News from The Arizona Republic

News from The Arizona Republic

06 January 2012

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USA — Arizona weather conditions in 2012 are shaping up like last year’s: warm and dry through early spring, conditions that laid the groundwork for the worst fire season in state history.

A record 1,036,932 acres of Arizona wildland went up in flames in 2011, the vast majority in eastern Arizona, where all five fires that burned 10,000 or more acres ignited.

They included the largest and fourth-largest wildfires in state history, the Wallow and Horseshoe Two fires, which burned more than 760,000 acres combined.

Experts say the southeastern corner of Arizona, where four of last year’s five big blazes burned, is not likely to see relief in the upcoming season.

“The southeast quadrant of the state is almost a lock (for high fire activity),” said Chuck Maxwell, meteorologist with the Southwest Coordination Center, a multiagency emergency task force.

That prediction is echoed by the Southwest Coordination Center’s 2012 fire-season outlook report, released in late December.

Weighing five major factors for fire potential — drought; the condition of fuels; seasonal temperatures and precipitation; spring and early-summer weather patterns; and monsoon activity — the report predicts an above-normal fire season for southeastern Arizona.

That potential could expand to apply to all but Arizona’s northern and westernmost sections.

However, the SWCC report indicates that critical wind events are less likely this May and June than they were last year, a period when every fire that burned more than 10,000 acres ignited.

But the hot, dry conditions that primed the landscape for ignition last year will likely return for five to eight years of the next decade, as La Nia — a phase of the climate cycle by which cooling in the eastern and central Pacific Ocean alters global weather patterns — becomes more prominent. Maxwell said it is impossible to determine which years they will be, only that the climate is trending that way.

La Nia causes the jet stream — a current of high-altitude, high-speed winds that usually runs from the Pacific Ocean into Arizona — to take a more northerly route. During non-La Nia years, the jet stream brings moisture from the ocean into Arizona in winter and early spring.

La Nia was in effect last year and is credited with drying out upper-elevation Ponderosa pine and mixed conifer forests, making them more susceptible to fires.

The emergence of a prevalent La Nia weather pattern in the next decade could dry out upper-elevation forests even more, making them increasingly vulnerable to severe fires, Maxwell said.

Over a normal decade, Maxwell said, there is an even mixture of years that have El Nio patterns (which creates wetter winters and springs in Arizona), La Nia patterns and neutral patterns.

The last time Arizona saw drought conditions like those expected during the next decade was in the late 1950s and early 1960s, Maxwell said.

That absence of moisture going into fire season does not bode well. According to the Southwest Coordination Center’s predictive report, recent precipitation, though significant, has not greatly affected long-term drought conditions.

“If you don’t go into the spring with some decent moisture on the ground, you’re already at a disadvantage,” Maxwell said.

Both plentiful rain and drought can cause dangerous conditions in the wildlands.

Too little rain can cause grasses and trees to dry out or die, giving upper-elevation fires more fuel. Too much rainfall will make grasses in the lowlands grow wildly and, when those die during the early summer, conditions become ripe for ferocious brush fires.

Before last year, the 2005 fire season reigned as the worst in state history with 975,178 acres burned.

Maxwell said that the winter and early spring leading up to the 2005 fire season were extremely wet, helping both perennial and annual grasses grow. More than 4,000 fires ignited that season, the most of any season since 2000.

The largest fire that year was the Cave Creek Complex Fire, the third-largest in state history. It burned nearly 250,000 acres.

Forecasts for this year do not call for excess rain.

Emily Irwin, assistant director for fuels and fire ecology with the U.S. Forest Service, said that in dry conditions, dead fuels — downed trees and grasses that can litter forest floors — are more susceptible to sparks. Living fuels like trees and green grasses will become more ecologically stressed.

While the Wallow Fire was raging last year, relative humidity for fuels dropped into the single digits. For days, the relative humidity for fuels hovered between 5 and 11 percent. Anything below 15 percent is considered dangerously dry.

Irwin said fuel conditions now are fairly similar to last year’s at this time.

“The probability of having another active fire season is good,” Irwin said.

Nonetheless, Maxwell said that just one storm can upend predictions and delay the beginning of a fire season considerably — sometimes by more than a month.

There have been previous dire predictions for fire seasons that were entirely changed by one huge snowstorm in upper elevations, Maxwell said.

A storm like that in early 2011 would have made the season “dramatically different,” Maxwell said.

Other factors, such as below-average temperatures, how grasses “green up” during the spring and wind strength, can also matter.

“Longer-term weather conditions set up a fire season, but shorter stuff that happens week to week makes fires occur or not occur,” Maxwell said.

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