PRECIPITATION TRENDS AND WATER-CONSUMPTION RELATED TO POPULATION IN THE SOUTHWESTERN UNITED-STATES - A REASSESSMENT

Water consumption figures for the southwest United States are compared for the last four decades. Past trends in consumption are evaluated i n the context of precipitation variability in the region and with rega rd to Colorado River streamflow changes. The study represents a follow -up look at a previous assessment of water consumption, regional preci pitation, and demographic trends in Arizona, California, Colorado, Nev ada, New Mexico, and Utah, which account for much of the annual deplet ions of Colorado River water. The previous study was completed during a wet spell in the West, and trends in all major categories of water c onsumption were consistently upward. This study indicates that a decli ne or reversal has taken place in water use in many of the western sta tes. The greater water efficiency (reduced per capita water use) is pa rticularly 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 ir rigation-related uses to civil consumption is evident in the 1980's. T aking into consideration a situation where multiyear dry spells are a normal part of the climate of the region, it appears that irrigation d epletions may have peaked in the West. In the future, allocations for civil supply, recreation, and other in-stream uses as well as for hydr opower generation may heighten the competition for available water sup plies, put pressure on existing pricing policies, and force users towa rd greater conservation efforts and improved efficiencies.