Lake Mead

Irfan Khan / Los Angeles Times 2015

A federal forecast of water levels at troubled Lake Mead took a big turn for the worse this week — a 20-foot drop in the lake’s expected January 2019 elevation.

The U.S. Bureau of Reclamation’s monthly prediction for Colorado River reservoir levels says the lake could drop to 1,076.53 feet by the end of 2018 or Jan. 1, 2019. That would be a foot and a half above where a Central Arizona Project water shortage would be declared. Last month, the forecast for the end of the year was 1,096.77 feet.

A shortage declaration would cut river water deliveries to Central Arizona farmers and Arizona Water Bank recharge projects. Tucson gets most of its drinking water from CAP but wouldn’t be affected by a shortage declaration at this point — only when and if the lake drops much lower.

The forecast is down sharply from the bureau’s May 2017 prediction because this spring’s river runoff levels are less than expected a few months ago although still above normal. That means the amount of water to be released from Lake Powell downstream to Mead this year won’t be as much as was thought a few months ago. The prospect of lesser releases from Powell has been known for some time, but the 20-foot-decline in the 2019 forecast was just released.

“The severe drop-off in anticipated flows into Lake Mead represents a shocking turn-around in expectations for the near-term health of the great reservoir,” said the Arizona Department of Water Resources in an article on its website.

The abrupt forecast change underscores the need for agreement on a near-term “drought contingency plus” plan for the state to reduce the risk of shortages, Water Resources Director Tom Buschatzke said Thursday. CAP officials have opposed that plan as unneccessary in light of earlier, more favorable forecasts, leaving negotiations stuck for months. CAP officials weren’t available for comment Thursday on the latest forecast.

At the same time, Mead’s bad January 2019 forecast doesn’t mean an immediate crisis. The forecast doesn’t take into account already planned water conservation efforts by the CAP that, if carried out, will push the lake up by a few feet compared to what the bureau is forecasting, a bureau spokeswoman said.

It does, however, take into account 350,000 acre feet that California users and Arizona’s Gila River Indian Community have pledged to leave in the lake in 2017. Lesser amounts are committed for 2018 and 2019.

The Phoenix City Council added to the conservation push this week by unanimously approving a deal to pay the Gila River Indian Community $2 million to leave 40,000 additional acre feet in the lake for a year. Arizona is spending $2 million. The non-profit Walton Foundation and the Bureau of Reclamation are kicking in another $1 million apiece.

The agreement isn’t a done deal yet because CAP must approve it. But it’s already being hailed by backers as a prime example of how cooperation among users can boost the lake’s levels.

The January 2019 forecast could rise or fall later, depending on the weather over the next 18 months, reclamation officials noted.

“We offer our best projections to help our water users plan, but the hydrology is extremely variable,” bureau spokeswoman Rose Davis said Thursday.

Contact reporter Tony Davis at tdavis@tucson.com or 806-7746. On Twitter@tonydavis987