From the August 2010 Battle Mountain News
Post date: Jul 1, 2014 8:15:00 PM
Fall Fires in Wet Years
Historically, damp years like the current one, following 3 years of drought, have seen major wildfires in October and November. Think of the October 20, 1991 Oakland Hill Firestorm.
How does a wet year after a drought produce such a fire threat? The key to understanding lies in the concept of fuel timelag. Fire fighters speak of 1-, 10-, 100-, and 1000-hour fuels. This is roughly the time it takes dead vegetation to reach the moisture level of the air. Grass and needles are 1-hour fuels, dead shrubs - 10-hour fuels, fallen branches – 100-hour fuels, and fallen tree trunks are 1000-hour fuels which take around a month and a half to respond. Fires in short timelag fuels generally start in a flash, while long timelag fuels start in a smolder.
After a prolonged drought, a wet winter brings forth an abundance of new growth. The vegetation that responds most dramatically to the return of winter rain becomes the shorter timelag fuels over the summer. Right now we are seeing grass fires race across fields and stop at the brush line.
October, though, is often our driest month. The inland heat engine that draws the ocean moisture in over the coast has slowed and the hot valley air starts to spill out over the mountains to our east. The relative humidity drops to the 20-30% range. Even when the rains return in late October and early November, it will be weeks or months until tree debris is no longer dry enough to burn. Apparently extinguished fires in the chaparral/forest interface can smolder unobserved as they did overnight in Oakland until the hot, dry Diablo winds picked up in the morning with historic consequences.
Our Bonny Doon Fire Safe is now legally incorporated in California and we are in the process of becoming a 501(c)(3) non-profit with the Federal Government. We are collaborating with the Soquel and South Skyline Fire Safe Councils to apply for a grant from the National Forest Service. We are beginning to consider and prepare projects for the primary annual grant cycle and update of our County Community Wildfire Protection Plan this winter. In November, we will elect a new FSC Board. We will have a formal call for nominations next month.