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Figure 1.1. Average number of days per year that tropical cyclones occurred in Australian waters in 1970-2000 (from Abbs et al, 2006). Figure 1.1 shows four regions of significant tropical cyclone occurrence: the northwest coastline of Western Australia near Broome, the Timor Sea off the Northern Territory coast, the Gulf of Carpentaria, and the Coral Sea offshore from Queensland. It is noted that cyclonic activity is closest to the coast line offshore from the Western Australian coastline near Broome. The regions of cyclonic activity shown in Figure 1.1 are largely reflected in the present regional zoning system for wind speeds in the Australian Standard AS/NZS1170.2:2002, although consideration of cyclonic wind speeds are not explicitly required by the Standard for Perth in Western Australia, or for the coastline of Northern New South Wales. It is noted that Cyclone ‘Alby’ produced significant wind speeds (up to 75 knots) in the Perth area in 1978. 1.4 Structure of this report In the following Chapter 2, the history of the development of design wind speeds from tropical cyclones, and the associated regional boundaries in AS/NZS1170.2:2002 and its predecessors, is outlined. In Chapter 3, probabilistic simulation methods that are currently used to determine hurricane design wind speeds in the United States, and have been used for guidance in Australia in the past, are discussed. Vertical profiles of wind speeds in tropical cyclones are discussed in Chapter 4. This is relevant, not only for conversion of design wind speeds at the standard reference height of 10 metres in open over-land terrain to other heights and other terrains, but also to convert upper-level wind speeds from simulation models and those given in the Bureau of Meteorology database, to surface conditions. Chapter 5 reviews recent work on the 6
inland penetration and weakening of tropical cyclones and hurricanes and compares it with the weakening implied by the regional system in Australia. Climate change issues are discussed in Chapters 6-8. Chapter 6 reviews observations of global changes in tropical cyclone activity in relation to increased greenhouse gas concentrations and sea surface temperatures. In Chapter 7, studies of changes in cyclonic activity in the Australian Region during the last few decades are reviewed. Recent simulations of future changes in tropical-cyclone activity in the Australian Region are discussed in Chapter 8. Chapter 9 reviews some recent work from Darwin concerning cyclone risk specific to the Northern Territory. Chapter 10 contains conclusions and recommendations, including some proposed changes to the cyclonic regional boundaries in the Australian Standard for Wind Actions AS/NZS1170.2:2002 (Standards Australia 2000a). References D.J. Abbs, S. Aryal, E. Campbell, J. McGregor, K. Nguyen, M. Palmer, T. Rafter, I. Watterson and B. Bates (2006), Projections of extreme rainfall and cyclones, Report to the Australian Greenhouse Office, CSIRO. V.F. Dvorak (1984), Tropical cyclone intensity analysis using satellite data, NOAA Technical Report NESDIS-11, National Oceanic and Atmospheric Administration, Silver Spring, Maryland. Standards Australia (2002a), Structural design actions. Part 2: Wind actions. AS/NZS 1170.2:2002. Standards Australia (2002b), Structural design actions-Wind actions-Commentary. (Supplement to AS/NZS 1170.2:2002). 7
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 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 52 and 53: (the ‘TIM’ cyclones). The latte
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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