7 March 2019
JBA’s event response team produced a report on 4 February 2019 providing details of the Townsville flood event, as well as additional event commentary on 7 February 2019. One month on from the event, as flood waters finally recede, we take a more detailed look at the onset of the event, its impact and JBA’s 5m flood footprint, which can be used to help clients assess the impact of this event. Finally, we consider this event in the context of ongoing flood risk management in Australia.
Event onset and impact
The Townsville floods followed sustained and heavy monsoonal rain that occurred between 27 January and 8 February 2019. Rainfall totals during this period reached a record high of 1,391mm at Townsville Airport weather station (Australia Bureau of Meteorology). Townsville was known to have a high flood risk as it was built on a natural floodplain in the lower reaches of the Bohle and Ross rivers. This risk was exposed during the latest event, where a total of 21,515 claims had been made as of 23 February 2019, with insured losses totalling AUD $887 million at the time of writing (Insurance Council of Australia, 2019; Martin, 2019a). Residential properties contribute 91.2% of the total claims while commercial claims make up the remaining 8.8% (Martin, 2019a).
Due to the unprecedented monsoonal rain received in Townsville, the water capacity of the Ross Dam peaked at 248% of its capacity (Australian Government Data, 2019). This prompted authorities to urgently release water from the Ross Dam into the Ross river at a rate of 1,900 cumecs (m3 per second), thereby inundating several suburban areas in Townsville (Riga, 2019) (Figure 1). Flooded neighbourhoods included Idalia and Oonoonba.
Many low-lying areas near the coastline of Queensland have been developed in recent years with houses built on swamplands. Flood maps produced by Townsville City Council did not identify suburban areas such as Oonoonba and Idalia to be at risk of a 1-in-100-year flood. The authorities have explained these areas not being included by highlighting that the low-lying suburban areas were inundated due to the sudden release of water from the Ross Dam (The Australian, 2019).
Based on a post-event onsite study, it is estimated that 3,300 properties were damaged due to the flooding in Townsville. Out of the 3,300 properties, 2,063 properties suffered minor damage, 1,101 properties suffered moderate damage and the remaining 135 properties were severely damaged (Townsville Bulletin, 2019).
Based on reports after the flood event, estimates at the time of writing suggest that total economic losses due to the Queensland flooding will exceed AUD $1 billion (Crockford, 2019). AgForce, an organisation representing Queensland’s rural producers, estimates that the total loss for farmers could be AUD $500 million, assuming each head of cattle is worth AUD $1,000 (Crockford, 2019).
Rainfall analysis
The total rainfall reported at Townsville Airport station in the month of February was approximately 1,000mm (Australia Bureau of Meteorology). Based on the total monthly rainfall for February 2019, the estimated return period of this accumulation of rainfall can be estimated as a 100-year event (Figure 2) based on experience from the 149 years of rainfall data recorded at gauges in Townsville. Based on gauge data from the Bohle River, the height peaked at 7m during the February 2019 flooding in Townsville (Figure 3) and this was classified as severe flooding by the Bureau of Meteorology in Australia. The highest record historically was set by the January 1998 flood event in Townsville. Our previous event commentary makes a comparison analysis between the amount of rainfall and the event’s duration.
Developing the JBA 5m flood footprint
Following the floods in Townsville, JBA ran a high-resolution hydraulic model on 5m lidar data with 1-in-100-year hydrology for the area downstream of the Ross Dam (Figure 4). The flow rates are based on JBA’s hydrological model for Australia which uses the Australian Rainfall Runoff (ARR) model.
Ongoing Challenges
As coastal development of property and infrastructure continues near the Queensland coastline, flood risk may be exacerbated in the future. Based on a recent report, flooding in Townsville is 20% more likely to occur than previously thought and total flood risk in the region is expected to increase by 130% by 2100. As a result, houses located in high-risk areas in Townsville and elsewhere in Queensland state may eventually become uninsurable in the future (Martin, 2019b).
Property penetration rates in Australia are fairly high and, overall, are comparable to rates in the United Kingdom and New Zealand (Table 2) (Swiss Re Institute, 2015). However, there are still a large number of uninsured properties. Many home-owners and small businesses may have insufficient insurance for their properties and may not realise this until after an event has occurred. As mentioned in our previous report, even though flood insurance has been available in Townsville since 2007, the insurance penetration remains low for commercial businesses in the city (Insurance Council of Australia).
Home insurance has become increasingly expensive to obtain in northern Queensland. According to a report by the Australian Competition and Consumer Commission (ACCC), home insurance premiums in northern Queensland can be three to five times higher than in other areas of the state. The average annual premiums in three of the largest cities in northern Australia (Mackay, Cairns, Townsville) are at least two times higher than in Metropolitan Brisbane (Table 3) (Australian Competition and Consumer Commission, 2018). The prices for premiums have increased as devastating floods and cyclone events have hit northern Queensland in recent years, including cyclones Yasi and Debbie. (North Queensland Home Insurance, 2018).
Australia has a comprehensive disaster management plan for various perils, including flood. However, these plans must be updated in order to cope with greater events that are likely to happen in the future due to changes in our climate. These changes can positively benefit the authorities in Queensland; a recent study conducted in the USA concludes that every dollar spent on mitigation measures can reduce post-event losses by six dollars (National Institute of Building Sciences, 2018).
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