I recently (happily) stumbled across a web version of the full 1995 publication of the Colorado River “Severe Sustained Drought” study, a comprehensive “what if” exercise done in the 1980s and early 1990s. From the forward::
The Severe Sustained Drought Study contemplates a much more dire water supply scenario than that which has occurred in the past century. Reconstruction of river flow records, based upon several centuries of data, suggests that periods of much reduced flow in the river have periodically occurred. These data are derived from analysis of growth rings in trees from around the Colorado River Basin states. Combining this information, the SSD researchers have created a highly plausible scenario of severe and sustained drought and used that as a means of assessing what the hydrologic, social, and economic impacts of such a drought would be under the current law of the river. As you will see, the impacts are substantial.
Full (big) pdf here, courtesy the University of Arizona.