Comments on "Estimation of Tropical Cyclone Wind Hazard for Darwin: Comparison with Two Other Locations and the Australian Wind-Loading Code"

Cook and Nicholls recently argued in this journal that the city of Darwin (Northern Territory), Australia, should be located in wind region D rather than in the current region C in the Australian/New Zealand Standard AS/NZS 1170.2 wind actions standard, in which region D has significantly higher risk. These comments critically examine the methods used by Cook and Nicholls and find serious flaws in them, sufficient to invalidate their conclusions. Specific flaws include 1) invalid assumptions in their analysis method, including that cyclones are assumed to be at the maximum intensity along their entire path across the sampling circle even after they have crossed extensive land areas; 2) a lack of verification that the simulated cyclone tracks are consistent with the known climatological data and in particular that the annual rate of simulated cyclones at each station greatly exceeds the numbers recorded for the entire Australian region; and 3) the apparent omission of key cyclones when comparing the risk at Darwin with two other locations. It is shown here that the number of cyclones that have affected Port Hedland (Western Australia), a site in Australia’s region D, greatly exceeds the number that have influenced Darwin over the same period for any chosen threshold of intensity. Analysis of the recorded gusts from anemometers at Port Hedland and Darwin that is presented here further supports this result. On the basis of this evidence, the authors conclude that Darwin’s tropical cyclone wind risk is adequately described by its current location in region C.