The part of Arizona where most of the Valley’s water comes from recorded one of the driest winters on record, making it the second parched winter in a row.
The 2012 runoff season produced only about one-third of normal moisture levels and was the 16th driest among the 114 years of records kept by Salt River Project. Only 193,474 acre-feet of water came from the Salt and Verde watersheds north and east of the Valley, according to SRP. That compares with a typical year off 534,336 acre-feet.
The year before was the 22nd driest on record.
The lack of rain and snow is typical of a La Nina, the pattern that ushers in cool Pacific Ocean temperatures and drier-than-normal conditions in the Southwest.
What isn’t typical is having back-to-back years of La Nina conditions, said Charlie Ester, SRP’s water resource operations manager.
But it may be time to say adios to La Nina.
Climate models predict the opposite of La Nina will take hold by the winter. That pattern is El Nino.
“There’s no guarantee of anything in Arizona — except maybe a hot June — but we typically have a tendency for wet winters in El Nino conditions,” Ester said.
That would replenish SRP’s diminishing reservoirs, which are 61 percent full. They were 83 percent full one year ago thanks to a wet 2010 that was the 20th most productive runoff season on record.
Winter snowfall is important to the Valley water supply because of the potential for snowmelt to flow into lakes and rivers. Monsoon rains rarely result in significant flows into the lakes where SRP stores water.
SRP shareholders will still get their full allocation of water despite the dry winters. The water and power company wouldn’t have to restrict water use until 2015 if current conditions persist, Ester said. Restrictions were last in place in 2003 and 2004.
While SRP uses news of dry spells like this to encourage water conversation, Ester said most customers don’t typically change their habits that quickly. But there has been a trend to converting lawns in to desert landscaping and changing other habits.
“People have started to use less water and it’s been a very slow, gradual shift,” Ester said. “But it has been significant.”
That could prove to be more significant in the coming decade. Ester said a 1995 shift in oceanographic conditions triggered a drought that began in 1995. The cycle typically lasts 30 years.
Even in droughts, a few very wet years come along that can replenish reservoirs and prevent rationing during drier times, Ester said.
“I’m hoping we can squeak by these next few years,” Ester said. “There’s nothing unusual about the last few years, and that’s why we have the reservoirs.”
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