The Colorado River's (nonexistent) emergency plan

Rob Davis in the Voice of San Diego points out a hole in the governance of the Colorado River’s water: The Colorado River, the lifeblood water supply of San Diego and the Southwest, made history late last year. And it wasn't good. Lake Mead, the reservoir holding the Colorado River back behind the Hoover Dam outside Las Vegas, hit its lowest point since being filled in the 1930s. Had it dropped just a few more feet, federal officials would've declared the first shortage in the river's modern history. Arizona and Las Vegas would've gotten less water.

Fortunately, the lake's decline stopped. Officials began a massive transfer of water from Lake Powell, the river's other major reservoir, on the Utah-Arizona border. Along with a wet winter in the Colorado Rockies, that staved off what was once unthinkable. The Colorado River wasn't supposed to come up short.

Though the Southwest got a reprieve, it was a troubling sign for a river relied on by 27 million people in places like San Diego, Los Angeles, Phoenix, Las Vegas and across the border in Mexico. The Colorado River today faces two serious threats, either of which would mean less water for the arid Southwest.

The first: The river's annual supply was divided in the 1920s during a historically wet period. The Southwest created its expectations of the Colorado's annual yield during one of the wettest centuries on record. If yields return to their historic average, there won't be enough water to go around.

The second: Climate change is projected to cut the Colorado's yield between 10 percent and 30 percent by 2050. Even a small reduction would have a major impact. In the lower Colorado basin, California, Arizona, Nevada and Mexico take nearly every last drop to which they're entitled. Scientists at the Scripps Institution of Oceanography say a 10 percent drop could cause shortages in six of every 10 years.

Underlying those dire projections is a major uncertainty: If the Colorado consistently comes up short, no one knows who will cut consumption to keep Lake Mead from running dry. A short-term plan is in place from the time the reservoir hits 1,075 feet above sea level until 1,025 feet. Arizona and Las Vegas take that hit. (At 895 feet, the reservoir wouldn't be able to distribute water and the Hoover Dam wouldn't produce power. The lake is currently at 1,096 and climbing.)…

Hoover Dam, shot by Tobi 87, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported