- McArthur Forest Fire Danger Index
Fire Danger Rating  Category Fire Danger Index Catastrophic (Code Red) 100 + Extreme 75 – 100 Severe 50 – 75 Very high 25 - 50 High 12 – 25 Low to moderate 0 - 12
The McArthur Forest Fire Danger Index (FFDI) was developed in the 1960s by CSIRO scientist A.G. McArthur to measure the degree of danger of fire in Australian forests. The index combines a record of dryness, based on rainfall and evaporation, with meteorological variables for windspeed, temperature and humidity. 
A similar approach was adopted by McArthur for Grassland areas. Luke and McArthur  details the early development and use of these indices.
In 1980 Noble et al  produced algorithms based on mathematical equations of best fit. These algorithms have been used since the early 1980's to enable easy computation. However they are often used with input values outside McArthur's intended design, resulting in FFDI values in excess of 100. The power function nature of the algorithm, together with limits of precision in measuring the input variables may result in a large range of uncertainty in the calculated FFDI. For example in conditions that produce an FFDI of 100, small fluctuations in wind speed and temperature would suggest a +/- 20% range in FFDI.
A fire danger rating of between 12 and 25 on the index is considered a "high" degree of danger, while a day having a danger rating of over 50 is considered an "Severe" fire danger rating, over 75 as "Extreme" and over 100 as "Catastrophic" (In Victoria the alternate rating name of "Code Red" has been adopted).
McArthur used the conditions of the Black Friday fires of 1939 as his example of a 100 rating.
The FFDI on Black Saturday, 7th of February, 2009, reached much higher than this, although at such extremes it is meaningless to specify a particular value of FFDI.
- ^ "New Warning System Explained". Country Fire Authority. http://www.cfaconnect.net.au/index.php?option=com_k2&view=item&id=873. Retrieved 6 February 2011.
- ^ Dowdy, et al (2009). "Australian fire weather as represented by the McArthur Forest Fire Danger Index and the Canadian Forest Fire Weather Index". http://cawcr.gov.au/publications/technicalreports/CTR_010.pdf.
- ^ Luke R.H. and McArthur A.G., "Bushfires in Australia", Australian Government Publishing Service, Canberra, 1978.
- ^ Noble I.R., Bary G.A.A., and Gill A.M. (1980), "McArthur's fire danger meters expressed as equations", Australian Journal of Ecology, 5, pp. 201 - 203.
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