Less than 50 millimetres of rainfall in the previous month predicts fire in Tasmanian rainforest

Rainforests can be eliminated by repeated fire, so we need to know when they require protection. We use data from 11 extensive fires in western Tasmania to determine the meteorological conditions in which rainforest will burn. The variables that discriminated between fires that burned rainforest and those confined to other vegetation types were the amount of rainfall in the previous 30 days, the amount of rainfall in the previous 60 days and the soil dryness index (SDI). Our analyses confirmed a previously-suggested critical figure of 50 mm of rain in a month, showed that this figure pertains to the month previous to the fire, and showed that the forest fire danger index (FFDI) was not a good predictor, with fires burning rainforest on days with an FFDI at the lower end of the scale (Lake Macintosh) and not burning rainforest on days when the FFDI was at the higher end of the scale (Reynolds Creek and Giblin River). We conclude that it is important to respond to dry conditions in fire response planning for areas with rainforest, rather than relying on the FFDI