“…all signs point to a future where every competing water use is a valid one and there isn’t enough water to quench them all” — Joanna Allhands #ColoradoRiver #COriver #aridification

From AZCentral.com (Joanna Allhands):

Opinion: We’ve known for years that a shortage is coming, but it’s alarming how quick the conditions are changing. The Colorado River system was not set up for this.

This warm, dry weather we’ve been having may be good for moving activities outside.

But it’s bad news for our water supply.

The chances are growing – and quickly – that a warm, dry winter could push Lake Powell to a trigger point about a year from now that could result in significantly less water for Lake Mead, which supplies about 40% of Arizona’s water supply.

That likely would push Mead into a first-time shortage declaration. And if the same thing were to happen the following year, it would likely plunge Mead into a more severe shortage – a depth from which the lake is unlikely to recover any time soon.

Like I said, bad news.

Why would Mead get less water?

The 2007 operational guidelines lay out how much water is released from the upstream Powell to the downstream Mead. In “normal” years (and yes, I use quotes because nothing about the Colorado River is normal these days), Mead gets about 8.23 million acre-feet.

That drops to 7.48 million acre-feet once Powell’s levels fall below a certain depth. This occurred once before, in 2014, and luckily, Mead was nowhere close to a shortage then.

But lake levels plunged that year and never recovered, even in wet years and despite millions of acre-feet of water that Arizona and others have stored in Mead.

The lake is currently less than 10 feet above its shortage elevation trigger of 1,075 feet. Yet a 7.48 million acre-feet release in water year 2022, which begins in October 2021, could drop levels on Lake Mead by nearly 20 feet.

That could plunge us into shortage

That would place us solidly into a Tier 1 shortage – which for Arizona, means no more Colorado River water for Pinal famers and some water lost from the non-Indian agricultural (NIA) pool, which is a rung higher on the priority list and despite its name, mostly supplies tribes and cities.

Should conditions persist and Mead get another 7.48 million acre-feet release in water year 2023, that would likely plunge us deep into a Tier 2 shortage, nixing most of the NIA water that some cities use for existing development and others had wanted to shore up their long-term supplies.

Without that water, cities will need to find other, more secure sources. Which means if the battle to transfer water from on-river communities to Queen Creek is fierce now, new ones are likely to get a lot fiercer.

How likely is this 7.48 scenario?

We’ve known for years that a shortage would eventually come to Lake Mead, and that when that happens, Arizona – the state with junior water rights – would be the first to face more severe consequences.

But it’s alarming how quickly the conditions are changing.

The chances of a 7.48 million acre-feet release have increased markedly – from less than 20% in April to more than 50% in August, depending on which hydrology forecast you use. The chances of a Tier 1 shortage on Mead were as high as 30% in August, up from roughly 10% in April.

That may not sound like a lot, but it’s enough to keep risk-adverse water managers up at night. Consider that a 1 in 5 chance of Lake Mead tanking was enough to drive ratification of the Lower Basin Drought Contingency Plan, which buys time for the lake through mandatory cuts to our water supply.

So, what is provoking such quick forecast changes?

Last winter was relatively wet. It looked like we were on par for an average runoff year. But the ground was dry before all that snow fell, and as it began to melt, a lot of it sunk into the parched soil.

In the space of a few weeks, what looked like a decent runoff year turned into a mediocre one.

Then we had a record-breaking hot and dry summer. The soil is again parched.

But, unlike last winter, we are now in a relatively strong La Nina weather pattern, which historically has meant warm and dry winters for all but a small corner of the Colorado River basin.

It’s a double whammy. If this winter plays out as expected, we’ll have a meager snowpack that is unlikely to produce much runoff because warm winds blowing over the snow can suck out moisture. And much of what is produced could sink into the ground before it ever makes it to our reservoirs.

If this is the future, then what?

It’s early in the snow season, of course. Things could change.

But while few parts of the Colorado River basin were facing drought conditions a year ago, most are now in extreme or exceptional drought, the most severe categories.

And some worry that this could be the beginning of a multiyear string of similar dry conditions – a la what we saw most recently in 2012-13, the lead-up to the last 7.48 million acre-feet release on Powell.

The good news, if you want to call it that, is that Arizona’s water leaders already assumed that we’d already be in a Tier 1 shortage by now. We have plans to handle these shortages in the short term, even if the details – like forcing Pinal farmers back solely on groundwater – are less than ideal.

The more daunting challenge lies in 2026, when the drought contingency plan and the 2007 guidelines expire. Because, as bad as this winter may look, the science suggests we are in for many more of them as the Colorado River basin gets warmer and drier.

We have a system that assumes water allocations will be steady as she goes, when the best-case scenario may be one of feast or famine.

And all signs point to a future where every competing water use is a valid one and there isn’t enough water to quench them all.

How do we decide who gets what when a dwindling supply becomes even more volatile? That is the fundamental question we must now address.

Reach Allhands at joanna.allhands@arizonarepublic.com. On Twitter: @joannaallhands.