That Los Angeles and Las Vegas might lose some water and power is not the bad news.  The bad news is that the article means that a total ecosystem collapse in a very large area is probably imminent.  The ecosystems in this area have been devastated by the disgusting Hoover Dam(n) and by human removal of far too much water from the Colorado River.  The river and its ecosystems are in terrible shape now, but this would be much worse.

...Though this doesn't bode well for the rivers in the short term, the constraints on the water supply may discourage unsustainable development in the arid regions over the long term.

Lake Mead running dry...wow, that will cost billions. This is not good news for those people who enjoy fresh fruit/vegetables during the winter months. A lot of those crops are irrigated from that lake-river structure.

-Bummed about the loss of tomatoes in January

Perhaps you should wait until the full article is published in the Journal.  This is only a brief news release about a prediction based on observations about water usage and climate predictions.  They say they included....

"evaporation rates, climate predictions, water allocation schedules, past water demand, and future projections, among other factors."

Is anyone forgetting that Lake Mead is also a really bad thing that we should in some ways be extremely happy to be rid of?  Go and read your Ed Abbey, folks, the lake itself is no good ecosystem but a man-made abomination that destroyed many incredible beautiful canyons.  Perhaps the abject failure of Lake Mead to produce long term power and water will convince us to stop swarming to the water-scarce southwest and convince us to find some alternative energy sources that don't rely on destroying precious and rare landscapes.

jabailo references the original reports.  It says - in its first sentence - that the cause of the 50% probility of Hoover Dam and the Colorado River drying up is "human demand and climate change."

Only an un-sane mind in denial of reality would ask for unnecessary studies in water volume, rainfall,  snowpack cover, etc., to confirm what is already obvious by way of simple observation.  Which is that Lake Mead is getting smaller year by year.

The problem is not "why" but "what can be done right now to avoid catastrophe?"  If it is a natural event, then people must stop moving into the Southwest and quit wasting water.  If it is  man-made people must stop moving into the Southwest and quit wasting water.

Above all else, it must be taken seriously. It is not about tomatoes, or lawns, or golf-greens, or even ecological eyesores, but it is a matter of life or death for millions of people.  

Though getting rid of the Hoover dam(n) is really what's needed.

As to Jbailo's usual anti-environmental comments, any idiot can see that if you dam rivers and unnaturally remove huge amounts of water from them, they will have greatly decreased flow and eventually dry up.  The Colorado in particular has suffered dramatically because of water diversions.  But I suppose Jbailo still thinks the Earth is flat and that global climate change isn't happening, or if it is, humans have nothing to do with it.

...as much as I would like to see the Hoover removed, it ain't gonna happen anytime soon.  It will probably be one of the last major dams that will ever be removed.  Besides it's intensive size, it has too much of an impact on energy production, water supplies, and the regional economy to even considered for removal anytime soon.

Just like Atlanta, we believe our economies depend on perpetual growth to remain healthy, so we implement dozens of public policies to drive population growth (which virtually guarantees rising GDP year after year, so far). Then we pretend we can't do anything about population growth; it's a free country.

Then we try every miraculous and expensive technological solution to exhausted water supplies imaginable. Experts suggest conservation, dams, pipelines, aquifer mining, aquifer injection, cloud-seeding, and ultimately idling of irrigated agriculture (let's use more oil and increase our carbon footprint shipping food 1,000s of miles to these arid urban centers). The simple solution is to get unhooked from population growth as an economic engine.

It will all be gone by 21.12.2012.
Relax, you can't stop destiny.