The Likelihood of a Water Shortage from the Colorado River is measured by the Bureau of Reclamation, based on annual projections of water levels in Lake Mead, the reservoir that supplies much of Arizona’s water.
Arizona uses approximately 7 million acre-feet (maf) of water each year from all sources, about 2.8 maf of which comes from the Colorado River. Of our Colorado River water, about 1.5 maf moves through a Central Arizona Project (CAP) canal into the metro areas of Phoenix and Tucson. The rest is used along the river, primarily for agriculture in Yuma. This regular delivery of water is dependent upon the water levels in the reservoirs that store the water on the Colorado River. Lake Mead is the reservoir that supplies Arizona’s water from the Colorado River. The region has suffered from a long-term drought, and Lake Mead water levels have declined significantly over the past two decades. The rules governing how water is distributed from the Colorado River focus on Lake Mead water levels. If the projected level falls below 1,075 feet of elevation above sea level, a shortage is declared, and Arizona must cut back its use of water.
Likelihood of Water Shortage from the Colorado River data are only available for Lake Mead, the reservoir from which Arizona’s supplies are received. Updated every January and August, the August projection of the following January 1 water elevation determines whether a shortage is to be declared on the system.