Assessing the Hazard of Compound Flooding from Tropical Cyclones in Cairns, Australia, in a Changing Climate

Co-occurring storm surge and inland heavy rainfall driven flooding during landfalling tropical cyclones (TCs) can lead to compound flooding, causing significantly greater damage than either hazard alone. Understanding how the frequency of these compound flooding events has changed, and will continue to change, in a warming climate is critical for effective mitigation and adaptation strategies. In this study, we present a physically based hydrodynamic framework to assess the hazard frequency of compound storm surge and rainfall-driven flooding under current and future climates in Cairns, Queensland, Australia.

We simulate high-resolution rainfall and storm surge heights (accounting for sea-level rise) using a large ensemble of synthetic TCs generated from nine CMIP6 climate models, covering the periods 1985-2014 and 2071-2100 under the SSP3 7.0 scenario. Using a 2D hydraulic model, we simulate the dynamics of compound flooding from surge and rainfall in both present and future climates. These simulations are integrated into a probabilistic framework to assess compound flooding hazard at different return periods.

By comparing the results for current and future climates, we quantify the contribution of anthropogenic warming to changes in TC-related compound flooding hazard. This approach is broadly applicable to other vulnerable regions and provides a tool to help authorities strengthen coastal resilience and adapt infrastructure to the increasing threat of compound flooding from future TCs.