What’s fueling New Mexico’s wildfires?

What’s fueling New Mexico’s wildfires?

19 April 2006

published by http://www.abqtrib.com 


A combination of hungry bark beetles, thirsty trees and the driest winter on record have set up New Mexico’s forests and bosques for one of the most destructive fire seasons ever.

Albuquerque Fire Department firefighters Steven Kehrer (left) and Randy Crews run from a falling tree they 
cut during a training session at Starfire Day Camp, south of Tijeras, in March. (Michael J. Gallegos/Tribune)

 

Why?

While out-of-control fires are always a danger in the dusty Southwest, this year is particularly worrisome, land managers say. Above-average precipitation in 2004-05 allowed for abundant grass and shrub growth last year. Then the weather reversed, and one of the worst droughts on record has set in.

Trees have about half their normal moisture levels, which leaves them susceptible to flames that last year might have merely blackened their bark but left them intact.

The abundance of “fuel” – dead grass and brush combined with the thirsty trees – is the perfect set-up for large-scale fires, officials say.

Making matters worse is an infestation of bark beetles. For the last two years they have been eating away at trees in the East Mountains, turning them into standing dead wood.

How does 2006 compare with other years for fire danger?

This year’s drought and weather conditions are on track to mirror 1996 and 2002, two of the busiest fire seasons ever.

In 1996, more fires burned – and burned more intensely – than ever before in the Southwest. The Dome Fire that burned 16,000 acres near Jemez Springs started in mid-April, which is early for New Mexico. Major fires kept firefighters busy all season.

And in 2002, at least 2,186 fires burned more than 424,710 acres in New Mexico, according to the Southwest Coordination Center. That was the worst year ever for Arizona, which saw 351,000 acres burned alone in the Rodeo-Chediski Fire near Show Low.

Exactly how dry are the trees, shrubs and grass?

Normally at this time of year, forest managers calculate tree moisture at what fire experts call 180 to 190 percent, said Tom Johnston, fuels specialist for Santa Fe National Forest.

At that level and above, “you couldn’t get the needles to burn with a blowtorch,” Johnston said.

At 100 percent moisture, the bark on trees will blacken and some will ignite.

“Now, forestwide, we’re at 93-111,” he said.

Shrubs, though, are drier because they don’t have as much capacity to hold water.

“Right now sagebrush is about 55-60,” Johnston said. “It is usually 110 percent.”

And those numbers are just for live trees and shrubs.

Dead grass, shrubs and trees are extremely dry – 12 percent, according to Johnston.

Branches or twigs could catch fire with just a spark, he said.

The likelihood that rainstorms will change this is low.

Los Alamos looked like a bomb hit following the Cerro Grande Fire of 2000. (Steven G. Smith/Tribune file)

 

How do forest managers categorize “fuel”?

Fire managers classify dead trees, shrubs and grass by the hours it would take to dry out or moisten.

Lawrence Garcia, fire management officer for the Espa?ola Ranger District north of Santa Fe, explained it like this:

1-hour fuels – grass and small shrubs;

10-hour fuels – shrubs and branches the diameter of a finger;

100-hour fuels – forearm-sized branches;

1,000-hour fuels – leg-sized branches and up.

A steady 100 hours of rain and humidity, let alone the rain needed to moisten the 1,000-hour trees, isn’t in the forecast until monsoon season, which generally starts around July 8-15, said Rich Naden, fire weather meteorologist.

How fast and how hot do types of fires burn?

With strong winds behind them, grass fires can move as fast as 60 mph, but they don’t burn very hot.

“They are kind of hard to control, but again they don’t burn as hot as heavy timber,” said Mary Zabinski, information officer for the Southwest Coordination Center.

She said most grass fires burn at about 4 to 6 mph, which is faster than most people can walk.

Heavy timber fires burn very hot, but usually travel a bit slower than grass fires, she said, estimating about 1-3 mph.

They can move more quickly in strong winds and when the fire makes its way to the treetops, or crowns.

Then, swept by the wind, the fire can jump from treetop to treetop, and can burn the tree from the top down.

Firefighters call those “crown fires,” and try to stay out of their way.

How do fires start?

In the Sandia Mountains, which are mostly in Cibola National Forest, about 47 percent of fires are human-caused. The most common causes are tossed cigarettes, misplaced campfires, catalytic converters igniting roadside grass and sparks from chain saws.

Lightning is responsible for most of the naturally occurring fires, concentrating a million volts of electricity in a small area for a fraction of a second.

Won’t the summer rains just put out the fires?

New Mexico’s monsoon season, which usually starts mid-July brings rain that in some places accounts for 40 percent of total precipitation, said Naden, the fire weather meteorologist with the Southwest Coordination Center.

“It’s months away before we can expect any significant precipitation in the Southwest region,” Naden said. “We’re anticipating a more robust monsoon and perhaps one that starts earlier than normal, but there is a lot of uncertainty.”

And while storms bring the moisture New Mexico desperately needs, they also bring lightning, and the chance of another big fire.

 

By Maggie Shepard
Tribune Reporter


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