Quantifying the impact of future climate change on the risk of coral rubble instability across the Great Barrier Reef by 2100.

Coral reef systems are facing unprecedented pressures due to climate change, and stable coral rubble substrates are crucial for facilitating large-scale coral regeneration. This study integrates the Sixth Phase of the Coupled Model Intercomparison Project climate models, sea-level rise projections from the Intergovernmental Panel on Climate Change Sixth Assessment Report, Shared Socioeconomic Pathway scenarios, and applies machine learning techniques to assess the risk of coral rubble instability in the Great Barrier Reef under future wave climate and depth change scenarios. Using the EC-Earth climate model under the SSP5-8.5 scenario-calibrated with data from 41 synoptic stations-we estimated various climate data for 2031-2100 and examined the impact of key factors such as wave climate and depth changes on the risk of coral instability. Coral rubble instability risk depends on future wave climate and depth changes from sea-level rise and deposition. Future changes in wave climate are expected to increase the risk of instability, while increased depth mitigates these destabilizing effects. Over the next 70 years, most areas of the Great Barrier Reef are projected to experience stable or decreasing risk of coral rubble instability. The proportion of no-risk areas is higher in the northern regions, whereas the far southern regions have fewer no-risk areas and more high-risk zones. High-risk and very high-risk areas are mainly concentrated along reef edges, reefs facing the Pacific Ocean, and shallow waters near the shoreline. The transition between high-risk and low-risk areas is gradual rather than abrupt. Annual projections align with long-term trends: coral rubble remains relatively stable in the northern and central regions, which is more conducive to future coral recovery. However, the persistent presence of high-risk and very high risk areas poses significant challenges to coral recovery in the far southern region. By providing insights into the spatial and temporal evolution of coral rubble instability risk, this study aims to support decision-makers, environmental scientists and researchers in formulating appropriate interventions to enhance the resilience of coral reefs under changing environmental conditions.