Southern California Wildfires Explained

Posted on October 27, 2003 in Disasters Fact-Dropping

Yes, I’ve turned right around and given a scientific/practical explanation of why fires happen after saying that none could provide one from a higher power. This merely lists the factors that contribute to a wildfire becoming a fire storm and explains why firefighters from across the nation feel our wildfires are the most dangerous to face:

• The Santa Ana Winds. Everyone knows about these. They come roaring out of the canyons at 70 mph or more, picking up the flames and moving them ahead of the actual fireline. They hit us in the autumn and in the spring. During the latter season, however, vegetation is too moist to allow spread.
• The Chaparral. Our native vegetation depends on fire. Many seeds will not sprout unless fire scorches their shells. There’s one plant in particular, called chamise or greasewood, that thrives on fire. During the periods between fires, chamise sends out long roots. The leaves and branches burn like gasoline when lit. This also helps to account for the rapidness of the fire’s spread. When the flames have passed and the rain comes, chamise sprouts from the roots, invading new territories.
• The Terrain. The San Gabriels and the San Bernardinos form steep fronts, some of the most precipitous in the world. They rise from about 1000 feet to 5000 feet or, in some places, more than 10,000 feet — all in the space of only one to seven miles. The terrain helps to account for the strange jumps that the fire makes, the places that are missed (homes in the bottom of canyons are often left untouched as the flames hurdle over them, for example), and the local, bizarre wind patterns that carry the storm on its way. It also makes it extremely hard for firefighters to get to where the fire is burning.

Now that the hills are denuded, we face the winter with trepidation. Those whose houses survived the strange hopscotching of the blaze now watch the clouds. If rains are heavy, the houses that were spared may be washed away. This is due to a curious chemical change in the soil, wrought by the chamise, local mineral chemistry, and the oxidation caused by the fire: the fire makes the ground waterproof. Liquid won’t soak in. Instead, more than 90% of what will fall this winter can be counted on to run off into the city of San Bernardino, undercutting the slopes where houses survived the firestorm, ripping out homes on the alluvial floodplain from their foundations, spreading a jam of rock, mud, and debris all over her carefully laid out streets.

The passage of the fire does not free the afflicted cities from dread, but subjects them to new uncertainties. If donations to the Red Cross are in excess of the amount needed to help the victims of the fire, you can rest assured that they will be needed when the January clouds open their hearts and bring new weeping.