Rapid Hydrologic Shifts and Prolonged Droughts in Rocky Mountain Headwaters During the Holocene

Rapid hydroclimatic shifts repeatedly generated centuries to millennia of extensive aridity across the headwaters of three of North America's largest river systems during the Holocene. Evidence of past lake-level changes at the headwaters of the Snake-Columbia, Missouri-Mississippi, and Green-Colorado Rivers in the Rocky Mountains shows that aridity as extensive and likely as severe as the CE 1930s Dust Bowl developed within centuries or less at ca. 9 ka (thousand years before CE 1950), and persisted across large areas of the watersheds until ca. 3 ka. Regional water levels also shifted abruptly at >11.3 and 1.8-1.2 ka. The record of low water levels during the mid-Holocene on the Continental Divide links similar evidence from the Great Basin and the Midwestern U.S., and shows that extensive aridity was the Holocene norm even though few GCMs have simulated such a pattern.