The simultaneous flammability of wildland fuels in the United States
An estimate is made of the fire hazard in the continental U.S. wildlands at a given time of year, to provide a basis for predicting wartime fire hazard and resource survival. Flammability, or dryness, is quantitively expressed by "burning indexes" for different plant types; "critical" levels were selected arbitrarily. The burning indexes are mathematical models derived from a 10-year set of daily weather observations made at 89 locations throughout the United States. It was necessary to devise a national wildland-fuel distribution inventory, a growth cycle (phenological) calendar for each principal species as a function of geographical location, and a method for simulating the fire-depressing effects of snow cover. Annual cycles of simultaneously flammable area for eight different fuel-type combinations at several frequency levels are shown graphically. Additional graphs present the principal results as recalculated by varying over a wide range the burning index level taken as critical.