# Wet Eucalypt

The Dry Eucalypt (VESTA) rate of spread model was developed by CSIRO for predicting fire spread rates in Eucalyptus Forest. VESTA was published in 2012 in the book Project Vesta, which can be found here. As there is no published wet eucalypt model for wildfire conditions, the model below was adapted from the dry eucalypt model as per the Amicus fire knowledge database, with adjustments made for under canopy wind speed and fuel moisture content as described on the Amicus website here.

### Vegetation

Wet Eucalypt Forest

### Fuel inputs

• temp
• rel_hum
• FHSs/FHSns
• Hns
• Temperature (degrees C)
• Relative humidity (%)
• Surface/Near-surface fuel hazard score
• Near-surface fuel height (cm)

### Code

```// Wet Eucalypt model - Adapted from Project VESTA

// -------------------------------------------
// Model parameters
// These must be defined below, or included as a user-defined layer
//
// 1. Temperature, 'temp' (input)
// 2. Relative humidity, 'rel_hum' (input)
// 3. Surface fuel hazard score, 'FHSs'
// 4. Near-surface fuel hazard score, 'FHSns'
// 5. Near surface height, 'Hns'
// 6. Shrub height, 'fuel_height'
// -------------------------------------------

// Calculating the wind speed which is used to calculate head fire ROS
REAL wind_speed = length(wind_vector);

// Calculating the normalised dot product between the wind vector and the normal to the fire perimeter

// Estimating fuel moisture content using Gould et al. (2007) and Matthews et al. (2010)
// Initialising the fuel moisture variable
REAL Mf;

// Calculating fuel moisture between 12:00 and 16:59 (valid for sunny days from October to March)
if (hour > 11 && hour < 17){
Mf = 2.76 + (0.124*rel_hum) - (0.0187*temp);}

// Calculating fuel moisture for other daylight hours (from 9:00 to 11:59 and 17:00 to 19:59 in this example)
else if ((hour < 12 && hour > 8) || (hour > 16 & hour < 20)){
Mf = 3.6 + (0.169*rel_hum) - (0.045*temp);}

// Calculating fuel moisture for night time hours (from 20:00 to 8:59) in this example
else{
Mf =  3.08 + (0.198*rel_hum) - (0.0483*temp);}

// Applying wind reduction factors and fuel moisture modifications for wet forest as per Amicus
// These factors depend on the height of the shrubs within the forest
if (fuel_height < 2){
wind_speed = wind_speed / 2;
Mf = Mf + 0.2052*Mf + 0.8554;}
else if (fuel_height > 5){
wind_speed = wind_speed / 3;
Mf = Mf + 0.5923*Mf + 1.9565;}
else{
wind_speed = wind_speed / 2.3;
Mf = Mf + 0.5248*Mf - 0.0568;}

// Calculate moisture coefficients from Burrows (1999)
REAL moisture_coeff = 18.35 * pow(Mf,-1.495);

// Calculate length-to-breadth ratio (LBR) which varies with wind speed
// Using the reduced under canopy wind speed in this case
// Equations are curve fits adapted from Taylor (1997)
REAL LBR;
if (wind_speed < 5){
LBR = 1.0;
} else if (wind_speed < 25){
LBR = 0.9286 * exp(0.0505 * wind_speed);
} else {
LBR = 0.1143 * wind_speed + 0.4143;
}
// Determine coefficient for backing and flanking rank of spread using elliptical equations
// Where R_backing = cb * R_head, R_flanking = cf * R_head,
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));