Tom Yulsman and Brendon Bosworth have an excellent piece over at Climate Central looking at drought and water supply on my favorite river*. They capture what I think is one of the key elements in understanding what’s happening on the Colorado: the realization that, independent of the drought that has plagued the river for more than a decade, the lower basin is using more water than their entitlement under normal conditions:

Traditionally, Lake Mead has been topped off with extra water from Lake Powell, unused by the upper basin states. But during the recent drought, water managers decided to provide only normal deliveries from the Lake Powell bank account. For Lake Mead, this has meant users have been removing more water than has been flowing in. And so inevitably, Lake Mead has dropped, from almost full in 2000 to about 42 percent full in mid-2010.

“What you’re really seeing here is a combination of drought and an overuse problem amongst the three lower basin states of California, Nevada and Arizona,” Udall says. “That overuse problem historically has been covered up by a little extra water that flows down from Colorado and the upper basin states. But over the last 11 years, with the most serious drought on record, that water hasn’t been there, and so the overuse problem has become readily apparent.”

* Sorry Rio Grande. What can I say? The Colorado and I have history.