Colorado River-Water Shortage

FILE - In this July 28, 2014, file photo, lightning strikes over Lake Mead near Hoover Dam that impounds Colorado River water at the Lake Mead National Recreation Area in Arizona. The Bureau of Reclamation is forecasting first-ever water shortages because of falling levels at Lake Mead and says the reservoir could drop so low that it might not be able to generate electricity at Hoover Dam. 

(CNN) -- A crippling drought in the western US is dropping the water level at Lake Mead and the Hoover Dam to a historically low level, putting pressure on the region's drinking water supply and the dam's electric capacity.

By Thursday, Lake Mead's water level is expected to sink to the lowest it's been since it began filling during construction of the Hoover Dam, according to Bureau of Reclamation spokeswoman Patricia Aaron.

"Lake Mead will most likely hit elevation 1,071.61 (feet) on Thursday, June 10. That will match the previous lowest elevation on record since the 1930s," Aaron said.

Lake Mead and the Hoover Dam straddle the Arizona-Nevada state line along the Colorado River, about 35 miles southeast of Las Vegas. The river provides drinking water to Arizona, Nevada, and part of Mexico. The dam generates electricity for parts of Arizona, California and Nevada.

While the lake's water level is expected to reach a new low this week, it won't be the bottom. "We anticipate the elevation of Lake Mead to continue to decline until November 2021," Aaron said.

Parts of the West and the Intermountain West have been in near continual drought conditions for decades. The Intermountain West is the area between the Rocky Mountains and Cascade Mountains in the Pacific Northwest and the Sierra Nevada Mountains in California.

Arizona water users preparing for first-ever cuts

"Some years are better than others and not in all places at all times, but the region has never fully recovered with enough rainfall and snowfall to erase the deficit," CNN meteorologist Brandon Miller said.

Miller described the drought as a "vicious cycle" in which dry land leads to less evaporation, which leads to fewer clouds and more sun, which equals more heat and evaporation.

"Climate change is clearly playing a role, as recent years have all been among the hottest in history. The warmer temperatures are driving that vicious cycle, and making it harder for normal or even above average rainfall years to make a dent in the drought," Miller said. "When one or two below average rainfall/snowfall years occur, as we have just seen, the results are disastrous."

As the water in Lake Mead drops, so does the dam's electrical output. Hoover Dam usually produces about 2,074 megawatts, according to the Western Area Power Administration. That's about enough electricity for nearly 8 million people. Tuesday's capacity is 1,567 megawatts, a drop of about 25%.

"Every foot of lake level decline means about 6 (megawatt) of lost capacity," Aaron said.

With no relief in sight, officials are planning for another unprecedented declaration in August, which is when operating conditions are set for the following year. It's likely a Level 1 Shortage Condition will be declared for 2022 for Lake Mead, Aaron said, meaning surrounding states will have to implement water-saving measures.

Arizona Department of Water Resources Director Tom Buschatzke said the planned drop in water coming from Lake Mead next year will be "painful," but the department is already working on contingency plans.

"While we may have less water coming to Arizona from the Colorado River in 2022, Arizona's water managers and suppliers have been taking measures to prepare and will continue to work to ensure the river remains stable for generations to come," Buschatzke said.

CNN has reached out to the Nevada Department of Conservation and Natural Resources about its planning for future water needs.

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