LAST month CSIRO and the Australian Bureau of Meteorology released their biennial report on the State of the Climate, which found “heavy short-term rainfall events are becoming more intense”.
Australia, the report states, has already warmed 1.5°C since national records began in 1910. In recent years, extreme rains have triggered devastating floods in New South Wales and Queensland.
The question now is – are we prepared for these more damaging floods?
This year, Australia updated the climate change section of Australia’s flood design guidance.
But while this will help ensure that future infrastructure is better able to weather extreme floods, our current bridges, roads and stormwater drains have not been built to weather these increases in extreme rainfall. Similarly, our flood planning levels – used to determine where houses, offices, hospitals and so forth can be built – have generally not factored in the reality of the threat.
MORE FLOODS AND MORE EXTREME
Climate change as detailed in a recent Intergovernmental Panel on Climate Change report showed rain is more likely to fall in intense short-duration bursts which are more likely to trigger floods.
Australia is not immune. The devastating northern New South Wales floods of 2022 took 24 lives and ravaged towns such as Lismore. These floods are the most expensive natural disaster to date in Australia, costing $5.65 billion in damages. February 28, 2022 set a new flood record for Lismore in NSW, at 14.4 metres – two metres higher than the previous record.
HOW DO YOU PREPARE FOR WORSE FLOODS?
When urban planners set flood planning levels, or engineers begin designing a new bridge or rail line, they have to take floods into account. To do so, they will inevitably reach for the local bible, Australia’s flood design guidance.
To provide better flood guidance, a comprehensive review was undertaken of over 300 scientific papers covering climate change in Australia and extreme rainfall.
The review proved we had been underestimating the threat of extreme rains and subsequent floods.
Rain events over a 24-hour period leading to flooding are likely to increase at 8% per degree of warming, not 5%. Hourly rainfall extremes are likely increasing even faster, at 15% per degree.
New figures have now been included in the August update of Australia’s flood design guidance.This is good news. It means future decisions on infrastructure and planning can now be well informed by the latest science on how climate change influences flood risk.Over time, this will ensure essential infrastructure can be built to endure worse floods. It will affect the design and construction of everything from local stormwater drains to levees, bridges, culverts and dam spillways.
