This paper considers the risk of drought and develops drought scenarios for use in the study of severe sustained drought in the southwestern United States. The focus is on the Colorado River basin and regions to which Colorado River water is exported, especially southern California, which depends on water from the Colorado River as well as the four major rivers in northern California. Drought scenarios are developed using estimates of unimpaired historic streamflow as well as reconstructions of streamflow based on tree ring widths. Drought scenarios in the Colorado River are defined on the basis of annual flow at Lees Ferry. Possible spatial manifestations of the Colorado River drought scenarios for input into a Colorado River system [...]
