Fire danger ratings
Fire Danger Ratings are determined daily for NSW Fire Areas by the Bureau of Meteorology (BOM). NSW Fire Areas are determined by the Rural Fire Service and have different boundaries to the Bureau's Weather Forecast Districts.
Fire Danger Ratings are measured as low-moderate, high, very high, severe, extreme or catastrophic and are based on weather conditions such as temperature, relative humidity, wind speed and rainfall.
To find out about fire danger ratings download the RFS Fire Danger Rating Factsheet (PDF 315.5 KB).
When fire danger conditions reach severe, the Bureau issues Fire Weather Warnings. Warnings are broadcast on radio and television. In most states and territories, fire authorities declare a Total Fire Ban when they receive a Fire Weather Warning from the Bureau.
Fire danger ratings also lead to specific alerts and advice for the public, based on the time of impact and the fire's potential. These alerts take the following form: Advice, Watch and Act, and Emergency Warning.
Information on public warnings, NSW Fire Areas and Total Fire Bans can be found at www.rfs.nsw.gov.au or by calling the Rural Fire Service on 1800 679 737.
Relative humidity is the most commonly used measure of atmospheric moisture and is defined as the ratio of the amount of water vapour actually measured to that which air could hold at saturation. Very low relative humidity of, say, less than 20 per cent, causes fuels to dry out and become more flammable (www.bom.gov.au, 2009).
Air movement provides the oxygen the fire needs to keep burning. Higher winds mean more oxygen and more intense flames. Doubling the wind speed will quadruple the rate of spread of the fire. Winds also carry burning embers downwind, which can start new fires. This is known as spotting (www.bom.gov.au, 2009).
Dry grass, parched native shrubs and dead leaves and twigs are fire's basic fuel. During droughts and in very hot, windy weather, even heavy fuels like large logs and the green leaves and smaller branches of large trees can become dry and flammable (www.bom.gov.au, 2009).
Climatic evens such as El Nino also affect the number and severity of bushfires in Australia (www.bom.gov.au).
Page last updated: 11 December 2015