This content forms a part of our issue briefing on sustainable cities and communities.
SDG 11.5 By 2030, significantly reduce the number of deaths and the number of people affected and substantially decrease the direct economic losses relative to global gross domestic product caused by disasters, including water-related disasters, with a focus on protecting the poor and vulnerable people.
SoE 2016: Built environment: Related key finding: “Climate change brings particular challenges for our built environments.”
The economic cost of natural disasters in Australia has not been comprehensively assessed since 2001. Although public data relating to disaster events is available through the Australian Disaster Resilience Knowledge Hub, trend analysis of these records is not advisable due to changes in event inclusion criteria over time.35 Heatwaves — a major cause of deaths in Australian cities — have also only recently been classified as a natural disaster event and up until recently lacked a standard definition, despite being estimated to account for half of all disaster-related fatalities between 1967 and 2013.36
Nonetheless, the range of threats posed to Australian cities by climate-related natural disasters requires a comprehensive response, with the SoE 2016 report highlighting various built environment threats ranging from potable water shortages to exposure to sea level rise.
The worsening of many existing extreme weather risks due to climate change is also already underway, with unprecedented heatwaves, bushfire conditions and accelerated coastal erosion and storm surge events being observed across many of Australia’s cities.
Severe storm events — including hailstorms — have been the most financially damaging disaster category in Australia over the last half-century, having accounted for 32 per cent of total losses, followed by flooding (28 per cent), cyclones (19 per cent) and bushfires (17 per cent).
Around one-third of the financial costs of these disasters can be attributed to only ten major events that occurred over this 46-year period, including a number that primarily affected major urban centres such as the 2011 Brisbane floods, the Black Saturday bushfires in 2009, the 1999 Sydney hailstorm, and Cyclone Tracy in 1974.
Australian cities occupy a range of distinct climatic zones that lead to different levels of exposure to a variety of climate-related natural hazards. As a result, the impacts of climate change vary from city to city and need to be assessed locally to be properly understood, with a range of climate analogues and differing climate projections able to be analysed through the CSIRO-developed Climate Change in Australia website.
However, some general trends and projected impacts of climate change can be considered at a national level. Average surface temperatures, for instance, have warmed fairly consistently across Australia, increasing by roughly 1°C since 1910, while levels of average annual rainfall across southern and south-eastern parts of the country, as well south-west Western Australia, have decreased significantly.
Projected annual temperature increases over the 21st century are reasonably consistent across the four major climate regions (Southern, Eastern and Northern Australia, as well as the Rangelands).
Under a high emissions scenario — referred to as Representative Concentration Pathway (RCP) 8.5 in reference to an average warming of 8.5 watts per square metre in 2100 — all four regions of Australia are likely to increase by an average temperature of 2.7°C to between 4.2°C and 5.3°C, with the central Australian rangelands having the potential to warm by 1°C more than southern Australia if the top end of this range is reached.
In contrast, both the direction and magnitude of changes in average annual rainfall are highly uncertain across each region, with the equivalent projected change in annual rainfall in northern Australia under RCP 8.5 being between 26 per cent less and 23 per cent more rainfall, even when excluding outlier model results.
This represents a critical challenge for cities, where building codes, design standards and drainage systems rely heavily on established understandings of rainfall return periods. Time in drought is also projected to increase in southern Australia and southern Western Australia in particular, threatening the security of urban water supplies in these areas.
Extreme heat conditions are becoming more prevalent nationally. “Very warm” monthly night-time minimum temperatures (a measure central to extreme heat factor calculations) that occurred around 2 per cent of the time between 1951 and 1980 are now occurring around 12 per cent of the time. This represents a particular threat to cities located in regions not acclimatised to extreme heat events due to infrastructure – such as power stations, train lines and building structures – not being designed to cope with heat events and urban heat island effects.
Higher and more prolonged extreme heat events also risk spikes in morbidity and mortality due to a lack of awareness about the risks posed by these events in vulnerable urban population groups. In hotter regions, other risks associated with infrastructure have also been observed, such as heavy rail buckling, heating, ventilation and air conditioning (HVAC) system failure, and blackouts associated with ageing baseload coal powerplant shutdowns.
Average sea levels around Australia rose at a rate of 1.4mm per year between 1966 and 2009, while sea surface temperatures have also increased by an average of 1°C since 1910.
The increasing threat of coastal erosion and inundation presents a particular risk to Australian cities and settlements, with much of the country’s population based in coastal areas. Average sea levels are expected to increase by another 38–88cm by 2090 under a high emissions scenario (RCP 8.5), or by 22–55cm if global emissions are rapidly reduced (RCP 2.6).
Bushfire risk threatens many urban fringe and peri-urban areas. These areas are often adjacent to vegetated spaces and parks, which can enable fires to spread rapidly. If the driest model outcomes for rainfall in eastern and southern Australia are realised, the number of severe fire danger days is likely to increase by 160 per cent to 190 per cent by 2090, representing an annual increase of 30–35 per cent in severe risk days.
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