The hardest working river: Drought and critical water problems in the colorado river basin

The Colorado River flows 2300 km (about 1400 mi) from the high mountain regions of Colorado through seven basin states to the Sea of Cortez in Mexico (Figure 1). The river supplies much of the water needs of seven U.S. states, two Mexican states, and 34 Native American tribes. These represent a population of 25 million inhabitants, with a projection of 38 million by the year 2020. Approximately 2% of the basin is in Mexico. The Colorado does not discharge a large volume of water. Because of the scale of impoundments and withdrawals relative to its flow, the Colorado has been called the most legislated and managed river in the world. It has also been called the most “cussed” and “discussed” river in the United States. About 86% of the Colorado’s annual runoff originates within only 15% of the area, in the high mountains of Colorado and the Wind River Range in Wyoming. In the semiarid Southwest, even relatively small changes in precipitation can have large impacts on water supplies. The coefficient of variation for the Colorado is about 33%.