This NCAR and IAG report examines current and future climate change impacts on the Australian climate and weather extremes that produce significant property, personal and economic damage and hardship.
The level of scientific knowledge and available tools has now reached the stage where it is possible to make confident assessments on the impacts of climate change at larger scales and longer time frames, with objective assessment of the associated levels of confidence.
But many personal, government and business decisions require information on climate and weather extremes at more local scales, such as states, cities and towns.
Key assessments are:
- The frequency of named tropical cyclones in the Australian region has declined in recent decades; the detail of how this will project into the future is unknown, although globally there is expected to be a further slight reduction in total numbers. However, the frequency of tropical cyclones making landfall throughout the western South Pacific region has increased. Over the past 30 years, the proportion of the most destructive tropical cyclones has increased at the expense of weaker systems, and this change is expected to continue.
- There has already been a southward shift of the regions where tropical cyclones reach peak intensity and this is expected to continue. Tropical cyclone risks are therefore expected to increase most rapidly in the south-east Queensland / north-east NSW regions, followed by the coastal districts south of Shark Bay in Western Australia.
- Marginal decreases in risk for wind impacts may occur in some other regions. Planning for inland penetration of tropical cyclones should be based on substantial increases in both rainfall rate and affected areas. Winds are also likely to decay more slowly, so increased winddriven rainfall ingress should be expected both at the coast and inland. More intense storms combined with rising sea levels point to increasing storm surge impacts, and these may be very substantial in some regions.
- Intense short duration rainfall is expected to increase almost everywhere in Australia, resulting in more frequent flooding in urban areas and in small river catchments. Storm rainfall totals from both east coast lows and tropical systems are also expected to increase, leading to increasing flood risk in the larger river catchments. More work is required to fully understand and confidently assess these changes.
- Areas at risk of large (2.0-4.9cm in diameter) and giant (>5.0cm in diameter) hail should progressively shift southwards, with the largest increase in risk likely to be in the region inland from the Hunter River south through the central and southern New South Wales highlands and central to eastern Victoria. Fewer increases are assessed to affect the south-west of Western Australia while severe hail risk is expected to decrease in Queensland.
- The multi-day impacts of east coast lows on the south-eastern seaboard of Australia are expected to increase because of wind-driven rainfall ingress, flash and riverine flooding. This effect will be compounded by rising impacts from storm surge, waves, and coastal erosion. Summer and autumn east coast low activity is expected to increase, while there will be a decrease in winter-spring systems. There is limited understanding of the rare extreme east coast lows that drive the majority of the impacts over land.
- Bushfire risk, as measured by the trends in fire danger indices, is likely to increase in almost all locations nationally, leading to more frequent and extreme events, and longer fire seasons. The rate of increase varies by location and will depend on weather system changes and sitespecific factors at regional scales.
- Sea level rise is expected to accelerate around the Australian coastline but at differing rates. It is notable that past assessments of sea level rise are lower than those that recent observations show. Sea level rise will contribute substantially to escalating impacts from storm surge and the impacts on coastal natural systems, buildings and infrastructure. The greenhouse gases that are already present will cause sea level rises to continue well into the next century even if there are significant emission reductions globally through the coming decade.