TUCSON, AZ (KOLD) - La Niña came through!
While Southeast Arizona remains in a drought, the major water supply for the state, the Colorado River, is looking much more promising.
The headwaters of the Colorado River start in Colorado, high in the Rocky Mountains. Tributaries extend as far north as Wyoming.
Higher snowpack near the headwaters ensures a better water supply for all the states that use water from the Colorado River - Arizona, California, Nevada, New Mexico, Utah, Colorado, and Wyoming.
La Niña has an influence on the winter snowpack in the watershed of the Colorado River.
La Niña is defined as cooler than average sea surface temperatures in the equatorial East Pacific.
Here in the western United States, La Niña generally drives the winter storm track north, dumping more snow than average on the northern Rocky Mountains, while producing drought in the Desert Southwest.
This is good for Colorado River flow with slow spring snowmelt raising the water level at the headwaters. Of course this all flows downstream, raising water levels in the entire river.
The March snowpack near the headwaters measured mostly near or above average.
Above Lake Powell, upstream of Lake Mead, the average snowpack for the Colorado River watershed is 112% of average.
As the snow melts, it's expected to raise water levels in Lake Powell, which will then allow an increased release of water downstream into Lake Mead.
The Bureau of Reclamation forecasts a 97 percent probability that more than 2.5 million acre-feet (more than 850 billion gallons) of additional river water will be released from Lake Powell into Lake Mead this year.
The above average release from Lake Powell will raise water levels in Lake Mead about 25 feet.
Currently Lake Mead is just above the Critical Shortage Level, which if reached would trigger emergency measures, including rationing, for the seven states that use Colorado River water.
A third of all water used in Arizona comes from the Colorado River.
The additional water release should hold the threat of emergency measures off until at least 2016.
However, the situation will never be stabilized until water withdrawal out of the Colorado River is reduced.
This problem first began back when the seven western states divvied up the Colorado River water flow.
This was done based on average river flow over about 10 years in the early 20th century.
This flow was well above average flow over the long term according to paleoclimatic data.
The reconstructions of ancient river flows was mainly done by tree ring researchers at the University of Arizona.
At present, the overdraft out of Lake Mead is over 1 million acre feet per year.
That means any year above average flows in the river will hold off emergency measures temporarily.
©2011 KOLD. All rights reserved.
7831 N. Business Park Drive
Tucson, AZ 85743