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(the ‘TIM’ cyclones). The latter events had little effect on Darwin, but a significant effect on the northern coastline and islands of the Northern Territory, and a stronger case can be made for upgrading the latter locations to Region D. However, there is scope for new probability-based simulations to determine wind speeds for the Northern Territory, incorporating recent information on cyclone tracks, such as the recent TIM events. The climate change studies for Australia using global climate simulation models described in Chapter 8 have, up to now, concentrated on the Queensland coastline (perhaps understandably given the population density). It would be desirable for these to be extended to the Northern Territory and Western Australian coasts, especially given the rapid development of resource projects (oil, gas, minerals) in these areas. Uncertainty in the future number and strength of tropical cyclones resulting from climate change for Darwin, and other locations, can also be handled by increases in the ‘Uncertainty’ Factor F C , and recommendations for this are given in the following chapter. References W.C. Arthur, A. Schofield, R. P. Cechet and L. A. Sanabria (2008), Return period cyclonic wind hazard in the Australian Region. 28th AMS Conference on Hurricanes and Tropical Meteorology, 28 April - 2 May 2008, Orlando, FL, USA G.D. Cook (2007), Has the hazard from tropical cyclone gusts been underestimated for northern Australia? personal communication (M.J. Syme), CSIRO Sustainable Ecosystems. P.N. Georgiou, (2000), On the probability of Darwin being struck by a category 5 cyclone. A report to the Northern Territory Department of Transport and Works and Colless & O'Neill Pty Ltd. Environment and Climate Risk Assessment, Pymble, NSW. B.A. Harper, (2005), Darwin TCWC Northern Region Storm Tide Prediction System. System Development Technical Report, pp. 112 + appendices. Systems Engineering Australia Pty Ltd, Bridgeman Downs, Qld. M. Nicholls et al (2007), Review of NT cyclone risks, Report by the Community Group for the review of NT cyclone risks, April 2007. (available on CD-ROM and at www.cyclone.org.au). 50
10. Conclusions and recommendations 10.1 Conclusions The Australian Standard for Wind Actions (Standards Australia, 2002a) sets wind speeds for structural design for return periods specified by the Building Code of Australia. The Standard has designated special regions for design wind speeds for tropical cyclones since 1975. However, possible effects of climate change due to global warming have, up to now, been deliberately excluded (Standards Australia 2002b). Now may be an appropriate time to incorporate, at least partially, current projections for building design wind speeds in cyclone regions. JDH Consulting has reviewed scientific literature and other sources, from both Australia and overseas, relevant to the problem of predicting cyclonic wind speeds in a warming climate. The trends in the last thirty years in which satellite images are available and consistent are still somewhat inconclusive. The following most recent statement by the International Panel on Climate Change (IPCC) summarizes the global situation: ‘There is observational evidence for an increase in intense tropical cyclone activity in the North Atlantic since about 1970, correlated with increases in sea surface temperatures. There are also suggestions of increased intense tropical cyclone activity in some other regions where concerns over data quality are greater. … There is no clear trend in the annual numbers of tropical cyclones.’ In the Australian Region there has been a fall in the total number of tropical cyclones during the last thirty years. This is correlated with the Southern Oscillation Index and the well-known El Nino phenomenon. The latter also manifests itself in the increase in sea surface temperature in the central Pacific Ocean, and may be a consequence of global warming. There is, however, evidence that the number of more intense cyclones (Category 3 and above) has increased slightly in the last thirty years. These more intense storms are those of relevance for ultimate limits states design of buildings and other structures. The apparent trend may be affected, at least partly, by changes in the observational practices of the Bureau of Meteorology, and reflected in the tropical cyclones database maintained by the National Climate Centre of the BoM. However, an increase in more intense cyclones due to global warming, for the Coral Sea region off the Queensland coast, is predicted by global climate models by several independent studies. Two studies also predict 2-3 o southward shift in average tropical cyclone occurrences off the Queensland coast. One study predicts a Category 3 cyclone could directly hit South-east Queensland, including Brisbane, in the middle of the century. The possibility of such a scenario should be considered in future revisions of AS/NZS1170.2. No comparable climate change studies have apparently yet been made for the Indian Ocean (Western Australian coast) or the Arafura Sea (Northern Territory). Studies of the average inland decay of hurricanes in the United States and for Cyclone ‘George’ (2007) in Australia, indicate the current widths of the regional boundaries 51
Page 2 and 3: IMPACT OF CLIMATE CHANGE ON DESIGN
Page 4 and 5: Executive Summary The objective of
Page 6 and 7: 1. Introduction 1.1 Project scope B
Page 8 and 9: Figure 1.1. Average number of days
Page 10 and 11: 2. History of cyclonic design wind
Page 12 and 13: The ratios of the current (2002) va
Page 14 and 15: Station Table 2.3. Comparison of de
Page 16 and 17: 2.3 Summary and Discussion The chan
Page 18 and 19: 3. Simulation methods for predictio
Page 20 and 21: with the hurricane. An imposed pres
Page 22 and 23: C.M.L. Dorman (1984), Tropical cycl
Page 24 and 25: In the absence of other comparable
Page 26 and 27: averaging of many individual normal
Page 28 and 29: T.F. Hock and J.L. Franklin (1999),
Page 30 and 31: A road-sign failure near the eye wa
Page 32 and 33: α β = cav (5.6) where c av is an
Page 34 and 35: References G.N. Boughton and D. Fal
Page 36 and 37: 6.3 Interpretations by Emanuel (200
Page 38 and 39: IWTC (2006) ‘The scientific debat
Page 40 and 41: 7. Observed trends in tropical cycl
Page 42 and 43: cyclones occurred in both the South
Page 44 and 45: 8. Predicted effects of climate cha
Page 46 and 47: environmental factors (that are kno
Page 48 and 49: 9. Observations and projections for
Page 50 and 51: 9.3 Report by Cook G.D. Cook (2007)
Page 54 and 55: are slightly conservative but adequ
Page 56 and 57: • Improving the understanding of
Page 58 and 59: Cyclonic wind speeds - Darwin 1960-
Page 60: ACKNOWLEDGEMENTS The support of Dr

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