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Is Lake Powell really shrinking?

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Jonathan Thompson | Sep 12, 2012 01:30 PM

The West is heating and drying up so much that the whole place could burst into flames at any second. At least, that’s the way it seems, reading the news these days. Every day it’s another item about the catastrophic, unprecedented drought and the “new normal” of months of consecutive 90+ degree highs in places like Denver and Boise. Worse, even the tubers are high-centering on rocks in my hometown river, the Animas, which has reached its fourth lowest level (after 2002, 1934 and 1977) in the past century. 

So, with the dismal water year of 2011-2012 (Oct. 1 - Sept. 30) coming to an end, I figured I’d get some perspective on the situation by looking at one of my favorite and reviled barometers of the state of the climate: Lake Powell.

Lake Powell Levels

Since it finished its long, slow fill-up in the early 1970s or thereabouts, Lake Powell’s surface elevation has reflected the health of the great big watershed above it. Generally speaking, the surface elevation goes up during and following wet years, and goes down during dry ones. Most famously, the lake’s level plummeted so far during the 2000-2005 drought that it left a 100-foot high bathtub ring, revealed treasures that had been submerged for decades and rendered many a boater’s guidebook obsolete. That big trough is apparent on this nifty graph I put together using surface levels in May and August of every year since Glen Canyon Dam’s completion (for 2012, I included average lake levels from every month thus far). 

What the graph doesn’t quite reflect, however, is the image, seared into many of our brains by the 2002 drought, of the ever-shrinking Lake Powell, a reservoir doomed by a climate that is getting drier and drier by the year. That prophecy (wish?) may yet come true, but for now the lake level trend is not a declining one, but a cyclical one, in which every dry period (and there were some doozies long before 2002) is countered by a series of wet years. There was even a rebound after the 2002 drought -- 2011 was one of the five wettest years in the last half-century. Had Glen Canyon Dam’s managers decided to hold back a bit more water last summer, they might have achieved even more of a comeback of the lake (instead, they were generous with their surplus, sending a lot more water down to Lake Mead than usual). As bad as 2012 has been, it has yet to wreck the comeback altogether. Lake levels held steady for most of the year, dropping off only in the past month. 

That’s not to say we shouldn’t worry about the climate. High temperature records are being smashed all over the place. Colorado and Wyoming had their warmest summers on record. During July and August, the high in Phoenix topped 100 degrees on all but 10 days, and on ten days during that period, the temperature never dropped below 90. And as I write this, the rivers feeding Lake Powell are at about half of their average flow for September. 

It’s just that, for now, we can’t hold up Lake Powell’s shrinkage problem as evidence that the region is dessicating. There’s also hope that things might get moist again, and that the cyclical pattern will continue. Buried in all the apocalyptic news is the fact that much of the Southwest had a wetter-than-average summer. The monsoons drenched southern Arizona and Nevada in August, and Las Vegas is getting flash-flooded as I type. 

Jonathan Thompson is a senior editor at High Country News. His Twitter handle is @jonnypeace. 

Jay Canode
Jay Canode Subscriber
Sep 14, 2012 01:33 PM
I disagree Mr T. The lake IS shrinking but BY VOLUME. Every year more and more silt from upstream displaces water and in affect can make the lake seem even more full than it actually is. How much?... thats another article huh? One day...hopefully in my lifetime the dam will be useless because of it.
Jonathan Thompson
Jonathan Thompson Subscriber
Sep 16, 2012 08:55 PM
Jay: Yes, the silt questions is a good one, although it's tough to suss its effect out of the data (total acre-feet data mirrors the surface elevation data). But as you say, that is another article. My point here was to gauge not total storage of the lake, but the abundance of the watershed that empties into the lake. The next graph I should show is total annual inflows into the lake, and there you'll see a similar cyclical pattern of a series of dry years offset by wet years (with 2000-2005 being unusually dry, but the 1980s being wicked wet!). There is not yet a visible declining trend in precipitations unless you start at 1999, and that's just too little time to detect a trend. At this point, 2012 looks like an anomaly -- a minor interruption in the wet cycle. But then, that could change if next year is as dry, or drier, than this year...
Jay Canode
Jay Canode Subscriber
Sep 17, 2012 09:15 AM
Thanks for your prompt, thoughtful, and poignant response Jonathan. I of course was attempting stir the pot....or in this case the Lake. Cheers.
Quin Ourada
Quin Ourada Subscriber
Sep 21, 2012 01:49 PM
The siltation question truly is relevant. Without knowing the exact annual influx of sediment to the Powell basin we DO know there is, in fact, an influx. Even if one imperfectly assumes a constant sediment influx that quantity will effectively reduce reservoir capacity for a given surface elevation.

Sure, there is clearly a cyclical component but since the mid 80s the underlying trend is down. That much is rather evident to those familiar with hydrologic data. We are fast approaching 30 years with that underlying trend, so it warrants attention.
Appreciate the article, and hope to see follow-ups addressing the siltation component as this phenomenon is one deserving of greater journalistic attention.
Tracey Douthett &
Tracey Douthett & Subscriber
Sep 25, 2012 04:36 PM
Good points. With more upstream usage and downstream committments perhaps inflow is not the best paramater to monitor. Elevation is skewed exponentially also since half the storage is in the upper 100 feet. Storage is a tough unit too since there is 75 million acre feet of storage on a river that flows 15 million acre feet per year and there are equalization issues with Lake Mead. There are lag times and normalized numbers to be modeled so the question to ask is 'is this climate normal with a few bad years or is this a long term drought with a few good years'. The upper basin still has to deliver 75 million acre feet over ten years and we have half a lake to do it with. Can we do it with a St George pipe or a Denver pipe or a Nuke Plant and still have water for fish and fun? Time will tell.

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