<I>Mega-Drought</I><BR>North Atlantic could be contributing factor
COTTONWOOD – Arizona could be in the grips of a mega-drought, and the temperature of the North Atlantic Ocean could be partly to blame.
Julio Betancourt of the U.S. Geological Survey's Desert Laboratory in Tucson offered a compelling argument for that conclusion during a Verde Watershed Association mini-seminar in Cottonwood Thursday night.
More than 15 years ago, scientists gained a basic understanding of the El Niño/La Niña effect, when temperatures in the eastern Pacific Ocean around the equator affect U.S. weather, Betancourt said. El Niño tends to bring wetter weather to the southwestern U.S., while La Niña does the opposite.
Climatologists can use the El Niño Southern Oscillation (ENSO) to predict the severity of the Southwest fire season a year in advance, Betancourt said. But this information was long under-utilized, he added.
Much more recently, scientists have gained some understanding of the Pacific Decadal Oscillation (PDO index). When the PDO is positive, the central and western Pacific Ocean is colder than usual, and the eastern Pacific is warmer. With the negative PDO, the opposite occurs. These events can last 20 to 30 years, while the ENSO events last only about a year.
Now scientists, including Betancourt, are starting to realize that temperatures in the North Atlantic could influence long-term U.S. weather patterns even more than the PDO.
An April 2004 statistical study by Betancourt and others shows that large-scale droughts in the U.S. tend to be associated with positive Atlantic Multi-Decadal Oscillation (AMO index), or warmer North Atlantic tempera-tures.
Large-scale droughts in the 1930s, 1950s and 1995 to the present matched North Atlantic warming trends.
The AMO is even more long-term than PDO, taking 40 to 70 years for North Atlantic temperatures to change, Betancourt said.
The PDO and AMO combined could account for more than 50 percent of U.S. drought frequencies, Betancourt said.
A positive AMO combined with a negative PDO generally shifts drought to the Southwest and central Plains, while positive AMO with a positive PDO leads to drought in the Northern Rockies and Pacific Northwest, the study by Betancourt, and others, concluded.
Since 1999, the PDO has been negative and the AMO has been positive, and the western half of the U.S. has been in a drought. The same PDO/AMO relationship existed during the mega-drought of the 1950s.
"Although droughts re-main largely unpredictable, there is concern that the current drought in the West could persist due to continued North Atlantic warming, although the focal region of the drought may shift with the more variable North Pacific sea surface temperatures," the study states.
Betancourt said he doesn't think the North Atlantic will turn cold again for at least a decade.
Betancourt recommended that people document the costs of the drought, and take full advantage of forecasting advances.
For example, if the Forest Service didn't take full advantage of the wet period of 1976 to 1995 to conduct prescribed burns, it could be a long time before such optimal conditions return, Betancourt said.
"I work for the government," Betancourt added. "I'm not supposed to say this. We've got to start thinking about limiting the number of (housing) hookups. If we don't, we're in trouble."
The standing-room-only audience of more than 100 in Cottonwood Thursday loudly applauded that comment.
They also clapped when the VWA's other Thursday mini-seminar speaker, Charlie Ester, who is charge of water resource operations for the Salt River Project, advised them to attend council meetings en masse to oppose large new housing developments in their communities, if that's how they feel.
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