Like the beat of a butterfly’s wings affecting far-off events, all it takes for drastic weather worldwide is unusually warm water in the Pacific Ocean. This phenomenon, known as El Niño, brings about forest fires in Australia, more sea ice in the Antarctic, fewer hurricanes in the Caribbean — and rain in Arizona.
El Niño is back, and its unexpected return caught meteorologists flat-footed.
Only in the past week have long-range forecasts taken El Niño into account. Say the experts at the University of Arizona’s Climate Assessment for the Southwest about the coming winter: “The outlook is above-average precipitation.”
What is El Niño?
Scientists have known of El Niño for 115 years, after Peruvian sailors noticed a warm current appearing every few years around Christmas and named it after the Christ child. Yet only in the last two decades have El Niño’s effects been researched in depth, and we still don't know why it happens. Torrential rains that drenched California and Arizona during the winter of 1982-83 triggered science's inquiry. From December through March, Phoenix’s official gauge took in 6.68 inches — double the normal amount.
Since then, it now is understood that El Niño usually means Arizona will have a wet, cool winter — not all the time, but enough for meteorologists to declare a trend. Researchers also have learned of La Niña, which is when the Pacific cools off. During those times, Arizona usually has little precipation. There was a La Niña last winter — and rain didn’t fall in Phoenix for nearly five months.
It might be a wet winter. . .
At Arizona Snowbowl north of Flagstaff, no white stuff means no green stuff. Last winter, La Niña kept snow away until March, and the season lasted a piddling 15 days. That’s a lot of skis not rented, lift tickets not purchased and cups of hot cocoa not sipped. But Snowbowl now couldn’t be more excited. Just check www.arizonasnowbowl.com, where a news item declares “El Niño Returns.”
In a typical winter, Snowbowl receives 260 inches of snow. The total for last year was about half that. But during an El Niño, it snows and snows and snows — 330 inches in 1997-98, 460 inches in both 2004-05 and 1992-93. And it’s not just the promise of powder; imagine a season that starts around Thanksgiving, about three weeks earlier than normal. The snowpack enjoyed by skiers also is important to life in Arizona’s lower elevations, because runoff refills the reservoirs that slake the Valley’s thirst. So little snow fell last year that water in the Salt River chain of lakes is down almost 20 percent.
. . . but the drought continues
Arizona isn’t too far past one of the wetter monsoons in recent memory, but the state remains locked in a drought. Over the last 10-plus years, in all but the farthest northern reaches precipitation amounts are off normal by as much as 30 percent. So, could winter rains delivered by El Niño, on the heels of the wet summer, end this dry spell? Probably not. First, experts say this El Niño’s strength is weak to moderate. Meteorologists also point out that El Niño doesn’t guarantee more rain and snow for Arizona. Third, it’s important to keep perspective on this drought’s severity. Since the beginning of 1998 through this week, Phoenix has received 61.28 inches of rain. To reach the 10-year average, from now until the end of 2007 about 14 more inches 1/ 2 must fall. Finally, for that much rain to fall in 15 months, a wet summer is necessary. But, UA experts say, El Niño usually leads to a weak monsoon.