Heavy rain in May 2025 New South Wales  floods locally intensified by human-driven climate change

Contact Authors

• Tommaso Alberti, INGV, Italy 📨 tommaso.alberti@ingv.it 🗣️Italian, English

• Davide Faranda, IPSL-CNRS, France  📨davide.faranda@lsce.ipsl.fr    🗣️English,French, Italian

Citation

• Alberti, T., & Faranda, D. (2025). Heavy rain in May 2025 New South Wales floods locally intensified by human-driven climate change. ClimaMeter, Institut Pierre Simon Laplace, CNRS. https://doi.org/10.5281/zenodo.15489583

Press Summary

• Meteorological conditions similar to that causing floods in New South Wales  are up to 3 mm/day (up to 15%) wetter over the coast in the present than they have been in the past. 

• This event was associated with very rare meteorological conditions 

• We mostly ascribe the increase in precipitation of the New South Wales  floods to human driven climate change and natural climate variability likely played a modest role.

Event Description

On 20 May 2025 torrential rains triggered severe flooding across parts of New South Wales, Australia, with thousands of residents facing isolation and evacuations. In just a few days, some regions received more than a month’s worth of rainfall, breaking historical records. Maps illustrate the vast extent of the deluge, showing many areas, particularly in the northeast, experiencing exceptional downpours. The rainfall has overwhelmed rivers and infrastructure, submerging roads and homes, and cutting off entire communities. Emergency services have conducted numerous rescues, and local authorities warn that conditions could worsen with more rain forecasted. Towns such as Lismore and Taree have been among the hardest hit, with schools closed and essential services disrupted. 

The meteorological conditions were characterized by positive surface pressure anomalies (up to +10 hPa) over the area. Temperatures were mostly higher than normal over the region, with anomalies up to +4°C over land and up to +2°C over the coast. Precipitation was mostly localized close to Taree during the event, with peak accumulation exceeding 200 mm/day. Moderate winds were observed over the sea. The data used in this analysis come from the ERA5 reanalysis, which combines model output with available observational data, including ground stations and satellite measurements. Differences with localized station observations may occur.

Climate and Data Background for the Analysis

The Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (AR6) highlights significant concerns regarding climate change and its impact on flooding in Australia. The report indicates that climate change is expected to increase the frequency and severity of heavy rainfall events, leading to more frequent and intense river floods across the country. This trend is particularly pronounced in Northern Australia, where models project an increase in heavy rainfall and river flooding by mid-century, with medium confidence. Additionally, the AR6 notes that sea-level rise is likely to reach 0.2–0.3 meters by 2050, significantly increasing the frequency of coastal flooding events. These changes are expected to have profound impacts on Australia's ecosystems and human systems. The report underscores that climate trends and extreme events have combined with exposure and vulnerabilities to cause major impacts for many natural systems, with some experiencing or at risk of irreversible change in Australia.  In response to these challenges, the AR6 emphasizes the need for effective and equitable conservation of approximately 30% to 50% of Earth's land, freshwater, and ocean areas, including currently near-natural ecosystems, to maintain biodiversity and mitigate the effects of climate change.  Overall, the IPCC AR6 underscores the escalating risks of flooding in Australia due to climate change, highlighting the urgency for comprehensive adaptation and mitigation strategies to protect ecosystems, infrastructure, and communities.

Our analysis approach rests on looking for weather conditions similar to those of the event of interest having been observed in the past. For this event, we have medium-to-high confidence in the robustness of our approach given the available climate data. We are unable to account for the  impact of human activities associated with land-use change and of changes in the human settlements. These factors help determine the vulnerability and the exposure of the territory to flood risk in presence of intense or exceptional precipitation events.

ClimaMeter Analysis 

We analyze here (see Methodology for more details)  how events similar to the meteorological conditions leading to the May 2025 New South Wales  floods have changed in the present (1987–2023) compared to what they would have looked like if they had occurred in the past (1950–1986) in the region [145°W 155°W 28°S 36°S]. Surface pressure changes show no relevant differences between the two periods. Temperature changes show increases of up to +0.75°C in the flood-affected area and over the coast. Precipitation changes reveal locally increased rain totals, with present-day conditions up to 4 mm/day wetter in parts of the coast. Wind changes display less windy conditions over the sea, especially close to Taree.

Similar past events show a seasonal shift, with an increase in June in the present period compensated by a decrease in occurrence in April in the past period. Changes in urban areas reveal that Taree, Sydney and Wollongong experienced significantly wetter (+3 mm/day) conditions during this event compared to similar past conditions.

These results suggest that meteorological conditions similar to those of the May 2025 New South Wales  floods are becoming more favorable for precipitation, in line with what would be expected under continued global warming. Our results also suggest that sources of natural climate variability, such as the Atlantic Multidecadal Oscillation (AMO), may have played only a secondary role in shaping the observed event.

Conclusion

Based on the above, we conclude that meteorological conditions leading to the May 2025 floods in New South Wales  are up to 3 mm/day wetter (up to 15%) compared to similar past events. We interpret this event as an event driven by very rare exceptional meteorological conditions whose characteristics can mostly be ascribed to human driven climate change.