Chapter 4 Climate Impacts and Responses

Impacts of Climate Change on Australia > Coastal communities and infrastructure

More than 80% of Australia’s population live within 50km of the coast, which is also used for recreation, industry, agriculture and mariculture. Growing coastal population adds to the exposure of the community to extreme events such as tropical cyclones, storm surges and river flooding. CSIRO (2002) reports that coastal communities and urban infrastructure will be affected by changes in sea level and extreme weather. Torrential rainfall over cities and surrounding catchments can produce severe runoff and flooding. Damage to buildings is caused by both the depth of floodwaters and by the force of the water flow. Both contribute to structural fatigue. Gales and strong winds directly damage buildings and also generate waves and storm surges that can contribute to coastal flooding. More frequent high-intensity rain in some areas could also be expected to increase the risks of landslides and erosion, particularly in the urbanised catchments on Australia’s east coast.

As sea level rises, sediment from sandy shorelines is eroded from the beach and the shoreline recedes. It is generally accepted that the coastline will retreat horizontally 50 to 100 times the vertical sea level rise. Hence global sea level rise of between 9 and 88 cm as projected to occur by 2100 under the IPCC range of emission scenarios would cause a coastal recession of sandy beaches by 5.5 to 88 metres.

A decrease in tropical cyclone numbers occurred in the Australian region between 1969 and 1996, but there has been an increase in the number of intense tropical cyclones with pressures of less than 970hPa. Recent decades have also seen a reduction in the number of mid-latitude storms to the south of Australia, but the intensity of these storms has on average increased. Climate models suggest a future decrease in the number of storm centres over southern Australia but an increase in their intensity (CSIRO, 2002). By 2050, sea level may rise 0.1 to 0.4 metres and tropical cyclone intensity around Cairns in northern Queensland could increase by up to 20%. This would increase the flood level associated with a 1-in-100 year flood in Cairns from the present height of 2.3 to 2.6 metres to 2.7 to 3.0 metres. This equates to floods occurring over an area about twice that historically affected.

Sediment transport and deposition following heavy rainfall can smother extensive areas of estuarine habitat, killing trees and resulting in loss of breeding habitat essential to many coastal fish species, dugong and turtles. Any increase in extreme rainfall events and sedimentation would be likely to have major impacts on river, lake, estuarine and coastal waters and lead to reduced ecosystem health and reduced recreational and tourist use. There may be impacts on commercially important fisheries such as prawns and barramundi but the economic impacts are unclear (CSIRO, 2002).

Mangroves occur on low-energy, sedimentary shorelines and are the nursery areas for many commercially important fish, prawns and mudcrabs. They are highly vulnerable but could be adaptable to climate change, migrating shorewards in response to gradual sea level rise. However, in many locations this adaptation will now be inhibited by human infrastructure such as causeways, flood protection levees and urban and tourist developments, leading to a reduction in the area of wetland or mangrove (CSIRO, 2002).

Warmer temperatures favour pathogen survival and extreme rainfall events may increase nutrient levels. As Australian coastal waters are sometimes contaminated with untreated sewage, it is possible these combined effects may favour the production of harmful algal toxins, resulting in fish and shellfish food poisoning.

The Bureau of Transport and Regional Economics (formerly the Bureau of Transport Economics) estimates that between 1967 and 1999, 112 storms occurred in Australia, each causing damage of more than $10 million. The total cost of damage from severe local storms over this period was A$9.4 billion. The data show a statistically significant increase in the damage due to severe storms over time, but this is due largely to increased population in the storm-prone coastal regions of Queensland and New South Wales.

Estimates of the economic costs of natural disasters can be uncertain due to the difficulty of quantifying indirect costs. However, the Bureau of Transport and Regional Economics reports that the total estimated costs of all natural disasters exceeding $10 million each for the period 1967-99 was $37.8 billion (see Table 4.1). Of this, only $5 billion was not due to climaterelated events. Floods were the most costly: for the past three decades, the total cost of floods has been about $10 billion. It has been estimated that more than 80% of the buildings at risk from flooding are located within Queensland and New South Wales. In Queensland, the Gold Coast City Council area has the greatest number of buildings at risk from a 100-year return period flood. Increases in population in risk-prone areas, combined with increases in storm intensities and rising sea levels, mean that the cost of flood damage to the built environment will increase. Severe storms and tropical cyclones have cost about $9 billion each over the past 30 years, while the cost of bushfires has been about $2 billion over the same period. The annual number of events shows an increasing trend in Australia as it has globally, but this is partly due to better reporting, increasing population and investment in vulnerable areas.

The Queensland Government, the Bureau of Meteorology and other agencies are undertaking a major project to look at the threat from storm tide flooding resulting from tropical cyclones, to improve the capability for real-time forecasts of storm tide heights, wave climate and flooding. They recommend allowance should be made for the estimated rise in sea level due to the enhanced greenhouse effect and a 10- 20% increase in the maximum intensity of tropical cyclones.

A study of flood damage along the Hawkesbury-Nepean corridor of New South Wales has shown that, by about 2070, average annual direct damage could increase from the current value of $6.10 million to $23.2 million for the worst-case scenario. At present, the 1-in-100 year flood would cause failure of about 70 weatherboard dwellings and for the 2070 worst case scenario this rises to 1200 dwellings. These estimates do not include intangible losses such as illness and death, nor do they account for indirect losses including alternative accommodation in the residential sector or loss of trading profit in the commercial sector (CSIRO, 2002).