Odds now favor a Lower Colorado River Basin shortage declaration in 2018

The latest U.S. Bureau of Reclamation two-year Colorado River operational forecast, released last week, projects that Lake Mead will end December 2017 at elevation 1,074.2 feet above sea level, about 10 inches below the level that would trigger a first ever shortage declaration on the Lower Colorado River. Here’s the legal mumbo-jumbo:

In years when Lake Mead content is projected to be at or below elevation 1,075 feet and at or above 1,050 feet on January 1, a quantity of 7.167 maf shall be apportioned for consumptive use in the Lower Division States of which 2.48 maf shall be apportioned for use in Arizona and 287,000 af shall be apportioned for use in Nevada in accordance with the Arizona-Nevada Shortage Sharing Agreement dated February 9, 2007, and 4.4 maf shall be apportioned for use in California. (emphasis added)

That would translate to a 320,000 acre foot cut in Arizona’s Central Arizona Project aqueduct supply, which carries water to Phoenix, Tucson, and neighboring communities. Las Vegas would also take a 13,000 acre foot cut, though Las Vegas last year is already using a lot less water (it only used 221,000 of its 300,000 acre foot allocation) so this is less important there. I wrote a much longer thing about what 1,075 would mean in practice.

Assuming this hydrology holds, it’s easy to see how the shortage could be avoided. All the lower basin water users are currently scheming to find ways to leave water in Lake Mead, and it wouldn’t take much success along those lines to keep Mead above 1,075. That is what I expect to happen. Also, this is very early, hydrology could push these numbers quite a bit in either direction.

Here’s the latest version of my sorta monthly graph, updated to include the end-of-2017 numbers.

Lake Powell and Mead total storage. Source: USBR

Lake Powell and Mead total storage. Source: USBR


Data from the USBR 24-month study (pdf)