Mixed rainfall trends highlight the significance of climate adaptation in coastal Novel South Wales

Between May 19 and 23, intense rainfall triggered widespread flooding across eastern New South Wales.

During this period, coastal regions received over 100 mm of rain daily, with the most severe downpours concentrated around Newcastle, Taree, and Port Macquarie in the Mid North Coast area.

The flooding resulted in five fatalities, necessitated rescue operations for approximately 700 residents, and left around 50,000 people cut off during and immediately after the event. While the full extent of the damage will become clearer in the coming weeks, agricultural communities bore the brunt-many lost livestock and essential resources needed for farming.

To determine whether human-induced climate change influenced the likelihood and severity of this heavy rainfall, leading to the flooding, a team of international scientists from Australia, the United States, the Netherlands, Sweden, and the United Kingdom conducted a comprehensive event attribution study. This peer-reviewed research analyzed rainfall over a four-day window from May 19 to 22, focusing on the region most affected, as shown in the map below.

The event occurred in a transitional climate zone, situated between southern Australia, which exhibits drying trends linked to climate change during cooler months, and northern Australia, where rainfall patterns are more variable. Additionally, the timing of the event-May-aligns with seasonal shifts from warmer to cooler periods. To account for these spatial and temporal complexities, the study employed two definitions: one focusing on the May-June (AMJ) season, and another considering the four wettest days of the year regardless of season. Historically, low rainfall and flooding can happen at any time in this region.

Key Insights from the Study

• The Mid North Coast region features several major rivers and floodplains, with urban centers situated along the coast. This area has experienced multiple recent disasters, including severe floods and wildfires, highlighting its vulnerability. Repeated emergencies have left communities exhausted, facing ongoing recovery challenges. Rural areas, in particular, suffer from increased property damage, limited access to services, and social isolation during crises.
• Early flood warnings issued three days prior by the Bureau of Meteorology enabled proactive measures such as relocating supplies and evacuating residents in high-risk zones, likely mitigating some impacts.
• Analysis of gridded climate data indicates that the rainfall event over the region is consistent with typical variability-expected roughly once every 10 years during April to June, and about once every three years across the entire year. However, some localized areas experienced their heaviest rainfall since records began, suggesting increasing extremes in certain spots.
• Comparing the May event with a hypothetical scenario in a climate 1.3°C cooler reveals a roughly 17% decrease in the likelihood and intensity of similar low-rainfall events. Conversely, when examining the maximum four-day rainfall totals annually, the probability of such extreme events appears to double with 1.3°C of global warming. The estimated increase in the rarity of such events is approximately 10% in terms of intensity.
• Climate model simulations over the past decades show significant variability-some models project increases in heavy rainfall, others suggest decreases-highlighting the complexity of attributing changes solely to climate change. When combining observational data with model outputs, the overall picture remains uncertain, emphasizing the need for cautious interpretation.
• Further, shifts in atmospheric circulation patterns have been observed. Earlier climate periods (1950-1980) showed different circulation dynamics compared to recent decades (1994-2024), which are more strongly influenced by climate change. Recent patterns tend to produce more frequent and intense heavy rainfall events in May, although not all historical analogs match current conditions, complicating trend analysis.
• Overall, the influence of climate change on heavy rainfall in the Mid North Coast remains ambiguous. Some models project increased extremes, others suggest reductions, and observed atmospheric shifts point to complex interactions beyond simple temperature-rainfall relationships. This uncertainty underscores the importance of flexible adaptation strategies that can handle a range of future scenarios.
• Effective adaptation measures should be versatile, emphasizing nature-based solutions, water management, and risk reduction techniques that are beneficial regardless of whether future conditions become wetter or drier. Such approaches are vital for building resilience in vulnerable communities facing unpredictable climate impacts.