Drought can kick operational structures in the teeth. The water budget for Lake Mead has become unbalanced due to the extended drought. Legal demands from the three Lower Basin states and Mexico plus losses require 9.6 million acre-feet to be released annually from Lake Powell to meet Lower Basin demands. Some 600,000 acre-feet evaporates each year off Lake Mead alone, with a lesser figure off other lakes and canals. The annual net deficit is 1.2 million acre-feet. Prior to 2000 both lakes held sufficient water to cover all demands plus losses, and no one worried. But in recent years, only 7.48 million acre-feet have been released from Lake Powell to transfer water between Upper and Lower Basins. The water level elevations in Lake Mead are now dropping over 12 feet per year, a “structural deficit.” While triggered by natural hydrology, the magnitude of the continuing declines is dictated by the allocations set in the Colorado River Compact, giving the decline rate its own momentum. And now everyone is worried.
If water is not received from Lake Powell in volumes sufficient to remedy the structural deficit, Lake Mead water level elevations may drop below 1075 ft in 2017 as water is released to satisfy California and Mexico. This triggers the first tier of agreed-upon shortages in Arizona and Nevada. Because of the geometry of the reservoir, the rate of water level declines in Lake Mead accelerates over time. The second tier of shortage sharing may occur in 2018 at 1050 ft and the third tier in 2019 at 1025 ft elevation. Or it might not—increased inflows into Lake Powell could stave off shortages for some years. Or the drought could end. But in a worst-case scenario with an extended drought, water levels in Lake Mead could reach 1000 ft in 2020. Shortage sharing criteria at this elevation have never been agreed upon by the Lower Basin states. At 1000 ft, only four million acre-feet of water will remain in Lake Mead. California’s annual allotment is 4.4 million acre-feet.
In a December speech the Secretary of the Interior said she might have to exercise her authority as Water Master of the Lower Basin if the states can’t come up with contingency plans. That’s a clear threat. But in water politics, threats can work. Accordingly, ongoing discussions on how to handle the shortage have picked up speed amongst the seven Basin states and Interior. Discussants have been extremely tight-lipped about their progress. Somehow, the parties must curtail demand and figure out how to operate the Colorado River so as to keep everyone going. That won’t be easy. But it must happen.