7997

• UCREFRP Catalog Number: 7997
• Author: Nash, L. L. and P. H. Gleick.
• Title: The Colorado River Basin and Climatic Change, The Sensitivity of Streamflow and Water Supply to Variations in Temperature and Precipitation.
• USFW Year: 1993.
• USFW - Doc Type: EPA 230-R-93-009,
• Copyright Material: NO

~

delivery from the upper to the lower basin is 82.5 maf in every 10-year period, except in those periods when
Mexican Treaty obligations are reduced.

The water apportioned between the basins has also been rather precisely divided among the

states within each basin by the Boulder Canyon Project Act (1928), the Upper Colorado River Basin

Compact (1949), and several court decisions handed down in Arizona v. California. In addition, water

delivered to California is divided among users by the Seven Party Agreement. (These agreements and

allocations are also discussed in Appendix B.)

Water allocation continues, however, to be a contentious issue in the basin. Future demands

for Colorado River water are predicted to outstrip supplies. The population of the region is more than 19

million; and, despite the fact that the area is approaching the limits of its water supply, population and

economic activity have continued to expand. Although severe shortages have not yet been felt in the basin,

there is growing concern that the pressures of increased demand and the potential for periodic supply

shortages will create problems in the future.

Droughts in the Colorado River Basin have generally been considered as isolated, temporary

events that can be overcome through storage and short-term conservation strategies. The validity of this

assumption is challenged by paleoclimatic data which indicate that the region has experienced much more

severe and sustained droughts in previous centuries than in our own (Stockton, at aI., 1991). Now the

prospect of anthropogenically induced climatic change offers the unsettling prospect that the region may

face both permanent and more extreme changes in its climate than previously considered. Enhanced

greenhouse warming wHI almost certainly cause increases in the region's average temperature, and could

cause either increases or decreases in average annual precipitation (IPCC, 1990; Mitchell and Qingcan,

1991). As a result, the basin could experience changes in the likelihood and severity of prolonged droughts

or extreme floods. In any case, the storage and supply facilities and institutions that have evolved in the

4