Wildfire news, October 30, 2008

California: revisiting the Camp fire near Concow

In July Wildfire Today covered the BTU (or Butte County) Complex east of Chico, a group of fires that started during the Siege of ’08, burning about 50 homes in Concow. This is what we wrote on July 9:

Monday night between 8 and 10 p.m., firefighters began a firing operation out ahead of the fire, between the fire and Concow. CalFire-Butte County Capt. Scott McLean said the firing was going well, until an unexpected change in the weather occurred after midnight. Strong down canyon winds and a drop in the relative humidity from 43% to 21% caused spot fires far ahead of the firing operation. 

McLean said:

We had to try something; the fire was going to get there anyway. 

On Tuesday the fire reached Concow and burned at least 50 homes. We don’t fault the firefighters…. we will take the spokesperson at his word, that the fire would have reached Concow anyway. The strong winds Monday night and Tuesday contributed to the extreme fire behavior that caused the fire to burn all the way to the outskirts of Paradise.

Today there is an interesting article at ParadisePost.com that tells the story of one of the residents of Concow who was forced to evacuate by two different fires that month. It has a happy ending…. his home was spared by the fire.

Researcher: global warming to mean weaker Santa Ana winds and smaller fires?

A team of researchers at UCLA has a theory that global warming is already causing the Santa Ana wind events in southern California to be less intense than in years past. Some of the Santa Anas this fall have been less strong and of shorter duration than the typical wind events, providing some evidence that they may be on to something.

Here is how this concept is described by Alex Hall, the research spokesman, for the vcreporter:

The UCLA researchers are confident in their findings because the underlying conditions that create the most powerful of Santa Ana winds have been well documented both observationally and in equations. As these fall and winter winds roar through mountain passes, in areas such as Simi Valley, they are powered by a spillover effect from a huge dome of high pressure air that builds up in the high desert area known as the Great Basin, in eastern California, Nevada and Utah. 

The vast airflows are drawn to low-pressure areas to be found over the ocean off the coast near Los Angeles, like water in a stream moving downhill.

But it’s not just the difference in elevation and air pressure between the high desert and the ocean that fuels these winds. “Temperature forcing” also plays a crucial role, and as the land warms more quickly than in the past, in the fall and early winter, this forcing loses some of its power. With a physics calculation, Hall’s team finds that this factor has fallen by about one-third, resulting in a slow but steady downtrend in the most dangerous winds.

“This is not a small effect,” Hall said. “It’s a well-known fact that the cool air that forms over the desert at night is part of the Santa Ana condition, and so, as the interior of California warms, the difference between the desert and the ocean air pressures is reduced. That’s why we’re seeing fewer Santa Ana conditions over Southern California, and why we should continue to see fewer until the warming of the ocean catches up to the warming of the land, which won’t be until sometime in the 22nd century.”

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