🔥 Interactive Fuel Moisture Calculator

Get instant fuel moisture predictions - follow the same process as the manual tables below

--
FUEL MOISTURE CONTENT
Note: Danger level classifications (Extreme/High/Moderate/Low) are based on empirically-derived thresholds for Mediterranean European ecosystems (Resco de Dios et al., 2022). These thresholds are most applicable to Mediterranean-climate regions with shrublands, pine forests, and oak woodlands. Users in other fire regimes should validate against local fire behavior observations.

Calculation Steps:

⚠️ Firefighting Implications:

Fuel moisture values typically range from 1-2% in extreme drought (very dangerous fire conditions) to over 200% for living vegetation. For Mediterranean firefighting operations, the critical threshold is 10-12% - below this convergent threshold identified by Resco de Dios et al. (2022), fires spread rapidly and account for 88% of burned area across Mediterranean European pyroregions.

LIVE FUEL MOISTURE ESTIMATION

Living vegetation moisture is critical for fires in shrublands, grasslands, and forest understory. Live fuel moisture varies seasonally based on plant physiology, recent rainfall, and temperature trends.

Live Fuel Moisture Quick Reference Table

Visual Indicators of Vegetation Stage Moisture Content
Fresh new growth, early spring green-up, high turgor pressure 300%
Maturing foliage, mid-season, full leaf development, still growing 200%
Mature summer foliage, growth complete 100%
Early dormancy, leaves beginning color change, some leaf drop starting 50%
Completely dormant or dead, brown/yellow color, brittle <30% (treat as dead fuel)
Field Example: You're assessing fire danger in Mediterranean scrubland in early October. Shrub leaves show early autumn color change with 10-20% leaves dropped. Some foliage still appears summer-green. Based on the table, estimate live fuel moisture between 50-100%. Use 75% as working value for fire behavior prediction.

HOW TO USE THE FUEL MOISTURE TABLES - FIELD PROCEDURES

STEP-BY-STEP DAYTIME PROCEDURE (08:00h-19:59h)

  1. Gather weather data: Current temperature (°C) and relative humidity (%) from weather station or forecast
  2. Get reference moisture: Use Table A - find intersection of temperature and humidity
  3. Select correction table: Choose based on season (Summer, Spring/Autumn, or Winter)
  4. Determine site characteristics:
    • Current time (hour)
    • Fuel shading: Exposed (<50% canopy) or Shaded (≥50% canopy)
    • Aspect: N, E, S, or W quadrant
    • Slope: 0-30% or 31%+ steepness
  5. Find correction value: Use characteristics to look up correction in appropriate table
  6. Calculate final moisture: Reference moisture + Correction = Field fuel moisture (%)

STEP-BY-STEP NIGHTTIME PROCEDURE (20:00h-07:59h)

  1. Gather weather data: Temperature (°C) and humidity (%)
  2. Get reference moisture: Use Table E
  3. Check for inversion: Is cold air trapped in valleys? (calm, clear night, valley location)
  4. If NO inversion: Use Table E value directly - you're done!
  5. If STRONG inversion exists: Use Table F to adjust for aspect differences

TABLE A - REFERENCE FUEL MOISTURE (DAYTIME)

For use during 08:00h-19:59h

Use this table to get your base fuel moisture from temperature and relative humidity

Temperature
(°C)		 RELATIVE HUMIDITY (PERCENT)
0-5101520253035404550 556065707580859095100
-12 to -1 1223455678 8899101112121314
-1 to 9 1223455677 7899101011121313
10 to 20 1223455667 788991011121213
21 to 31 1122345567 788891010111213
32 to 43 1122344567 788891010111213
43+ 1122344567 788891010111212
NEXT STEP: Go to seasonal correction table based on month

SEASONAL CORRECTION TABLES - SUMMER (May, June, July)

Add these corrections to your reference moisture from Table A

EXPOSED SITES - Less than 50% canopy shading

Aspect
Slope		 08:00h10:00h12:00h14:00h16:00h18:00h
N 0-30%+3+100+1+3
N 31%++4+2+1+1+2+4
E 0-30%+2+100+1+3
E 31%++200+1+3+5
S 0-30%+3+100+1+2
S 31%++3+1+1+1+1+3
W 0-30%+3+1000+2
W 31%++5+3+100+1

SHADED SITES - Greater than or equal to 50% canopy shading

Aspect 08:00h10:00h12:00h14:00h16:00h18:00h
N+5+4+3+3+4+5
E+4+4+3+4+4+5
S+4+4+3+3+4+5
W+5+4+3+3+4+4

SEASONAL CORRECTION TABLES - SPRING/AUTUMN

(February, March, April, August, September, October)

Add these corrections to your reference moisture from Table A

EXPOSED SITES - Less than 50% canopy shading

Aspect
Slope		 08:00h10:00h12:00h14:00h16:00h18:00h
N 0-30%+4+2+1+1+2+4
N 31%++4+4+3+3+3+4
E 0-30%+4+2+1+1+2+4
E 31%++3+1+1+2+4+5
S 0-30%+4+2+1+1+2+4
S 31%++4+2+1+1+2+4
W 0-30%+4+2+1+1+2+4
W 31%++5+4+2+1+1+3

SHADED SITES - Greater than or equal to 50% canopy shading

Aspect 08:00h10:00h12:00h14:00h16:00h18:00h
N+5+5+4+4+5+5
E+5+4+4+4+5+5
S+5+4+4+4+4+5
W+5+5+4+4+4+5

SEASONAL CORRECTION TABLES - WINTER

(November, December, January)

Add these corrections to your reference moisture from Table A

EXPOSED SITES - Less than 50% canopy shading

Aspect
Slope		 08:00h10:00h12:00h14:00h16:00h18:00h
N 0-30%+5+4+3+3+4+5
N 31%++5+5+5+5+5+5
E 0-30%+5+4+3+3+4+5
E 31%++5+3+2+4+5+5
S 0-30%+5+4+3+2+4+5
S 31%++5+3+1+1+3+5
W 0-30%+5+4+3+3+4+5
W 31%++5+5+4+2+3+5

SHADED SITES - Greater than or equal to 50% canopy shading

Aspect 08:00h10:00h12:00h14:00h16:00h18:00h
N+5+5+5+5+5+5
E+5+5+5+5+5+5
S+5+5+5+5+5+5
W+5+5+5+5+5+5

TABLE E - REFERENCE FUEL MOISTURE (NIGHTTIME)

For use during 20:00h-07:59h

Use this table to get nighttime base fuel moisture from temperature and relative humidity

Temperature
(°C)		 RELATIVE HUMIDITY (PERCENT)
0-5101520253035404550 556065707580859095100
-12 to -1 12455678910 11121214151719222525+
-1 to 9 1234567899 11111213141618212425+
10 to 20 1234566889 10111112141617202325+
21 to 31 1234456789 10101112131517202325+
32 to 43 1233456789 9101011131416192225+
43+ 1223456688 991011121416192124+
NEXT STEP: If no temperature inversion, use this value. If strong inversion exists, continue to Table F

TABLE F - NIGHTTIME INVERSION CORRECTIONS

Use only when cold air is trapped in valleys (20:00h-07:59h)

Aspect 20:00h22:00h00:00h02:00h04:00h06:00h
N or E +1+1+2+1+1+2
S or W 000000

WORKED EXAMPLES FROM THE FIRELINE

Example 1: Mediterranean Hillside Fire - Summer Afternoon

Situation: Active wildfire on south-facing slope, 14:00h in August

  • Current conditions: 27°C, 20% RH
  • Terrain: 35% slope, south aspect, open grassland
  • Sky: Clear

Calculation:

  1. Table A: 27°C + 20% RH = 2% reference moisture
  2. Spring/Autumn Table: South aspect, 31%+ slope, 14:00h, Exposed = +1% correction
  3. Final: 2% + 1% = 3% fuel moisture

Tactical Implications: 3% fuel moisture = EXTREME fire behavior expected. Direct attack likely impossible. Consider indirect tactics, safety zones, and evacuation triggers. Request aerial resources immediately.

Example 2: Night Operations Assessment

Situation: Planning night shift operations, 23:00h

  • Conditions: 16°C, 50% RH
  • Terrain: North aspect, moderate slope
  • Weather: Clear calm night, no temperature inversion evident

Calculation:

  1. Table E: 16°C + 50% RH = 9% fuel moisture
  2. No inversion = Use Table E value directly
  3. Final: 9% fuel moisture

Tactical Implications: Overnight moisture recovery to 9% = Good conditions for direct attack and mop-up operations. Fire spread rate significantly reduced from afternoon conditions.

🔥 QUICK FIELD REFERENCE

Step 1: Choose DAY or NIGHT

  • DAY = 08:00h - 19:59h
  • NIGHT = 20:00h - 07:59h

DAYTIME PROCEDURE:

A. Get BASE moisture (Table A)

  1. Temperature (°C) + Humidity (%) → Table A
  2. Write down reference moisture %

B. Apply CORRECTIONS (Seasonal Tables)

Select based on:

  • Season: Summer / Spring-Autumn / Winter
  • Time: 08:00h, 10:00h, 12:00h, 14:00h, 16:00h, 18:00h
  • Shading: Exposed (<50%) or Shaded (≥50%)
  • Aspect: N, E, S, W
  • Slope: 0-30% or 31%+

C. Calculate Final Value

Reference + Correction = FUEL MOISTURE

NIGHTTIME PROCEDURE:

  1. Temperature + Humidity → Table E
  2. No inversion? Done!
  3. Inversion? Add Table F correction

Decision Flow:

DAY (08:00-19:59h)? 
  ↓
Table A + Seasonal Correction
  ↓
FINAL FUEL MOISTURE (%)

Scientific References

Rothermel, R.C. 1983. How to predict the spread and intensity of forest and range fires. General Technical Report INT-143. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 161 p.

Fosberg, M.A. 1971. Moisture content calculations for the 100-hour timelag fuel in fire danger rating. Research Note RM-199. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 7 p.

Resco de Dios, V., Fernández-García, V., Balaguer-Romano, R., Vacchiano, G., Feudis, A., Lacroix, K., Gianelle, D., Karavani, A., Vega-García, C., Ferrauto, F., Dios-Viéitez, M., Alonso-González, E., & Rodrigues, M. 2022. Convergence in critical fuel moisture and fire weather thresholds associated with fire activity in the pyroregions of Mediterranean Europe. Science of the Total Environment, 806 (Part 4), 151462. https://doi.org/10.1016/j.scitotenv.2021.151462

Espinosa de los Monteros, B. (In preparation). Automated Tool for Fine Dead Fuel Moisture Content Estimation for Mediterranean Wildfire Management Applications. Technical Paper. ForestFire.app Wildfire Forecasting Systems.

About This Tool

This fuel moisture calculator is a metric adaptation of the Fosberg-Rothermel system, developed for Mediterranean wildfire management applications. The underlying fuel moisture estimation methodology (Rothermel, 1983) has been validated globally across diverse ecosystems. This specific implementation—with seasonal consolidation and metric units—is optimized for Mediterranean European contexts.

Seasonal Tables: The seasonal corrections (Summer: May-Jul; Spring/Autumn: Feb-Apr, Aug-Oct; Winter: Nov-Jan) are calibrated for Northern Hemisphere conditions. Southern Hemisphere users should adjust months accordingly (e.g., Summer = Nov-Jan, Winter = May-Jul).

Danger Level Classifications: The fire danger thresholds (Extreme/High/Moderate/Low) are based on empirical research from Mediterranean European pyroregions (Resco de Dios et al., 2022) and are most applicable to Mediterranean-climate ecosystems including shrublands, pine forests, and oak woodlands. The convergent critical threshold of 10-12% fuel moisture is specific to Mediterranean fire regimes. Users in other fire regimes (boreal, tropical, temperate, arid) should validate these classifications against local fire behavior observations and consult regional fire management protocols.

Fuel Moisture Estimation: The fundamental fuel moisture calculation methodology applies universally based on physical sorption principles, though the danger categorizations are ecosystem-dependent.

Metric conversion prepared 2025 for global firefighting community. Maintained and distributed for operational wildfire management and firefighter safety applications by ForestFire.app Wildfire Forecasting Systems. All rights reserved.

Disclaimer: This tool provides field estimates for operational firefighting. For critical decisions involving significant values at risk or firefighter safety, consult with qualified fire behavior analysts and local fire management authorities. Always prioritize firefighter safety over property protection.