Last August the U.S. Bureau of Reclamation (BOR) released its annual water report for the upper and lower Colorado River basins which stated there’s a 90 percent chance that Lake Mead will drop below 1,075 feet in elevation, which will trigger the BOR to declare a Tier 1 water shortage.

If a Tier 1 water shortage is declared it will have a huge impact on the lower basin states of Arizona, California and Nevada. Arizona agriculture will be particularly hard hit as approximately half the water currently allocated for farming and agriculture will be cut off. In the event of a Tier 1 Arizona will forfeit 220,000 acre feet of water annually, which, rather than be distributed to Arizona water users, will remain in Lake Mead.

With the possibility of a Tier 1 water shortage looming, Arizona’s water stakeholders – led by the Central Arizona Project (CAP) and the Arizona Department of Water Resources – have been crafting a water shortage plan, called the Lower Basin Drought Contingency Plan, or LBDCP.

In a statement released by CAP dated Aug. 5, the LBDCP “is not designed to keep Lake Mead above the first tier of shortage, rather its meant to keep Lake Mead from further dropping to the most critical elevation levels, at which point Arizona’s Colorado River water uses will face deep cuts to their water supplies and the river system would be in extreme stress.”

Under Tier 1 cuts, when Lake Mead falls below 1,075 feet, Arizona must leave 220,000 acre feet of water unused. If Lake Mead water levels drop below 1,050 Arizona must forfeit 400,000 acre feet. If the elevation drops below 1,025 Arizona must forfeit 480,000 acre feet.If Arizona reaches Tier 2 Arizona agriculture will lose approximately two-thirds of its water currently allocated for agriculture. If it reaches Tier 3 it must forfeit all of its agriculture water. At least, as the contingency plan is currently written.

Lake Mead’s elevation is currently at 1,078 feet, just three feet above the Tier 1 mark, but it’s expected to get a big boost next month if the BOR continues with its planned High Flow Experiment scheduled for Nov. 5.

Arizona water managers have been leading a series of biweekly meetings since July 2018 to work out details of the proposed drought-contingency plan.

According to the Arizona Dept. of Water Resources, if a Tier 1 water shortage goes into effect and Arizona must leave 220,000 acre feet of water unused in Lake Mead, the first pool of water usage to get cut is water currently being used to replenish aquifers and other underground water storage facilities. The next group of water users to lose water will be water customers without long-term allocations, then, as mentioned above, the non-Indian agricultural users.

According to the Arizona Dept. of Water Resources, the last groups to lose water usage will be Native American nations, and municipal and industrial users.

“There’s a wide understanding throughout Arizona right now that the entire agriculture pool is in real danger of evaporating,” said Doug MacEachern, Communications Administrator with the Arizona Department of Water Resources.

Even Tier 1 water restrictions will hit several central Arizona agriculture counties, such as Pinal and Yuma, very hard. A tier 2 water restriction would be devastating for those counties.

Arizona agriculture is wide-ranging and provides food for tables across the globe; everything from beef, chicken, dairy, eggs, citrus, nuts and vegetables. It also includes many non-table crops such as alfalfa and cotton. A large percentage of America’s winter vegetables are grown in Arizona and California using Colorado River Water.

If half of its agricultural water was cut off it will have a massive ripple effect across the U.S. and the globe.

According to the Arizona Dept. of Agriculture, Arizona agriculture contributes $17 billion to the state’s economy and employs more than 77,000 workers.

“Right now, it’s very clear-cut which groups will lose water first,” said MacEachern. “What isn’t clear-cut is deciding which farmers and ranchers get water and how much each one will receive.”

This is what Arizona’s various water resource groups, steerage committees and counties are trying to work out right now, said MacEachern. He calls it pain-sharing. Rather than have the agricultural community bear the full brunt of the water restrictions, maybe some of the municipalities and industries and Native American groups might give up some of their allocation, or find new ways to conserve water.

According to National Oceanic and Atmospheric Administration (NOAA), the Western U.S. is in its 18th year of drought. For six of the last 17 years inflows into Lake Powell have been less than five million acre feet.

And NOAA’s long-term projections show the problem will only worsen as snowpack for the Colorado River drainage areas steadily decreases as the planet warms. Further exacerbating the problem is the shape of Lake Mead.  The reservoir isn't a flat hole in the ground, but shaped more like a funnel, as elevation drops the water is stored in smaller space.

Officials fear that the reservoir's shape, like grading on a curve, will bring shortages faster.

The water decreases quickly once the lake levels drop below the funnel portion of the reservoir, said Bart Fisher, board member of California's Palo Verde Irrigation District and the state's Colorado River Board. "Everything happens faster when you get into the low reaches of the reservoir."

The Arizona Dept. of Water Resources is working closely with California and Nevada in an effort to conserve water.

Kathryn Sorensen, director of Phoenix's water-services department, said the Valley has been preparing for water cutbacks for years by banking millions of acre-feet of water underground for future use.

"Certainly, the city of Phoenix supports collaborative efforts to keep more water in Lake Mead," she said. "None of this is a surprise, right. We know the Colorado River is over-allocated, we are in a 20-year drought, we've known since 1968 that our priority on the river is the lowest in the lower basin, and we've been planning for a shortage for 30 years."