Saturday, November 3, 2007

Preparing for the Next One...

One thing we can be certain of, unfortunately, is that wildfires will attack our community again. Some areas (such as Lawson Valley, where I live) have 35 years or more of chaparral fuel build-up. While a fire can start almost anywhere, areas with large amounts of fuel upwind of them have the highest risks during a Santa Ana – any fire upwind of such areas will move quickly toward them.

The general direction of the Santa Ana winds is from the northeast (blowing toward the southwest). However, local geological features (hills, canyons, etc.) can modify this, so the direction could be different in your immediate neighborhood – and those same features can also affect the intensity of the winds. The Pine Valley canyon is a good example of a geological feature that intensifies the wind; the I-8 bridge there is notorious for its fierce crosswinds during a Santa Ana.

It can be very instructive to see how much fuel is left near your home, and especially to the northeast of your home. The map at right, above (click to expand it) shows the fire history in our area for the past 18 years, since 1990. The blue hatched areas are where the Harris Fire burned last week. The pink hatched areas are where fires burned since 2000. The green hatched areas show fires that occurred in the 1990s. The areas that have no hatching (plain gray) have had no fires since 1990.

You’ll note that some areas have burned multiple times – it only takes a few years after a fire for enough fuel to regrow to be able to sustain a fire. However, fires in those more recently-burned areas are much less intense, for the simple reason there is less fuel there. In general, the longer it has been since an area has burned, the more difficult it is to fight a fire there. From the perspective of future risk, it’s definitely better to have recently burned areas upwind of you.

If you examine the map carefully, you’ll note that there’s a large area unburned since 1990 stretching from roughly the Descanso area southwest to the town of Jamul. Those of us living in that area should recognize the risk we face from fires starting during a Santa Ana, especially severe Santa Anas such as the one we had last week. There is a mild Santa Ana forecast for tomorrow and Sunday; even this elevates our risk considerably. If you live in this area that hasn’t been burned for a long time, be especially watchful this weekend and during any other Santa Anas we have.

An excellent resource that allows anyone in our area to watch for fires are the cameras on Lyons Peak. These are operated by HPWREN, and they update every two minutes. You can get the raw feeds directly from this page, or get them processed (with location annotations and automatic updating) from this page. Either way, keeping an eye on these cameras will give you the earliest possible warning of any fires breaking out, and exactly where they are located.

Cross-posted from Jamul Fire Help


  1. The colored pics of the area are very informative.
    Can you tell me or send me to a site that states exactly when the Harris fire moved thru Deerhorn Valley. Was it Monday or Tues or both?

  2. Hello! The answer to that is a complicated sort of "both" -- because it depends on exactly what part of Deerhorn Valley you mean. If you look at my posts during the fire (use the index on the right sidebar), you can see what the MODIS data and camera images looked like over that period, and you might be able to figure it out for the exact location you're concerned with. Also you might want to see the movies from the HPWREN site (referenced in one of my older post); they're very informative about the fire's movements.