Forest Fire Index Bushfire Management Overlay Sorrento Victoria Australia Black Saturday Mornington Peninsula

1. APPENDIX XXXX
Black Saturday 7 Feb 2009:
Sorrento Fire Danger Rating and FFDI Evaluation
1. FDR/FFDI Relevance
The CFA advice that “The Fire Danger Rating (FDR) predicts how a fire would behave if one started, including how difficult it would be to put out. The higher the rating, the more dangerous the conditions. The rating is your trigger to act, so to stay safe you need to stay aware of the Fire Danger Rating in your district.”
The FDR bands to set FDR rating of CODE RED, Extreme etc. are equal to the correlation used for the FFDI or “Forest Fire Danger Index”. The Weather Bureau advices the predicted temperature, humidity, wind speed and drought factor when are then used to calculate the FFDI/FDR and are then published to the community.
The CSIRO have studied the statistical relationship between FFDI and house loss in Australia between 1957 and 2009. (Meteorological conditions and wildfire related house loss in Australia between 1957 and 2009 Blanchi et al International Journal of Wildland Fire 2010, 19,914-926).
Key conclusions were that:-
A. Majority of house losses occurred when FFDI>100,
B. Virtually all of the house loss has occurred above the 99.5th percentile level in the distribution of daily FFDI,
C. Little house loss has occurred on days where the FFDI did not exceed 50 suggesting that historical building practices may be maintained in regions where this level is not likely to be exceeded.
Further a statistical review by Leonard (as per below excerpt from “Australia’s revised arrangements for bushfire advice and alerts, AMEC) showed the following house and life loss when correlated with FFDI which clearly shows the elevated risk of house loss and loss of life at higher FFDI’s.
The fire danger rating (FDR) system used by CFA as a state wide warning system directly correlates to FFDI.

2. 2. Sorrento Black Saturday FFDI
The table below shows the number of hours on 7 Feb 2009 for each Fire Danger Rating.
Black Saturday Fire Danger Rating Frequency
Hourly Number of Occurrences
Rye
Sorrento (estimate)
Rhyll (Phillip Island)
Cerberus
Aireys Inlet
Melb Airport
Wallan Catastrophic >100
0
0
0
0 3 5 4 Severe/Extreme 50-100 0 0 1 5 1 4 4 Very High 24-50 1 4 3 0 1 4 2 High 12-24 3 2 2 3 3 4 11 Low & Moderate 0-12 20 18 18 16 16 7 3
> Moderate 4 6 6 8 8 17 21
Rye, Sorrento and Rhyll did not reach Severe/Extreme or Catastrophic and spent a small number of hours at Very High and the rest of the day at High or Moderate. Interestingly the maximum FFDI measured at Rye by Mornington Peninsula Shire Council staff was 25 which lasted for one hour.
As an example the known bushfire areas of (say) Airey’s Inlet and Wallan had FFDI’s in the 150-160 range for extended periods. Also it is interesting to note that Cerberus had high FFDI’s ranging 78-97 which shows that the Fire Risk varies significantly within the same region.
The reason the area between Rye and Sorrento and Phillip Island had low FFDI’s on Victoria’s worst ever extreme fire weather day significant “water fetch” to the north & south which generates much higher humidity and more temperate conditions relative to Victoria inland areas and also coastal areas like Aries Inlet and Cerberus which only have significant land mass to the north. The Google map below illustrates the “water fetch”.

3. 3. Conclusion
FFDI/FDR is used by the CFA as one indicator of fire risk.
On Black Saturday Sorrento, Rhyll and Rye recorded FDR’s significantly lower than known fire areas of Victoria and hence provide a much lower risk of property and loss of life

4. FFDI Black Saturday: Supporting Information
A. Data Assumptions
Note 1
All data is from Bureau of Meteorology except Rye is from Mornington Peninsula Shire Council
Note 2
Humidity, Temperature ex Rhyll as Sorrento and Rhyll are surrounded by water. Because Sorrento has more water to the north it would be expected that humidity would be higher and temperature lower than Rhyll. Cerberus only has land to the North so not appropriate.
Note 3
Windspeed is taken at 25 William Buckley Way with the relationship between South Channel and William Buckley way has been measured using a Davis Weather Station installed at 10m height above the ground over 35 days and 1680 data points. William Buckley Way is 66% on average of South Channel Windspeed across all wind directions.
Note 4
Drought Factor = 10 = worst case, which is probably high for Sorrento given its proximity to the sea and the prevalence of coastal showers

5. B. FFDI for Black Saturday
Table below indicates the extreme conditions inland and also at coastal areas where there is no water mass to the north., eg. Airey’s Inlet and Cerberus. Hence, significantly lower risk at locations like Sorrento, Rye and Rhyll.
Time of Day AESDT, Black Saturday, 7 Feb 2009
Aireys Inlet
Cerberus
Melb Airport
Rhyll
Sorrento Notes 2,3,4
Wallan
Rye Note 3
0 10 4 7 4 2 14 NA
1 6 3 9 3 2 14 NA
2 3 3 23 3 3 15 NA
3 2 2 26 2 2 17 NA
4 2 2 14 4 3 16 NA
5 2 1 5 3 3 15 NA
6 2 2 4 2 3 15 NA
7 2 3 37 4 3 22 NA
8 2 6 64 3 3 30 NA
9 3 10 78 4 4 39 NA
10 11 16 91 8 10 71 4
11 88 78 133 12 17 92 4
12 117 85 133 63 29 159 6
13 145 97 114 47 27 106 9
14 150 85 104 46 40 155 12
15 45 97 83 38 39 131 14
16 15 21 115 21 19 97 16
17 10 9 43 7 7 81 25
18 17 22 39 7 8 16 19
19 18 6 17 4 3 19 10
20 2 5 13 3 2 11 6
21 1 3 10 3 2 8 NA
22 2 2 3 1 1 9 NA
23 7 5 7 5 3 14 NA

6. The table below shows that Sorrento and Rye did not reach catastrophic levels and the hours in excess of Moderate Fire danger are significantly lower than Melbourne and Wallan.
Fire Danger Rating Frequency
Hourly Number of Occurrences
Aireys Inlet
Cerberus
Melb Airport
Rhyll
Sorrento Notes 2,3,4
Wallan
Rye Note 3 Low 0-5 11 11 3 15 15 0 15 Moderate 5-12 5 5 4 3 3 3 5 High 12-24 3 3 4 2 2 11 3 Very High 24-50 1 0 4 3 4 2 1 Extreme 50-100 1 5 4 1 0 4 0 Catastrophic >100 3
0 5
0
0 4 0
> Moderate
8
8
17
6
6
21
4

7. The above frequency data for FFDI in graphical form.

8. C. Windspeed and Direction
On Black Saturday during the peak FFDI period at Sorrento (1200h to 1500h) the wind was from the North or North West and theoretically any fire in the Sorrento part of the Mornington Peninsula National would burn into Bass Strait within 2-10 minutes using the rate of spread correlations, ie. The fire would burnout.
Wind Speed, km/hWind DirectionWind Speed, km/hWind DirectionWind Speed, km/hWind DirectionWind Speed, km/hWind DirectionWind Speed, km/hWind DirectionWind DirectionWind DirectionWind Speed, km/hWind DirectionTime of Day AESDT, Black Saturday, 7 Feb 2009Aireys InletAireys InletCerberusCerberusMelbAirportMelbAirportRhyllRhyllSorrento Notes 2,3,4South Channel IslandWallanWallanRyeNote 3RyeNote 3022N 13NNE 15N 31NE 8NE 26NNE 19N 13NE 17N 17NE 13NE 30NNE 218SSW 8NNE 31N 11N 10ENE 28NNE 35N 11S 33N 18S 17S 30NNE 411N 9W 21SSW 28ESE 10ESE 31NNE 515NNW 2WNW 8S 18ENE 15E 30NNE 69NNW 8NNE 2W 5NNE 12NE 30N 717S 9N 35N 18NNE 9NNE 39N 84N 11NNE 54N 9N 10WSW 42N 911ENE 11NE 54N 5NE 6NNE 46N 1015NNE 11NE 48N 8ESE 17N 55N 8NE 1146NNW 39NNW 54N 9N 23N 55N 11NNE 1252NNW 37NNW 48N 54NNW 29N68N 10N1357NW 39N 42NNW 42NNW 19N 46NNW 19N1457NW 31NNW 39NW 35NNW 29NNW 63NNW 18N1535W 37NW 46NW 22NNW 23NW 54NW 18N1637SSW 39SW 41NW 35SW 31SSW 44NW 17N1726S 28SSW 42SW 28WSW 24SSW 37NW 16N1824W 37SW 41SW 11SSW 16SSW 26SSW 20N1930W 15SSW 17SSW 15SSW 4SSW 31SSW 25S2028SW 8ENE 15SE 13N 4WNW 24S 20SW 214S 35SW 15E 33SW 22S 21S 2217SSW 21SW 31S 17S 14S 22SSE 2322NNE 13NE 18N 30NE 8ENE 17ENE

9. D. Charted FDI variables by hour of day. FFDI, Humidity, Wind Speed @10m height, Temperature

13. E. Definition of the Fire Danger Ratings (CFA Website) and Technical Basis for FDR
Sorrento/Rhyll/Rosebud FDR on Black Saturday