6 December 2018
Torrential rain fell in Sydney on 28 November 2018, with reports of more than 100mm of rain falling across various areas of Sydney in less than two hours, inundating parks, roads and houses (The Sydney Morning Herald, 2018).
The amount of rainfall was comparable to the average rainfall that Sydney receives in the month of November- the historical average and median for November is 84.2mm and 66.9mm respectively (Reuters, 2018; Bureau of Meteorology Australian Government). Wind gusts of 96km/h were also reported at Wattamolla during the passage of the storm (The Sydney Morning Herald).
Two deaths have been attributed to the storm as it hit during morning rush hour. It resulted in chaos for many commuters, causing widespread disruption. The flood water and fallen trees resulted in power failure for several thousand households (The Sydney Morning Herald).
Initial observations suggest this was the wettest day since November 1984, when rainfall totals of 235mm were recorded (the highest since 1858), and the first day since that event to achieve rainfall totals in excess of 100mm (ABC; Bureau of Meteorology Australian Government). The Observation Hill gauge in Sydney recorded 105mm of rainfall in less than two hours as a result of the 2018 storm. Based on historical data from the gauge, this would translate to a 24-hour rainfall return period of 20 years (calculated by applying the Generalised Pareto Distribution curve to the historical daily data for the month of November, as shown in Figure 4).
However, because the downpour occurred within a two-hour period, the event is estimated to have a 1 in 100-year return period by the authorities (Bureau of Meteorology Australian Government; The Sydney Morning Herald; Reuters, 2018). At the time of writing, insured losses for the storm are thought to be relatively low in comparison to other flood events of 2017 and 2018. Claims for the 2018 Sydney flood are estimated to be around AUD $13.5 million (USD $9.96 million), with the majority of these claims relating to damaged roofs and vehicles (InsuranceNEWS).
Major flood losses in Brisbane, 2011
At the time of writing, the most severe flooding in Australia in the last decade has occurred in south-east Queensland in late 2010 to early 2011. Thousands of people living in the Toowoomba and Ipswich districts of Brisbane were evacuated, with total insurance pay-outs reaching over AUD $2.4 billion and total economic damage estimated at AUD $10 billion (Reuters, 2011). The floods occurred due to persistent heavy rainfall and a diminishing Tropical Cyclone Tasha in December 2010. At the same time, Australia was experiencing a strong La Nina event, which is typically associated with high rainfall and floods in eastern Australia. The floods claimed 44 lives and more than 200,000 people were affected (Munich Re). An estimated 18,000 properties were inundated in the affected regions. The mining, agriculture and tourism industries were amongst the hardest hit as losses in the Central Business District of Brisbane reached AUD $4.46 million.
However, from a hydrological perspective, the maximum flood level recorded during the 2011 floods was actually lower than the 1893 and 1841 floods, both of which peaked at 8.35m (Zurich Australian Insurance Limited).
An overview of flood losses in 2018
Since the Brisbane floods of 2011, far more infrastructure has been developed to help mitigate and reduce flood risk in Australia. Insurance markets are estimated to have covered approximately 50% of the economic losses incurred by these floods. In 2018 alone, the total insured losses caused by floods and tropical cyclones has been estimated at AUD $261 million (USD $191 million) (Insurance Business Australia). Out of the total losses, the storm that hit Hobart and the surrounding suburban areas in Tasmania resulted in total claims of approximately AUD $100 million ($USD 73 million) (Insurance Council of Australia). In early 2018, Tropical Cyclone Marcus hit Darwin and resulted in insured losses totalling AUD $62 million (USD $46 million). Tropical Cyclone Marcus was named as the strongest cyclone in Darwin in the last 30 years (The Guardian). In comparison, the total insured losses for the Sydney storm is relatively lower, at an estimated AUD $13.5 million (USD $9.96 million).
JBA Risk Management has just released nationwide return period flood maps for Australia at 30m resolution. Please get in touch for further information.
