1. Forecasting Fire Danger

2. Module Goals At the end of this module, you’ll be able to:
Name the fire danger indices used in our region and their inputs.
Describe the sensitivities of the fire danger indices used.
Describe the inadequacies of the fire danger indices
Find and use calculation and monitoring tools for current observations and forecasts.

3. Fire Danger
A measure of the difficulty in controlling or suppressing fires.
A function of fuel state and weather.

4. Fire Danger Indices Usual inputs… Fuel State Wind speed Temperature
Humidity
Other relevant meteorological factors…
Lightning
Stability

5. Fire Danger Indices Used
Tasmania
Forest FDI (McArthur MkV)
Moorland FDI (Marsden-Smedley)
Heathland FDI (Marsden-Smedley)
Victoria, NSW, Queensland, SA
Grassland FDI (McArthur MkIV)
Northern Territory
Western Australia
CALM calculates Forest Fire Danger…???

6. Jump Slide Continue Fire Danger Indices Forest Fire Danger Index
Grassland Fire Danger Index
Moorland and Heathland Fire Danger Indices
Other Relevant Indices
Haines Index
Continue

7. Jump Slide
Local links and information
Victoria
Continue

8. So now, can you… End Slide Show
Name the fire danger indices used in our region
Describe the sensitivities of the fire danger indices used.
Describe the inadequacies of the fire danger indices
Find and use calculation and monitoring tools for current observations and forecasts.
End Slide Show

9. Forest Fire Danger Index - FFDI
McArthur Forest FDI integrates effect on difficulty of
suppression of fire due to:
Temperature
Relative Humidity
Wind Speed
Drought Factor (measure of Forest Fuel State)
The Descriptive Fire Danger Rating system for Public Information is:
Low to Moderate FFDI of 0-11
High FFDI of 12-24
Very High FFDI of 25-49
Severe FFDI of 50-74
Extreme FFDI of 75-99
Catastrophic FFDI of 100+
(aka Code Red)

10. Calculating FFDI
Calculated automatically on Fire Weather Forecast Forms
Exercise: Where can you find FFDI calculated on current observations?
Several calculators exist for manual calculation. Ensure that you can use at least one.

11. FFDI formula Based on Drought Factor (DF) Air temperature (TºC)
Relative Humidity (RH%)
Wind speed (V km/h) (generally 10 metre, 10 minute average)

12. Sensitivity of FFDI Explore the sensitivity of the FFDI.
Choose likely extreme weather conditions. What DF is required for Extreme Fire Danger?
For DF=10, T=30°C, Td=10 °C, Wind spd=20kt, the Fire Danger is Very High (FFDI=30). What change in T, Td and wind spd respectively are required for Fire Danger to reduce to High?
For DF=9, T=30°C, Td=10 °C, Wind spd=15kt, the Fire Danger is High (FFDI=23). What change in T, Td and wind spd respectively are required for Fire Danger of Extreme?

13. Example of FFDI Calculations
FFDI and corresponding weather parameters for three days at Latrobe Valley (13-15 April 2004).

14. FFDI Limitations
As calculated the FFDI assumes 12.5 tonnes/Ha of available fuel. In many cases in Tasmania, fuel load is higher, in some cases lower.
No account of aspect or slope is taken– fire managers must make an adjustment as they require.
No account is taken within the model for cloudiness, insolation or gustiness.
Moderate instability is assumed in the McArthur FFDI model. Often, mornings will be more stable (lower “real” fire danger). Dangerous days will usually be more unstable than the model assumes.
Appropriate for broad-scale warning process.

15. FFDI Guidance
During the fire season, BMRC trialled fire weather guidance from 5 km MesoLAPS for Victoria.
FFDI was calculated from the following to minimise model biases:
Wind speed - mean of the sigma value and that of calculated maximum gust
Relative Humidity based on the mean mixing ratio of the lowest half of the mixed layer
Screen-level temperature
Drought Factor calculated from the Finkele scheme, based on a 25-km grid
Max gust is the max mean wind in the mixed layer
The mixed layer is determined as that with virtual potential temperature within 1°C of that of the lowest sigma level

16. FFDI Guidance The following example shows Top Left: FFDI as calculated
Top Right: Wind speed in knots as used in calculation
Lower left: Screen-level temperature (in red) and DF calculated from the Finkele scheme (in black)
Lower Right: Screen level Dewpoint corresponding to Relative Humidity used in calculation

17. FFDI Guidance from MesoLaps
Wind speed (kt)
FFDI Td
T & DF
Valid 00UTC 1 February 2005

18. FFDI Guidance – Tasmanian Response
Experience over the fire season suggested that the guidance was extremely useful.
Potentially dangerous FFDI conditions were highlighted that might otherwise have been overlooked given the volume of data being considered by forecasters
FFDI conditions develop and change rapidly during the course of an event. This was illustrated well by the guidance.
It is noted that the scheme is based on a 25-km grid, and can mask local variations (eg Derwent Valley/Midland areas in Tasmania)

19. FFDI Summary Return to Index Slide
Sensitive to rain (through Drought Factor)
Return to Index Slide

20. Grassland Fire Danger Index - FDI
FDI integrates effect on difficulty of
suppression of fire due to:
Temperature
Relative Humidity
Wind Speed
Curing (measure of Grassland Fuel State)
The Descriptive Fire Danger Rating system for Public Information is:
Low to Moderate FDI of
High FDI of
Very High FDI of
Severe FDI of
Extreme FDI of
Catastrophic FDI of
aka Code Red
NOTE: Victoria and Western Australia use different thresholds

21. Grassland Fire Danger Index - Formula
where
Curing (C%)
Air temperature (TºC)
Relative Humidity (RH%)
Wind speed (V km/h) (generally 10 metre, 10 minute average)
Note: 100kt=185km/h; 100km/h=54kt

22. GFDI and rainfall
At various times/places adjustments have been made for rainfall. However the moisture levels of grass recover very quickly following rain (order of 2 hours) and current practice is to allow no dependence on rainfall.

23. GFDI and fuel load
No fuel must mean no Fire Danger. However for continuous grasslands the load in tonnes/ha appears to have little effect on the fire rate of spread.
The local fire authorities in many regions assess fire danger as varying on fuel quantity, or other factors. This is often incorporated through a setting a fuel load.

24. GFDI and fuel load The standard fuel load is Q=4.5t/ha.
An FDI calculator with a fuel load option multiplies the standard FDI by Q1.027/4.5.
A McArthur Mark V meter allowed for fuel load in this (almost linear) manner. Purton combined this with the Mark IV Fire Danger.
Exercise: what reference, if any, is there to fuel load in the regional procedures?

25. Calculating FDI
Calculated automatically on Fire Weather Forecast Forms
Exercise: Where can you find FDI calculated on current observations?
Several calculators exist for manual calculation. Ensure that you can use at least one.

26. Sensitivity of FDI Explore the sensitivity of the FDI.
Choose likely extreme weather conditions. What Curing is required for Extreme Fire Danger?
For Curing=90%, T=35°C, Td=5 °C, Wind spd=15kt, the Fire Danger is Very High (GFDI=24). What change in T, Td and wind spd respectively are required for Fire Danger to reduce to High?
For Curing=100%, T=28°C, Td=10 °C, Wind spd=15kt, the Fire Danger is High (GFDI=19). What change in T, Td and wind spd respectively are required for Fire Danger of Extreme?

27. GFDI Limitations No account of aspect or slope No account of lightning
No account of gustiness
No account of difficulty of accessing terrain
No account of varying resources

28. FDI Guidance
Guidance from operational runs of MesoLaps may be found at
The following inputs are used:
Wind speed - mean of the sigma value and that of calculated maximum gust
Relative Humidity based on the mean mixing ratio of the lowest half of the mixed layer
Screen-level temperature
100% curing everywhere.
Max gust is the max mean wind in the mixed layer
The mixed layer is determined as that with virtual potential temperature within 1°C of that of the lowest sigma level

29. FDI Summary Return to Index Slide Very sensitive to curing
Very sensitive to wind speed
Return to Index Slide

30. Buttongrass Moorland Extensive areas of Western and
Southern Tasmania, particularly
national parks and reserves.

31. Characteristics of BGM Meter
Strong dependence on wind, but little dependence on RH, temp
Strong sensitivity to rain <=3mm in last 24 hours but no dependence on previous rain
Heathland FD meter similar but more strongly wind dependent (and still experimental!)
Note: increasing temperature from 10 to 20 Celsius makes very little difference, all else being constant
Return to Index Slide

32. Stability Indices An unstable profile can enhance fire activity via…
Convection enabling gusty surface winds
Large smoke columns creating strong inflow
Increased spotting with embers lofted by smoke columns
Dust devils or fire whirls
The most common index used to capture the stability in a fire weather context is the Haines Index.

33. Haines Index
Haines Index combines information on upper level dryness and instability using two levels.
Three versions of the Index exist:
Low (uses 950 and 850 hPa data)
Mid (uses 850 and 700 hPa data)
High (uses 700 and 500 hPa data)

34. Haines Index
Relevant index has data from just above highest orography (eg Tasmania use mid-level index)
Values range from 2 to 6:
“low” when H < 4
“moderate” when 4<=H<5
“high” when H>=5
I.E. “low” to “high” fire activity anticipated, should a fire be burning…

35. Haines Index Calculation

36. Haines Index Tools
Haines Index guidance is available from the NMOC MLAPS web pages.
Note that the vertical structure of inversions is sometimes not well represented in MLAPS, affecting Haines Index values
A Haines Index calculator is available, for evaluating the Index from F160s, or other model data.
Background on the application of the Haines Index in Tasmania is available in John Bally’s paper.

37. Haines Index Cautions…
Haines Index is a 2-level index, and discards a lot of information. It may not be representative of the broader atmosphere, depending on the level of any inversion present.
The Haines Index calculated for the left trace is representative of the atmosphere, but an inversion just above 850 hPa renders the Haines Index from the righthand trace unrepresentative.
Return to Index Slide