Rothermel

Dynamic fuel load transfer from live herbaceous to dead herbaceous fuel based on live-herbaceous fuel moisture, per Andrews (2018) Table 6c. Migrated from WildlandFire.jl@126976f2 src/rothermel.jl:320 (`DynamicFuelLoadTransfer` @component). Observed-only: w0_live_herb and Mf_live_herb are inputs (parameters); T_fraction, w0_dead_herb, and w0_live_herb_remaining are algebraic outputs.

Effective midflame wind speed UE — combines the actual wind factor and slope factor into an equivalent wind speed for fire-behavior calculations. Migrated from WildlandFire.jl@126976f2 src/rothermel.jl:410 (`EffectiveMidflameWindSpeed` @component). Observed-only: C_coeff, B_coeff, E_coeff, beta_ratio, phi_w, phi_s are inputs (parameters); phi_E (combined wind+slope factor) and UE (effective midflame wind speed in m/s) are algebraic outputs. Implements Eq. UE, Table 7, Andrews (2018) RMRS-GTR-371.

Anderson (1982) 13 fuel-model parameter lookup: maps integer fuel model code (1–13) to the six Rothermel fire spread fuel properties (σ, w₀, δ, Mₓ, h, Tᶠ). Aggregates the six registered fuel_* functions (fuel_savr, fuel_load, fuel_depth, fuel_mce, fuel_heat, fuel_weight) into a single observed-variable component. Out-of-range codes (including LANDFIRE non-burnable codes 91–99) return fuel-model-1 defaults for σ, w₀, δ, Mₓ, and Tᶠ, and 0 J/kg for h. Migrated from WildlandFire.jl@126976f2 src/coupling.jl:155 (`FuelModelLookup` @mtkmodel). Resolves the gt-p3ep blocking gap via ifelse + interp.linear for the five variable-valued properties and a simple ifelse for the constant heat content.

Live fuel moisture of extinction (M_x,live) from dead-fuel moisture, dead-to-live effective load ratio, and dead fuel moisture of extinction. Migrated from WildlandFire.jl@126976f2 src/rothermel.jl:367 (`LiveFuelMoistureExtinction` @component). Observed-only: Mx_dead, W_ratio, Mf_dead are inputs (parameters); Mx_live is an algebraic output. Implements Eq. M_x,live, Table 6b in Andrews (2018) RMRS-GTR-371.

Rothermel (1972) surface fire spread model — predicts rate of spread (R), fireline intensity (IB), flame length (F_L), and related outputs from fuel-bed properties, fuel moisture, wind speed, and terrain slope. Migrated from WildlandFire.jl@126976f2 src/rothermel.jl:70 (`RothermelFireSpread` @component). Observed-only (algebraic): all 27 unknowns are defined by algebraic equations; no ODE states. Implements Table 3 and Table 7 in Andrews (2018) RMRS-GTR-371 using SI units. All empirical coefficients are converted from US customary. See reference notes for the complete Unicode→ASCII identifier map and the coupling interface (RothermelCoupler couple2 methods).

Rothermel (1972) fuel-bed spread parameters as evaluated by fire_behavior's Set_ros_parameters_wrffire (physics/ros_wrffire_mod.F90) for one cell: from the category's fuel properties and the ground fuel moisture, the packing ratio, optimum packing ratio, reaction velocity, moisture and mineral damping, reaction intensity, propagating flux ratio, heat of preignition and effective heating number, and hence the no-wind no-slope spread rate r_0 (ft/min, and ros_base in m/s), the wind-factor coefficients bbb (exponent B) and phiwc, and I_R t_r (iboros) for Byram's flame length. The fits are evaluated in US customary units exactly as the Fortran does (SI load and depth converted with 0.3048 and 2.205), so the intermediates are dimensionless carriers of lb/ft^2, ft, 1/ft, Btu/lb quantities. DIFFERENCES from the EarthSciModels rothermel/fire_spread.esm (Andrews 2018 SI form), which is therefore NOT reused: (1) the reaction-velocity exponent is Rothermel's original A = 1/(4.774 savr^0.1 - 7.27), not Albini's 133 savr^-0.7913; (2) the net load is w_0/(1 + S_T), not w_0 (1 - S_T); (3) the moisture ratio and the mineral damping are not capped at 1; (4) the load entering the fits is the DRY part (1 - M/(1+M)) of fgi, fire_behavior treating fgi as the moist load; (5) the wind factor is split into the cell constants B and phiwc = C (beta/beta_op)^-E applied per time step in ROSWRFFire. The no-fuel category (has_fuel = 0) returns betafl = bbb = 1, phiwc = r_0 = iboros = 0 as the Fortran does. Tests are the dumped per-cell intermediates of the instrumented fire_behavior test7 run (real32; a real64 re-evaluation of the same formulae agrees to <= 8e-7 relative), rel 1e-5.

Maximum effective wind speed (U_limit) above which the wind factor in the Rothermel surface fire spread model saturates. Migrated from WildlandFire.jl@126976f2 src/rothermel.jl:465 (`WindLimit` @component). Observed-only: IR is the input parameter; U_limit is the algebraic output. Both upstream branches are preserved here as a single `ifelse` on the dimensionless `use_corrected` indicator parameter — corrected (Andrews et al. 2013) when use_corrected > 0.5 (the upstream default), original when use_corrected ≤ 0.5. Implements Eq. Ulimit, Table 7 in Andrews (2018) RMRS-GTR-371.