Future frequencies of coastal floods in Australia: a seamless approach and dataset for visualising local impacts and informing adaptation

The rise of pathways-based approaches to coastal adaptation in Australia has changed user requirements for coastal flood hazard information to support decision-making. This study identifies and addresses three aspects not considered in the existing Australia-specific scientific guidance for planning adaptation to sea-level rise. First, changes in the frequency of present-day extreme sea levels are compared between locations. Second, extreme sea levels are related to impact-based thresholds associated with past flood events. Third, the potential for chronic flooding emerging is assessed. This complements global studies that provide some Australian results on these topics. We survey these to identify the methods most suitable for our application and apply the chosen methods to the reference dataset for monitoring Australian coastal sea-level change. This yields a water-level frequency dataset covering daily to centennial water levels for 37 Australian tide gauges. We analyse the dataset to provide a national picture of how sea-level rise is expected to influence the future frequencies of coastal floods in Australia. For example, 85% of Australian locations expect present-day centennial extremes to occur 30 days per year with less than 1-m sea-level rise. The locations with the largest increases in the future frequency of these extremes have the smallest present-day sea-level extreme magnitudes relative to mean sea level, and lower flood thresholds relative to these extremes. We demonstrate three further potential applications of our dataset and methods using local case studies: impact-based forecasting, climate risk services and identifying the required sea-level rise for adaptation triggers and thresholds to be reached.