This is one of our most frequently asked questions, especially over the past couple months in the midst of an epic wet winter in the western U.S. We last answered it on 11/24/16, before the storms, at which point the water level was hovering around a record low for the second year in a row.
In January 2000, Lake Mead was at 92% of capacity. On Jan. 1, 2017, Lake Mead was at about 36%, a whopping 130 feet lower than in 2000.
The lake last approached full capacity in the summer of 1983, 34 years ago. It’s been declining ever since, but especially over the past 16 years, as drought in the Colorado River watershed took an enormous toll on Lake Mead, and Lake Powell upriver on the Colorado.
The water level bounced around the 1,075-foot mark during this past summer's irrigation season, but rebounded during the cool fall season to almost 1,085 feet.
That was a small relief, since falling below the critical threshold of 1,075 feet would have triggered a Level 1 Water Shortage declaration, signaling the start of potential water cuts to Arizona and Nevada.
And then, heavy snowfall on Colorado’s Western Slope and Utah’s Wasatch Range in December and early January boosted snowpack in the five-state Upper Colorado River Basin to 157% of average, way higher than the past several years.
(To answer another question we received, the storms in California and Nevada don't, in general, impact the water levels of Lake Mead and Lake Powell.)
In mid-January, the federal Colorado Basin River Forecast Center projected an April-July flow from the Rockies into Lake Powell of 9.8 million acre-feet, more than 33% better than the historic average and 3.2 million acre-feet higher than last year's total.
But by mid-February, that amount had been downgraded considerably, and federal projections released on February 17 called for the Colorado to carry about 94% of its average flow during the all-important April-July collection period.
Further complicating the situation, lakes Powell and Mead operate under a federal "equalization" policy in which, to maintain hydropower generation at both Glen Canyon and Hoover dams, the lakes must be kept at approximately the same level. However, since 2000, Lake Mead, which evaporates much more quickly (being lower and hotter), has declined more than Lake Powell, setting up an Upper Basin and Lower Basin conflict over the water.
Powell has to release water to account for Mead’s allocations and this year, Lake Mead is scheduled to receive approximately nine million acre-feet, but that exact amount is what will also go out to users. Then, due to evaporation and seepage, the lake could, and probably will, according to forecasters, drop more.
In fact, the Bureau of Reclamation's latest forecast calls for Lake Mead to continue to drop over the next two years, with new record lows predicted for May-June 2017 and April-June 2018. Even so, the Bureau says that the lake should stay just above the critical 1,075-foot level, avoiding the dreaded shortage declaration, which would force Nevada and Arizona to cut back on the water they get from the Colorado River.
The good news is that even an average year, if the 94% or so inflow holds up, is measurably better than the exceptionally dry past four-five years.
Also, there are still up to two more months of snow accumulation and in a statement, the U.S. Department of Agriculture's National Water and Climate Center said it remained "optimistic."
The bigger problem, of course, is that one wet winter can’t undo a 16-year drought.
This situation is, obviously, extremely fluid and only time will tell.
