Why worry about the water levels in Lake Mead?

Above is a satellite image of part of Lake Mead, taken in August of 1985. You can see the Colorado River flowing in on the right.

This was the same part of Lake Mead in August of 2010:

Lake Mead is the reservoir that sits behind the massive Hoover Dam, where it generates electricity and provides water to most of the American Southwest. The water level in Lake Mead has pretty much always been up and down, depending on drought and other factors. You can see how this normal fluctuation has played out since the high point of 1941 in a graph on NASA's Image of the Day page.

The low you're looking at here is the lowest the Lake has been since 1956. Why? The National Park Service sums up the problem: "In an "average" year, the amount of water flowing out of Lake Mead exceeds the amount of water flowing into Lake Mead."

Now, that's a bit of a "duh" statement, but it's important to remember that the problem really is that simple. There's no black magic going on here, just basic math. Part of the problem is an ongoing 12-year drought that's limiting inflow from snow melt in the Rockies. But, as seen throughout Lake Mead's history, droughts come and go. The really worrying issue here is on the demand side.

Decades of population growth have led to increased water demand in the Southwest. Take, for instance, Las Vegas, which gets 90 percent of its water from Lake Mead. Back in the 1940s, fewer than 9,000 people lived there. In 2006, the population was estimated at more than 550,000, and growing. Rapidly.

Multiplied throughout the region, that added demand means the tolerance for expected drought fluctuation becomes more brittle. And if the cycle of drought and rain doesn't behave like it has in the past—a change some scientists say you can see happening now, and others say is likely under climate change scenarios going forward—it puts more people at risk for water shortage.

In a nutshell, that's what's got people freaking out about Lake Mead. It's not so much the current water level, but concern about what happens if the rains take a particularly long time to return. Or don't last as long as we'd like them to before another long drought.

Thanks to Mr. Bad Example, who sent the photos in via Submitterator.

Maggie Koerth-Baker is the science editor at BoingBoing.net. She writes a monthly column for The New York Times Magazine and is the author of Before the Lights Go Out, a book about electricity, infrastructure, and the future of energy. You can find Maggie on Twitter and Facebook.

Maggie goes places and talks to people. Find out where she'll be speaking next.

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The Snowden Principle

Brian

Type “Lake Mead” into Google Maps and you will see the picture used above. Now zoom out and note just how big this lake really is. The article is showing a decade of drought on the smallest of the three arms that make up the lake.

It may also be worth noting that the “before” picture was taken two years after a period of flooding significant enough to actually use the Hoover Dam spillways.

I’m not saying there isn’t cause for concern or advocating wasteful use of water, but this strikes me as rather alarmist.
- Anonymous
  
  Google maps happens to be archived photos, there’s no way to tell when it’s from. Lake Mead is like a champagne glass, with the highest percentage of storage at high elevation.
  
  Level over time is good to consider here
  http://www.arachnoid.com/NaturalResources/
  
  and the current conditions (37% full) are good to see here
  http://www.azgfd.gov/h_f/edits/lake_levels.shtml
  
  You can see that it’s only down 50% surface area, but by 73% volume.
  
  I’m in San Diego, and have no grass around my house, even reuse washing machine water. The amount of waste I see around here is staggering.
Colby Seider

One word: desalinization.
Anonymous

I live in Las Vegas, and even though I love lawns (I came from Wisconsin), we DO NOT need them in Southern Nevada. On the Las Vegas Sun’s website, it says that landscaping accounts for about 70% of all water usage here. Amazing. I honestly think if we got rid of lawns, and other water sucking landscaping, we could save tons and tons of water. But, what about desalination? Why not pump water from the Pacific into Lake Mead? OF course it would have to be desalinized, but it would work.
Anonymous

Flying from San Francisco to Boston you can see in the desert a lot but I mean a lot of drying or dry lakes some of them really big. I am concern about this. I was wondering how recent is this phenomenon?
Tim S

A good book on water use throughout the nation
Unquenchable: America’s water crisis and what to do about it By Robert Jerome Glennon

http://books.google.com/books?id=DRT07ltvmYsC&printsec=frontcover&dq=unquenchable+glennon&source=bl&ots=j99wf0BkpF&sig=FLbHBF2WHunxc0lVrmq8k01zZGo&hl=en&ei=yXaiTLKEPILInAe8uv24Aw&sa=X&oi=book_result&ct=result&resnum=1&ved=0CBIQ6AEwAA#v=onepage&q&f=false
Teller

The Vegas boom is over for now, if you blame Vegas for Lake Mead’s poor showing. http://www.lasvegassun.com/news/2010/jun/11/building-boom-recessionary-bust-local-real-estate-/ In addition to droughtish Rocky Mtn winters – dust on the snowpack itself from poor land management is another contributor to poor replenishment of the Colorado River. Still – Colorado’s the best fuckin’ river to run.
Anonymous

The current La Nina condition is going to extend the western states drought.
Colorado Bob

Every time the winds blow east from the deserts of the Southwest, it means less water for 27 million people who depend on the Colorado River.

Layers of dust form every year on snowfields in the Rocky Mountains, blown in from pastures, farms, dirt roads and off-road vehicle parks. For decades, according to a study released this week by the National Academy of Sciences, this dust on snow both accelerates the annual runoff by weeks and reduces what reaches the Colorado River by 5 percent.

http://www.miller-mccune.com/environment/rocky-mountain-dust-up-runoffs-dirty-secret-23223/
Cochituate

Let me say from hundreds of miles away, that just because you in ARIDzona don’t know how to live within your means is no reason to think that you’re going to get your hands on water from the Great Lakes. Ain’t gonna happen. Uh uh.
- JohnnyOC
  
  “Let me say from hundreds of miles away, that just because you in ARIDzona don’t know how to live within your means is no reason to think that you’re going to get your hands on water from the Great Lakes. Ain’t gonna happen. Uh uh.”
  
  Yeah, like people from around the Great Lakes know about conservation of water.
  
  Hah!
  
  I grew out in Ohio, right off of Lake Erie, and almost of my family is still there. Let me tell you, my immediate family, my extended, my home-town friends, their families..conservation of water doesn’t compute with them.
  
  Just because you have a resource doesn’t mean jack if you are going to use it properly and being regional protectionist is not going to make matters better.
  
  Hell, there are 4 chemical plants in my hometown alone that are within a 1/4 mile of the lake.
- Anonymous
  
  It’s not Arizona sucking all the water. It is Las Vegas and the other suburban cities they built where the only option was to take from the Lake.
  
  Arizona also gets its water from the Salt River and Verde Rivers.
  - Colorado Bob
    
    Central Arizona Project is designed to bring about 1.5 million acre-feet of Colorado River water per year to Pima, Pinal and Maricopa counties. CAP carries water from Lake Havasu near Parker to the southern boundary of the San Xavier Indian Reservation southwest of Tucson. It is a 336-mile long system of aqueducts, tunnels, pumping plants and pipelines and is the largest single resource of renewable water supplies in the state of Arizona.
    
    http://www.cap-az.com/
- MrsBug
  
  You read my mind. I wonder WHY there fountains and golf courses with sprinkler systems in this part of the country at all. It makes no sense to me.
  - xzzy
    
    Las Vegas is actually fairly responsible about it.. there was a documentary on it I saw a ways back, but I can’t remember what it was called.
    
    Basically, most of the water that keeps the fountains flowing and the golf courses green is the grey water that comes from people’s homes. They do some filtering, then use it to water the lawn.
    
    I believe they capture the runoff and put it back through the system as well.
    - MrsBug
      
      Well, that’s pretty impressive. I’m always glad to see gray water systems being used.
    - Colorado Bob
      
      THIRD STRAW’: Water authority digs deep for third intake pipe at Lake Mead
      
      $25 million boring machine built just for project
      
      http://www.lvrj.com/news/water-authority-digs-deep-for-third-intake-pipe-at-lake-mead-79158322.html
      - Brainspore
        
        When I hear “straw” in this context I just think of the “I DRANK YOUR MILKSHAKE!!” rant from “There Will Be Blood.”
      - Colorado Bob
        
        Brain -
        That straw is so they can suck water from deeper in the lake . Otherwise the toilets will be empty on the strip.
      - Brainspore
        
        Yep, I can hear the giant slurping noises already.
        
        But if they’re really worried about keeping the toilets running in Vegas I’d start by discouraging all those casinos from building ginormous artificial lakes in the middle of an arid desert.
    - inphiknit
      
      I am in Las Vegas at the moment near the UNLV stadium. There are several very large verdant green fields nearby and every entrance to mobile home and prefab home lots is filled with greenery.. this is certainly not all coming from greywater recycling…nice try though.
      - Anonymous
        
        Actually, if you are near the Silver Bowl, it absolutely IS grey water. The Silver Bowl sits along the natural Las Vegas Wash, the section of the valley with the lowest elevation. One of the reasons you see mobile home parks there instead of houses is that run-off water from the city collects in the ground there, making it unstable for housing developments. Its great for making green parts of the city though; those “verdant green fields” (which, by the way, means ‘green green fields’ FYI) you pointed out are the meadows, or “Vegas”, for which the city was named 100 plus years ago.
        
        Also, golf courses and casinos COMBINED only make up about 18 percent of the water use in the Las Vegas Valley. Overwhelmingly water usage here is done by residential landscaping and the Southern Nevada Water Authority has done a great job of encouraging residents to switch to water-smart landscaping. Something I wish Los Angeles was a little better at.
  - Karl Jones
    
    “I wonder WHY there fountains and golf courses with sprinkler systems in this part of the country at all. It makes no sense to me.”
    
    Nothing say Wealth like a lush green garden in a barren wasteland.
- Anonymous
  
  As an addendum to this, see Waukesha. The city and county of Waukesha are looking for a new source to replace their radium contaminated aquifer. Due to the Great Lakes Compact, communities which border on the Grate Lakes Basin can apply to have water diverted as long as they replace it when they are done. No community out side of the immediate states (and provinces) surrounding the Great Lakes can gain access to water from the lakes.
- Anonymous
  
  Hoping that future Canadians can preserve the water from usurpation.
  
  (Use a dictionary!)
Antinous / Moderator

The Coachella Valley gets its water from our local aquifer with partial replenishment from the Colorado River, or if you live in a really nice neighborhood, from creeks coming down from the mountain.
Anonymous

more problems ahead:

http://www.sciencemag.org/cgi/content/full/328/5986/1642
Colorado Bob

In August, Alexandra Cousteau’s Expedition Blue Planet crossed over the Arizona/Mexican border to follow the Colorado’s dry riverbed to its historic mouth in the Upper Gulf of California where its nutrient-rich waters no longer reach the sea. This short film tracks the ghost of a mighty river that used to run free over this land half a century ago.

http://www.alexandracousteau.org/field/expedition-films/death-river-colorado-river-delta
shannigans

Shouldn’t the cost of water increase as the resource becomes more scarce? Seems it is a self regulation problem unless there is an unnatural force adjusting prices.
- mdh
  
  More often than not the invisible hand is picking someones pockets.
Colorado Bob

The last time the Colorado river flowed into the Sea of Cortez was in 1996.
spool32

Oh goodness, you’d NEVER find an unnatural force affecting prices for a critical resource managed by state and local governments that sustains billions of dollars of growth and profit for state and local governments.

Never in a million years!
Anonymous

I was inside Hoover Dam two weeks ago, and there’s another concern: the guide stated that if the water level dropped another 8 feet (82? ft below normal now) then the generators would become inefficient. He said something about “they aren’t geared for it” and modifications would be $millions… no indications that anyone is planning for mods. Does anyone know more about this?
tomrigid

@spoo32: nice try, but water rights in the American west are a bit more of a libertarian nightmare than a big-state boondoggle.
- HarveyBoing
  
  Whatever the root cause, the fact remains that water in Arizona costs relatively little. I don’t recall the exact numbers off the top of my head, but when my parents and I compared water rates between their utility in Arizona and ours here in the Pacific Northwest (where a “drought” means people who water their lawns can only do it once a week instead of twice), they were paying a fraction what we were. No more than half, and I think more like a third or a quarter.
  
  There’s clearly a disconnect between the normal supply/demand and what’s going on with water supplies.
  
  It certainly also doesn’t help that by far the biggest user of water in Arizona (and I surmise, in California too) is agriculture, which is a fairly powerful lobby.
Anonymous

I’d say that most of the American Southwest does not see a drop of water from Lake Mead considering that a good portion of the Southwest is on the other side of the continental divide from the lake. Even Northern Arizona has Lake Powell to draw water from instead of from Mead. So, rather than the “sky is falling” in TX, NM, AZ, NV, & CA, it’s more like parts of AZ, NV and CA get some water from Mead.
spool32

Same problem with the TVA, really… they got rain, though, and were able to kick the can down the road a few years. Again.

:/
Dean W. Armstrong

Remember that it’s less about Nevada’s allocation of 300,000 acre-feet (and the fact that the return goes right back into the lake) and more about the half-a-million to a million acre-feet overage that California consistently takes for mostly desert farming and never returns to the river.
- LightningRose
  
  Whatever water California takes from the Colorado River, it has *no* effect on Lake Mead as the water is removed *downstream* from the Hoover Dam.
  - Anonymous
    
    The water doesn’t magically appear at California’s downstream pumps. Water is released from Lake Mead to fill California’s portion of the (flawed) Colorado River Compact.
  - GlenBlank
    
    Whatever water California takes from the Colorado River, it has *no* effect on Lake Mead as the water is removed *downstream* from the Hoover Dam.
    
    And where do you think the water downstream of Lake Mead comes from?
    
    Yes, the MWD’s Colorado River Aqueduct taps the river at Parker Dam below Lake Havasu (as does the Central Arizona Project).
    
    But the water in Lake Havasu is river water released from Lake Mead.
    
    Releases from Lake Mead are governed by downstream demand – California, Arizona, and Mexico.
    
    The very minor amount of local runoff added to the river between Hoover dam and Parker dam is nowhere near the amount that California (or Arizona or Mexico) consumes.
    
    The lake level is down because the amount of water released from the lake is greater than the amount coming in.
    
    And the amount released is governed by downstream demand.
    
    The idea that California’s use of river water doesn’t affect the level of Lake Mead is simply absurd.
laukarlueng

Since water is considered a public good and the prices for water set by government fiat, the rationing aspect of prices have not controlled the supply and demand of water in the region. Government failure and economics denialists have at it.
Anonymous

Quantum of Solstice?
Anonymous

When will Lake Mead go dry? Scripps study:
http://www.agu.org/journals/ABS/2008/2007WR006704.shtml
Colorado Bob

The metaphor that is Vegas is a perfect example of life in the 21st century . They got bubbles popping where ever one looks.

It’ll make a lovely set of ruins.
MichaelRN

You think oil wars are bad? Wait ’til they start fighting over water.
Anonymous

So Steven Colbert was right–we should all stop eating fruits and vegetables. That would solve the Mexican problem, the welfare problem, the jobs problem, the various state budget problems, and now the water problem. Sure, why not?
richlb

Can you say “Aral Sea”?
pjcamp

Perhaps we can convince retirees in Phoenix to not throw water on the ground for their grassy lawns and swimming pools and live like they’re living in a desert.

But more likely they’ll go to war with Michigan over a pipeline to the Great Lakes.
- adamnvillani
  
  Perhaps we can convince retirees in Phoenix to not throw water on the ground for their grassy lawns
  
  Have you ever been to Phoenix? Yes, they have lots of golf courses and swimming pools, but one thing they’ve definitely got right when it comes to water conservation is that having a grassy lawn is anything but the norm. Arizonans have learned to live with climate-appropriate xeriscapes in their yards. We Californians could learn from their example and make a greater effort to use climate-appropriate landscaping (which needn’t be as severe as in Phoenix).
Anonymous

Vegas (and the rest of us) should go solar quickly before this situation becomes a huge disaster.
Spencer Cross

Here’s a quick rollover comparison I threw together:

http://tokyofarm.com/lakemead/
Simon Bradshaw

Around about the time that first picture was taken, Marc Reisner wrote Cadillac Desert, in which he pointed out that the south-western states of the USA were, not to put too fine a point on it, trying to terraform themselves – and that they were depleting a finite supply of ground water to do so.

As the ground water runs out, more and more is taken from reservoirs, and we end up with Picture 2. All predicted 25 years ago.
- pencilbox
  
  *love* cadillac desert.
  
  Whisky’s for drinkin’. Water’s for fightin’.
ncinerate

Lake powell is similarly low. Makes for some breathtaking cliffs alongside the lake, but it’s scary when you look up and see the old water level high above you on the wall.

I think last I checked it was about 20% down, but that’s actually a good thing as it was considerably lower a few years ago. We’ve had some good rain and snow over the last few years that have started to bring things back from the brink…

That said, the fact is we have -plenty- of water to keep everyone in california, AZ, and Nevada happily hydrated for a good long time into the future. A -massive- amount of water is currently released from these lakes to feed the colorado and supply for extremely wasteful water-rights of farmers along the southern most part of Arizona and California to grow massive crops of things like lettuce in the middle of the fricken desert with flood irrigation techniques.

If water levels reached a point deemed critically dangerous to the lives of millions you can bet those farmers are going to bear the brunt of it when they cap off lake mead to supply the people instead. The nice clean hydroelectric power generation will suffer, but they could -easily- refill the lake if need be. FAR less water from lake mead is used for -people- then is commonly assumed. On the plus side, Capping the hoover dam off to fill her up this gives us enough water even with today’s wasteful systems to nearly double the local populations in the region without any real fear or difficulty.
a random John

The agreement for gets how much water from the Colorado was drafted assuming that all time highs in terms of water availability would be the norm. It wasn’t written with normal years in mind, not to mention droughts. It was insane right from the get-go.
Anonymous

Interesting and dramatic pictures. I am a little confused, though. On a whim, I checked out Lake Mead on Google Maps — it shows the lake at the 1985 high level.

I know the past few times I’ve flown into Vegas (where I enjoy a weekend of gambling, drinking, and letting water hoses run unattended on full blast) the lake is noticeably down. Does this mean the Google Maps image was taken in the winter when snow melt has filled the lake?
Anonymous

I live in Chicago, and I often think in a thousand years archaeologists from Chicago will visit the ruins of Vegas and Phoenix and marvel at how dumb it was to build cities there. Vegas in particular just seems like a bad idea.
redesigned

A great website on the issues faced by the Colorado river:
http://www.savethecolorado.org/
Greg@Lake Mead

Actually, Arizona takes a larger percentage of Lake Mead than Las Vegas. In the bigger picture though, neither are a real factor once you consider the amount of water California takes. In fact, California not only has the largest percent of allocation, our fine friends to the “left” also take the largest percentage over their allocation.
What really burns me is the apparent total lack of any sort of water conservation in California, other than some degree of lip service, without much substance (imagine that!)
While I don’t profess to be a expert on California’s water conservation policies, I think it goes without saying, it is time for the Governator to start building desalinization plants along the nearly 800 mile coastline to satisfy the thirst of the world’s seventh largest economy!
- adamnvillani
  
  What really burns me is the apparent total lack of any sort of water conservation in California, other than some degree of lip service, without much substance (imagine that!)
  
  I suppose it depends on how you define “substance,” but echoing what GlenBlank said above, you can check out the population growth of the LADWP’s service area from 1970 to 2005 on page ES-4 of the 2005 Urban Water Management Plan:
  http://www.ladwp.com/ladwp/cms/ladwp007157.pdf
  
  Water demand has not shown any long-term increase despite the service population rising from under 3 million to 4 million. Per capita water consumption has fallen considerably.
  
  This didn’t happen without some effort. You can find a bunch of links to various DWP water conservation programs, both mandatory and voluntary, here:
  http://www.ladwp.com/ladwp/cms/ladwp001257.jsp
  
  To summarize, there is a water conservation ordinance limiting when lawn-watering can be performed, and the DWP has various rebates available for switching to more conservation-minded fixtures.
  
  I work for the City of L.A. Department of City Planning, and we’re requiring water-conserving features on any large new construction projects, including low-flow, auto-shutoff faucets, low-flow toilets and urinals, etc. There’s also a big push toward drought-tolerant and/or native landscaping.
  
  If you have a plan for “substantial” water conservation that isn’t covered by what we’re already doing, feel free to let us know. We’re always looking for more ways to save water.
  - Teller
    
    First, give back Owens Lake!
    :)
    - adamnvillani
      
      That’s a goal, not a conservation measure!
      
      Anyway, we’re working on getting Mono Lake back up to a healthy level. Ask the people of San Francisco when they’re going to stop using water from a dam erected in Yosemite National Park against John Muir’s wishes.
      - Teller
        
        I don’t know, Hetch Hetchy water’s pretty damn good. Not likely they’d ever find a better, more reliable source just for the pleasure of Sierra backpackers – of which I’m one. But its infrastructure needs some $$$ attention. And hey, Muir got plenty done, wouldn’t you say? btw, Mono’s only improved over time. *tips hat*
- JohnnyOC
  
  “What really burns me is the apparent total lack of any sort of water conservation in California, other than some degree of lip service, without much substance (imagine that!)”
  
  Don’t talk smack that you even admit to know too much about (and nice “left” jab you got there).
  
  Places like the city of Pasadena spend tons on shame marketing and awareness to get people to use less water. They even have a quarterly resident newsletter to say the current weather and drought conditions and tips on how to save water and will pay $300 to residents who buy water-efficient clothes washers (one of the highest rebates in the country).
  
  The water bills are graduated for people who are abuse of their intake and there are days of the week where if you are seen watering your lawn you get a pretty hefty fine.
autark

I just finished driving through Uzbekistan on my way to Mongolia and we stopped at the Aral Sea… It was really sad to see how devastated the area was, not just by the loss of water but by the toxic dust that blows around, pesticide laden sediment from the bottom of the sea after years of pollution that flowed into it before the Amu Darya was cut off for irrigation.

The flip side – the rest of Uzbekistan (along the road anyway) is lush with farms, and millions of Uzbeks could not live without this irrigation. You drive along the Amu Darya through Nukus, and you can see the massive irrigation channels splitting off in all directions towards the farms. If they were to restore the flow to the Sea, these people’s lives would be at risk.

I’m not saying the destruction of the Sea was right, but the consequences of trying to “fix” the disastrous Soviet planning now would be horrible too.

We need to be very careful and thoughtful about water planning here and avoid making the same mistakes.
Anonymous

“Forget it, Jake. It’s Chinatown.”
anomalous3

In the desert, water is life.
DJFitz

Here is a Google Maps image of Lake Mead I found today. Presumably this was taken with the previous year.

Lake Mead Google Maps Image 2010

It looks almost identical to the image taken in 1985. Is the low water-line image from the article a super low year? Because the thesis of the author, that water has almost disappeared, seems to be completely false.
deckard68

This is why I feel guilty when washing out bottles and cans to recycle. So much water going down the drain to clean garbage… there must be a better way.
Anonymous

Awesome! Soon I’ll be able to stand at the foot of the Boulder Dam intake towers and view the river bed.
Anonymous

I do not understand why they don’t just back up the flow of the river so the water does not in the end empty into the Gulf of California, (perhaps redirecting it back into the dams?)
Anonymous

Delta! It has a new delta, yeah. Just wait till our man made lakes fill up with sediment. Then what?
Anonymous

As much as Lost Wages tries to put a good spin on it, the reality is that water to Las Vegas is lost. It infiltrates into the ground or evaporates. All their efforts at efficiency are commendable, but what they return to Lake Mead is negligible. But as many others point out, the big problem is wasteful irrigation and use by Southern California.
Colorado Bob

LA set their all time record high temperature today 113 F downtown .
GlenBlank

What really burns me is the apparent total lack of any sort of water conservation in California, other than some degree of lip service, without much substance (imagine that!)

As of 2005, the Los Angeles area consumed no more water than it did 30 years earlier, despite a 30 per cent increase in population in that same period.

That substantial reduction in per-capita consumption is the result of a wide variety of water-conservation practices – some official policy, and some voluntary custom.

I don’t profess to be a expert on California’s water conservation policies

Imagine that!
Anonymous

The Future is Ocean Borne Solar Powered Desalinization.
rhamantus

Las Vegas may be the closest major city to Lake Mead (Boulder City is closer, but hardly “major”), the greatest beneficiaries of the lake’s water reside in Southern California. Yes, we in Vegas get 90% of our water from the lake, but our usage is a small percentage compared to the farmers in CA. S. California even gets most of the electricity from the dam, so when lake levels drop to unsustainable levels, it won’t only be the farmers who lose out, but the millions of people sucking up who knows how many kilowatt hours out of the Hoover Dam.
Additionally, there are half a million *residents* in the city, yes, but we also get between 35-38 million visitors every year (mainly from, you guessed it, Southern California), which also has an impact on the city’s water usage.
Anonymous

To understand the level of lake mead you have to go back to the Colorado river compact. This is a contentious issue, that at one point resulted in Arizona Governor calling out the National Guard,and pointing machine guns to stop California’s construction of a dam.

The compact allocated water based upon the prior years flows, which we now know to be higher than the actual average. But who wants to give up their water? Farmers in the Imperial Valley? Subcribers to the CAP in Arizona? Those along the colorado delta in mexico long gave up theirs.

Nevada is not the problem. Las Vegasâ€™s water use dropped by 19.4 percent in the seven years ending in 2008, even as the metropolitan area added 482,000 people, bringing the total to 2 million. It is indicative of the problem however.

Interestingly, Lake powell, which is the reservoir controlled by the upper compact states is low (66% of full pool – 80% storage capacity, with some marinas unusable) has recovered somewhat from the absolute low in 2005. Although inflows are down for year average (80% IIRC), there is a net improvement as flows downstream have decreased as well. This means less water going to Lake Mead and the lower compact states.
http://earthobservatory.nasa.gov/Features/WorldOfChange/lake_powell.php