From:
https://cis.org/Population-Immigration- ... -Southwest
The allocation formula so critical to the future of the Southwest was based on a gaffe of proportions only now being understood. It was believed in 1922 that most years the Colorado River would carry 16.4 million acre-feet of water. The Upper Basin states of Colorado, Utah, Wyoming, New Mexico, and part of Arizona were allocated 7.5 million acre-feet a year; Lower Basin states California, Nevada and the rest of Arizona were allocated 7.5 million acre-feet, with the
remaining water from the mythical 16.4 million acre-feet promised to Mexico.
But the 16.4 million-acre-foot estimate was based on rosy optimism springing from measurements of the river during what later research showed was one of the wettest periods along the river in 400 years. Soon after the signing, flows began to change on the river and the states slowly realized that they had apportioned at least 1.3 million acre-feet of water more than usually flows in the Colorado.13
Recent tree-ring studies have shed an even grimmer light on the Colorado River Compact’s mistaken assumptions. These studies of precipitation in the Southwest over the last few hundred years indicate that it is likely the river’s flow —
even without global warming — will be on average three million acre-feet less than allocated, not the million-or-so shortage originally assumed. Based on actual stream-gage readings, the flow of the Colorado River has averaged only 14.2 million acre-feet per year since 1950 (overall an uncharacteristically damp period). The Southwest may well have to get by on about 13.5 million acre-feet — a stark reality that was beginning to dawn by the 1990s as reservoirs dwindled in size like leaking bathtubs.
Almost simultaneously the region’s already rapidly growing population began to explode after 1990, delighting real estate agents, land speculators, developers, and politicians, but worrying those who study climate and water supplies. This happened directly via birthrates and arriving immigrants and indirectly via United States residents migrating into the Southwest. Immigration is responsible for virtually all of the population growth in California. In other states of the Southwest, immigration has caused between 30 and 60 percent of the population growth. This growth occurs despite level birth-rates and the recommendations of two presidential commissions that the United States should move toward population stabilization; limiting immigration is key to their recommendations.
