Estimating Scorch Height from Fireline Intensity

Relationship between fireline intensity,
ambient temperature, and scorch height

Van Wagner (1973) developed the following graph depicting the relationship between fireline intensity, ambient temperature, and crown scorch height base on the below equation using Canadian conifer species. This graph is commonly used prior to ignition to calculate the scorch line from the expected weather conditions and fire behavior. It likely overpredicts scorch height in southern pines (Wade 1986), so it will err on the safe side if used to solve for scorch height.

Comparing this predicted height with the height of the stand to be burned can help project expected crown scorch. Although solving the equation below for I provides a way to reconstruct fireline intensity after burns using crown scorch, Cain (1984) reported that this technique seriously underestimates fireline intensity in southern pines.

Equation for estimating crown scorch height from fireline intensity

S = (35/ (60 - T)) * ( I^7/6/(0.79(I +47W³)^1/2))

where:

• S = scorch height (m)
• T = air temperature (C)
• I = fireline intensity (kW/m)
• W = windspeed (m/sec) (Van Wagner 1973)