Article
BAMOS Dec 2024
11 impacts were generally consistent with minor flooding , as defined by the Bureau of Meteorology with closure of minor roads , submergence of low-level bridges and inundation of bicycle and pedestrian paths . Flooding could be considered moderate given the inundation of a low-lying restaurant above the floor level and the impacts on lanes of major traffic routes although these routes remained open . It is worth noting that many impacted locations were not directly connected to the Yarra River ( Figure 3 ). This is because flood waters can flow back up storm water drains to inundate low-lying areas , a common way that high sea levels impact land around the world .
The new normal ?
The highest sea level recorded during this recent event — based on the hourly average of three-minute observations — was 1.06 m AHD *. This is the third-highest since the high-confidence data began in 1966 . Research by Hague et al . ( 2024 ) shows that , relative to 2022 mean sea level , a sea level of 1.06 m AHD has a 6 % chance of occurring each year . However , in 1966 when Melbourne ’ s mean sea level was 0.08 m lower , a sea level of 1.06 m AHD was associated with a 1 % annual probability . Thus , a halfcentury of sea-level rise has made this event 6 times more likely , turning what was once a " 1-in-100-year " event into a " 1-in-16- year " event in the present .
With future sea-level rise , coastal flooding will become increasingly common in Melbourne . Hague et al . 2024 have shown that a 0.15 m sea-level rise will cause the peak sea levels observed during this recent event ( 1.06 m AHD ) to occur on average once a year . A 0.5 m sea-level rise would result in these peaks being reached or exceeded 50 days per year . Victorian coastal managers are planning for 0.8 m of sea level rise by 2100 , which could lead to these peak sea levels occurring 290 days
per year . Under this scenario , chronic flooding could occur in the city .
CO 2 emissions and associated warming to date have already committed the world to multi-metre sea level rise regardless of 21st century emission pathways ; a rise of 0.8 m is not a matter of if , but when . While following a lower emissions pathway can delay the emergence of this chronic flooding until after 2100 , the impacts seen on 2nd September 2024 will become the " new normal " unless we can successfully adapt to the impacts of sealevel rise .
Adaptation strategies may include nature-based solutions ( e . g ., environmental restoration and management ), accommodation measures ( e . g ., raise floor levels ), retreat ( e . g ., relocation of communities and / or assets ) and / or protective adaptation strategies ( e . g ., new engineered structures to prevent water ingress ). The AMOS community has a pivotal role to play in developing , promoting and applying the science to help shape the required adaptive responses .
Figure 2 : Tide gauge observations from Melbourne ’ s suburb Williamstown ( upper panel , black lines ) separated into the astronomical tide ( upper panel , blue lines ) and storm surge ( lower panel , red lines ) components . Data from Bureau of Meteorology and Victorian Ports Corporation . Nuisance flood level ( Hague et al . 2022 ) is shown in dashed black and highest astronomical tide ( maximum possible level under average weather conditions ) is shown in dashed blue .
Figure 3 : Flooding impacts in Southbank , Melbourne . Photos taken by Ben Hague between 1545 and 1645 local time on 2 September 2024 .
* AHD ( Australian Height Datum ) is used to quantify land heights relative to sea , with 0 m AHD being approximately mean sea level in 1966 - 1968 .