Newsletter Volume 18, Issue 4 – October 2019

What areas of Australia are most at risk from natural perils?

by Andrew Gissing and Foster Langbein

The Commonwealth Government recently released a National Disaster Risk Reduction Framework. A key priority of the framework is accountable decision making which includes a strategy to identify highest priority disaster risks and mitigation opportunities. The strategy is based on the principle that it is not possible to reduce all identified risks and that investments must be targeted to minimise risks with the greatest potential impacts. The Australian Prudential Regulation Authority has also recently outlined the importance of mitigation investment in increasing insurance affordability across Northern Australia. The Commonwealth Government in October announced an additional $50 million dollars annually in mitigation funding.

Catastrophe loss models can be used to develop an understanding of the relative risk profile of Australia. Catastrophe loss models are decision support systems used extensively in the (re)insurance industry to assist in pricing risk and aggregate exposure management. Risk Frontiers has developed a suite of Australian probabilistic catastrophe loss models to quantify the impacts of flood, bushfire, hail, tropical cyclones and earthquake. These hazards contribute the majority of disaster losses in Australia as shown in Table 1. Risk Frontier’s catastrophe loss models have national coverage and are comprised of hazard, exposure and vulnerability modules (read more in Briefing Note 399). The models provide scientifically based damage estimates that can be used to rank the risk profiles of different communities nationally.

Table 1: Breakdown of normalised losses by peril based on ICA disaster list (1966-2017). (Source: (McAneney et al., 2019))

To identify what areas of Australia pose the greatest risk of financial loss to insurable assets such as residential and commercial property we have used the full suite of Risk Frontiers catastrophe models (hail, flood, tropical cyclone, earthquake and bushfire) to calculate average annual losses (AAL) for each Australian postcode based on exposure information derived from the NEXSIS database. The results of this analysis are illustrated in Figure 1 from which we can identify the top 20 priority postcodes nationwide as listed in Table 2.

Figure 1: National natural hazards relative risk profile.
Table 2: Postcodes ranked based on total average annual loss including damages from flood, bushfire, cyclone, earthquake and hail.

All the highest rated postcodes are in WA, QLD or NSW, with flood and cyclone being the most significant perils. Bundaberg (4670) is rated as the postcode with the highest AAL relative to other post codes, with its total AAL contributing 0.02% of the nation’s overall total AAL. The total AAL for Bundaberg is over twice that of the estimated AAL for 10th placed Townsville (4814) and over two hundred times greater than the lowest ranked postcode of Cooladdi (QLD) (4479). Such information about relative disaster risks is useful in determining national mitigation investment priorities.

Results can also be dissected by peril. Table 3 provides the highest rated postcode for each of the five modelled perils nationally.

Table 3: Top postcode for each peril.

Postcodes were chosen to best represent Australian towns and suburbs. Results will vary depending upon the loss metric utilised, for example a return period, AAL or probable maximum loss. They will also vary depending upon the geographic boundaries used for example post code, statistical area, local government area or electoral boundary. Using post codes ignores potential losses attributable to wider regional scenarios. For example, potential losses due to flooding in the Hawkesbury-Nepean Valley are greater than just the post code of Windsor and are said to be the greatest nationally by the insurance industry. Such comparison of wider scenarios could be considered in a future analysis.

Understanding Future Risk

Risks are likely to change into the future due to climate change and urban development and future mitigation investment decisions should consider this. Risk Frontiers’ catastrophe loss modelling framework is ideally suited to consider influences on future risk such as climate change, mitigation investment, increased development and changes to building codes. The Geneva Association, a peak insurance industry think tank, concluded that by combining catastrophe models with latest climate science an enhanced understanding of future weather-related risk impacts could be developed. Such use provides greater insights into the impacts of climate change on natural hazards not currently possible using Global Climate Models.

More information on Risk Frontiers catastrophe loss models can be found at riskfrontiers.com.

References

AUSTRALIAN PRUDENTIAL REGULATION AUTHORITY. 2019. Submission – Northern Australia Insurance Inquiry Second Update Report. Available: https://www.apra.gov.au/sites/default/files/submission_-_northern_australia_insurance_inquiry_second_update_report_september_2019.pdf [Accessed 8/10/2019].

DEPARTMENT OF HOME AFFAIRS. 2018. National Disaster Risk Reduction Framework. Available: https://www.homeaffairs.gov.au/emergency/files/national-disaster-risk-reduction-framework.pdf.

MCANENEY, J., SANDERCOCK, B., CROMPTON, R., MORTLOCK, T., MUSULIN, R., PIELKE, R. & GISSING, A. 2019. Normalised insurance losses from Australian natural disasters: 1966–2017. Environmental Hazards, 1-20.

Bushfire and tropical cyclone activity for 2019/20

By Ryan Crompton

The most recent ENSO Wrap-Up was released by the Bureau of Meteorology (BoM) on 29 October 2019 under the headline ‘Strong positive Indian Ocean Dipole persists’. The wrap-up was summarised as:

The strong positive Indian Ocean Dipole (IOD) event continues while the El Niño–Southern Oscillation (ENSO) remains neutral.

As explained in Crompton et al. 2010 a positive IOD (pIOD) event is when the eastern Indian Ocean is cooler than normal and the western Indian Ocean is anomalously warmer and often associated with a more severe fire season for southeast Australia. Their analysis of building damage due to Australian bushfires concurred with this and interestingly, in terms of the current conditions, they found that the two most damaging combined IOD and ENSO phases were pIOD/neutral and pIOD/El Ninõ in terms of average annual normalised damage for years 1925-2008.

Compounding the bushfire risk for this season is another phenomenon called ‘sudden stratospheric warming’ which is when temperatures in the stratosphere high above the South Pole begin rapidly heating. (The stratosphere is the second layer above the Earth’s surface and is roughly 10-50km above the ground). In a Conversation article published at the beginning of September authors from the BoM discussed how this warming commenced in the last week of August and:

Record warm temperatures above Antarctica over the coming weeks are likely to bring above-average spring temperatures and below-average rainfall across large parts of New South Wales and southern Queensland.

At the time, the BoM was predicting the strongest Antarctic warming on record, likely to exceed the previous record of September 2002, with the impacts reaching the Earth’s surface during October and possibly extend through to January.

The increased risk of fire and heatwaves along eastern Australia has already been borne out with fires, at the time of writing, currently raging throughout the mid-north coast of NSW and northern NSW, including around my hometown of Forster-Tuncurry.

The ENSO phase also impacts tropical cyclone activity in the Australian region as discussed in the recently released BoM Australian Tropical Cyclone Outlook for 2019 to 2020. The outlook is ‘Fewer cyclones than average likely for Australia this season’ with this based on the historical relationships between the status of ENSO over the preceding July to September and the subsequent tropical cyclone season. The Outlook notes that indicators have been ENSO-neutral since April 2019 and the majority of climate models forecast neutral ENSO for the remainder of 2019 and into the first quarter of 2020.

The outlook of fewer cyclones than average not only applies to Australia but all other regions as shown in Figure 1. The Australian region has a 35% chance of more tropical cyclones than average, meaning a 65% chance of fewer tropical cyclones than average. The Outlook states that around four tropical cyclones cross the Australian coast in a season and the accuracy for the Australian region is high. Similar descriptions are presented in the Outlook for other regions.

Figure 1. Long-term average number of tropical cyclones, using data from the 1969–70 season to this (2019) season and the percentage chance of more tropical cyclones than average (Source: BoM).

WeatheX needs you, the citizen scientist, to watch and report severe weather events wherever you are using your smartphone.

Severe weather events are often missed by weather instruments and are difficult to capture. Your reports will vastly improve our ability to capture these events and contribute to better understanding.

WeatheX allows you to report the severity, location and timing of hail size, wind damage, flooding and tornadoes. You can also capture a photo or add a description of the event. This information will be used by weather and climate researchers, including the ARC Centre of Excellence for Climate Extremes, Monash University and Australian Bureau of Meteorology. All reports and photos will remain anonymous and no identifying information is collected.

The app also allows you to view the location and time of recent reports across Australia. Zoom, pan and investigate what’s happening locally or the other side of the country. You will also see your own report on the map immediately after reporting too!

To get started with reporting, download the WeatheX app from Google Play or the App Store.

The WeatheX app is funded by The Centre of Excellence for Climate Extremes (CLEX) and is managed by the School of Earth, Atmosphere and Environment at Monash University and is supported by Risk Frontiers.

Coastal flooding and coral bleaching: what the latest IPCC Special Report means for Australia

Thomas Mortlock, Risk Frontiers

On 24 September, the Intergovernmental Panel on Climate Change (IPCC) published the latest of three Special Reports in the Sixth Assessment Cycle, this time focussing on the Ocean and Cryosphere. Our Briefing Note 377 outlined some of the key points of the previous Special Report on Global Warming.

The focus of the third Special Report is of particular relevance to Australia, given the importance of the ocean in modulating Australia’s climate; the large portion of the population exposed to coastal hazards; and the significance of the Great Barrier Reef to the tourist industry. This briefing note highlights some of the key findings of the report[1] and relevance for Australia.

Sea level rise

Global mean sea level (GMSL) is rising and accelerating due to increased ice loss from the Greenland and Antarctic ice sheets, as well as land-based glacier mass loss and thermal expansion of the ocean. The rate of GMSL rise over the past decade was 3.6 mm/yr, about 2.5 times greater than the average rate over the past century. Mass loss from Antarctica over the past decade has tripled relative to the previous decade and doubled for Greenland over the same period.

Figure 1. Ice sheet melt in Antarctica is a major source of uncertainty for global sea level rise projections. Source: Reuters/Pauline Askin (2019).

While Greenland is currently contributing more to GMSL than Antarctica, Antarctica could become a larger contributor by the end of the 21st century because of ongoing, rapid ice sheet retreat. Beyond 2100, the increasing divergence between Greenland and Antarctica’s relative contribution to sea level rise, if global greenhouse gas (GHG) emissions continue unabated, has important consequences for the pace of relative sea level rise around Australia.

In Australia, the rate of sea level rise is lower than the global average (1.6 mm/yr at Sydney between 1966 and 2009, when ENSO is removed). Similarly, projections are lower: 0.38 m under Representative Concentration Pathway (RCP) 2.6 and 0.66 m under RCP8.5 for Sydney for the end of the 21st century (CSIRO, 2015), compared to 0.39 m and 0.71 m globally. This is because land is still rising from post-glacial rebound and atmospheric pressure is increasing around Australia, suppressing relative sea levels. However, there are large uncertainties attached to these projections, mainly associated with Antarctic contribution to future GMSL but also the longevity of the “suppression effect” around Australia (e.g. Sniderman et al. 2019).

Another component of sea level rise is thermal expansion of the ocean. It is virtually certain that the global ocean has warmed since 1970 and has taken up more than 90 % of the excess heat in the climate system, and up to 30 % of total anthropogenic CO2 emissions since the 1980s. This has several additional consequences, including; acidification of the ocean; higher energy potential for the formation of tropical cyclones (noting other factors also influence formation); and, a higher number, length and severity of marine heatwave events associated with coral bleaching.

Coastal flooding

Sea level rise impacts coastal communities by contributing to an increased frequency of extreme sea level events resulting in coastal flooding. Extreme sea level events that are historically rare (once per century in the recent past) are projected to occur frequently (at least once per year) at many locations by 2050 in all RCPs, especially in the tropics. As a result, annual coastal flood damages are projected to increase by 2-3 orders of magnitude by 2100 compared to today.

In tropical Australia, this effect is compounded by changes to storm surges associated with tropical cyclones. While the sign and magnitude of changes to tropical cyclones in the Australian region remains uncertain, some research indicates they may track further south (Sharmila and Walsh, 2018) with the poleward extension of warmer SSTs, and slow down as tropical circulation changes (Kossin, 2018), although there is only limited evidence to suggest this is occurring at present. Other research suggests a decrease in the number of tropical cyclones forming in the Australian region (Knutson et al., 2015).

Outside the tropics, coastal vulnerability is associated with changes in ocean waves in addition to sea level rise. In the Southern Ocean, a strong trend of increasing wave heights is observed (Young and Ribal, 2019), resulting from a ‘spin-up’ in the mid-latitude westerly winds, with potential consequences for coastal flooding and erosion along Australia’s southern margin. As the tropics expand, it is expected that changes in wave direction will also occur, which can be hugely impactful for sub-tropical coastlines (Goodwin et al., 2016). Erosion caused by the 2016 East Coast Low along Sydney’s Northern Beaches (Figure 2) was an example of the impact of an ‘unusual’ storm wave direction for the coast (Mortlock et al., 2017).

Figure 2. Coastal erosion and flooding on Sydney’s Northern Beaches associated with the June 2016 East Coast Low. Source: UNSW WRL (2016).

Overall, attribution of current coastal impacts on people to sea level rise remains difficult in most locations since impacts are exacerbated by human-induced non-climatic drivers (e.g. groundwater extraction, habitat degradation and sand mining).

Coral bleaching

A major impact of ocean warming and acidification for Australia is the impact of marine heatwave events on coral bleaching and mortality, particularly for the Great Barrier Reef. Marine heatwaves have doubled in frequency and have become longer-lasting, more intense and more extensive.

Climate model-based attribution studies suggest it is very likely that up to 90 % of all marine heatwaves that occurred between 2006 and 2015 are attributable to anthropogenic temperature increases. By 2081-2100, climate models project increases in the frequency of marine heatwaves by approximately 50 times under RCP8.5 and 20 times under RCP2.6 for the tropical oceans.

Because of the sensitivity of tropical corals to sea surface temperatures, marine heatwaves often result in coral bleaching or mortality. When bleaching occurs, recovery is slow (more than 15 years) and may be impeded if the next bleaching event follows too soon.

Figure 3. Extreme coral bleaching on the Great Barrier Reef. Source: Australian Marine Conservation Society (2019).

Tangible impacts on the Great Barrier Reef extend from losses to the tourist and associated industries, and degradation of an important coastal defence. Research suggests the Great Barrier Reef dissipates up to 90 % of all offshore wave energy (Gallop et al., 2014), acting effectively as an underwater breakwater. As this defence reduces, increased wave energy and coastal erosion may be expected for the North Queensland region.

Uncertainties and risk appetite

A particularly important component of sea level rise for Australia is ice sheet instabilities in Antarctica. Acceleration of ice flow and retreat has been observed in both West and East Antarctica and may be the onset of irreversible ice sheet instability. Processes controlling the timing of future ice-shelf loss and the extent of ice sheet instabilities could increase Antarctica’s contribution to sea level rise to values substantially higher than the IPCC’s likely range on century and longer timescales.

Ice sheet instabilities pose a difficult question for coastal planning because there is no time horizon or probability assigned to ice sheet collapse. Uncertainties related to the onset of ice sheet instability arise from limited observations, inadequate modelling and understanding of processes.

Despite the large uncertainties about the magnitude and rate of sea level rise post 2050, many coastal decisions with time horizons of decades to over a century are being made now. The sea level rise range that needs to be considered for planning depends on the stakeholder’s risk tolerance.

Stakeholders with higher risk tolerance (e.g. planning for adaptable investments) may adequately use the likely range of IPCC projections, while it may be prudent for those with a lower risk tolerance (i.e. planning for critical coastal infrastructure) to also consider sea level rise above the upper end of the likely range (i.e. typically > 1 m by 2100). We argued in our recent article in The Conversation that planning for many airports in Australia should include consideration of extreme sea level rise associated with Antarctic ice sheet collapse.

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In summary, the IPCC’s latest report highlights that coastal erosion, flooding and coral bleaching are the three main coastal hazards likely to be experienced with either greater frequency or intensity over the coming century. Given that over 80 % of Australia’s population lives within 50 km of the coast, these changes are likely to have a significant financial and economic impact for business and government.

Risk Frontiers has recently launched its ClimateAUS framework to assist business to understand physical climate change risks. For more information contact info@riskfrontiers.com.

References

CSIRO and BoM (2015). Climate Change in Australia: Projections for Australia’s NRM Regions. Commonwealth Scientific and Industrial Research Organisation and Bureau of Meteorology.

Gallop, S., Young, I., Ranasinghe, R., Durrant, T., Haigh, I. (2014). The large-scale influence of the Great Barrier Reef matrix on wave attenuation. Coral Reefs, 33(4), 1167–1178.

Goodwin, I.D., Mortlock, T.R., Browning, S. (2016). Tropical and extratropical‐origin storm wave types and their influence on the East Australian longshore sand transport system under a changing climate. Journal of Geophysical Research Oceans, 121(7), 4833-4853.

Knutson, T.R., Sirutis, J.J., Zhao, M. (2015). Global Projections of Intense Tropical Cyclone Activity for the Late Twenty-First Century from Dynamical Downscaling of CMIP5/RCP4.5 Scenarios. Journal of Climate, 28, 7203-7224.

Kossin, J. (2018). A global slowdown of tropical-cyclone translation speed. Nature, 558, 104-107.

IPCC, 2019: Summary for Policymakers. In: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate [H.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, M. Nicolai, A. Okem, J. Petzold, B. Rama, N. Weyer (eds.)].

Mortlock, T., Goodwin, I., McAneney, J., Roche, K. (2017). The June 2016 Australian East Coast Low: importance of wave direction for coastal erosion assessment. Water 9(2), 121, 1-22.

Mortlock, T., Gissing, A., Goodwin, I., Wang, M. (2019). Rising seas threaten Australia’s major airports – and it may be happening faster than we think. The Conversation, 28 May 2019.

Sharmila, S., Walsh, K.J.E. (2018). Recent poleward shift of tropical cyclone formation linked to Hadley cell expansion. Nature Climate Change, 8, 730-736.

Young, I.R., Ribal, A. (2019). Multiplatform evaluation of global trends in wind speed and wave height. Science, eaav9527.

Sniderman, J.M.K., Brown, J.R., Woodhead, J.D., King, A.D., Gillett, N.P. et al. (2019). Southern Hemisphere subtropical drying as a transient response to warming. Nature Climate Change, 9, 232-236.

[1] The Special Report uses CMIP5 climate model projections and mainly RCP2.6 and RCP8.5 (RCP2.6 represents low greenhouse gas (GHG) emission, high mitigation future, which in CMIP5 gives a two in three chance of limiting global warming to below 2 °C by 2100. RCP8.5 is a high GHG, low mitigation scenario).