LAS VEGAS (AP) — Pray for snow.
That’s about all Southwestern water users can do as the drought-stricken Colorado River enters what figures to be its most important snow season in recent memory.
After 14 years of record drought, it will take an unusually wet year — one like the basin saw in 2011 — to stave off the first-ever water shortages on the overdrawn river and slow the decline of its two main reservoirs.
Lake Mead, the source for 90 percent of the Las Vegas Valley’s water supply, has seen its surface fall by more than 100 feet since the drought began. Current projections call for it to lose another 25 vertical feet of water and sink to a record low by November 2014.
Should the lake keep falling from there, it could force the shutdown of one of two intake pipes used to deliver water to the valley. The Southern Nevada Water Authority is rushing to complete a new $817 million intake that will draw from the deepest part of the reservoir, but the complicated project is unlikely to be finished until late next year or early 2015.
“This is an alarming trend, and one that we would really like to see come to an end,” water authority spokesman J.C. Davis told the Las Vegas Review-Journal (http://bit.ly/15PQXWa). “Even if we have an ‘average’ year on the Colorado this year, Lake Mead is projected to continue falling. In order to make a significant dent, we would need at a minimum something on the order of 150 percent of normal.”
Almost all of the river’s flow starts as snow that collects in the mountains of Colorado, Utah and Wyoming from November to late May. Lake Powell, on the Utah-Arizona border, fills with that water in early summer, rising sometimes by a foot or more a day as the snow starts to melt and water flows downstream.
The federal water regulators mark time on a similar schedule with a water year that runs from Oct. 1, when the first snow begins to collect in the mountains that feed the river, to Sept. 30, when the last of the runoff hits Lake Powell.
“We’re just into the 2014 water year now,” said Angus Goodbody, water supply forecaster for the U.S. Department of Agriculture’s Natural Resources Conservation Service in Portland, Ore. “Usually by the end of October is when the seasonal snowpack is starting to build. It will be interesting to see what happens.”
At least one commercial weather service is predicting a white winter where it will matter most.
Pennsylvania-based AccuWeather is forecasting a wet, snowy season in the Northwest, the Rockies and in California, where heavy precipitation in December and January could help fill reservoirs drained by dry conditions in that state.
“I think this can definitely alleviate some drought issues,” said Paul Pastelok, a long-range forecaster for AccuWeather.com.
Just don’t get your hopes up quite yet, Goodbody said. “I’d be reluctant to put a whole lot of stock in forecasts like that. They’re fairly low-skill.”
Long-range forecasts for the Rockies are tricky because the mountains rest between two areas generally influenced by the El Niño and La Niña weather phenomena. It’s even more complicated right now, Goodbody said, because the climate is in what he called a “neutral phase” between El Niño and La Niña.
But the stage is set for a good winter on the Colorado.
The heavy downpours that triggered devastating floods in eastern Colorado last month also soaked the headwaters for the river, moistening soil left parched by the long dry spell. Goodbody said that could allow more snowmelt to flow down into the river system rather than be absorbed by the dry ground.
The flow of water into Lake Powell was more than twice what it normally is in September, which is the driest month of most water years but ranked as the third wettest of water year 2013.
That’s almost unheard of, Goodbody said, and it serves to illustrate just how unusually wet September was and how unusually dry it was during the rest of last year.
The stakes are high this snow season, and not just for southern Nevada. The Colorado supplies water to more than 30 million people across a region that produces roughly a quarter of the nation’s gross domestic product.
Under normal conditions, Lake Powell releases at least 8.23 million acre-feet of water a year downstream to Lake Mead for use by Nevada, Arizona, California and Mexico. This year’s release was cut to 7.48 million acre-feet, the lowest amount ever, to slow the decline of the upstream reservoir.
Each lake is now more than half empty, and the combined amount of water left in them is nearing its lowest point since Powell was filled for the first time.
Even in an average year, the Colorado does not carry enough water to fill the allocations parceled out decades ago to seven Western states and Mexico.
Nevada’s annual share is 300,000 acre-feet, or about 2 percent of the total. If the Las Vegas Valley went one year without using any water from Lake Mead, the impact on the reservoir would be a rise of about 3 feet.
One acre-foot of water is more than enough to serve two average valley homes for a year.
“Under the most likely scenario,” Davis said, the release from Lake Powell to Lake Mead will be cut to 7.48 million acre-feet again next year, pushing Mead even lower.
The only thing that can change that now is snow.