As North America approaches the end of the 2021 water year, the two largest reservoirs in the United States stand at their lowest levels since they were first filled. After two years of intense drought and two decades of long-term drought in the American Southwest, government water managers have been forced to reconsider how supplies will be portioned out in the 2022 water year.
Straddling the border of southeastern Utah and northeastern Arizona, Lake Powell is the second largest reservoir by capacity in the United States. In July 2021, water levels on the lake fell to the lowest point since 1969 and have continued dropping. As of September 20, 2021, the water elevation at Glen Canyon Dam was 3,546.93 feet, more than 153 feet below “full pool” (elevation 3,700 feet). The lake held just 30 percent of its capacity. To compensate, federal managers started releasing water from upstream reservoirs to help keep Lake Powell from dropping below a threshold that threatens hydropower equipment at the dam.
The natural-color images above show Lake Powell in the late summer of 2017 and 2021, as observed by the Operational Land Imager on Landsat 8. The September 2017 image was chosen because it represents the highest water level (3,630.76 feet) from the past decade. The line plot below shows water levels since 1999, when Lake Powell approached 94 percent capacity.
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Image via NASA Earth Observatory