Canyon Wildfires--Real and Simulated

To help people visualize the problem wildfire may present, T-CEP commissioned two studies. The first is an historical analysis of the November 1977 fire that started in the Garapito Creek watershed, ran through the Cheney/Callon neighborhood into the Arteique area without crossing Topanga Canyon Boulevard. It represents a significant fire at the low end of the scale.

The second simulates fires that get started at two different places under three sets of wind and weather conditions. One fire starts well outside Topanga Canyon, between the southern end of Van Alden Avenue and the unpaved section of Mulholland Highway in Encino. The other starts just north of the water tanks at the crest of Topanga Canyon Boulevard.

There is not room here to discuss either study in detail. Copies are available on loan from T-CEP. But, a few of the main points are sufficient to set the parameters for present purposes.

The historical study of the November 1977 fire makes the following major points:
1. Wildfires move very fast. From its start at about 2 p.m., the fire reached its fullest extent by dusk--about 5 p.m. In that time half a dozen homes were destroyed or severely damaged, and all of Topanga east of Topanga Canyon Boulevard and north of the Center had been ordered to be evacuated.
 

2. Wind and weather are critical variables. Fortunately the wind was from the north and helped confine the fire to the east side of Topanga Canyon Boulevard. Most important, at around dusk the wind shifted to an onshore breeze, bringing in lower temperatures, higher humidity and fog, all of which conspired to slow and damp down the fire, making it possible for the firefighters to contain it overnight. Had those conditions not prevailed, the fire was headed for the Post Office Tract where it might have done considerably more damage.

3. In the years since 1977 all these homes have been rebuilt, most in similar style, and the burned-over vegetation has regrown to pre-fire condition--sometimes worse. New construction has greatly increased the density of homes and plantings, while the roads have not improved and in some cases have deteriorated. A new fire of the 1977 type is not only possible, but increasingly likely as time goes on and brush, plantings and homes multiply.

4. In terms of evacuation, the Cheney/Paradise Lane/Callon area has only one means of exit--Cheney Road. This narrow, winding road is also the only means by which firefighters can enter the area, creating the potential for collisions that could prevent aid reaching the scene of the fire. Similar conditions would have prevailed in the Arteique area as well as the Post Office Tract.

The simulation was done using the FARSITE computer model in use by the Los Angeles County Fire Department, the National Park Service and others having to deal with wildfires. It may be the best available model for studying the interaction of fire, terrain and vegetation in an effort to develop improved fire prevention and control strategies. We must emphasize that FARSITE does not predict outcomes. It can only suggest possibilities. Even so, it enables us to pose questions whose answers may give us some insight into how a major wildfire might impact the Canyon.

This simulation was intended to show the impact of different ignition points and different wind conditions on the spread of a major fire. Computer simulations are not intended to produce answers-they are designed to improve the quality of the questions one asks. On that standard the simulations were quite successful.*

(*By the way, T-CEP is acquiring the machinery and training to do simulations like this itself as well as to create databases to better accomplish its purposes.)

Question: Why were only two ignition points tried, and both at the north end of the Canyon?

Answer: It was not practical to try more points or more complex base conditions. Other efforts are underway to look at other fire models. But fire is a very complex phenomenon and the models themselves are complicated and don't pretend to predict conditions with sufficient precision to provide reliable advice in real situations.

Question: Could a wildfire that started outside the Canyon be blown into Topanga and then involve the entire Canyon?

Answer: Yes, and it is more than possible, although no one can be precise about where or when such a disaster might occur.

Question: Under moderate conditions, how long does it take for the fire to hit populated neighborhoods in Topanga?

Answer: Fires starting at either of the ignition points simulated would reach clusters of homes in a minimum of two, and a maximum of six hours, depending on wind conditions and ignition point. It should be clear, however, that these estimates are only suggestive.

Question: From a fire's start to its arrival at the coast, how long?

Answer: A minimum of 12 hours and as much as 23. In November 1993, however, the fire burned from Old Topanga Canyon Road to the coast in five to six hours.

Question: Are there any protected or fireproof places?

Answer: Not really, but there are places when fire seems to be slowed. These seem to be canyon bottoms, especially if they have water in them, and places where the fire has to burn downhill or against the wind.

These models are educational tools. Our purpose in pursuing them is to try to bring the best tools available closer to the people who need them. But individual judgment is still essential. It's your family and your home and there is no shortcut to safety in a wildfire.