This winter has been an astonishingly wet one for Arizona.
Last week, Phoenix saw yet more rain. In February, Flagstaff ground to a halt, blanketed by record snows. An overwhelmed water treatment plant in the San Tan Valley overflowed, dumping some 20 million gallons of treated wastewater into Queen Creek. And last October? It was the wettest ever recorded in Arizona.
Mother Nature has filled local reservoirs and soaked the ground with much-needed moisture. Regionally, it even seems to be staving off imminent shortages on the Colorado River.
But the Southwest needs several more winters like this before it can emerge from the regional drought, experts say.
"This winter has been excellent as far as the rain and snow we’ve received in Arizona," said Mark O'Malley, the lead forecaster for the National Weather Service in Phoenix. But, he added, "this is just one year, and one year doesn’t make up for a couple decades of drought."
In the past 20 years of drought, Arizona had seen very few winters as wet as this last one. In the past seven years, he said, winters have been exceptionally dry.
Phoenix has seen record rain four times since October, when the National Weather Service begins its so-called water year. The most recent was February 21, when 1.01 inches of rain drenched Phoenix, shattering the record of just under three-quarters of an inch in 1973, according to the National Weather Service.
In the mountains in northern Arizona, along the Mogollon Rim, snowfall since October 1 is now at about 150 percent of the average, O'Malley said. At the beginning of this winter, Lake Roosevelt, the largest reservoir on the Salt River, was less than half full. "By the end of this spring, we're probably going to be up near 75 percent of capacity," he said. "That's a very nice jump."
In the greater Southwest, so much rain and snow have fallen that it pushed back projections by the Bureau of Reclamation for shortages in Lake Mead, the reservoir from which Arizona draws its Colorado River.
Last month, the Bureau predicted that elevation levels at Lake Mead would probably drop below 1,075 feet above sea level — that's known as a Tier 1 shortage, and means states have to take less water from the river — in June 2019.
In its projections from this month, released Friday, Reclamation pushed that date back to May 2020. For the seven states that depend heavily on Colorado River water, including Arizona, that's a very good thing, because it could delay those planned cutbacks to their supply of that water.
“These developments may lessen the chance of shortage in 2020,” Terry Fulp, Reclamation's Lower Colorado regional director, said in a release. But the Colorado River basin still faces substantial long-term risks from the ongoing drought, he added.
That's the basic message that O'Malley is trying to send, too — that while this winter has been a good one, Arizona and the Southwest need several windfall winters before they're out of the hole.
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Filling up larger reservoirs, like Lake Mead and Lake Powell on the Colorado River, which are fed primarily by snow that falls in western Colorado and Utah, takes a lot more water. O'Malley explained. "We're going to need multiple years like this to see a much larger effect on those storage basins," he said.
It turns out that the record rain that showered Arizona in October, when Phoenix received a whopping 5.35 inches, have been crucial to helping fill the Salt, Verde, and Gila rivers, and surrounding reservoirs. That rain soaked the soil so that subsequent rains would flow into rivers and streams rather than saturating dry ground.
Last June, the entire state of Arizona was in a drought, some regions to a more extreme degree than others. This month, just 16 percent of the state is, data from the National Oceanic and Atmospheric Administration show. But the state could easily return to the state it was in just nine months ago.
“Arizona’s a dry climate," O'Malley said. "We’re always going to be dealing with the looming prospects of drought.”