CLIMATE CHANGE STATE OF PLAY: I keep waiting for Northern NSW to get some really good news - this isn't it

A reputable study was published in September this year which raises some concerns for communities in Northern NSW. 

"Using large climate model ensembles to assess historical and future tropical cyclone activity along the Australian east coast" [Bruy`ere, C.L. et al, Sept 2022] is a collaborative effort supported by the National Center for Atmospheric Research (USA), Insurance Australia Group Limited (Aust), Cyclone Testing Station, James Cook University (Aust) and Environmental Sciences and Management, North-West University (South Africa).

The message bottom line is that Australian East Coast Tropical Cyclones (TCs) are now anticipated to extend their range into south-east Queensland and on into Northern NSW as far south as the Clarence Valley and possibly Coffs Harbour City local government area.

At the same time the frequency of strong tropical storms and cyclones are expected to increase, their heavy rainfall areas to widen, intensify and in some instances their wind fields to remain over locations for longer periods. 

The following is an excerpt from the Introduction to the aforementioned study. 

"Building codes can be highly effective at reducing TC losses (Done et al., 2018). They are commonly designed to safeguard people from injury caused by structural failures (e.g., the Australian Wind Loading Standards - ASNZS1170.2).......

A collection of recent work demonstrates that Australian TC statistics are non-stationary. Holland and Bruyère (2014) detected an increasing proportion of the strongest storms. Kossin et al. (2020) found that the absolute numbers of intense storms have increased. Not only are the peak wind speeds increasing, but the latitudes of storm-lifetime peak winds have likely shifted poleward in this region (Kossin et al., 2014). Cyclone forward motion has also slowed down over Australia (Kossin, 2018), meaning that locations experience strong winds for longer, all other things being equal.

TC rainfall is also changing. Studies show heavier TC rain rates in some regions (e.g., Risser and Wehner 2017; Emanuel 2017). Bruyère et al. (2019) showed that when changes in thermodynamical conditions alone are considered (i.e., thermodynamic climate change scenarios), TCs penetrated much further inland with a marked expansion of the heavy rainfall area. Should these wind and rainfall trends continue (as indicated by Knutson et al., 2020; Walsh et al., 2016a; Lavender and Walsh 2011), this raises the prospect that current wind loading codes and flood planning zones may not protect people and property as well as they have in the past and may severely underperform in the future.

The region of southeastern Queensland and northeastern New South Wales (NSW) (referred to as the QLD-NSW sub-region hereafter) may be particularly vulnerable to these anticipated changes. QLD-NSW is located at the current southern limit of TC occurrence and, does not adhere to the stronger building codes implemented further north along the coast (Fig. 1). Consequently, Saffir Simpson scale intensities of high category 1 to low category 2 will exceed the wind loading standards for buildings in this region - designated wind loading region B. Any future southward shift or expansion of the current region of the most intense TCs would threaten structures built to current codes and land planning zones. Moreover, new structures with design lives of 50–100 years will need to account for these expected climate change effects and associated uncertainties." [my yellow highlighting]

NOTE: Click on image to enlarge

Fig. 1. Map indicating the South-West Pacific (SWP) search domain and the Gulf of Carpentaria (northern box) and QLD-NSW sub-region of interest (box around Brisbane). The colored areas indicate where the Australian wind loading standards apply. The wind-load standards for the regions are A: 45 m/s, B: 57 m/s, C: 70 m/s, and D: 87 m/s. The blue circles indicate select Geoscience Australia TC gates (refer to section 3). (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

At this point in time it appears that the building code for housing (AS4055-2012) that is applied for most Northern NSW coastal zone housing has a requirement to be built to withstand a 0.2 second wind gust duration at 57m/s for the 500 year return period. This does not appear to be changing when the most recent version of the National Construction Code (NCC 2022) comes into force.