Wind characteristics over complex terrain with implications for bushfire risk management

Understanding spatially distributed wind fields over complex terrain is important for a variety of applications including pollutant dispersion modelling, fire spread modelling and bushfire risk management. Directional changes in surface winds are particularly important in the context of fire management. In this paper terrain-modified winds are analysed using joint probability distributions derived from wind speed and direction data collected in rugged terrain to the west and southwest of the Australian Capital Territory. The analyses focus on two landform elements; a steep slope and a moderately steep valley. The joint distributions prove to be useful tools for identifying and characterising the dominant states of the wind-terrain systems. Several processes, including thermally-driven winds, lee-slope eddies and dynamic channelling are identified and discussed. The analyses also reveal the stochastic nature of the wind-terrain systems, and thus raise some doubts about the suitability of some deterministic approaches used to model terrain-modified surface winds. Implications of the results relevant to fire behaviour and bushfire risk management are also discussed.