PDF | 2 MB - Australian Building Codes Board

Executive Summary
The objective of the study, carried out by JDH Consulting on behalf of the Australian
Building Codes Board, is to determine whether there is sufficient information and
justification to change design wind speeds in cyclonic regions of Australia in the
Australian Standard for Wind Actions (AS/NZS1170.2): a) with reference to
currently available wind data, and b) with particular reference to climate change.
The history of the regional wind speed system for the tropical-cyclone affected
coastlines of Australia, developed since the 1970s, is described, and the probabilistic
simulation approach used for hurricane wind speed prediction in the United States,
and used in the past for guidance in Australia, is outlined. Available data on the
vertical profile of cyclonic wind gusts with height is reviewed, and the background to
the gust profiles in the Standard is given. The inland weakening and penetration of
tropical cyclones is reviewed; in comparison with U.S. data, on average the current
regional widths in AS/NZS1170.2 appear to be adequate.
Recent studies of climate change effects on tropical cyclones are reviewed. These
indicate that in the Australian Region, the total number of cyclones has diminished.
This can be related to the preponderance of El Nino events affected Australia’s
climate during the last few decades. However, there is evidence that the number of
the more severe events has increased. Simulations of future climate, with projected
increases in CO 2 concentrations, indicates further increases in the more severe tropical
cyclones and a southerly drift in the genesis region on the Queensland coast. This
indicates a greater risk of a severe cyclone affecting Brisbane and South-east
Queensland than was assumed in the past.
A review of the recent cyclones affecting the Northern Territory indicates that the risk
to the northern coastal strip and offshore islands may also be greater than currently
implied by the Standard. However, upgrading of Darwin to Region D is not justified
on present evidence.
A number of recommendations have been made both with respect to the Standard,
AS/NZS1170.2, and more generally with regard to the database and measurements of
the Bureau of Meteorology are made. The main recommendations are as follows:
• Extensions of the current Region D boundaries on the coasts of Western
Australia and Northern Territory.
• Extension of the southerly limit of Region C on the Queensland coast from
25 o S to 27 o S.
• Introduction of a general cyclone ‘uncertainty’ factor of 1.1 applicable to
Regions B, C and D. This factor should be reviewed periodically.
• Ongoing monitoring of predictions emerging from global climate models as
their resolution and reliability improves.
• More emphasis should be given to predictions for Western Australia and the
Northern Territory.
• Rectification of errors and removal of inconsistencies in the assessment of
wind speed in the tropical cyclone database maintained by the Bureau of
Meteorology are required.
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