#LakeMead could be in a Tier 2 shortage by 2023. What’s that mean for #Arizona? — #AZ Central #ColoradoRiver #COriver #aridification

In a photo from 2020, a distinct line around the rocky shore shows how much the water level has decreased in Nevada’s Lake Mead. Mead is expected to drop 15 feet in 2021 Photo credit: Roberto (Bear) Guerra/High Country News

From Arizona Central (Joanna Allhands):

Opinion: The latest forecast suggests for the first time that Lake Mead could fall into a Tier 2 shortage by 2023, thrusting even deeper water cuts on Arizona.

Lake Mead’s water levels are heading the wrong way and going there alarmingly fast.

If the forecast holds, it’s now likely that we will fall into a more severe Tier 2 shortage by 2023, spreading painful cuts to even more water users in Arizona.

That nugget of bad news comes from the U.S. Bureau of Reclamation’s 24-month study, which is updated each month to predict reservoir conditions for the next two years. In April, the projection was that Lake Mead – the reservoir that provides nearly 40% of Arizona’s water – would most certainly be in a Tier 1 shortage in 2022 but would miss the Tier 2 cutoff for 2023 by three-tenths of a foot.

Now, in May, the most likely projection is that Lake Mead will end 2022 at 1,048.83 feet of elevation – more than a foot past the trigger to put us in Tier 2.

We’re hot, dry and low – a volatile mix

The good news (if you can call it that) is that the predictions didn’t change nearly as rapidly from April to May as they did from March to April. Projected lake levels for December 2022 dropped last month by about 5 feet, thanks to horribly anemic and earlier-than-expected runoff.

It’s also worth noting that if we didn’t have the Drought Contingency Plan (DCP) in place to conserve water, we would already be in this shape. That agreement didn’t solve our problems, but it has bought us time and certainty as deeper cuts play out – which is exactly what it was intended to do.

West Drought Monitor map May 18, 2021.

That said, we’re still hot and dry, with more than half of the Colorado River basin now in extreme drought, the most severe category. Unless that trajectory changes, the forecast is probably not going to get much better.

And, even worse, we’re getting down into the V-shaped part of Lake Mead, meaning it takes a loss of less water to drop lake levels than it once did. Losing smaller volumes of water can have bigger impacts.

Which is why there’s also a 1 in 4 chance that we could fall into a Tier 3 shortage by 2025 – the worst-case scenario spelled out under DCP and one that would much more heavily impact metro Phoenix cities.

How a Tier 2 shortage could play out

But a Tier 2 shortage in 2023 wouldn’t be a walk in the park. Technically, there are two levels of Tier 2 shortage for Arizona – a Tier 2a that’s triggered at 1,050 feet of elevation on Lake Mead and a Tier 2b that would occur at 1,045 feet.

It’s a small variance in elevation, but it would increase required cuts statewide, from 592,000 to 640,000 acre-feet, and decimate Central Arizona Project’s Non-Indian Agriculture (NIA) pool, which despite its name mostly supplies tribes and cities.

Luckily, Arizona’s DCP implementation plan includes water to temporarily mitigate the impact of those cuts. But the amount replenished in 2023 would fall from 75% to 50% in a Tier 2b shortage. That will still be painful, particularly for metro Phoenix cities that use NIA water to serve a few existing customers.

The May projection is already within about 3 feet of reaching a Tier 2b shortage. And let me underline that – we’re talking about the most probable projection. Not the best or worst case, but the most likely.

We’ve planned for this, but it’ll still hurt

We’re also less than 20 feet from triggering what might be called the doomsday provision within DCP.

If the lake is projected to fall below 1,030 feet any time within two years, Arizona, California and Nevada must reconvene to decide what additional steps they will take to keep Mead from falling below 1,020 feet – an elevation that many consider the crash point. The next milestone below that is “dead pool,” where no water leaves the lake.

And that provision is triggered by any part of the forecast – not just the maximum or most probable scenario, but the minimum probable scenario, too.

It’s anyone’s guess what will happen then.

But, hey, at least we’ve got plans in place to handle Tier 2 and 3 shortages. And, in even better timing, Arizona has just completed a multiyear effort to flesh out how cities and other users can begin withdrawing the millions of acre-feet of water they have stored underground.

Explaining the benefits and pitfalls of that effort is for another blog on another day, but for now, let’s just say it’s a good thing we have water stored for a (non)rainy day.

Because the outlook for Arizona’s major renewable water source is parched and bleak – and growing more so every day.

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