Bushfire risk at the urban interface estimated from historical weather records: consequences for the use of prescribed fire in the Sydney region of south-eastern Australia

The urban/bushland interface around Sydney in south-eastern Australia is extensive. A history of destructive bushfires has led to intensive management of fuel at this interface. Prescribed burning is the major management technique. The rationale is to manipulate fuel so that the intensity of unplanned fires is reduced to a level where suppression is possible at the urban interface, Managers are faced with many options in terms of where, when and how often they burn at the urban interface but the effectiveness of differing strategies in terms of protection, has not been evaluated. Prescribed burning was examined in the northern suburbs of Sydney in terms of its effect on the average annual risk of uncontrollable fire adjacent to buildings. The potential for uncontrollable fire in the three predominant plant communities (shrubland, woodland and forest) was estimated using daily (15:00 h) values of the McArthur Forest Fire Danger Index (FFDI) for the period 1955-1996 and related fire behaviour equations. The study considered a 100 m wide zone at the urban interface (similar to 200 km in length), and integrated the effects of varying aspect, topography, and vegetation (fuel) types. Based on trends in fuels and daily weather data for 1955-1996, large amounts of this zone (40, 34 and 27%) would need to be burnt annually to achieve average risk levels of uncontrollable fire of 1, 5 and 10 days per annum, respectively. The risk of uncontrollable fire was highly sensitive to the frequency and extent of prescribed burning. Constraints on prescribed burning, such as available resources and suitable weather will therefore have a large effect on protection. Other consequences of a range of prescribed burning scenarios are discussed. (C) 1998 Academic Press Limited.