Storms and floods are part of Sydney’s climate, but it is essential for residents in flood-prone areas to understand their risks and prepare accordingly.
The intense rainfall that lashed parts of NSW this week had many causes, yet on social media some are attributing it to “cloud seeding” or other forms of weather manipulation.
Natural climate processes
Sydney has been battered with torrential rainfall over the last week, depositing almost a month’s worth of water and prompting emergency evacuation warnings in low-lying areas. Warragamba Dam in Sydney has already started overflowing, while WaterNSW predicts further floods to occur.
Floods are a natural part of NSW’s climate, caused by oceanic weather systems like El Nino Southern Oscillation (ENSO). But climate change will alter these weather systems by increasing rainfall and flood risk in NSW.
Though many NSW communities have climate adaptation plans in place, regional vulnerabilities remain high. This paper introduces a novel method for mapping flood vulnerability at local scale using high-resolution hydrological-hydraulic modelling and socio-economic data at high resolution. We demonstrate its utility by applying it to Marrickville where recent flooding events triggered evacuation orders; our results demonstrate how combining geophysical and socio-economic flood data provides the clearest picture of vulnerability that local governments can use to create effective mitigation and adaptation strategies.
Sea level rise
Sea level rise contributes to coastal flooding and erosion by raising tide levels, and playing an integral part in creating storm surges which can extend further inland than normal.
According to research, every 10cm rise in sea level increases the frequency of coastal floods threefold – this has serious repercussions for Sydney where more frequent, high-impact coastal floods can be expected.
Persistent rainfall across New South Wales caused widespread flooding and property damage, particularly along the Hawkesbury-Nepean River system where flood waters reached their highest level since 1961.
Floods in Sydney are partly a consequence of climate change. By the end of this century, weekly minor floods can be expected despite significant reductions in greenhouse gas emissions; tides fluctuations are the dominant force driving coastal inundation frequencies while ocean and weather variability play only minor roles.
Human-induced climate change
Torrential rain in Sydney and Australia washed over areas on Monday, flooding homes, affecting traffic flow and forcing some residents to evacuate their homes. Footage shared to X by user MunsieGlenn shows water gushing down stairs at Town Hall train station in central Sydney while floodwaters blocked car parks and threatened nearby restaurants – images shared to X by MunsieGlenn show this clearly.
Multiple rivers in New South Wales (NSW) have flooded following heavy rainfall that caused dams to overflow, flooding low-lying suburbs and prompting emergency evacuation orders. Of particular note is Hawkesbury River which supplies 80 per cent of Sydney drinking water supply and was expected to crest major flood levels in northwestern Sydney.
Climate change will alter the risk of extreme weather events such as tropical cyclones and east coast lows by increasing storm frequency and intensity, amplifying their effects, as well as amplifying effects from other drivers such as sea level rise. Furthermore, it is predicted to prolong certain events.
Weather systems
Sydney has been hit with eight months’ worth of rain in four days, inundating homes and shutting businesses. Residents are bracing themselves for what might come, with evacuation centres opened across western Sydney to shelter from rising waters. Cafe owner Darren Osmotherly has taken measures such as moving equipment every six to eight hours into higher ground to stay ahead of potential damage from floodwaters.
Flash floods typically form when low pressure systems form high in the atmosphere and cause instability that attract thunderstorms, but global warming is altering this behavior with warmer oceans providing more energy for storms to form.
This has allowed a thick front of warm air to move eastward across the Pacific and bring moist air across NSW – similar to El Nino in early 2000s which caused flooding throughout NSW – although its exact influence is uncertain; most evidence points towards it accelerating short duration rainfall that caused deluge, but its effect on longer lasting rainfall which ultimately resulted in flooding is harder to assess.
