Diaz, H. F., and C. A. Anderson, 1995: Precipitation trends and water consumption related to population in the southwestern United States: A reassessment. Water Resour. Res., 31, 713-720.


Water consumption figures for the southwest United States are compared for the last four decades. Past trends in consumption are evaluated in the context of precipitation variability in the region and with regard to Colorado River streamflow changes. The study represents a follow-up look at a previous assessment of water consumption, regional precipitation, and demographic trends in Arizona, California, Colorado, Nevada, New Mexico, and Utah, which account for much of the annual depletions of Colorado River water. The previous study was completed during a wet spell in the West, and trends in all major categories of water consumption were consistently upward. This study indicates that a decline or reversal has taken place in water use in many of the western states. The greater water efficiency (reduced per capita water use) is particularly noteworthy in California, which alone accounts for the lion's share of water depletions from the Colorado River Basin. The years since the mid-1980's have been predominantly dry in much of the West. At the same time, population in the six-state region has increased at about the same pace it had grown during prior decades. A shift from irrigation-related uses to civil consumption is evident in the 1980's. Taking into consideration a situation where multiyear dry spells are a normal part of the climate of the region, it appears that irrigation depletions may have peaked in the West. In the future, allocations for civil supply, recreation, and other in-stream uses as well as for hydropower generation may heighten the competition for available water supplies, put pressure on existing pricing policies, and force users toward greater conservation efforts and improved efficiencies.