Assessing the impacts of tropical cyclones

Tropical Cyclone (TC) Tracy impacted Darwin early on Christmas Day, 1974, resulting in 71 deaths, the destruction of thousands of homes and the evacuation of over 35000 people. Several factors contributed to the widespread destruction, including the intensity of the cyclone, vegetation overhanging buildings and construction materials employed in Darwin at the time. Since 1974, the population of Darwin has grown rapidly, from 46000 to nearly 115000 in 2006. If TC Tracy were to strike Darwin in 2008, the impacts could be catastrophic. However, tools such as Geoscience Australia’s Tropical Cyclone Risk Model (TCRM) could be used to allow emergency managers to plan for such a scenario. We perform a validation of TCRM to assess the impacts TC Tracy would have on the 1974 landscape of Darwin, and compare the impacts to those determined from a post-impact survey. We find an underestimate of the damage at 36% of replacement cost (RC), compared to survey estimate of 50–60% RC. Some of this deficit can be accounted for through the effects of large debris. Qualitatively, TCRM can spatially replicate the damage inflicted on Darwin by the small cyclone, identifying localised areas of increased damage. For the 2008 scenario, TCRM indicates a nearly 90% reduction in the overall damage (% RC) over the Darwin region. Once again, the spatial nature of the damage is captured well, with the greatest damage inflicted close to the eye of the cyclone. Areas that have been developed since 1974 such as Palmerston suffer very little damage due to the small extent of the severe winds. The northern suburbs, rebuilt in the years following TC Tracy, are much more resilient, largely due to the influence of very high building standards in place between 1975 and 1980.