-related improvement almost entirely throughout the western United States, with drought removal predicted in the east.

Exceptional drought, the NWS’s most extreme drought rating, is not present in this prediction for the first time in several years. Areas of drought development are predicted, however, in areas of California and Texas. 

Drought conditions are expected to persist in areas of Colorado, New Mexico, Kansas and Oklahoma. Drought removal and improvement is expected elsewhere in Colorado and New Mexico, as well as in Nevada, Utah, Arizona and Southern California.

​For more information about anticipated conditions, visit the National Weather Service’s Climate Prediction Center at

​Note: Reed is a public affairs specialist.

Hydro generation chart

Last modified on March 7th, 2024