A method for predicting the time-dependent nature of fine fuel moisture is badly needed to support fire behavior prediction systems used in fire management. Of the models available, none met all the requirements of the BEHAVE fire behavior prediction system. The Canadian Fire Fuel Moisture Code (FFMC) came closest to meeting our needs and was selected as a base model. Improvements to the FFMC were concentrated on providing a means of accounting for annual and diurnal variation due to solar heating of woody fuels. This was necessary because the FFMC was developed for fuels located within forest stands, a generally shaded condition. Solar heating raises the temperature of the fuel surface and lowers the relative humidity of the film of air surrounding the fuel particle. Formulas describing this near-fuel environment produce the temperature and relative humidity that are then used by FFMC to derive the moisture content. The solar intensity that drives the fuel temperature and relative humidity accounts for latitude, time of year, time of day, aspect, slope, elevation, atmospheric haze, and shade. Shade can be from clouds or overstory trees. Provisions are made to guide the user through tree descriptors necessary to determine expected amount of shade.
United States Department of Agriculture, Forest Service, "Modeling Moisture Content of Fine Dead Wildland Fuels: Input to the BEHAVE Fire Prediction System" (1986). Wildfires. Paper 3.