Rothermel Surface Rate of Spread Calculator
Explicit Rothermel propagation balance IR ξ(1+φw+φs)/(ρb ε Qig) with independently established fuel/wind/slope factors in consistent kJ/kW/metre units, not Byram intensity or full fuel-model derivation. Caller independently verifies units, applicability and matching conditions; no operational recipe, safety certification, causal efficacy or legal/resource classification is inferred.
Description
A Rothermel-style spread relation balances reaction intensity and propagation factors against the energy needed to heat fuel.
A Rothermel-style spread relation balances reaction intensity and propagation factors against the energy needed to heat fuel.1
This calculation uses independently supplied intermediate parameters rather than deriving them from a complete fuel model. Use this tool to calculate rothermel surface rate of spread from the supplied measurements and assumptions.
When to use Rothermel Surface Rate of Spread Calculator
Use this tool to calculate rothermel surface rate of spread from the supplied measurements and assumptions. Establish the species/site, survey protocol, units, sampled area or exposure, and the independently chosen reference or model.
How to use Rothermel Surface Rate of Spread Calculator and understand its results
- Establish the species/site, survey protocol, units, sampled area or exposure, and the independently chosen reference or model.
- Enter callerReactionIntensityKwM2, callerPropagatingFluxFraction, callerWindFactor, callerSlopeFactor, observedFuelBedBulkKgM3, callerEffectiveHeatingFraction, callerHeatOfPreignitionKjKg, using the field meanings and rules below, then run the tool.
- Read rothermelModeledSurfaceSpreadMSecond. Interpret the fields using their units, signs and evidence conventions below.
- If input validation fails, correct the reported field and run again. Before applying the result, check reference scope, model assumptions and any missing evidence or placeholder values.
| Input field | Meaning | Value type | Requirement |
|---|---|---|---|
| callerReactionIntensityKwM2 | Caller reaction intensity kw m2 | number | Required |
| callerPropagatingFluxFraction | Caller propagating flux fraction | number | Required |
| callerWindFactor | Caller wind factor | number | Required |
| callerSlopeFactor | Caller slope factor | number | Required |
| observedFuelBedBulkKgM3 | Observed fuel bed bulk kg m3 | number | Required |
| callerEffectiveHeatingFraction | Caller effective heating fraction | number | Required |
| callerHeatOfPreignitionKjKg | Caller heat of preignition kj kg | number | Required |
Require positive reaction intensity in kW/m², fuel bulk density in kg/m³ and preignition heat in kJ/kg. Propagating flux fraction is in [0,1], effective heating fraction in (0,1], and wind/slope factors are nonnegative. Divide reaction×flux×(1+wind+slope) by density×effectiveFraction×heat and return m/s. No intermediate parameters are derived, fuel calibration selected or operational forecast validated.
spreadMPerSecond=IR×flux×(1+windFactor+slopeFactor)/(fuelDensity×effectiveHeatingFraction×preignitionHeat) Use the exact units, boundary rules, ordering and missing-evidence conventions above.
| Output field | Meaning | Value type |
|---|---|---|
| rothermelModeledSurfaceSpreadMSecond | Rothermel Modeled Surface Spread M Second; follow the units, sign, ordering and evidence convention stated above | number |
{
"input": {
"callerReactionIntensityKwM2": 100,
"callerPropagatingFluxFraction": 0.1,
"callerWindFactor": 1,
"callerSlopeFactor": 0.5,
"observedFuelBedBulkKgM3": 10,
"callerEffectiveHeatingFraction": 0.5,
"callerHeatOfPreignitionKjKg": 100
},
"output": {
"rothermelModeledSurfaceSpreadMSecond": 0.05
}
}Limitations and assumptions
This calculation uses independently supplied intermediate parameters rather than deriving them from a complete fuel model. Interpretation depends on the units, sampling scope and exact model described above.
All listed fields require explicit values. Unexpected fields, incorrect types, nonfinite numbers and sparse evidence arrays fail validation; the specific bounds and alignment requirements are stated above. Extremely large inputs or outputs can also be rejected. An input error is distinct from a successful result reporting false, no matches or missing evidence.
Alternative or Complementary methods
Use Heat Per Unit Area Frontal Calculator for this related task: Released heat per unit area combines consumed fuel mass, heat content and a supplied release fraction.
Use Active Crown Fire Spotting Distance Calculator when its separate inputs and assumptions fit the question: Integrating horizontal wind over an independently sampled ember flight time gives a conditional advection displacement.
References
Similar or alternative tools
- Heat Per Unit Area Frontal Calculator
Released heat per unit area combines consumed fuel mass, heat content and a supplied release fraction.
- Active Crown Fire Spotting Distance Calculator
Integrating horizontal wind over an independently sampled ember flight time gives a conditional advection displacement.