The design of urban stormwater infrastructure is generally performed assuming that climate is static.
For engineering practitioners, stormwater infrastructure is designed using a peak flow method, such as the Rational
Method as outlined in the Australian Rainfall and Runoff (AR&R) guidelines and estimates of design rainfall
intensities. Changes to Australian rainfall intensity design criteria have been made through updated releases of
the AR&R77, AR&R87 and the recent 2013 AR&R Intensity Frequency Distributions (IFDs). The primary focus
of this study is to compare the three IFD sets from 51 locations Australia wide. Since the release of the AR&R77
IFDs, the duration and number of locations for rainfall data has increased and techniques for data analysis have
changed. Updated terminology coinciding with the 2013 IFD release has also resulted in a practical change to
the design rainfall. For example, infrastructure that is designed for a 1 : 5 year ARI correlates with an 18.13%
AEP, however for practical purposes, hydraulic guidelines have been updated with the more intuitive 20% AEP.
The evaluation of design rainfall variation across Australia has indicated that the changes are dependent upon
location, recurrence interval and rainfall duration. The changes to design rainfall IFDs are due to the application
of differing data analysis techniques, the length and number of data sets and the change in terminology from
ARI to AEP. Such changes mean that developed infrastructure has been designed to a range of different design
criteria indicating the likely inadequacy of earlier developments to the current estimates of flood risk. In many
cases, the under-design of infrastructure is greater than the expected impact of increased rainfall intensity under
climate change scenarios.
Australian rainfall and runoff, flood, uncertainty