Tropical Cyclone Oma: How much could she cost us?
In northern NSW and southeast Queensland, migration and continued development of the coast is leading to large concentrations of population, property, and infrastructure at risk to both natural coastal processes and natural disasters. The ever-changing forecast track of Tropical Cyclone Oma may see her arrive in this location over the next week. What could this look like? In 2010 Kevin M. Roche, K. John McAneney, Keping Chen, and Ryan P. Crompton examined a similar scenario.
Approximately ten years ago we looked into the impact of the Tropical Cyclone that made landfall on February 20th 1954, just inside the Queensland border at Coolangatta. Often referred to as TC137, it was never given an official name - a practice not adopted in Australia on a consistent basis until 1964, although some systems were named prior to this.
The objective of the research was to estimate the insured losses that might be expected if a similar event were to occur today and to generalise about the expected economic costs that might occur. Remembering that this was a fairly underdeveloped region back in 1954. These days it is one of the fastest growing regions in Australia with the south-east Queensland region population expected to exceed 4 million by 2026.
The other main objective was to provide a learning tool for future reference. We hoped that if society had a better understanding of historical natural hazard impacts from large scale events that it should lead to reducing the risks to the community from extreme weather events through either mitigation activities and / or community resilience.
At the time, the economic cost of natural disasters across the globe was increasing dramatically and many were keen to attribute this to climate change. On the other side of the argument there was an ever-growing body of evidence (across multiple jurisdictions) that showed that this increase in losses could be largely explained by changing social factors – such as changes in population, wealth, and inflation.
This was the approach we took. In effect, this evidence showed that there were more people living in vulnerable places with more to lose. And this has only increased over the last ten years. Society did not seem to want to learn from its previous mistakes. And sadly it still does not. We continue to build poor quality houses in poor locations. Historically, over 93% of all property destruction due to natural disasters in Australia has been due to weather related events, with tropical cyclones and floods being the most deadly after heatwaves.
Cyclone Track of TC137 (Source: Bureau of Meteorology)
Tropical cyclones are unique in that they can have up to three major impacts from the one event: destructive winds, heavy rainfall, and damaging storm surges. TC137 made landfall on the 20th February near the Queensland / New South Wales border, before heading in a southerly direction for some 500 km where it developed into a rain depression and exited the coast not far from Coffs Harbour.
TC137 was a fairly small cyclone in terms of wind impacts, registering as an Australian Category 1 cyclone. A Cat 1 cyclone is defined by the BOM as having typical wind gusts over open flat land of between 90 and 125 km/h. You would expect to see damage to crops, trees and caravans but negligible damage to houses. But the accompanying rainfall led to nearly all major rivers and creeks in the region experiencing their highest recorded levels right up until TC Debbie (March 2017) decided to take a few of these records for herself.
The Nerang, Tweed, Brunswick, Richmond, and Clarence catchments all flooded simultaneously. Parts of the lower Clarence River were estimated at being 11km wide.
Springbrook, just inside the Queensland border, received 900mm rainfall in 24 hours. The Richmond catchment was hardest hit with most towns including Lismore, Kyogle, Casino, and Nimbin experiencing their highest ever recorded flood heights, as did Murwillumbah.
But of more interest to the surfing population is what happened down in Byron Bay, long before it became the poster child of legal disputes between beachside land owners and the local council. Although Byron these days is full of wealthy escapees from the major cities, backpackers, and those seeking a bohemian lifestyle, it was not always this way. Back in 1954 it was an avid fishing town with an estimated one-fifth of the town employed by the fishing industry.
And overnight the fishing industry was obliterated. The resulting storm surge that arrived with TC137 was the cause. There are limited facts on wave heights and the magnitude of the swell event but the anecdotal evidence is compelling. Wave action breached the sand hills and was reported five blocks back from the beachfront, reaching Marvel Street and the Recreation Ground. It also caused major damage to the wharf.
Byron Bay’s first wharf was built in 1888 and had been replaced in 1928 after heavy seas damaged it. This second one was rebuilt in 1948, before approximately 200m of it was washed away by TC137. In those days, the fisherman used to lift their boats up on to the wharf to protect them from heavy seas. On that fateful night, 23 of the 24 boats which made up the Byron fishing fleet were loaded on top of the wharf - and subsequently never seen again. The last of the boats survived as it was stuck up at Brunswick in the river, initially annoyed that they could not make it back down to the so-called safety of the wharf.
The image below shows the wharf in the early 1940’s with a few of the fishing fleet on top.
Byron Wharf in the 1940’s
Almost immediately after TC137, Byron Bay became a whaling town – worthy of another discussion at a different time.
To estimate the cost of TC137 if it had occurred in 2010 we used a combination of local council flood maps, Census information, and Risk Frontiers’ proprietary flood loss model, a model used by many insurance companies. Essentially we used mathematical techniques to take into account that the value of real estate in the region had increased over ten times since 1954 and the population by an order of magnitude, and combined this with our knowledge of the impact a similar type of event would have.
I will not get into the detail too much here but if you are interested you can read more about it here (https://journals.ametsoc.org/doi/full/10.1175/WCAS-D-12-00018.1)/.
TC137 occurred prior to the availability of reliable insurance statistics. Our best estimate of losses in the dollars of the day was approximately £7.5 million with 28 people losing their lives (some reports have this number as high as 30). Our best estimate at the time using 2010 levels of exposure - think houses, people, business, and infrastructure - whilst assuming 100% insurance penetration (in Australia it is about 96%) could reach $3.4 billion, with economic losses approximately twice this. We would expect these losses to be higher if a cyclone was to be more intense when it reached landfall.
Remember these are 2010 numbers. In today’s terms we would expect them to be even higher.
To put this in perspective, here are the top 5 natural disasters (since 1967) ranked as if if they occurred in 2017, taking into account changes in build codes, trades and material costs, population and demographics from the Insurance Council of Australia:
$5.6bn, Sydney Hailstorm, 1999
$5.0bn, Cyclone Tracy, 1974
$4.7bn, Cyclone Dinah, 1966
$4.2bn, Earthquake, 1989
$3.2bn, Brisbane Flooding, 1973
So yes, Tropical Cyclone Oma could potentially be both devastating and expensive.
// DR KEVIN ROCHE
Dr Kevin Roche is an economist who spends his time advising governments and corporates how to manage their exposure to natural hazards and climate change across the Asia-Pacific region.