Moab, Utah, gets just 8 inches of rain per year, yet rainwater flooded John Weisheit’s basement last summer. Extremes are common in a desert: Rain and snow are rare, and a deluge can cause flooding.

Weisheit, 68, co-director of Living Rivers and a former Colorado River guide, has long warned the U.S. Bureau of Reclamation that its two biggest dams on the Colorado River could become useless because of prolonged drought.

Although recently, at a BuRec conference, he also warned that “atmospheric rivers” could overtop both dams, demolishing them and causing widespread flooding.

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