Spinifex

Vegetation

Fuel inputs

• Compound fuel moisture content (%)
• Spinifex ground coverage (%)

Code

// Hummock spinifex grasslands
// Burrows (2018)

// -------------------------------------------
// Model parameters
// 1. Spinifex clump profile (mean) moisture content (% oven dry weight), 'm' (input)
// 2. Fuel cover (live and dead spinifex and other vegetation <1.5m high) (%), 'cover' (input)
// -------------------------------------------

// Backing and flanking coefficients compared to head fire ROS
REAL wind_speed = length(wind_vector);
REAL wdot = dot(normalize(wind_vector),advect_normal_vector);

// Calculate length-to-breadth ratio (LBR) for grassland
REAL LBR = 1.0;
if (wind_speed < 5){
    LBR = 1.0; 
} else {
    LBR = 1.1*pow(wind_speed, 0.464); 
} 

// Determine coefficient for flank rank of spread
REAL cc = sqrt(1.0-pow(LBR, -2.0)); 
REAL cb = (1.0-cc)/(1.0+cc); 
REAL a_LBR = 0.5*(cb+1.0); 
REAL cf = a_LBR/LBR; 

// Determine shape parameters 
REAL f = 0.5*(1.0+cb); 
REAL g = 0.5*(1.0-cb); 
REAL h = cf; 

// Now calculate a speed coefficient using normal flow formula 
REAL speed_fraction = (g*wdot+sqrt(h*h+(f*f-h*h)*wdot*wdot)); 

// Calculate spread criteria 
REAL SI = 0.305*wind_speed + 0.311*cover - 0.676*m - 4.073; 
REAL head_speed; 
REAL wind_speed_e = wind_speed / 1.35; // Eye level wind speed
if (SI > 0) {

   // Calculate speed
   head_speed = 40.982 * pow(wind_speed_e,1.399) * pow(cover,1.201) / pow(m,1.699);

   // Convert from m/h to m/s
   head_speed *= 0.000277778;

} else {
   head_speed = 0;
}

// Adjust for calculated speed coefficient for fire flanks
speed = head_speed * speed_fraction;